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					                                                            REF :     RCCT-ASPI-TN-7
ROBUST CONTROL TECHNIQUES FOR
  PLANETARY SPACE VEHICLES                                  DATE :    06/06/05
                                                            ISSUE :    4.0       Page : i
PRECISION AGILE CONTROL SYSTEM
 ITT/AO/1-4334/02/NL/AG

PRECISION AGILE CONTROL SYSTEM
                        DOCUMENT DISTRIBUTION

From: LE PEUVEDIC Catherine

      Project Name:                    Robust Control Techniques for Planetary Space
                                       Vehicles
      Title:                                Executive Summary

      Issue :                              4.0
      Reference :                          RCCT-ASPI-TN-7
      Date :                               06/06/05
      Pages Number:                        26
      ESA’s Technical officer:             Mr. Guillermo ORTEGA (TOS-ESN)
      ESA’s Contract number:               17432
      Alcatel Space Emitting Entity:       DAV/CAV

To:
                                   Internal Distribution
  Service          Name          N.B. Ex.       Service             Name           N.B. Ex.

DAV/CA         Busseuil J.             1
DRT/RPS        Maini M.                1
DAV/           Roser X.                1
DOS/M/M        Bessudo R.              1
DAV/CAV        Pautonnier S.           1


                                  External Distribution
 Company     Name                N.B. Ex.   Company            Name                N.B. Ex.
ESA      Ortega G.                  1      NGC             J.         De              1
                                                           Lafontaine




                               EUROPEAN SPACE AGENCY




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PRECISION AGILE CONTROL SYSTEM
 ITT/AO/1-4334/02/NL/AG

PRECISION AGILE CONTROL SYSTEM
                        CONTRACT REPORT
           The work described in this report was done under ESA contract.
  Responsibility for the contents resides in the author or organisation that prepared it.




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                                   Executive Summary




    ESA’s contract number: 17432



        Written by                     Responsibility-Company                       Date        Signature

Catherine LE PEUVEDIC   Robust Control Project manager – Alcatel Space            06/06/05
                        (France)

        Verified by

Stéphane PAUTONNIER     Head of AOCS Studies Section – Alcatel Space
                        (France)

        Approved

Pierre-Yves RENAUD      Head of AOCS Department – Alcatel Space
                        (France)

Guillermo ORTEGA        Technical officer of the contract – ESA (TOS-ESN)




                                EUROPEAN SPACE AGENCY




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                                        CONTRACT REPORT
               The work described in this report was done under ESA contract.
      Responsibility for the contents resides in the author or organisation that prepared it.



      ORGANISME EMETTEUR                                                     CLASSIFICATION

                                                             SECRET MILITAIRE                     SECRET INDUSTRIEL

                                                      NC       DR      CD          SD     NC         DR         CA      SA
                                                       X                                         X                 
             Alcatel Space Industries                                     MARCHE ou CONTRAT
                                                           NUMERO du MARCHE
                                                                                                  ORGANISME CLIENT
                                                             ou du CONTRAT

                                                                 17432                                    ESA

       CONTRACT                       PROJECT          LOT        POSTE                        OE ou OF

                                   Aurora Robust
                                      Control
       TITLE         Executive Summary

       AUTEUR      (S)    LE PEUVEDIC Catherine
       (Personne
       physique)



          DATE                NUMERO D'ORIGINE DU DOCUMENT                               NOMBRE
                                                                                                             Réferences
                                                                    Pages               Figures
                                                                                                          bibliographiques
       06/06/05
                         Adm. :

                         Tech. :


       ABSTRACT
       The Robust on-line Control Customization Techniques for Planetary Space vehicles
       Project aims at developing and testing on a simulation tool several robust control
       techniques applied on different Martian mission phases.

       The issue 4.0 of this document contains the executive summary of the analysis
       phase (phase 1), the development phase (phase 2), the test phase (phase 3) and
       the delivery phase (phase 4).




        NUMERO DE DOCUMENTATION                 NATURE DU DOCUMENT                            COTE ARCHIVE



                                                                                                                      IP002-05
NOTION D'INDEXAGE   Catégorie de Diffusion
                                             3D      3I
                                                    
  AURORA            Service        :    BO/DAV/CAV
  ROBUST CONTROL    Nom            :   S. PAUTONNIER
                    Signature
                    Département :       BO/DAV/CA
                    Nom         :      J. BUSSEUIL
                    Signature




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                                      CHANGE RECORDS

ISSUE      DATE                        § : CHANGE RECORD                                AUTHOR


1.0      05/11/03   First issue                                                      LE PEUVEDIC
                                                                                      Catherine
2.0      05/10/04   Addition of the executive summary of phase 2                         CLP
3.0      15/04/05   Addition of the executive summary of phase 3                         CLP
4.0      06/06/05   Addition of the executive summary of phase 4                         CLP
                    Correction of sensors/actuators table




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                                     TABLE OF CONTENTS



1.     INTRODUCTION                                                                          6

     1.1 Reference Document                                                                  6

     1.2 Acronyms                                                                            7

2.     PHASE 1 EXECUTIVE SUMMARY                                                             9

     2.1 Mission Scenarios                                                                   9

     2.2 Vehicles and Environment                                                            9

     2.3 AOCS/GNC Architecture                                                           10

     2.4 Control Techniques                                                              11

     2.5 Requirements                                                                    11

3.     PHASE 2 EXECUTIVE SUMMARY                                                         13

     3.1 Simulation Tool Development                                                     13

     3.2 AOCS Controllers Development                                                    14

     3.3 Selection of the Best Control Approach                                          16
       3.3.1   Normal Modes (NOMP, NOMR)                                                 16
       3.3.2   Orbit Control Modes (OCM1, OCM2, OCML, OCMH)                              16
       3.3.3   Atmospheric Modes (ARCM, ENTM)                                            17
       3.3.4   Rendez-Vous Mode (RDVM)                                                   17

     3.4 Conclusion                                                                      18

4.     PHASE 3 EXECUTIVE SUMMARY                                                         19

     4.1 Simulation Tool Testing                                                         19

     4.2 Scattering Definition                                                           19

     4.3 Final Performances Evaluation                                                   20
       4.3.1   Normal Modes (NOMR, NOMP)                                                 20
       4.3.2   Orbit Control Modes (OCM1, OCM2, OCML, OCMH)                              20
       4.3.3   Atmospheric Modes (ARCM, ENTM)                                            20
       4.3.4   Rendez-Vous Mode (RDVM)                                                   21




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5.     PHASE 4 EXECUTIVE SUMMARY                                                       23

     5.1 ‘RCCT – Software Delivery’ CDROM                                              23

     5.2 ‘RCCT – Technical Notes for ESA’ CDROM                                        23


                                      LIST OF FIGURES

FIGURE 2-1: OVERVIEW OF THE MSR AND MM VEHICLES                                        10
FIGURE 2-2: SENSORS AND ACTUATORS CONSIDERED IN THE ROBUST CONTROL PROJECT             11
FIGURE 2-3: AOCS MODES CONSIDERED IN THE ROBUST CONTROL PROJECT                        11
FIGURE 2-4: CONTROL TECHNIQUES VERSUS AOCS MODES                                       11
FIGURE 2-5: CONTROL MAIN REQUIREMENTS AND JUSTIFICATIONS                               12
FIGURE 3-1: ESCAPELIGHT MAIN WINDOW AND POST-PROCESSING MANAGER                        13
FIGURE 3-2: ARCM, ENTM, RDVM CONTROL ENVIRONMENT                                       14
FIGURE 3-3: NOMR, OCM1, OCM2, NOMP, OCML, OCMH CONTROL ENVIRONMENT                     14
FIGURE 3-4: CONTROL TECHNIQUES UNDER STUDY FOR EACH AOCS MODES                         15
FIGURE 3-5: CONTROLLER GENERIC ARCHITECTURE                                            15
FIGURE 3-6: NOMR CONTROLLER DESIGN (CRUISE TO MARS) FOR THE MSR DESIGN                 16
FIGURE 4-1: OVERVIEW OF MONTE-CARLO SIMULATION RESULTS                                 22




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1. INTRODUCTION

This document summarizes the main hypothesis, activities and results obtained in the
frame of the Robust on-line Control Customization Techniques for planetary Space vehicle
project.

The Robust Control Project aims at developing and testing on a simulation tool several
robust control techniques applied on different Martian mission phases.

1.1 Reference Document

The following documents shall be taken as reference documents. The documents listed in
this section are referenced throughout the document by [symbol] as in the list below.

[RD01]   Robust Online Control Customisation Techniques Alcatel Space technical
         for planetary space vehicles                     proposal     8332011 - 28th
                                                          january 2003
[RD02]   Mission Scenarios technical note                 RCCT-ASP-TN-1
[RD03]   Control requirement specification technical note RCCT-ASP-TN-2
[RD04]   AOCS modes and control synthesis technical note RCCT-ASP-TN-3
[RD05]   Equipment technical note                         RCCT-ASP-TN-4
[RD06]   Simulation tool specification technical note     RCCT-ASP-TN-5
[RD07]   Inputs to aurora technology map (PM1 slides)     RCCT-ASP-TN-6
[RD08]   Executive summary                                RCCT-ASP-TN-7
[RD09]   Mars atmospheric model TN                        RCCT-ASP-TN-8
[RD10]   RDVM control environment TN                      RCCT-ASP-TN-9
[RD11]   ARCM control environment TN                      RCCT-ASP-TN-10
[RD12]   ENTM control environment TN                      RCCT-ASP-TN-11
[RD13]   Hinfinity and EA tech. for NOM, OCM attitude RCCT-ASP-TN-12
         control
[RD14]   EA technique for ARCM attitude control law       RCCT-ASP-TN-13 (002-NGC)
[RD15]   Mars gravity model TN                            RCCT-ASP-TN-14
[RD16]   Simulation tool user manual TN                   RCCT-ASP-TN-15
[RD17]   Simulation tool test plan TN                     RCCT-ASP-TN-16
[RD18]   PM2 slides                                       RCCT-ASP-TN-17
[RD19]   Robust Control design techniques                 RCCT-ASP-TN-18 (001-NGC)
[RD20]   ARCM ENTM guidance algorithms                    RCCT-ASP-TN-19 (003-NGC)
[RD21]   NDI technique for ARCM ENTM translation control  RCCT-ASP-TN-20 (004-NGC)
[RD22]   QFT and EA techniques for RDVM translation RCCT-ASP-TN-21 (005-NGC)
         control
[RD23]   LPV technique for ARCM attitude control          RCCT-ASP-TN-22 (006-NGC)
[RD24]   EA and LQR techniques for ENTM attitude control  RCCT-ASP-TN-23 (007-NGC)
[RD25]   LPV technique for ENTM attitude control          RCCT-ASP-TN-24 (008-NGC)
[RD26]   PC technique for ARCM translation control        RCCT-ASP-TN-25 (009-NGC)
[RD27]   Hinfinity and LQR techniques for RDVM attitude RCCT-ASP-TN-26 (010-NGC)
         control
[RD28]   Synthesis tools user manual                      RCCT-ASP-TN-27 (011-NGC)



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[RD29]   Criteria for selection of control synthesis techniques   RCCT-ASP-TN-28 (013-NGC)
[RD30]   Simulator detailed design document                       RCCT-ASP-TN-29
[RD31]   A Posteriori Linear Robustness Analysis of Static        RCCT-ASP-TN-30 (012-NGC)
         Controllers
[RD32]   Selection of Control Techniques for phase 3              RCCT-ASP-TN-31 (014-NGC)
[RD33]   PC technique for ENTM translation control                RCCT-ASP-TN-32 (015-NGC)
[RD34]   CDR slides                                               RCCT-ASP-TN-33
[RD35]   Simulator Test Run Compilation document                  RCCT-ASP-TN-34
[RD36]   NOM Final Performances                                   RCCT-ASP-TN-35
[RD37]   OCM Final Performances                                   RCCT-ASP-TN-36
[RD38]   RDVM, ARCM and ENTM Final Performances                   RCCT-ASP-TN-37 (016-NGC)
[RD39]   PM3 slides                                               RCCT-ASP-TN-38
[RD40]   Conclusions and Recommendations                          RCCT-ASP-TN-39
[RD41]   FR slides                                                RCCT-ASP-TN-40


1.2 Acronyms

ACC                 accelerometer
AOCS                Attitude & Orbit Control System
ARCM                Aerocapture mode
ARD                 Atmospheric Reentry Demonstrator
CoG                 Center of Gravity
EA                  Eigenstructure Assignment
EEV                 Earth Entry Vehicle
EMCD                European Martian Climate Database
ENTM                Entry Mode
GNC                 Guidance navigation and control
GYR                 gyrometer
HGA                 High Gain antenna
Hinf                Hinfinity Control Technique
IMU                 Inertial measurement unit
Isp                 Specific impulse
LIDAR               Light detection and ranging
LM                  Landing Module
LPV                 Linear Parameter Varying
LQR                 Linear Quadratic Regulator
MAV                 Mars ascent vehicle
MCI                 Mass, center of gravity, inertia
ME                  Main Engine
MIB                 Minimum Impulse Bit
MIMU                Miniaturized inertial measurement unit
MM                  Manned Mission
MSR                 Mars Sample Return Mission
NDI                 Dynamic Inversion
NEP                 Nuclear electrical propulsion
NOMP                Normal Operational mode on Propulsion
NOMR                Normal Operational Mode on Reaction wheels



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NTP               Nuclear thermal propulsion
OCM               Orbit control Mode
OCM1              Orbit Control Mode 1
OCM2              Orbit Control Mode 2
OCMH              Orbit Correction Mode High
OCML              Orbit Correction Mode Low
OM                Orbiter Module
PAV               Planetary Ascent Vehicle
PC                Predictive Control
QFT               Quantitative Feedback Technique
RCCT              Robust Control Customization Techniques
RDVM              Rendez-Vous Mode
RLG               Ring laser gyro
RW                Reaction wheels
SA                Solar array
SM                Surface Module
STR               Star-Tracker
TBC               To be confirmed
TBD               To be defined
TBW               To be written
THR               thruster




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2. PHASE 1 EXECUTIVE SUMMARY

The phase 1 of the project aims at defining the inputs necessary to the control study:
   the mission scenarios,
   the vehicles and the environment:
      vehicles mass, center of gravity, inertia, internal disturbances,
      Mars gravitational and atmospheric models, external disturbances,
   the AOCS/GNC architecture:
      sensors and actuators,
      AOCS modes,
   the control techniques for each AOCS mode,
   the control and simulation tool requirements.


2.1 Mission Scenarios

Two mission scenarios have been defined as reference mission [RD02] for the study:
   a Mars Sample Return mission (MSR): This mission consists in 2 vehicles, both directly
   injected towards Mars by launchers. The first module lands on the Mars surface, fetches
   a Martian sample and then takes-off to put the sample in low Mars orbit. Meanwhile,
   the second module performs an aerocapture, then catches the sample using Rendez-
   Vous technique and finally comes back to Earth ejecting the sample into Earth
   atmosphere.
   a Manned mission (MM): a huge vehicle is assembled in low Earth orbit, mainly
   composed of a propulsion module, a crew module, and a landing/ascent module. The
   vehicle inserts into Mars orbit using the high thrust nuclear thermal propulsion. Once in
   orbit, the landing/ascent module separates from the main vehicle with cosmonauts
   on-board. It performs a controlled atmospheric entry, and then takes off back to a low
   Mars orbit as soon as the mission on the Mars surface is achieved. It performs a Rendez-
   Vous with the main vehicle and the whole vehicle comes back to Earth ejecting the
   crew capsule into Earth atmosphere.

Both missions enable to study various critical phases such as aerocapture, propulsive
insertion, rendez-vous and entry.

2.2 Vehicles and Environment

For each mission, the vehicles characteristics (size, mass, CoG, inertia, internal
disturbances) and their environment (disturbances, gravitational and atmospheric
models) have been defined [RD02].

The MSR and MM vehicles are depicted on Figure 2-1. The main MSR vehicles internal
disturbances are the solar arrays flexible modes and the propellant sloshes. The main MM
vehicles internal disturbances are the structural flexible modes and the cosmonauts
motions. It is assumed, indeed, for the manned mission, that the power is generated by a
nuclear reactor, and that the moving propellant mass inside one of the several tanks is
negligible with respect to the vehicle total mass.




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                                                                                                        heatshield
                      heatshield

                                                             EEV
            2nd stage                                                                                                             2nd stage containing:
         with propellant                                                               3m                                         - Surface Module
 3m                                                          Main engine
              tanks                                                                         backcover                             - Planetary Ascent Vehicle

             1st stage                                Stowed SA
                                                                                               1st stage
                thrusters           deployed SA
                                                                                                  thrusters      deployed SA

                                       3m                                                                             3m

              MSR orbiter module (2.4t)                                                             MSR landing module (1.9t)
                                             Crew + Life support + EEV
                                               (Cruise Crew Module)                Landing module:
       Nuclear engine,                                                       Mars Descent & Ascent Vehicle           Mars Launcher (MAV)
      AOCS & Powerplant        Fuel + ta nks
                                                                                                                                                   aeroshell
                                                               35 t

 Ø 10m                                                                                                        Ø 8m


              10 t                                                    80 t
                     RCM     TEM     MIM      CM      TMM                                                                                       crew module
                     70 t    35 t     70 t    150 t   50 t
                                                                                                                           Landing gear
                             80m                               15m     15m
                                                                                                                                    15m
                            MM orbiter module (500t)                                                             MM landing module (80t)
                                    Figure 2-1: overview of the MSR and MM vehicles
Moreover, thanks to very accurate environment models, the Robust Control project
enables a fine restitution of the vehicles trajectories:
   The Mars gravity model is the Mars50c model as defined for the Mars Pathfinder
   project,
   The Mars atmospheric model is the European Martian Climate Database (EMCD)
   v3.1 developed by the Laboratoire de Méteorologie Dynamique (Paris),
   The aerodynamic torques and forces are based on:
      The Mars premier aerodynamic database for the aerocapture,
      The Apollo aerodynamic database for the controlled entry (TBC).

2.3 AOCS/GNC Architecture

The sensors and actuators that are considered in the project have been defined in [RD05]
and are summarized in the following table.
Eqpmt       Mission                     Baseline                    Development Status
IMU      MSR         Honeywell MIMU block 3 (YG9666N) developed
                     composed of 3 ACC QA3000 + 3 Ring Laser
                     GYR GG1320
IMU      MM          Northrop SIRU with gyro based on HRG developed
                     techno
STR      MSR/MM Sodern SED16                                       developed
LIDAR    MSR         MD Robotics and Optech                        To be adapted
RW       MSR         Teldix 0.15Nm/18Nms                           developed
THR      MSR         22N Astrium S22-02                            developed
         MM          400N Astrium S400/2 in pulse mode operation To be adapted



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ME        MSR           400N Astrium S400/2                       developed
NEP       MM            Isp=5000s, thrust=125N, based on 2 YaE-1M To be developed
                        engine performances
NTP       MM            Isp=900s, thrust=300kN                    To be developed
        Figure 2-2: sensors and actuators considered in the Robust Control Project

The AOCS modes that are considered in the project have been defined in [RD04] and are
summarised in the following table:

mode   detailed mode name                    mission   principle
NOMR   Normal Mode Reaction wheels           MSR       3 axis stabilisation on RW
OCM1   Orbit Control Mode 1                  MSR       3 axis stabilisation on thrusters (off-modulation)
OCM2   Orbit Control Mode 2                  MSR       3 axis stabilisation on thrusters (on-modulation) + chemical ME
ARCM   Aerocapture Mode                      MSR       atmospheric flight control with exit orbit
ENTM   Entry Mode                            MSR       atmospheric flight control until parachute deployment
RDVM   Rendez-Vous Mode                      MSR       3 axis stabilisation on RW + DV in any direction + traj. guidance
NOMP   Normal Mode Propulsion                MM        3 axis stabilisation on thrusters (on-modulation)
OCML   Orbit Control Mode Low                MM        3 axis stabilisation on NEP (thrust-modulation)
OCMH   Orbit Control Mode High               MM        3 axis stabilisation on thrusters + orientable NTP + traj. guidance

             Figure 2-3: AOCS modes considered in the Robust Control Project

2.4 Control Techniques

Several Robust Control techniques are traded-off in phase 2 according to the following
table for the different AOCS modes. Their description is provided in [RD04].
                                                                                                      )
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        ARCM, ENTM       X            X          X     X            X
        RDVM             X                       X           X             X
        NOM, OCM                                 X           X

                      Figure 2-4: Control techniques versus AOCS modes
The trade-off leads to the selection of 1 or 2 control techniques per mode. Then the
controller design and development shall be performed for those selected control
techniques.

2.5 Requirements

The controller performances are checked through Monte-Carlo simulations in phase 3.




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The simulation tool shall be developed under the Matlab/simulink environment using the
version 6.5 release 13. A simulation scheme shall be defined for each AOCS mode. The
simulation tool shall enable the configuration of the simulation scheme, the definition of
the scatterings, the run of Monte-Carlo simulations based on those scatterings, and the
post-processing of the simulation results.

The main expected controller performances for each AOCS mode are summarized in the
following table:

   mode                                   main requirements                                                justification
All modes > 6dB/ 15deg equivalent linear stability margins                              Alcatel SB4000 experience
NOMR      pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.05°/ s (3 )                                           LIDAR needs
NOMP      pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.003°/ s (3 )                                          optical navigation camera needs
OCM1      DV accuracy < 6mm/ s up to 1m/ s                                              nav. accuracy at atmosphere entry ~ 100m
          pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.1°/ s (3 )                                            STR needs
OCM2      DV accuracy < 0.3% for DV > 100m/ s                                           propellant alloc. for nav. correction
          pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.1°/ s (3 )                                            STR needs
OCML      pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.1°/ s (3 )                                            STR needs
OCMH      pointing accuracy < 0.05° (3 )                                               HGA needs
          pointing stability < 0.1°/ s (3 )                                            STR needs
          Mars insertion with + / -1000km semimajor axis accuracy                       propellant alloc. for circularization
ARCM      Mars insertion with + / -100km apoapsis and + / -0.5° inclination accuracy    propellant alloc. for circularization
ENTM      horizontal accuracy at parachute deployment < 30km                            Pathfinder controlled entry study result
          terminal velocity at parachute deployment < 0.75km/ s                         parachute needs
RDVM      pointing accuracy < 0.2° (3 )                                                LIDAR needs
          pointing stability < 0.05°/ s (3 )                                           LIDAR needs
          transverse accuracy for the docking < + / -5cm                                basket size wrt sample size
          axial speed for the docking < 5cm/ s                                          basket mechanism needs

                          Figure 2-5: control main requirements and justifications




                                                                                                                           IP002-05
                                                            REF :     RCCT-ASPI-TN-7
ROBUST CONTROL TECHNIQUES FOR
  PLANETARY SPACE VEHICLES                                  DATE :    06/06/05
                                                            ISSUE :   4.0        PAGE : 13/26
ITT/AO/1-4334/02/NL/AG


3. PHASE 2 EXECUTIVE SUMMARY

The phase 2 activities are focused on 2 major activities:
  First, the simulation tool development, including the development of the control
    environment,
  Second the implementation of the AOCS controllers for each identified mission
    phases, followed by the selection for each mission phases of the best control
    approach.


3.1 Simulation Tool Development

The EscapeLight simulation tool provides the possibility to:
 Define the configuration of a Matlab/Simulink simulation scheme,
 Define scatterings,
 Perform the simulations,
 Post-Process the results.




On the main window (left), the user can display the configuration of each Matlab/Simulink
 block. The configuration of the entire simulation scheme is stored in a set-up file. On the
 post-processing window (right), the user can select the post-processing functions to be
applied to the simulation results once the simulation is finished. This window is used to plot
                                         the results.

           Figure 3-1: EscapeLight Main window and Post-Processing Manager

A set-up file has been defined for each control scenario under study. It determines the
configuration of each block contained in the simulation scheme. Two different set-up files
can provide the same configuration for one block. The tables below summarize the
correspondence between set-up files and configuration files for the control environment
of each mode.




                                                                                            IP002-05
           mode.
                                                                                                                                                                                                                        set-up
                                                                                                                                                                                                                                                                                                                                                                                   set-up




                                                                                                                                                                                                                system (.sys) file (.suf)




                                                                                                                                                                                                                ocm2 simu_msr_om_orbit
                                                                                                                                                                                                                        simu_msr_om_orbit




                                                                                                                                                                                                                        simu_mm_om_orbit
                                                                                                                                                                                                                        simu_mm_om_orbit
                                                                                                                                                                                                                        simu_msr_om_cruise2
                                                                                                                                                                                                                ocm1 simu_msr_om_cruise1
                                                                                                                                                                                                                        simu_msr_om_cruise2
                                                                                                                                                                                                                nomr simu_msr_om_cruise1




                                                                                                                                                                                                                        simu_mm_om_cruise2
                                                                                                                                                                                                                ocml simu_mm_om_cruise1
                                                                                                                                                                                                                        simu_mm_om_cruise2
                                                                                                                                                                                                                nomp simu_mm_om_cruise1




                                                                                                                                                                                                                ocmh simu_mm_om_capture
                                                                                                                                                                                                                                                                                                                                                                           system (.sys) file (.suf)
                                                                                                                                                                                                                                                                rcct_str_sodern_sed16




                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                rcct_acc_siru_northrop




                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                           entm simu_msr_lm_entry
                                                                                                                                                                                                                                                                                                                                                                           rdvm simu_msr_om_orbit




                                                                                                                                                                                                                                                                                                 sensors
                                                                                                                                                                                                                                                                rcct_gyr_siru_northrop




                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                           arcm simu_msr_om_capture
                                                                                                                                                                                                                                                                rcct_acc_mimu_honeywell
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            ITT/AO/1-4334/02/NL/AG




                                                                                                                                                                                                                                                                rcct_gyr_mimu_honeywell




                                                                                                                                                                                                                                            X X
                                                                                                                                                                                                                                            X X
                                                                                                                                                                                                                                            X X
                                                                                                                                                                                                                                              X
                                                                                                                                                                                                                                              X
                                                                                                                                                                                                                                              X
                                                                                                                                                                                                                                                                                                 ENVIRONMENT
                                                                                                                                                                                                                                                                rcct_thr_mm                                                                                                                                                                    rcct_str_sodern_sed16




                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                           X
                                                                                                                                                                                                                                                                rcct_thr_msr




                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_str_sodern_sed16_inhib
                                                                                                                                                                                                                                                                rcct_ntp_mm




                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                            actuators
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_acc_mimu_honeywell
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                sensors




                                                                                                                                                                                                                                                                rcct_rw_teldix




                                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_capture_300kN                                                                                                                                                   rcct_gyr_mimu_honeywell




                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                             X X X
                                                                                                                                                                                                                                                                                                                                                                             X X X
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_cruise1_500N




                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_lidar
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_orbit_500N




                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                ENVIRONMENT




                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_thr_msr_1Hz




                                                                                                                                                                                                                                                                                                                                                                               X X X X
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_cruise2_500N




                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          thr.




                                                                                                                                                                                                                                                                rcct_dyn_mm_om_cruise1                                                                                                                                                         rcct_thr_msr_x2




                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                                                                                                                                       X
                                                                                                                                                                                                                                                                                                                                                                                       X
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_orbit




                                                                                                        3.2 AOCS Controllers Development
                                                                                                                                                                                                                                                                                                 attitude dynamics




                                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_rw_teldix
                                                                                                                                                                                                                                                                rcct_dyn_mm_om_cruise2




                                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_dyn_msr_om_orbit_rdvm


                                                                                                                                                                                                                                                                                                                                                                                         X X
                                                                                                                                                                                                                                                                rcct_dyn_msr_om_orbit_400N




                                                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                dyn.




                                                                                                                                                                                                                                                                rcct_dyn_msr_om_cruise2_400N




                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                                                                                                                                                                             X                                                 rcct_dyn_msr_om_capture
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       PLANETARY SPACE VEHICLES




                                                                                                                                                                                                                                                                rcct_dyn_msr_om_cruise1_88N




                                                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_dyn_msr_lm_entry
                                                                                                                                                                                                                                                                rcct_dyn_msr_om_cruise1




                                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_mars
                                                                                                                                                                                                                                                                                                                                                                                                 X
                                                                                                                                                                                                                                                                rcct_dyn_msr_om_orbit




                                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                rcct_dyn_msr_om_cruise2                                                                                                                                                        rcct_mars_atm
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     ROBUST CONTROL TECHNIQUES FOR




                                                                                                                                                                                                                                                                rcct_grav_mars_J2 (spacecraft)




                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                X X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_grav_mars_J2 (spacecraft)


                                                                                                                                                                                                                                                                                                 traj.
                                                                                                                                                                                                                                                                rcct_traj_spacecraft




                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Mars traj.




                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_traj_spacecraft
                                                                                                                                                                                                                                                                                                                                                                                               X X X X X
                                                                                                                                                                                                                                                                                                                                                                                                 X X X X




                                                                                                                                                                                                                                                                rcct_dist_cruise1_msr




                                                                                                                                                                                                                X X
                                                                                                                                                                                                                X X
                                                                                                                                                                                                                                                                rcct_dist_orbit_msr




                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_grav_mars_J2 (sample)
                                                                                                                                                                                                                                                                rcct_dist_cruise2_msr




                                                                                                                                                                                                                      X
                                                                                                                                                                                                                      X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_traj_sample
                                                                                                                                                                                                                                                                rcct_dist_cruise1_mm




                                                                                                                                                                                                                        X
                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                                                 disturbances

                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_dist_orbit_msr
                                                                                                                                                                                                                                                                                                                                                                                                     X X X X X




                                                                                                                                                                                                                                                                rcct_dist_orbit_mm




                                                                                                                                                                                                                          X
                                                                                                                                                                                                                          X
                                                                                                                                                                                                                          X
                                                                                                                                                                                                                                                                rcct_dist_cruise2_mm
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             REF :




                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_dist_aero_arcm
                                                                                                                                                                                                                                                                                                                                                                                                               X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      ISSUE :
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      DATE :




                                                                                                                                                                                                                                                                rcct_str_dp




                                                                                                                                                                                                                            X X
                                                                                                                                                                                                                              X
                                                                                                                                                                                                                              X
                                                                                                                                                                                                                              X
                                                                                                                                                                                                                              X
                                                                                                                                                                                                                              X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_dist_aero_entm
                                                                                                                                                                                                                                                                                                 D/ P




                                                                                                                                                                                                                                                                rcct_acc_dp
                                                                                                                                                                                                                                                                rcct_gyr_dp                                                                                                                                                                    rcct_str_dp




                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                            X X X X
                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                              X X X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                disturb. d/ p




                                                                                                                                                                                                                                                                rcct_thr_mf_mm_set1




                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_acc_dp
                                                                                                                                                                                                                                                                                                 SOFTWARE
                                                                                                                                                                                                                                                                                                       C/ P




                                                                                                                                                                                                                                                                rcct_thr_mf_mm_set1_capture




                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      4.0




                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_gyr_dp
                                                                                                                                                                                                                                                                                                                                                                                                                 X X X X
                                                                                                                                                                                                                                                                                                                                                                                                                   X X X




                                                                                                                                                                                                                                                                rcct_thr_mf_mm_setnep




                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                  X
                                                                                                                                                                                                                                                                                                                        Figure 3-2: ARCM, ENTM, RDVM control environment




                                                                                                                                                                                                                                                                rcct_thr_mf_mm_setnep_off                                                                                                                                                      rcct_lidar_dp
                                                                                                                                                                                                                                                                                                                                                                                                                   X X X X




                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                    X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         SOFTWARE




                                                                                                                                                                                                                                                                rcct_thr_mf_mm_ntp




                                                                                                                                                                                                                      X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_thr_mf_msr_capture
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      06/06/05




                                                                                                                                                                                                                                                                                                                                                                                                                           X




                                                                                                                                                                                                                                                                rcct_thr_mf_msr_orbit_set1_off



                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_thr_mf_msr_entry
                                                                                                                                                                                                                                                                                                                                                                                                                             X




                                                                                                                                                                                                                                                                rcct_thr_mf_msr_orbit_set1
                                                                                                                                                                                                                                                                rcct_thr_mf_msr_orbit_setab                                                                                                                                                    rcct_thr_mf_rdvm
                                                                                                                                                                                                                                                                rcct_thr_mf_msr_orbit_setcd
                                                                                                                                                                                                                          X X X
                                                                                                                                                                                                                            X X                                                                                                                                                                                                                rcct_H_unload
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             RCCT-ASPI-TN-7




                                                                                                                                                                                                                                                                rcct_thr_mf_msr_cruise2_set1
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_rw4_mf
                                                                                                                                                                                                                                                                                                                                                                                                                               X X X




                                                                                                                                                                                                                                                                rcct_thr_mf_msr_cruise2_setab




                                                                                                                                           Figure 3-3: NOMR, OCM1, OCM2, NOMP, OCML, OCMH control environment
                                                                                                                                                                                                                                                                rcct_thr_mf_msr_cruise2_setcd                                                                                                                                                  rcct_mars
                                                                                                                                                                                                                                X X X
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      PAGE : 14/26




                                                                                                                                                                                                                                                                rcct_rw4_mf                                                                                                                                                                    rcct_mars_atm
                                                                                                                                                                                                                                                                rcct_estimator_gyr_str



                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                      X X
                                                                                                                                                                                                                                      X X
                                                                                                                                                                                                                                      X X




                                                                                                                                                                                                                                                                rcct_estimator_nav_cruise
                                                                                                                                                                                                                                                                                                                                                                                                                                               rcct_estimator_gyr_str

                                                                                                                                                                                                                    X
                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                            X
                                                                                                                                                                                                                                                    X




IP002-05
                                                                                                                                                                                                                                                                                                 estim.




                                                                                                                                                                                                                                                                rcct_estimator_nav_orbit                                                                                                                                                       rcct_estimator_nav_orbit
                                                                                                                                                                                                                X
                                                                                                                                                                                                                        X
                                                                                                                                                                                                                                                X
                                                                                                                                                                                                                                                                                                                                                                                                                                         X X
                                                                                                                                                                                                                                                                                                                                                                                                                                     X X X X
                                                                                                                                                                                                                                                                                                                                                                                                                                     X X X X




           have been studied separately, thus enabling the possible use of 2 different techniques per
           During phase 2, the table (cf. figure 2.4) depicting the control techniques to study for
           each mode has been detailed. Indeed the trajectory control and the attitude control
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 actuators mf Mars estim.
                                                                             REF :     RCCT-ASPI-TN-7
ROBUST CONTROL TECHNIQUES FOR
  PLANETARY SPACE VEHICLES                                                   DATE :    06/06/05
                                                                             ISSUE :   4.0        PAGE : 15/26
ITT/AO/1-4334/02/NL/AG




                                                                                                         )
                                                                                                        FT
                                                                                                      (Q
                                                                                                     )




                                                                                                    e
                                                                                                   R




                                                                                                 qu
                                                                                                  )
                                                                                                  )
                                                                                                 Q




                                                                                               PV
                                                                                               EA




                                                                                               ni
                                                                                              (L




                                                                                            (L


                                                                                            ch
                                                                                            t(
                                                                                           or




                                                                                         en




                                                                                        Te
                                                                                          g
                                                                                        at


                                                                                        I)




                                                                                       in
                                                                                     m
                                                                                     D
                                                                                     ul




                                                                                      )




                                                                                    ry


                                                                                   ck
                                                                                  PC
                                                                                  gn
                                                                                  (N
                                                                                 eg




                                                                                Va


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                                                                               l(
                                                                               si
                                                                               R


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                                                                            ed
                                                                           as




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                                                                            io




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                                                                           ic

                                                                        rs




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                                                 at




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                                                                        e




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                                                                     ve




                                                                     m
                                                                    ur
                                               dr




                                                                    in
                                                                   C




                                                                    e
                                                                  ra
                                                                  In


                                                                  ct
                                             ua




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                                                                tiv
                                                                 e




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                                                              tru
                                                      ic
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                                                            i ta
                                                           ity
                                                  am


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                                                 yn




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                                  Li




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                                              D




                                                  H
ARCM/ENTM attitude control        X                    X                 X
ARCM/ENTM trajectory control                 X              X
RDVM attitude control             X                               X
RDVM trajectory control                                X                        X
NOM, OCM attitude control                              X          X
  The Predictive control and the NDI technique fit better the trajectory control than the
 attitude control. The QFT technique is applied to the Clohessy-Wiltshire equations of the
                                 RDVM trajectory control.

               Figure 3-4: control techniques under study for each AOCS modes

Two generic controller architectures have been defined in order to re-use as far as
possible the same Simulink scheme for 2 different tunings: the first one is used for controllers
tuned with EA, LQR, Hinfinity, QFT control techniques, the second one is dedicated to the
LPV control technique. The implementation of the NDI and PC control techniques require
dedicated Matlab functions.




 This architecture uses Matlab LTI systems in                     This architecture corresponds to a state-
order to be as generic as possible. It allows                   space representation with variable A,B,C,D
  state feedback action and feedforward                                           matrixes.
action, in addition to the classical high-level
                  controller.

                               Figure 3-5: controller generic architecture

The robustness of the controller depends on the technique used. Some techniques take
into account the system uncertainties or variations during the synthesis:
 Hinfinity for RDVM attitude controller takes into account the flexible modes
    uncertainties,
 QFT for RDVM translation controller takes into account the spacecraft mass
    uncertainty,
 LPV for ARCM or ENTM attitude controller takes into account the dynamic pressure
    variation along the trajectory.




                                                                                                             IP002-05
                                                             REF :     RCCT-ASPI-TN-7
ROBUST CONTROL TECHNIQUES FOR
  PLANETARY SPACE VEHICLES                                   DATE :    06/06/05
                                                             ISSUE :   4.0        PAGE : 16/26
ITT/AO/1-4334/02/NL/AG

When it is not possible, the robustness is tested a posteriori through linear Monte-Carlo or
further in phase 3 with non-linear Monte-Carlo.

3.3 Selection of the Best Control Approach


3.3.1 Normal Modes (NOMP, NOMR)

The main mission of the Normal Mode is to achieve the required pointing and stability
accuracies while following a possible attitude profile (for instance: yaw or roll steering,
slew for reorientations). Moreover, in the case of NOMR, it shall cope with a limited
actuation capability due to the use of reaction wheels. In the case of NOMP, it shall cope
with the thrusters deadband due to their minimum impulse bit.

The Hinfinity technique fits better to Normal Modes than the Eigenstructure assignment
technique. It enables the filtering of sensors noises, the cut-off of flexible modes, while
ensuring suitable control margins. The controller complexity is after reduction equivalent to
a PID controller with 2 or 3 second order filters. The synthesis effort is limited to the choice
of 4 weighting functions. It can be completed by the addition of a thruster modulator in
case of NOMP in order to cope with the natural thruster deadband. The agility
performance can be improved by the use of a feedforward action.




           Figure 3-6: NOMR controller design (cruise to Mars) for the MSR design

3.3.2 Orbit Control Modes (OCM1, OCM2, OCML, OCMH)

The main mission of the Orbit Control Mode is to achieve the required V accuracy. The
OCM performance will depend mainly on the controller capacity to cope with a
disturbing torque due to the thrust misalignment with the spacecraft center of gravity.
Moreover the controller shall minimize the excitation of the flexible modes and cope with
the thrusters deadbands.

The Eigenstructure Assignment (EA) technique fits better to Orbit Control Modes. It enables
the controller design with high bandwidth in order to reduce the transient pointing error
due to the thrust misalignment with the center of gravity. It can be completed by the
addition of a state feedback that compensates faster the disturbing torque than the
classical integral action of the EA corrector. Thus the performance is better, but the




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robustness shall be carefully checked through a posteriori simulations, due to the possible
excitation of the flexible modes when the synthesis is performed on the rigid dynamics.

However, the technique selected for OCML (L=low) is the Hinfinity technique like in NOMP
because of the low thrust level of this mode.

3.3.3 Atmospheric Modes (ARCM, ENTM)

The Aerocapture and Entry modes tuning is critical because of the high coupling between
translation and attitude control, and because of the large variations in the aerodynamic
forces and torques. Moreover, the controller shall be as far as possible robust to the
environment uncertainties (Mars atmosphere and winds, aerodynamic effects, …).

Concerning the attitude control, the PP, EA, LQR and LPV techniques have led to very
close non linear simulation results. The EA is selected for the next project phase because of
its lowest complexity and greatest tuning flexibility. The EA robustness has been
demonstrated by Linear Monte-Carlo (i.e. root-locus analysis on the controller applied to a
set of linear models covering the model uncertainties and variations). However, its
robustness on non-linear simulations (including the actuators saturation) shall have to be
checked carefully.

Concerning the trajectory control, the classical model-based nonlinear predictive control
has been implemented and discarded because of its high computation load compared
to the poor improvement it brings compared to the selected technique. The selected
technique is composed of (1) an analytical predictor-corrector guidance and control
algorithm (very similar to the classical predictive control technique, but with an analytical
solution) combined with (2) the NDI technique, to obtain a linear controller structure. The
preliminary performances obtained with this combination are promising but the robustness
of the trajectory control can probably be improved by an on-board estimation of the
aerodynamic accelerations and the suitable adaptation of the prediction algorithm.

3.3.4 Rendez-Vous Mode (RDVM)

Simulation results have shown the necessity to implement an estimator of the sample
position in order to be able to achieve the translation control even if the sample is outside
the LIDAR field of view due to transient attitude control error. Thus the coupling between
translation and rotation is only due to the guidance function which aims at aligning the
sample with the LIDAR line of sight at any moment.

The control techniques that have been simulated (LQR and Hinfinity for attitude control,
EA and QFT for translation control), have led to very similar docking performances. For
Hinfinity and QFT, some uncertainties have been taken into account in the synthesis, for
LQR and EA the robustness has been evaluated a posteriori.

In definitive, the controllers designed with the LQR and QFT techniques have been
selected for the phase 3.




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3.4 Conclusion

The list below summarises the techniques that we intend to pursue in phase 3:
 NOMR: Hinfinity
 OCM1: Eigenstructure assignment (EA)
 OCM2: EA with state feedback
 ARCM: EA for attitude control, Dynamic Inversion for translation control
 ENTM: EA for attitude control, Dynamic Inversion for translation control
 RDVM: LQR for attitude control, QFT for translation control
 NOMP: Hinfinity with thruster modulator on x axis
 OCML: Hinfinity with thruster modulator on x axis
 OCMH: EA with state feedback




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4. PHASE 3 EXECUTIVE SUMMARY

The phase 3 of the project focuses on:
 the simulation tool tests and validation of the simulation environment and functions,
 the scattering definition for the Monte-Carlo simulations,
 the AOCS modes final performances evaluation with respect to the control
   requirements.

4.1 Simulation Tool Testing

The Simulink blocks configuration mechanism, the post-processing functions, and the
EscapeLight user interface have been widely tested both by Alcatel and NGC during this
phase.
The scattering function has been tested in accordance with project needs.

4.2 Scattering Definition

The scattering aims at testing the controller robustness for each AOCS mode. It is applied
on the control environment for MSR and MM vehicles, i.e:
 The spacecraft dynamics,
      mass 10%, inertia 20%, flexible modes frequencies 20% and BT/BR 5%, sloshes
        10%,
      The CoG scattering depends on the AOCS mode and the vehicle: 0.5 m for the
        Manned Vehicles, 3 cm for the MSR Vehicles with 2 exceptions: 5 cm for the
        Rendez-Vous due to the 3 dof translation capability and 0.5 cm for atmospheric
        modes due to their criticity.
 The sensors and actuators (IMU, STR, LIDAR, Reaction Wheels, thrusters and nuclear
   engines), in accordance as far as possible with the supplier datas.
 The critical disturbances (EMCD atmospheric model and aerodynamic coefficients):
      The atmospheric model is the Viking scenario with a scattering of small and large
        scale perturbations,
      The aerodynamic coefficients considering a 10% uncertainty on the tables.
   The initial conditions (attitude, angular rate, position and velocity), mainly:
       The initial position and velocity for the atmospheric modes through the latitude
          (0.5 deg), the longitude (0.5 deg) and the flight path angle (0.2 deg),
       The initial attitude (1deg/0.02deg) and rate (0.01deg.s-1/0.005deg.s-1) for the
          NOM/OCM modes,
       The initial position (10m), velocity (10cm/s), attitude (180deg) and rate
          (0.01deg.s-1) for the rendez-vous mode.




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4.3 Final Performances Evaluation


4.3.1 Normal Modes (NOMR, NOMP)

The Hinfinity design has led to very robust controllers that achieve fully the required
performances.

In NOMR, the main difficulty concerns the possible excitation of the solar arrays flexible
modes by the reaction wheels unloading thrusters pulses. This problem has been solved by
introducing a random delay on the pulse command.
In NOMP, the main difficulty concerns the pointing and stability accuracy on x axis limited
by the thrusters minimum impulse bit. This problem could be solved by modifying the
thrusters configuration (for instance twice more thrusters of the half thrust).

4.3.2 Orbit Control Modes (OCM1, OCM2, OCML, OCMH)

The Eigenstructure Assignment design for OCM1, OCM2 and OCMH has led to high-
performance controllers, with quite good robustness:
 Good performance and robustness in OCM1: the DV accuracy is achieved with
   margins for all the simulation cases.
 Quite good performance and only 1 case of divergence in OCM2 cruise back to Earth,
   due to the excitation of the solar array flexible mode. It appears indeed that the
   controller tuning was challenging due to the stringent DV accuracy requirement, the
   high thrust (400N) and the pessimistic 0.001 solar arrays flexible modes damping factor.
   The increase of the damping factor to a more realistic value (0.003) has improved both
   pointing and stability performance, and removed the divergence. However, the
   pointing stability accuracy is not compatible of Star-Tracker measurement and should
   be replaced by integration of gyrometer measurement.
 Good performance and robustness in OCMH: the final orbit semi-major axis accuracy is
   about a few kilometers, far below the specification.

The exceed in some cases of the pointing requirement is not considered as critical due to
the short duration of the maneuvers and the fact that communications are still possible
with the LGA.

The Hinfinity design for OCML has led to very robust controllers. However, the pointing
accuracy on X axis exceeds the specification due to the control in deadband imposed by
the thrusters minimum impulse bit, and reduces the possible communication with the HGA
during the cruises to Mars and back to Earth. This problem could be solved by modifying
the thrusters configuration (for instance twice more thrusters of the half thrust).

4.3.3 Atmospheric Modes (ARCM, ENTM)

The combination of EA and NDI techniques for attitude and translation control have led to
mitigated results which are not related with the control aspect.




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The main difficulty stems from the saturation of the thrusters: they are not sufficiently
powerful to follow the commanded angle, meaning that either the guidance, either the
thruster configuration need improvements.

For ENTM, the by-passing of the thrusters generates excellent results: 95% of simulation
cases comply with the 30km horizontal accuracy and the 750m/s maximal terminal
velocity.

For ARCM, the by-passing of the thrusters generates quite good results: 80% of simulation
cases achieve a 1700km final apoapsis with 100km accuracy and a 0.5deg inclination
accuracy.



4.3.4 Rendez-Vous Mode (RDVM)

The combination of LQR and QFT techniques for attitude and translation control has led to
good performance controllers, with good robustness in coherence with the linear
analyses.

In RDVM, the main difficulty concerns the coupling effect between the translation and the
rotation due to CoG offsets. The problem has been solved by disabling the thrusting
command when the attitude error is too important. Another problem is the pointing
stability performance which is not compatible of a continuous LIDAR measurement,
meaning that an estimator of sample position, that is regularly updated by available
LIDAR measurement, should be implemented.

With these improvements, only 5 cases over 100 simulations are outside the 10cm
docking accuracy.




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RDVM docking performance:                      ENTM horizontal accuracy (*):




                                               * assumes a by-pass of the thrusters
NOMR Hinfinity controller robustness:          ARCM apoapsis accuracy (*):




                                               * assumes a by-pass of the thrusters
OCM1 Delta-V Realization Error:                OCMH final orbit semi-major axis accuracy:




                    Figure 4-1: overview of Monte-Carlo simulation results




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5. PHASE 4 EXECUTIVE SUMMARY

The phase 4 is dedicated to the final delivery of the study. The delivery consists in :
- a CDROM, named ‘RCCT – Software Delivery’, that was provided to ESA during the 3rd
   Progress Meeting, the 09th June 2005. The following paragraph describes briefly the
   content of this CDROM.
- A CDROM, named ‘RCCT – Technical Notes’, that gathers all the documentation
   produced during the study. The list is given in paragraph 1.1 entitled reference
   document. A subset of these technical notes is dedicated to ESA internal diffusion and
   stored on a CDROM, named ‘RCCT – Technical Notes for ESA’.

5.1 ‘RCCT – Software Delivery’ CDROM

The delivered CDROM RCCT – Software delivery contains :

       -   the latest version of EscapeLight tool, provided as a gzipped tar archive (.tar.gz).
           The installation of the software is entirely described in [RD16].
       -   the simulated systems, gathered in the directory rcct. Each system corresponds
           to an AOCS mode. Five or six examples of simulation results per mode are given,
           in order to enable the user to test EscapeLight facilities without running the
           simulations. [RD16] also provides a quick guide to replay already existing
           systems, that can be useful. The nomenclature of the different kind of files is
           available in [RD16] and [RD35].
       -   some controllers synthesis tools, provided in the directory synthesis_tools. A
           complete description of this directory and keys to use the synthesis tools are
           provided in [RD28].

Extra inputs to run the provided files :

       -   ENTM and ARCM modes use the EMCD database as an atmospheric model. You
           have to provide the path towards this database in the corresponding
           configuration files (configs.dir/model_emcd31.lit/rcct_atm_emcd31_dat.m).
       -   Files to synthesize RDVM use the Matlab QFT Toolbox. In order to do the controller
           synthesis you will have to put this toolbox in the corresponding directory, as
           specified in [RD28].

5.2 ‘RCCT – Technical Notes for ESA’ CDROM

This CDROM contains the following notes :
       - Executive Summary
       - Robust Control Design Techniques
       - Simulator Test Run compilation document
       - NOM Final Performances
       - OCM Final Performances
       - RDVM, ARCM, and ENTM Final Performances
       - EscapeLight User’s Manual
       - Conclusion and Recommendations




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      -   Slides of the Final Review




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