Repeat Cycle:
17 DAYS
- Spacecraft Brief Description -
The GEOdetic SATellite (GEOSAT) was a dedicated US Navy military oceanographic
satellite consisting of a radar altimeter designed to obtain closely spaced,
precise
... mapping of the earth's geoid over the ocean. On November 8, 1986, the
satellite was moved into an Exact Repeat Mission (ERM) orbit with a repeat
cycle of 17.05 days. The GEOSAT mission was originally managed by the Office of
Naval Research (ONR). During the development phase, the program responsibility
was transferred to the Naval Electronics Systems Command, now called the Space
and Naval Warfare Systems Command (SPAWAR) in Washington, D.C. The Applied
Physics Laboratory (APL) was the prime contractor for the spacecraft and radar
altimeter and performed spacecraft command and control operations and collected
the satellite data. The data was distributed to the Naval Surface Weapons
Center (NSWC), the Naval Ocean Research and Development Activity (NORDA), and
NOAA. An arrangement was made with the National Ocean Service of NOAA to obtain
the classified GEOSAT geophysical data records (GDR) providing wind, wave and
sea-level products and made available to the user community. NASA obtained
GEOSAT data for extensive waveform modeling and ice sheet research.The basic
structure of the GEOSAT is similar to the GEOS-3 satellite: The design consists
of a conical structure below the core for the structural attachment of the
velocity control system. The GEOSAT attitude control subsystem was designed to
point the radar altimeter to within 1 degree of nadir 98 percent of the time.
The system components were a 20-foot scissors boom with 100-pound end mass,
redundant momentum wheels for roll and yaw stiffness, and pitch and roll
attitude control thrusters. Attitude sensing was provided through the use of
three digital sun-attitude detectors and a three-axis vector magnetometer.
Spacecraft command was accomplished via a VHF uplink from the APL ground
station. The telemetry subsystem consisted of two S-band transmitters, two tape
recorders, and two encryption units. The GEOSAT was equipped with two Odetics
dual-track high-density tape recorders that independently recorded the 10.205
kbps telemetry stream and played it back at 833 kbps for transmission to the
ground. The GEOSAT also included redundant Doppler beacons for continuous
tracking by a network of ground stations within the Defense Mapping Agency
(DMA) and for a source of accurate timing to the radar altimeter and the
telemetry subsystem. A C-band transponder was also included on GEOSAT. See
Jensen,J.J. and F.R.Wooldridge, 'The Navy GEOSAT Mission: An Introduction';
McConathy, D.R. and C.C.Kilgus, 'The Navy GEOSAT Mission: An Overview', and
Frain,W.E., M.H.Barbagallo, and R.J.Harvey,'The Design and Operation of
GEOSAT', all in Johns Hopkins APL Technical Digest, Volume 8, Number 2 (1987).
- Auxiliary Information -
Launch Date and Time : 1985-03-12
Epoch Date and Time :
Apogee (km or AU): 814.
Perigee (km or AU): 757.
Inclination (degree) : 108.1
Orbit Type :
Information last updated on 1992-05-20 
