Geosat
| Geosat | |
|---|---|
|
|
| Type: | Earth observation satellite |
| Country: |
 United States
|
| Operator: | United States Navy |
| COSPAR-ID : | 1985-021A |
| Mission dates | |
| Dimensions: | 635 kg |
| Begin: | March 12, 1985, 02:00 UTC |
| Starting place: | Vandenberg SLC-3W |
| Launcher: | Atlas-E / OIS 41E |
| Status: | Out of service |
| Orbit data | |
| Rotation time : | 100.6 min |
| Orbit inclination : | 108.1 ° |
| Apogee height : | 814 km |
| Perigee height : | 757 km |
Geosat ( Geodetic Satellite ) was an Earth observation satellite, the US Navy , with a radar - altimeter equipped and satellite geodesy and the ocean topography served. The satellite was on a disarmed and converted to the satellite carrier March 12, 1985 Atlas-E - intercontinental ballistic missile from Vandenberg AFB in a polar orbit (km 757 × 814, 108.1 °) started.
construction
The body of the satellite, based on the structure of the GEOS-3 satellite, weighed 635 kg and was developed by the Applied Physics Laboratory at Johns Hopkins University .
The GRA (Geosat Radar Altimeter), which was developed on the basis of the altimeter of NASA's Seasat satellite, served as a scientific instrument . This enabled the sea level to be measured with a vertical accuracy of 3 cm. The horizontal resolution was 10-15 km. The data of up to 12 hours measurements were recorded by means of two tape recorder and when flying over the ground station via an S-band - telemetry system transmitted.
The power supply was secured by eight folded solar cell arms. The satellite was aligned vertically to the earth with a weight extended on a boom by gravitational stabilization with a deviation of less than 1 °.
mission
Geosat used the radar altimeter to determine the exact distance between the sea surface and its precisely known orbit. The aim was to determine the spatial and temporal changes in sea level.
Geosat's mission was divided into two phases:
- In the first 18 months, the primary mission was a secret geodetic survey of the oceans. Instead, the satellite was in an orbit with a non-repeating overflight cycle. The data from this survey enabled a more precise image of the earth's gravity and thus an increased targeting accuracy of submarine-supported ballistic missiles .
- In the second phase, which lasted from September 1986 to January 1990, geodetic data accessible to science were obtained. For this, the orbit was changed in such a way that the overflight over a certain point was repeated every 17 days. Because of the orbit, the mission phase was called ERM ( Exact Repeating Mission )
In January 1990, the serviceability ended when both data recorders failed. By 1995, all previously secret survey data were released in several steps.
Follow-up missions
After the end of the life of the Geosat satellite, the mission was to be continued with a radar altimeter mounted on the N-ROSS ocean observation satellite planned for the early 1990s . When N-ROSS was canceled for cost reasons, the US Navy planned to launch the radar altimeter as the sole instrument on the SALT microsatellite , which, however, was also canceled. Only in 1998 was a follow-up mission available with the Geosat Follow-On satellite.
literature
- The Navy GEOSAT Mission: An Overview , Johns Hopkins APL Technical Digest, Volume 8, No. 2, 1987
Individual evidence
- ↑ Geosat in the NSSDCA Master Catalog , accessed on July 8, 2012 (English).
- ^ David T. Sandwell, Walter HF Smith: Exploring the Ocean Basins with Satellite Altimeter Data. December 2, 2011, accessed on October 29, 2012 (English): “the Geosat satellite was launched by the US Navy in 1985 to map the geoid height at a horizontal resolution of 10-15 km (6-10 mi) and a vertical resolution of 0.03 m (1 in). "