ERS 2

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General

Designation	23560 / 95021A
Launch date	21 Apr 1995
Country of origin	Europe
Mission	Remote sensing
Perigee/Apogee	783/786 km
Inclination	98.6°
Period	100.5 min
Launch vehicle	Ariane V72

Cost: FRF 3.1 billion including FRF 2 billion for the satellite. The launch was not insured

It had gyroscope problems and was reprogrammed to operate without gyroscopes in early 2001 with the help of the Digital Earth Sensor. With some improvements, such as noise filtering, the instrument is now used to estimate pitch and roll errors. That still left the final yaw (or downward) pointing error, which could no longer be measured by the gyro-less spacecraft. The yaw drift can be checked on the ground by analysing Doppler frequency shifts in the ERS-2 radar instrument signals. However, processing the raw signal takes up to three hours, too long to keep the spacecraft correctly orientated in real time. Instead, ERS 2 was monitored over a 105-day period of time, during which recurring patterns that cause spacecraft mispointing were recorded. These patterns, mainly caused by terrestrial magnetic field variations as well as pressure from the solar wind, were rendered into a detailed model and uplinked to the satellite. This enables mispointing to be anticipated and compensated for.

In Jun 2003 the low bit rate recorder failed and a network of ground stations wat setup to collect most of the data in near-real time.

Still operating well in Apr 2010 (15 years anniversary)

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End of life

Out of service	Jul 2011
Cause	Retired. Orbit to be decreased to 550 km to provide quicker de-orbit
Decay	planned in 2030-2040

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External resources

sat-index articles

Technical data

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Specifications

Prime contractor	Dornier
Platform	MMS Spot Mk 1
Mass at launch	2500 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

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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.

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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.

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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.

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Microwave Sounder

Frequency	23.8 and 36.5 GHz
Altitude accuracy	0.02 m

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GOME (Global Ozone Monitoring Experiment)

Waveband	0.24-0.79 µm
Resolution	40 x 40 km max. (horizontal) 1 km (vertical)
Swath width	120-960 km

Mission: stratospheric and tropospheric ozone profiles, cloud distribution and surface spectral reflection.

Also equipped with Laser Reflectometer (LR), Precise Range and Range-rate Equipment (PRARE) and Instrument Data Handling and Transmission (IDHT). The on board tape recorder (6.5 gigabit) can store data from a full orbit.

The telemetry is sent in S-band. The scientific data and a replication of the telemetry is sent on 2 X-band transponders.

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