Having given excellent service for nine years, over three times its planned lifetime, the ERS-1 mission was ended on Friday 10 March by a failure in the on board attitude control system. Since its launch on 17 July 1991, ESA's first sun-synchronous polar-orbiting mission, has made 45 000 orbits, acquiring more than 1.5 million individual Synthetic Aperture Radar (SAR) scenes. ERS-1 SAR images, together with the data from other instruments on board, were delivered to a worldwide community of some 4000 users in science and applications. Surface winds derived from the scatterometer and altimeter have been supplied to meteorological services worldwide since 1991. The duration of the mission has also meant that scientists have already observed several El NiÁ o phenomena through combined observations of surface currents, topography, temperatures and winds. The measurements of sea surface temperatures, critical to the understanding of climate change, made by the ERS-1 Along-Track Scanning Radiometer are the most accurate ever from space. All these critical measurements are being continued and enhanced by the current ERS-2 mission.
The most exciting results from the ERS-1 mission have been in the field of SAR interferometry, where for the first time precise topographic information could be routinely produced from space data. The ERS-1 and ERS-2 tandem operations demonstrated this technique for various applications and paved the way for the definition of new dedicated SAR interferometry missions.
ERS-2 (launched in 1995) took over the operational services of ERS-1 in 1996. It too has now exceeded its nominal lifetime and remains in excellent condition. Next year Envisat will be launched to continue this series of Earth Observation missions.
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