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China Geomagnetism Satellite Mission
Spacecraft System and Payload
Tielong Zhang
On behalf of the CGS Team in the Institute of Geology
and Geophysics, Chinese Academy of Science
Magsat
 First high resolution vector field measurement
 Nov 1979 – May 1980 – 7 month data
Vector magnetometer and
star tracker are not collocated
Degraded vector data accuracy
Ørsted
 1991: Selection of idea to fly a
magnetometer on a Danish satellite
 1991-1992: Feasibility study
• International Review, March 1992
 1993: Funding for the total project
decided
• Work package contracts
Vector• Research Announcement
magnetometer
 1995: First Ørsted International Science
Team (ØIST)
meeting
co-located
with
star imager
• 100 participants, 60 foreign
 1997: Ready for launch!
 1999: Launch on February 23
Heritage
 Ørsted
Launched on 23th February 1999
Polar orbit, 650-850 km altitude
all local times within 790 days (2.2 years)
 CHAMP
Launched on 15th July 2000
low altitude (<300 - 450 km)
all local times within 130 days
 SAC-C
Launched on 21th November 2000
700 km altitude, fixed local time 1030/2230
China Mission Baseline
 5 satellites
constellation
 4 polar orbit + 1
equtorial orbit
 Identical payload for
all satellites
Spacecraft System Architecture
Fluxgate Magnetometers
Payload
Advanced Stellar Compass
Absolute Scalar Magnetometer
Spacecraft
Structure and Mechanism Subsystem
Attitude and Orbit Control Subsystem
Power Supply Subsystem
Platform
On-boardd Data Handing Subsystem
Thermal Control Subsystem
Communication Subsystem
Spacecraft Configuration
 Main body plus tripod
bracket
 3 m deployable boom
 Cross section ~0.4m2
S/C Configuration
Spacecraft Configuration
 Octagon Prism
 Φ0.8m×1.0m
S/C Configuration
 Main body Shape:
 Octagon prism with a
tripod bracket
 On orbit status:
 5m boom attaches to
the bracket
 Size:
 Φ0.8m×3.5m (in
Launch Status );
 Φ0.8m×8.5m (in Flight
Status)
boom folded
boom
deployed
Main Technical Performance Specification
Spacecraft Mass Budget
Mass（kg）
Spacecraft
95
Bus
25
ACS
6
OBDH
8
TC/TM
10
Thermal
6
Power
25
Boom
15
Payload
10
System Contingency
10
Total
115
Spacecraft Power Budget
Average（W）
Spacecraft
Maximum（W）
40
AOCS
3
OBDH
15
TC/TM
10
Thermal
5
Power supply
7
Payload
20
Total
60
30
80
Structure and Mechanism Subsystem (SMS)
 Structure:
 The structure consists of several aluminum-honeycomb
panels.
 Mechanism:
 Mainly mechanism:2 deployable Boom (for each is 2.5m
long)
 Function:
 ensure a magnetic clean environment
 stable accommodation for the sensors.
Boom
folded
Boom
deployed
Attitude and Orbit Control Subsystem (AOCS)
 Attitude & Orbit Determination
 ASC (star imager with 3 camera
head)×1
 Magnetometer×1
OBDH System
AOC software
 Sun Sensor×1
On board CAN bus
 GPS Receiver×1
 Attitude Control
ASC
 Gravity gradient stabilization
 3 Magnetorquers for active
control
Attitude control unit
Magnetometer
GPS receiver
Magnetorquers
Sun sensor
Attitude Control
Attitude &Orbit determination
RF Communication Subsystem (RFCS)
 The RFCS is responsible for
 Telemetry, Tracking and Command (TT&C),
 Payload data transmission.
 The RFCS consists of communication receive & transmit
device and two antennas.
 Uplink and downlink in S-band
 Downlink data rate is 2 Mbit/s;
 Uplink date rate is 2 kbit/s.
Thermal Control Subsystem (TCS)


Mode: passive means.
Temperature range in cabin:-10°C － +35°C
On-board Data Handling Subsystem (OBDH)
 The OBDH is responsible to:
 data and task management;
 onboard timing;
 onboard command
 The OBDH consists of :
 on board computer,
 tele-command unit,
 payload data storage and control unit,
 thermal control unit,
 On board net: CAN bus.
 On board computer:
 20 MHz CPU
 2 MByte SRAM
Power Supply Subsystem (PSS)
 The PSS is responsible to:
 Power generation,
 Power distribution
 Power storage.
 Operation mode：
 the solar-panel generates electrical power in sunlight
 Li-ion batteries supply power in eclipse.
 PSS consists of solar panels, batteries and Power Control Unit
 Solar panels：
 GaAs triple-junction
 body-mounted solar panels
 Area: ~3m2
 Output power: 150w in average;
 Batteries：7-cell Li-ion battery packs, 10Ah;
 Single-primary-bus mode distributes power to equipments (28.5±1V)。
Orbital Parameter
。
Equatorial
Polar
Altitude
550 km
550 km
Inclination
15
87.4，86.8
Orbit
 RAAN variation
 15°equatorial：period 49 day
 87.4°polar：period 1060 day
 86.8°polar：period 861day
15°equatorial
87.4°polar
86.8°polar
Orbit decay Equatorial Satellite
Orbit decay Polar Satellite 87.4
Orbit decay Polar Satellite 86.8
Orbit Decay
Equatorial
Initial altitude
km
Altitude after
5 year km
Time when
altitude at
200km
Polar 87.4
Polar 86.8
550.0
506.0
477.5
477.0
9 yr 8 mth
8 yr 4 mth
8 yr 4 mth
Eclipse
 15°equatorial satellite，longest eclipse duration 35.8min
Duration(s)
2140
2110
2080
2050
2020
1990
1960
1930
1900
20150601
20160327
20170121
20171117
Date
20180913
20190710
20200505
Eclipse
 87.4°polar satellite，longest eclipse duration 36min
Duration(s)
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
-200
20150601
20160327
20170121
20171117
Date
20180913
20190710
20200505
Eclipse
 86.8°polar satellite，longest eclipse duration 36min
Duration(s)
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
-200
20150601
20160327
20170121
20171117
Date
20180913
20190710
20200505
Ground Stations for Data Receiving
Ground Stations for Data Receiving
 Equatorial satellite: Sanya station, 60 min visible time per day
 Polar satellite, 3 stations, 80 min visible time per day for data
downloading
Ground
station
Orbits
visible
per day
Visible
time per
day (min)
Visible
time per
day (min)
Total visible time
per day (min)
15°
Sanya
7
5.689
10.234
61.444
87.4
°
Beijing
4
4.367
9.826
28.913
Kashi
4
6.119
9.651
31.817
Sanya
4
6.261
8.690
30.114
Beijing
4
2.783
9.874
25.670
Kashi
4
7.448
9.341
33.655
Sanya
4
3.843
9.294
26.583
86.8
°
Payload
 Two fluxgate magnetometers
 One scalar magnetometer
 One star sensor