ICESat carries two JPL BlackJack GPS receivers. Each receiver is connected to a unique antenna. In addition, ICESat carries a laser reflector arrary to enable ranging from the network of ground-based satellite laser ranging stations.
Prelaunch measurements determined the location of the GPS antennas with respect to the ICESat spacecraft coordinate system. The spacecraft center of mass changes with fuel expenditure. The spacecraft axes, which are fixed in the spacecraft, are defined as follows (an illustrating diagram will be provided soon):
GPS receiver FM1-02685/ANT1-257206
Powered on: January 17, 2003 15:00:00.00 UTC
Powered off: -
Comments: on January 31, 2003, the receiver was commanded to track no more that 8 GPS satellites (down from 9)
Position vector in spacecraft coordinates of "upper" surface of choke ring:
x = 1.313 m y = 0.189 m z = 0.586 m
RINEX data from this receiver (available from CDDIS and NSIDC) have file name convention ICE1dddf.yyo; ddd=day of year, f=0, 1, ..., yy=year - 2000
GPS receiver FM2-02686/ANT2-257307
GPS receiver FM2-02686/ANT2-257307
The center of mass changes a small amount with fuel expenditure used for each orbit maneuver. The maneuvers are required to maintain the exact repeat track in the presence of atmospheric drag. To obtain the the center of mass location of the antenna reference point, the above vector from the spacecraft origin to the antenna must be combined with the appropriate center of mass vector given below.
For center of mass information prior to February 11, contact schutz@csr.utexas.edu.
Orbit maintenance maneuvers (center of mass location applies after completion of maneuver until next maneuver):
2003 February 11 03:35:11 UTC xcm = 0.052 m ycm = 0.004 m zcm = 0.984 m
2003 February 19 12:11:44 UTC xcm = 0.052 m ycm = 0.004 m zcm = 0.984 m