Spacecraft System and Payload

Tielong Zhang

On behalf of the CGS Team in the Institute of Geology and Geophysics, Chinese Academy of

Science

Spacecraft System and Payload

China Geomagnetism Satellite Mission

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

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

• Research Announcement

1995: First Ørsted International Science Team (ØIST) meeting

• 100 participants, 60 foreign

1997: Ready for launch!

1999: Launch on February 23

Ørsted

Vector magnetometerco-located withstar imager

Heritage

ØrstedLaunched on 23th February 1999 Polar orbit, 650-850 km altitudeall local times within 790 days (2.2 years)

CHAMPLaunched on 15th July 2000low altitude (<300 - 450 km)all local times within 130 days

SAC-C Launched on 21th November 2000700 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

Spacecraft

Payload

Platform

Advanced Stellar Compass

Power Supply Subsystem

Attitude and Orbit Control Subsystem

Structure and Mechanism Subsystem

On-board Data Handing Subsystem

Thermal Control Subsystem

Communication Subsystem

d

Absolute Scalar Magnetometer

Fluxgate Magnetometers

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

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 Mass Budget

Average （ W ） Maximum （ W ）Spacecraft 40

AOCS 3

OBDH 15

TC/TM 10 30

Thermal 5

Power supply 7

Payload 20

Total 60 80

Spacecraft Power Budget

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

Sun Sensor×1

GPS Receiver×1

Attitude Control

Gravity gradient stabilization

3 Magnetorquers for active control

ASC

Magnetometer

GPS receiver

Attitude &Orbit determination

Sun sensor

Attitude control unit

Magnetorquers

On board CAN bus

OBDH System

AOC software

Attitude Control

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 Polar 87.4 Polar 86.8

Initial altitude km

550.0

Altitude after 5 year km

506.0 477.5 477.0

Time when altitude at 20

0km9 yr 8 mth 8 yr 4 mth 8 yr 4 mth

Eclipse

15°equatorial satellite ， longest eclipse duration 35.8min

Durat i on(s)

1900

1930

1960

1990

2020

2050

2080

2110

2140

20150601 20160327 20170121 20171117 20180913 20190710 20200505

Date

Eclipse

87.4°polar satellite ， longest eclipse duration 36min

Durat i on(s)

- 200

0

200400

600

800

1000

1200

1400

16001800

2000

2200

20150601 20160327 20170121 20171117 20180913 20190710 20200505

Date

Eclipse

86.8°polar satellite ， longest eclipse duration 36min

Durat i on(s)

- 200

0

200400

600

800

1000

1200

1400

16001800

2000

2200

20150601 20160327 20170121 20171117 20180913 20190710 20200505

Date

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 downloadingGround

stationOrbits 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

86.8° Beijing 4 2.783 9.874 25.670

Kashi 4 7.448 9.341 33.655

Sanya 4 3.843 9.294 26.583

Payload

Two fluxgate magnetometers

One scalar magnetometer

One star sensor