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Designation 21574 / 91050A
Launch date 17 Jul 1991
Country of origin Europe
Mission Remote sensing
Perigee/Apogee 768/769 km
Inclination 98.5°
Period 100.2 min
Orbital cycle 3, 35 and 176 days
Launch vehicle Ariane V44

ESA's first remote sensing satellite. Cost: $500 million

Since early 1994 the satellite transmits with the backup travelling wave tube because the primary one failed.

End of life

Out of service 10 Mar 2000
Cause failure of the attitude control system

sat-index articles

Technical data


Prime contractor Dornier
Platform MMS Spot Mk 1
Mass at launch 2400 kg
Payload mass 1100 kg
Dry mass 2080 kg
Length 11.8 m
Solar array 11.7 x 2.4 m
SAR antenna 10 x 1 m
Radar altimeter 1.2 m (diameter)
Stabilization 3-axis
DC power 2500 W
Design lifetime 3 years

Downlink: 2225 MHz

AMI (Active Microwave Instrument)

Frequency 5.3 GHz (C-band)
SAR resolution 26 m
SAR swath width 99 km
Scatterometer resolution 47 km
Scatterometer swath width 613 km (fore and aft)
809 km (mid)

Mission: payload all-weather high-resolution images of land and ocean, windspeed and direction, ice mapping, pollution monitoring.

RA (Radar Altimeter)

Frequency 13.8 GHz (Ku-band)
Accuracy (wave height) +/- 0.5 m
Altitude accuracy 0.1 m

Mission: windspeed and sea surface elevation, ice sheet topography.

ATSR (Along-Track Scanning Radiometer)

Wavelengths 1.6, 3.7, 10.8 and 12.0 µm
Accuracy (sea surface temperature) +/- 0.5 K

Mission: images of sea surface temperature, total water vapour content of atmosphere, cloud, aerosols, haze, land and ice surface emissivity.

Microwave Sounder

Frequency 23.8 and 36.5 GHz
Altitude accuracy 0.02 m
Telemetry/data S-band

Also equipped with Laser Reflectometer (LR), Precise Range and Range-rate Equipment (PRARE) and Instrument Data Handling and Transmission (IDHT).

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