|General Spacecraft Information (Twin Satellites)
Width: 1942 mm
Length: 3123 mm
Height: 720 mm
Mass: 487 kg per satellite
Design Life: 5 years
Two satellites, co-orbiting at near polar inclinations at 300-500 km altitude.
Separated along track by 220 km.
K-band Ranging System. Provides precise (within 10 µm) measurements of the distance change between the two satellites and hence measures the fluctuations in gravity.
S-band Boom. Used to send data from the satellites back to Earth for processing.
SuperSTAR Accelorometers. Precisely measures the non-gravitational accelerations acting on the satellite.
Star Camera Assembly. Precisely determines satellite orientation by tracking them relative to the position of the stars.
Ultra Stable Oscillator. Provides frequency generation for the K-band Ranging system.
Coarse Earth and Sun Sensor. Provides omni-directional, reliable and robust, but fairly coarse Earth and Sun tracking. To be used during initial acquisition and when GRACE is operating in "safe mode."
Center of Mass Trim Assembly. Precisely measures offset between the satellite's center of mass and the "acceleration-proof" mass, and adjusts center of mass as needed during flight.
Black-Jack GPS Receiver and Instrument Processing Unit. Provides digital signal processing; measures
the distance change relative to the GPS satellite constellation; and provides secondary atmospheric occulation experiments.
Laser Retro-Reflective Assembly. Provides measurements of the GRACE satellite orbits relative to terrestrial tracking networks.
Globalstar Silicon Solar Cell Arrays. Covers the outer shell of the spacecraft and generates power.
Three-axis Stabilized Attitude Control System: Uses star camera and gyro sensors and a cold-gas nitrogen thruster system, with magnetorquers for fine corrections of spacecraft position.
1750-A Microprocessor for Flight Computer. Performs calculations for attitude adjustment and telemetry
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