European Remote-Sensing Satellite

European Remote Sensing satellite (ERS)
Company type	Space programme
Industry	Earth observation, Satellite technology
Founded	1991; 35 years ago
Founder	European Space Agency
Defunct	2011
Headquarters	Paris, France
Products	Earth observation satellites: ERS-1, ERS-2
Website	www.esa.int/Applications/Observing_the_Earth/ERS_Mission

European Remote Sensing satellite (ERS) represented the European Space Agency’s inaugural programme for Earth observation employing a polar orbit. The initiative comprised two spacecraft, ERS-1 and ERS-2, with the first, ERS-1, launched in 1991.

ERS-1

ERS-1 was deployed on 17 July 1991 from the Guiana Space Centre via an Ariane 4 launch vehicle. It maintained a Sun-synchronous polar orbit at an altitude ranging between 782 and 785 km. After nearly a decade of service, ERS-1 concluded operations on 10 March 2000.

Instruments

The ERS-1 satellite was equipped with multiple sensors designed to gather comprehensive data on terrestrial, aquatic, cryospheric, and atmospheric conditions:

RA (Radar Altimeter): a single-frequency radar altimeter operating in the K_u band.
ATSR-1 (Along-Track Scanning Radiometer): a four-channel infrared radiometer combined with a microwave sounder to measure sea surface and cloud-top temperatures.
SAR (synthetic-aperture radar) functioning in the C band to detect surface height variations at sub-millimeter precision.
Wind Scatterometer: instrumented to assess wind speed and direction over oceans.
MWR (Microwave Radiometer): utilized for atmospheric water content measurement and calibration of altimeter data.

For accurate orbital positioning, ERS-1 included PRARE (Precision Range and Range-Rate Equipment) alongside a laser retroreflector. However, PRARE failed soon after deployment due to radiation-induced memory latchup. The retroreflector enabled calibration of the radar altimeter within an accuracy margin of 10 cm.

Mission

ERS-1 executed diverse mission cycles such as 3-day, 35-day, and prolonged 168-day repeats aimed at geodetic mapping of Earth's oceanic bathymetry and geoid using its Radar Altimeter.

The satellite’s mission terminated when its attitude control system malfunctioned on 10 March 2000 due to gyroscope failure.

ERS-2

ERS-2 was launched on 21 April 1995 aboard an Ariane 4 rocket from ESA’s Guiana Space Centre near Kourou, French Guiana. While largely mirroring ERS-1’s design, it incorporated upgraded instruments including:

GOME (Global Ozone Monitoring Experiment), a nadir-viewing ultraviolet and visible spectrometer.
ATSR-2, enhanced with three visible spectrum bands tailored for monitoring chlorophyll concentrations and vegetation health.

At the time of launch, ERS-1 and ERS-2 shared the same orbital plane, facilitating a tandem operation whereby ERS-2 passed over identical ground locations one day subsequent to ERS-1. ERS-2 followed a 35-day repeat orbit cycle.

Starting February 2001, ERS-2 functioned without gyroscopes, which led to some degradation in data quality. Following the failure of its tape recorder on 22 June 2003, instrument operation was limited to periods when the satellite was within range of ground stations. To mitigate this constraint, additional ground stations were established. The Wind Scatterometer and GOME instruments aboard ERS-2 remained unmatched until the launches of MetOp-A and Envisat, respectively.

Although superseded by Envisat, launched on 1 March 2002 with advanced instrumentation, ERS-2’s operational life was prolonged until 2011. Between July and September that year, fuel depletion burns were conducted culminating in official decommissioning on 5 September at precisely 13:16:38 when batteries were switched off. Subsequently, the spacecraft was lowered into a reduced orbit to guarantee atmospheric reentry and disintegration within 25 years in compliance with international debris mitigation policies.

The fuel exhaustion process required several maneuvers; initial burns lasting approximately 40 minutes on 2 and 3 September did not fully consume remaining propellant. A final burn on 5 September successfully drained fuel reserves, reducing orbital altitude from about 785 km down to 573 km.

In February 2024, ESA projected that ERS-2 would undergo uncontrolled atmospheric reentry between the dates of 16 and 22 February. The satellite ultimately reentered Earth’s atmosphere at 17:17 UTC on 21 February over the Pacific Ocean region located between Alaska and Hawaii.

Notes

External links

ESA ERS mission page
ESA's Next SAR Toolbox designed for visualization, calibration, and processing of ERS 1 & 2 SAR Level 1 and advanced data