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SEASAT

Jump to: Mission Objectives, Mission Instrumentation, Mission Parameters, Additional Information

Mission Photos:

Seasat Satellite
Courtesy of NASA GSFC

Mission Objectives:

Seasat was the first satellite designed for remote sensing of the Earth's oceans with a variety of microwave instruments, including an ocean radar altimeter for measuring sea surface height, a scatterometer for measuring surface winds, a Visible/Infrared Radiometer, and a synthetic aperture (imaging) radar. In addition to studying the oceans, the SAR instrument also obtained spectacular data over land areas, however SAR data were returned only when the s/c was in range of a handful of ground stations. The mission was designed to demonstrate the feasibility of global satellite monitoring of oceanographic phenomena and to help determine the requirements for an operational ocean remote sensing satellite system. Specific objectives were to collect data on sea-surface winds, sea-surface temperatures, wave heights, internal waves, atmospheric water, sea ice features and ocean topography. The mission ended on 10 October 1978 due to a failure of the vehicle's electric power system. Although the spacecraft was operational for only just over three months, the mission demonstrated the feasiblity of using microwave sensors to monitor ocean conditions, and laid the groundwork for future missions to monitor the worlds oceans and cryosphere.

The spacecraft was mounted on the Agena launch module, from which it was not detached after orbit insertion. The spacecraft had dimensions of 21 m in height, with a quasi-cylindrical bus that had a diameter of 1.5 m. The SAR antenna had dimensions of 2.1 x 10.7 m, and the two solar arrays had a surface area of 14.5 m**2. Attitude control for the spacecraft was provided by a combination of momentum wheels, magnetic torquers, and passive gravity gradient stabilization. The spacecraft included a ring-retroreflector array (such as on TOPEX/Poseidon and GEOS-3) for laser ranging. In addition the spacecraft carried a dual-frequency Doppler beacon for tracking by the Tranet network, and was also tracked at S-Band by Unified S-Band ground stations. The laser and Doppler tracking data to SEASAT were used to compute precise orbits for the spacecraft, to enable the generation of science products. The tracking data (laser, Doppler, S-Band) were used in gravity models at NASA GSFC from PGS-S1, PGS-S2, GEM-T2, GEM-T3, JGM-1, JGM-2, to EGM96.

The SAR data from SEASAT were re-released by the University of Alaska satellite Facility in 2013. (URL: https://www.asf.alaska.edu/seasat/)

The nominal flight attitude of the spacecraft is as follows:

Z: Towards the Earth's center
Y: Parallel to the negative of the orbit normal vector.
X: In the inertial flight direction (obtained from Y x Z)

More information about attitude determination on SEASAT is obtained from the following publication:

Seasat Final Report
Volume IV: Attitude Determination
by Alfred J. Treder,
JPL Publication 80-30, Volume IV, July 1, 1980
Jet Propulsion Laboratory, Pasadena, CA
(NASA-CR-163943)
(URL: https://ntrs.nasa.gov/search.jsp?R=19800021326)

Mission Instrumentation:

Seasat had the following instrumentation onboard:

  • Radar altimeter
  • Scatterometer system
  • Synthetic aperture radar
  • Visible and infrared radiometer
  • Scanning multi-channel microwave radiometer
  • Retroreflector array
Mission Parameters:
Sponsor: NASA
Expected Life: 1-3 years (stop functioning on 10 October 1978)
Primary Applications: ocean topography
Primary SLR Applications: calibrate radar altimeter
COSPAR ID: 7806401
SIC Code:
NORAD SSC Code: 10967
Launch Date: June 28, 1978
RRA Diameter:
RRA Shape:
Reflectors:
Orbit: near-circular
Inclination: 108 degrees
Eccentricity: 0.001
Perigee: (Oct 5, 1978): 775 km
Apogee (Oct 5, 1978): 790 km
Period: 100 minutes
Weight: 2290 kg

Additional Information:

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