GRACE 1 and GRACE 2 (nicknamed Tom and Jerry) are a pair of American-German (NASA-DLR), identical, Earth-research, 500-kg satellites that were launched by a Rockot booster from Plesetsk at 09:21 UT on 2002 March 17. The acronym stands for Gravity Recovery And Climate Experiment. They aim to map the local gravitational mini-variations caused by sea-level changes, glacial motions, and seasonal melting/freezing of ice sheets. It is accomplished by measuring the relative distance between the pair, nominally 220 km, by means of K-band microwave sounding at an accuracy of few microns, and in conjunction with GPS fixes (by JPL Blackjack GPS Receivers) of their locations. The major perturbations due to air drag and solar radiation pressure will be accounted for by accelerometer data.
The ranging instrument is named KBR (K-Band Ranging); the accelerometer, ACC is the ONERA SuperSTAR Accelerometer. Star Camera Assemblies (SCA) on each spacecraft will provide attitude data. Finally, a Laser Corner-Cube Reflector Assembly (LRA) mounted on the underside of each spacecraft will enable (redundantly) orbit verification. Mission operations is controlled by the DLR which will provide the raw Level-0 data to the investigators.
Initial orbital parameters of each were period 94.5 min, apogee 508, km, perigee 483 km, and inclination 89 deg.
Alternate Names
27391 = 2002-012A = Tom = Gravity Recovery and Climate Experiment 1
27391 = 2002-012B = Jerry = Gravity Recovery and Climate Experiment 2
Facts in Brief
Launch Date: 2002-03-17
Launch Vehicle: Rokot
Launch Site: Plesetsk, Russia
Mass: 500.0 kg
Nominal Power: 620.0 W