Ulysses Attitude and Orbit Operations Years of International

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					Ulysses Attitude & Orbit Operations
13+ Years of International Cooperation




                                                                   Khee Chan (presenter)
                        SciSys (Space & Defence) Ltd, Pasadena, CA, USA; Khee.Chan@jpl.nasa.gov

                                                                        Ephrem Paredes
                              Raytheon ITSS, Pasadena, CA, USA; Ephrem.S.Paredes@jpl.nasa.gov

                                                                                Mark Ryne
                                Jet Propulsion Lab, Pasadena, CA, USA; Mark.S.Ryne@jpl.nasa.gov
             Ulysses Attitude and Orbit Operations
                SpaceOps 2004, Montreal, 17-21 May 2004



         Outline of Presentation
•   Overview of Ulysses mission
•   AOCS description
•   Attitude operations
•   Orbit operations
•   Nutation damping operations
•   Questions and answers




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                  Ulysses Attitude and Orbit Operations
                      SpaceOps 2004, Montreal, 17-21 May 2004



                  Mission Overview
• Joint ESA-NASA mission
   – “… to make the first-ever measurements of the unexplored
     region of space above the Sun's poles.”
   – Launched on 6th October 1990
      • Delayed 4 years due to Challenger accident
   – Mission extended till March 2008
      • Completion of 3rd set of solar polar passes
• Ground stations
   – Routine support - NASA Deep Space Network
   – Non-routine support:
      •   ESA Kourou, French Guiana
      •   ESA New Norcia, Australia
      •   DLR Welheim, Germany
      •   Univ of Chile, Santiago station (uplink only)

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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



       Mission Operations Team
• Joint ESA-NASA mission operations team
  – At Jet Propulsion Laboratory, Pasadena, USA
  – Multi-national, multi-agency, multi-contractor
  – ESA
     • Flight control team
     • 12 full-time including management & admin support
  – NASA/JPL
     • Ground operations, navigation & data management
       teams
     • 6 full-time



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Ulysses Attitude and Orbit Operations
   SpaceOps 2004, Montreal, 17-21 May 2004



   1st Solar Orbit




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Ulysses Attitude and Orbit Operations
   SpaceOps 2004, Montreal, 17-21 May 2004



  3rd Solar Orbit




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               Ulysses Attitude and Orbit Operations
                  SpaceOps 2004, Montreal, 17-21 May 2004



            AOCS Description 1
• Spin stabilised at 5 rpm
• Attitude sensors
  – Sun direction
     • 2 cross-beam sun sensors
     • 2 meridian slit sun sensors
  – Earth direction
     • Conical scanning of S-band uplink from ground station
         – S-band antenna feed offset by 1.8º from spin axis
     • Modulation of uplink carrier
         – Amplitude  Off-pointing from Earth
         – Phase  Direction to Earth


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                 Ulysses Attitude and Orbit Operations
                    SpaceOps 2004, Montreal, 17-21 May 2004



              AOCS Description 2
• Reaction control
  – Blow-down system
  – Monopropellant hydrazine
     • 33.5 kg at start-of-life
     • 7.9 kg end-Jan 2004
     • 4.7 kg end-Dec 2008 (est)
  – Nitrogen pressurant
  – 8 thrusters in 2 blocks of 4
     •   1 pair lower & upper axial
     •   1 pair spin up & down
     •   2 N (@ 22 bar) at start-of-life
     •   0.6 N (@ 5 bar) at end-of-life


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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



  Routine Attitude Manoeuvres 1
• Open-loop slew to maintain Earth pointing
  – Pulsed firing of axial thruster
     • Pulse width 3.2º ( 107ms @ 5 rpm)
     • LA1 used predominantly – well characterised
     • UA2 to be avoided – plume impingement
• Manoeuvre schedule driven by:
  – Earth drift rate and max Earth off-pointing
     • Link margin determines max Earth off-pointing
     • Varies from 0.3º to 1.2º
  – On-board activities
     • command buffer can only hold 40 time-tag blocks
  – Power sharing

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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



  Routine Attitude Manoeuvres 2
• Power constraints for manoeuvres
  – At least 6 W for catalyst bed preheating
  – Preheating reduced to 85 min
     • Just enough to reach holding temperature (~150ºC)
  – No uplink
  – No tape recorder operation




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               Ulysses Attitude and Orbit Operations
                  SpaceOps 2004, Montreal, 17-21 May 2004



 Non-Routine Manoeuvre Example
• Solar Conjunction Manoeuvres
  – Sun between Earth and spacecraft
     • Telecoms disrupted due to solar noise
     • S/C loses attitude reference below 0.5º sun angle
     • Next conjunction on 1-Sep-2004
         – Earth range - 6.4AU
         – Sun angle < 0.4º @ Earth pointing attitude
  – Open-loop slews to avoid Sun
  – CONJ on-board program
     • Thruster parameters (# of pulses & phase delay)
     • Repetition count
     • Execution interval


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Ulysses Attitude and Orbit Operations
   SpaceOps 2004, Montreal, 17-21 May 2004



CONJ Manoeuvres




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             Ulysses Attitude and Orbit Operations
                SpaceOps 2004, Montreal, 17-21 May 2004



            Orbit Operations 1
• Launch
  – On-board space shuttle
    Discovery to low Earth orbit
  – 2 solid rocket motor upper
    stages
     • Inertial Upper Stage (IUS)
     • Payload Assist Module (PAM-S)




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                 Ulysses Attitude and Orbit Operations
                    SpaceOps 2004, Montreal, 17-21 May 2004



               Orbit Operations 2
• Gravity assist at Jupiter
   – Orbital plane rotated from in-ecliptic to over the Sun’s poles
   – Ecliptic relative inclination changed from 2.3 to 85.1º
   – Perihelion distance raised from 1.0 to 1.4 AU
       • Ulysses was never closer to the Sun than on launch day


• Jupiter closest approach
   – 8th February 1992 06:00:34 UTC
   – Jovicentric distance – 408,894 km (6.3 Rj)


• Data from fly-by improved knowledge of Jupiter’s
  position


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             Ulysses Attitude and Orbit Operations
                SpaceOps 2004, Montreal, 17-21 May 2004



    Orbit Determination Strategy
• Monthly solution
  – 90 day data arc
  – 60 day overlap
• Post-fit orbit propagation assumes:
  – Continuous Earth pointing
  – Predicted attitude manoeuvres based on Earth
    drift rate
• Predicted solution spans 1 year and 1 month



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             Ulysses Attitude and Orbit Operations
                SpaceOps 2004, Montreal, 17-21 May 2004



                    Nutation 1
• Serious spacecraft nutation appeared on 4th
  November 1990
  – 2.3º full cone nutation within 6 hours
  – Max of 6º full cone over the next 11 days
• Differential solar heating causes axial boom
  to flex
• Boom flexing made worse by:
  – Free play at boom root
  – Efficient motion transmission from boom to
    spacecraft body at deployment motor
  – Nutation dampers not tuned for this behaviour

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             Ulysses Attitude and Orbit Operations
                SpaceOps 2004, Montreal, 17-21 May 2004



                    Nutation 2
• If nutation left unchecked:
   – Large antenna off-pointing  Lower data rate 
     Lower science return
   – Large uncertainties in attitude  Degraded
     science return
   – Possible structural failure of boom  Damage to
     rest of spacecraft




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Ulysses Attitude and Orbit Operations
   SpaceOps 2004, Montreal, 17-21 May 2004



       Nutation 3




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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



           Nutation Damping 1
• 1st nutation season
  – November to December 1990
  – Enable Closed-Loop CONSCAN
     • Autonomous control mode to fire thruster to reduce Earth
       off-pointing
     • Thruster firings reduce nutation
  – Works only when
     • Uplink signal available
     • Nutation angle > CLC deadband
     • Earth off-pointing > CLC deadband



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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



           Nutation Damping 3
• 3rd nutation season
  – November 2000 to December 2001
  – Similar technique to 2nd season
     • Open-loop slew away from Earth
     • Closed-loop CONSCAN enabled during slew!
     • Leave CLC enabled after slew
  – Results in more closed-loop CONSCAN thruster
    firings
     • Nutation damped to lower levels in shorter time




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      Ulysses Attitude and Orbit Operations
         SpaceOps 2004, Montreal, 17-21 May 2004



Ulysses Mission Ops Web Site



http://ulysses-ops.jpl.esa.int/




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  Ulysses Attitude and Orbit Operations
     SpaceOps 2004, Montreal, 17-21 May 2004




Reserve slides follow
                  Ulysses Attitude and Orbit Operations
                     SpaceOps 2004, Montreal, 17-21 May 2004



              Orbit Characteristics
• Polar Heliocentric Orbit
   – Earth Mean Equator 1950 reference frame
   – Data for 1-Jan-2004 00:00:00 UTC
      •   Semi-major axis:                    506540923.365 km (3.39 AU)
      •   Eccentricity:                       0.596
      •   Inclination:                        100.976º
      •   Argument of perihelion:             350.268º
      •   Longitude of ascending node:        337.346º
      •   True anomaly:                       170.876º
      •   Mean anomaly:                       151.390º
      •   Period:                             6.23 years
      •   Perihelion radius:                  204449137.356 km (1.37 AU)
      •   Apohelion radius:                   808632709.373 km (5.41 AU)
      •   Distance to Earth:                  2414.982 light seconds
                                              (40.25 light minutes)

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Ulysses Attitude and Orbit Operations
   SpaceOps 2004, Montreal, 17-21 May 2004



  2nd Solar Orbit




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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



        Attitude Determination
• Preprocessing of measurements
  – Solar aspect angle
     • Calculated on-ground from time of Sun transits
  – CONSCAN sine & cosine components
     • From telemetry
• Linear least squares fit of measurements
• How good is the solution?
  – Statistics of measurement residuals
  – “Global accuracy” value derived from the error
    covariance matrix

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                 Ulysses Attitude and Orbit Operations
                     SpaceOps 2004, Montreal, 17-21 May 2004



              AOCS Description 3
• Autonomous AOCS modes
  – Closed-loop CONSCAN control
      • Maintain Earth pointing by firing axial thruster
  – Closed-loop spin control
  – Solar aspect angle control
      • Slew to a given SAA
  – Constant solar aspect angle slew
• CONJ program
  – Repeat pre-planned attitude manoeuvre multiple times
  – Intended for solar conjunctions when uplink not possible




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 Ulysses Attitude and Orbit Operations
    SpaceOps 2004, Montreal, 17-21 May 2004



AOCS Description 4




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                 Ulysses Attitude and Orbit Operations
                    SpaceOps 2004, Montreal, 17-21 May 2004



   Routine Attitude Operations 1
• Routine Phase Management System (RPMS)
  – Subset of the Ulysses Flight Dynamics System for non-FD
    specialists
  – Shell driven manual execution of routine attitude operations
    procedures
      •   Manoeuvre planning
      •   Manoeuvre telecommand generation
      •   Manoeuvre monitoring
      •   Attitude determination
      •   Manoeuvre performance evaluation
      •   Attitude history file update
  – No need to refer to written procedures
  – Input range checking

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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



    Routine Attitude Operations 2
• Manoeuvre description file
   – Contains observed and estimated attitude and
     thruster data
   – E-mailed to navigation team
• Attitude history file
   – Made available via mission ops web site
   – Used by
      • Navigation team
      • Data management team
      • Science teams


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               Ulysses Attitude and Orbit Operations
                  SpaceOps 2004, Montreal, 17-21 May 2004



         Trajectory Corrections
• Trajectory correction manoeuvres
  – Three TCM’s outbound to Jupiter
  – Implemented as “vectored” V
     • Thrust in axial and radial directions separately
     • Vector sum of axial and radial V = required V
  – Compared to “turn and burn” V
     • NO loss of Earth pointing (!)
         – Continuous high rate telemetry
         – No Earth reacquistion to re-establish comms
     • Higher fuel consumption



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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



                 Tracking Data
• DSN 34 m and 70 m antennas
  – S-band uplink
  – X-band downlink
• Tracking data corrected for spin induced
  Doppler bias
• Measurement types & weights:
  – Doppler data (~ 1 pass per day)
     • Weight: 0.2 mms-1
  – Range data (~ 1 pass per week)
     • Weight: 5 m

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                 Ulysses Attitude and Orbit Operations
                     SpaceOps 2004, Montreal, 17-21 May 2004



         Orbit Estimation Strategy
• Orientation modelling based on spacecraft attitude
   – Improves accuracy of solar radiation pressure acceleration
• Estimated parameters:
   – Spacecraft state
   – Attitude manoeuvres
       • Radial direction from spacecraft to Earth
   – Specular reflectivity coefficient
• Stochastically estimated parameters:
   – Station range measurement bias
   – Miscellaneous non-gravitational accelerations




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                 Ulysses Attitude and Orbit Operations
                    SpaceOps 2004, Montreal, 17-21 May 2004



              JPL Orbit Software
• DPTRAJ (Double Precision Trajectory)
   – Trajectory modeling and propagation programs
• ODP (Orbit Determination Program)
   – Orbit estimation and prediction set
• NavShell
   – PERL wrapper for the DPTRAJ/ODP programs
   – Sequential ODP calls
   – More user-friendly interface
• ARGOS
   – Monitor spacecraft nutation and thruster firings
   – Uses received AGC signals at ground stations


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              Ulysses Attitude and Orbit Operations
                 SpaceOps 2004, Montreal, 17-21 May 2004



           Nutation Damping 2
• 2nd nutation season
  – August 1994 to August 1995
  – Open-loop slew
     • N thruster pulses
     • Away from Earth to increase off-pointing
  – Then enable closed-loop CONSCAN




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