European Remote Sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite programme using a polar orbit. It consisted of 2 satellites, ERS-1 and ERS-2. ERS-1 ERS-1 launched 17 July 1991 from Guiana Space Centre aboard an Ariane 4 rocket. The satellite was put into a Sun-synchronous polar orbit at an altitude of 782–785 km. ERS-1 failed on 10 March 2000 after nine years in orbit. Instruments 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: RA (Radar Altimeter) is a single frequency nadir-pointing radar altimeter operating in the Ku band. ATSR-1 (Along-Track Scanning Radiometer) is a 4 channel infrared radiometer and microwave sounder for measuring temperatures at the sea-surface and the top of clouds. SAR (synthetic-aperture radar) operating in C band can detect changes in surface heights with sub-millimeter precision. Wind Scatterometer used to calculate information on wind speed and direction. MWR is a Microwave Radiometer used in measuring atmospheric water, as well as providing a correction for the atmospheric water for the altimeter. To accurately determine its orbit, the satellite included the PRARE (Precision Range and Range-Rate Equipment) and a laser retroreflector. The PRARE became non-operational shortly after launch; later analysis concluded that the failure was due to a memory latchup caused by radiation. The retroreflector was used for calibrating the Radar Altimeter to within 10 cm. Mission ERS-1 had various mission phases using 3-day and 35-day repeat cycles. During the geodetic mission, ERS-1 was put in two long repeat cycles of 168 days, which is equivalent to a single 336-day cycle. The geodetic mission allowed for accurate mapping of the Earth's bathymetry and geoid over the seas using the Radar Altimeter. On 10 March 2000, ERS-1's attitude control system failed due to a gyroscope malfunction and its mission was officially declared finished. ERS-2 Its successor, ERS-2, was launched on 21 April 1995, on an Ariane 4, from ESA's Guiana Space Centre near Kourou, French Guiana. Largely identical to ERS-1, it added additional instruments and included improvements to existing instruments including: GOME (Global Ozone Monitoring Experiment) is a nadir scanning ultraviolet and visible spectrometer. ATSR-2 included 3 visible spectrum bands specialized for chlorophyll and vegetation 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