Mission Requirements - CubeSat by fjzhangweiyun

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									University of Leicester                  PLUME                  Ref: PLM-SYS-MRD-603-1
                                                                          Date: 29/02/2009

                          Mission Requirements Document

                                       D.S.W.Gray



         Date              Updated Reference Number                      change

      25/02/2009              PLM-SYS-MRD-603-1                    first version issued




The purpose of this document is to assign strict budgets to satellite sub-systems for
reference by team members. The limit of mass, volume, power, dimensions and in some
cases cost of each of the sub-systems is stated. The sub-systems considered are PAY,
COMS, OBDH, PSU and ADCS (adopting standard PLUME vocabulary). The data budget
of the system shall also be considered.



PSU

The power supply (PSU) has been purchased from a commercial company. It has a mass of
153g and volume of 155000mm3, and occupies 1 printed circuit board (PCB). Internal power
consumption should be under 36mW. Power supply depends on the side of the cubesat that
is facing the Sun and whether the cubesat is in eclipse.



PAY

The payload (abbreviation PAY) consists of 2 Micro Channel Plates and an optical camera.
Total mass of the system should not exceed 250g. The power consumption of both the
MCPs and the camera on average should be less than, and not exceed 830mW.



$3250 has been assigned to flight hardware procurement, though this will change with the
economic climate.



The MCPs will attach to the external faces of the cubesat. Solar panels will occupy unused
space around them. The payload electronics will occupy a single PCB of dimensions 90mm
by 96mm. The selected camera will occupy a volume of 11200mm3. Total payload volume
must not exceed 90000mm3, however this will largely depend on the PCB layout. The MCPs



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University of Leicester                     PLUME                    Ref: PLM-SYS-MRD-603-1
                                                                               Date: 29/02/2009

will not extend beyond 6mm of the surface of the cubesat to ensure a clean release from the
orbital deployer.



MCP data is not considered by the sub-system. The camera will produce raw images of 5
Mbits, however OBDH will introduce JPEG compression.



ADCS

The ADCS uses a specialist chip (HMC1053) containing 3 magneto-resistors. The change
in resistance indicates the change in the local magnetic field caused by the satellite rotating
in the Earth's magnetosphere. Solar panel voltage will also give indication as to the attitude.
No attitude control will be included. Time of flight will indicate the satellite's position based
on radar data (TLEs) from Norad.



The total cost of the subsystem will be approximately £400 depending on the economic
climate.



The maximum power available less than 100mW. The average power is estimated to be
62mW. 6g have been allocated for ADCS components, not including the PCB, comprising
mostly of FR-4. 45 by 25 by 10mm will be allocated for the system. The subsystem will
share PCB space with PAY.



Attitude readings will not be greater than 12 bytes per reading for the solar panel voltage
component, and 6 bytes for the magneto-resistors not including time tagging. ADCS will be
handled by OBDH in association with position confirmation, satellite tumbling rates and
payload events.



OBDH

The on-board computer (OBDH) is a Cubesat Kit using an FM430 micro-processor. The
system has a mass of 74g and a power consumption of 20mW. The board has a volume of
121500mm3. This sub-system has already been procured and so cost is not considered in
this document.



The main consideration for OBDH is the data rates produced. The payload requires 32
bytes per reading. This includes a time reading, temperature, ADCS data, solar panel
voltage and charge reading from the MCPs. The OBDH can trigger a number of calibration
readings periodically or on demand from the satellite by uploading the request during a pass
of the satellite in range of a project ground station. All data must be stored to solid state

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University of Leicester                    PLUME                  Ref: PLM-SYS-MRD-603-1
                                                                            Date: 29/02/2009

memory in preparation for transmission to a ground station. OBDH must compress 5 Mbit
images from the camera in JPEG formate so that these images may be downloaded and
leave time for MCP data and command uploads. The level of compression depends on the
number of calibration and event readings taken.



OBDH must be able to recover the satellite data bus should a Single Event Anomaly occur.



COMS

The communication sub-system must have a mass under 150g excluding the antenna. The
power consumption must be 200mW or less when on standby (waiting for a command), and
2W when transmitting. COMS will occupy a secondary board connected to the OBDH
board. The dimensions of this board has already been determined by the mechanical
interface of the board. The height of the system above the OBDH board must not exceed
25mm.



The communication system must be capable of downloading 300 bytes per second, which
will be sufficient for the data rate of OBDH given a time in view of 3 minutes every 24 hours.



MEC

Mechanical interfaces are laid out in the PCB dimensions document. A stacking document
will detail the mechanics of interfacing the PCBs with the cubesat structure.



All components will have 'mil-spec' tolerances to temperature, between -45 to 80 degrees
Celsius, and be hardened to the effects of the launch environment (~400Hz large amplitude
vibrations).



The passive thermal design will ensure that the satellite does not exceed its maximum
allowed temperature in full sunlight and does not freeze out in eclipse.



Total Budgets

The mass allocated presently to the subsystems is 633g of 800g. The power consumption
during transmission is 2985mW. All other times it is 1186mW. Currently 377750mm 3 of
volume has been allocated of a possible 729000mm3. Not included in the allocated space is
the volume of the OBDH or PSU board.




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University of Leicester    PLUME        Ref: PLM-SYS-MRD-603-1
                                                  Date: 29/02/2009




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