GEOS-3

 1975-027A

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The Geos 3 satellite was a follow on to the Geodetic Explorers, Geos 1 and 2. However, its acronym was given a different expansion (Geodynamics Experimental Ocean Satellite) and at the time of launch it was not identified as part of the Explorer series, so programmatically it is somewhat anomalous. It bridged the National Geodetic Satellite Program and NASA's later Earth Science efforts, under the EODAP (Earth and Ocean Dynamics Applications Program).

The Geodynamics Experimental Ocean Satellite, Geos C before launch and Geos 3 after launch, was the first mission to carry out a global altimetry survey of the oceans, and the Geos 3 database was a key tool for geophysicists for over a decade. The altimetry was championed by NOAA's John Apel, who later helped design the Seasat mission. Later missions which expanded on the Geos 3 results were NASA's Seasat and the US Navy's Geosat. Geos 3 was built by the Applied Physics Lab and was similar in structure to Geos 1 and 2. The program was managed by NASA's Wallops Center.

Geos 3 has a 6m gravity boom. 340 kg mass.

Geos 3 was launched at 2358 on 1975 Apr 9 by a two stage Delta 1410 (some sources incorrectly give 2410) rocket into a 101.8 min, 839 x 853 km x 115.0 deg retrograde orbit. The altimeter system operated until 1978 Dec, and the satellite transmitted until May 1981.

Geos 3
Date	Time	Event	Orbit
1975 Apr 9	2358:02	Launch by Delta 1410	V
		T+0:38? SRM 1-4 burnout
1975 Apr 10	0000	T+2:00 SRM 1-4 sep, 26 km
	0002	T+4:29 MECO 96 km
	0002	T+4:40 St 1 sep
		T+4:45 SES-1
	0003	T+5:05 Fairing sep
	0007	T+9:36 SECO-1 185 km 7.854 km/s
	0055:01	T+56:59 SES-2 842 km 7.140 km/s
	0055:08	T+57:06 SECO-2 7.314km/s
	0056:23	T+58:21 St 2 sep	101.8 839 x 853 x 115.0
1975 Apr 10	0457	Boom extended 0.8m
1975 Apr 12	0242	Boom extended to 6.5m
1975 Apr 16		First ATS-6 tracking pass
1978 Dec		Altimeter end of ops
1981 May		end of tx

Payload:

• Radar altimeter system (5 m ocean surface heights)

• S-band tracking system (also used with ATS6 for sat-sat tracking expt)

• C-band system (for radar calibration)

• Laser reflectors (MIT-LL)

• USN Doppler geodetic system