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Technical Specifications

General Spacecraft Information (Twin Satellites)
  • Width: 1942 mm
  • Length: 3123 mm
  • Height: 720 mm
  • Mass: 487 kg per satellite
  • Design Life: 5 years

    Orbit Characteristics
  • Two satellites, co-orbiting at near polar inclinations at 300-500 km altitude.
  • Separated along track by 220 km.

    Key Components
  • 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
    processing.
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    The GRACE mission is jointly implemented by NASA and DLR under
    the NASA Earth System Science Pathfinder Program.

    Last Modified: Tue Feb 10, 2004
    CSR/TSGC Team Web