European Remote-Sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite. It was launched on July 17, 1991 into a Sun synchronous polar orbit at a height of 782–785 km.
ERS-1 carried an array of earth-observation instruments that gathered information about the Earth (land, water, ice and atmosphere) using a variety of measurement principles. These included:
To accurately determinte its orbit, the satellite included the PRARE (Precision Range and Range-Rate Equipment) and a Laser Retroreflector. The PRARE was non-operational since launch. The Retroreflector was used for calibrating the Radar Altimeter to within 10 cm.
ERS-1 failed on March 10, 2000, far exceeding its expected lifespan.
Its successor, ERS-2, was launched on April 21, 1995. It is largely identical to ERS-1, with the addition of the GOME (Global Ozone Monitoring Experiment) and absorption spectrometer. When ERS-2 was launched, ERS-1 shared the same orbital plane. This allowed a tandem mission, with ERS-2 passing the same point on the ground 1 day later than ERS-1. ERS-2 has been operating without gyroscopes since February 2001, resulting in some degradation of the data provided by the instruments. The tape drive aboard failed on June 22, 2003, leaving some of the instruments operating only within visibility of a ground station.
The successor to ERS-2 is Envisat.
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