The first European Remote Sensing Satellite (ERS 1) was a major element of the European Earth Observation Program covering a number of disciplines including meteorology, climatology, oceanography, land resource inventory and monitoring, geodesy and geodynamics. The objectives of ERS 1 were primarily oriented towards ice and ocean monitoring with all-weather high resolution active microwave imaging over land and coastal areas. The primary objectives were to meet economic and scientific needs to (1) develop and promote applications to further knowledge of ocean parameters, sea state and ice conditions and (2) increase the scientific understanding of coastal zones and ocean processes. The ERS 1 carried the following instruments: (1) Active Microwave Instrumentation (AMI), which combined a Synthetic Aperture Radar (SAR) and a wind scatterometer to acquire all-weather images over polar ice, coastal zones and land area and to measure wind field and wave spectra over oceans; (2) a Radar Altimeter (RA) to measure wave height, ocean surface wind speed and ice parameters; (3) the Along-Track Scanning Radiometer (ATSR), which consisted of two instruments: infrared radiometer (IRR) for measuring sea surface and cloud top temperature and a microwave sounder (MWS) for measuring total precipitable liquid and vapor water; (4) the Precise Range and Range-rate Equipment (PRARE) to provide accurate altitude measurements for geodetic applications, sea surface topography, crustal dynamics and ocean circulation; and (5) the Laser Retroreflector (LRR), which was a passive optical device used to assist satellite tracking. The ERS 1 spacecraft was based on the French SPOT platform with a three axis stabilized earth pointed attitude control and a bias of 0.11 deg with an absolute error rate of less than 0.0015 deg/s. The spacecraft consisted of the following modules: Service Module (SM), Reaction Control Module (RCM), Solar Array, PFM Thermal Control, Power Supply Subsystem (PSS), Communications and Data Handling Subsystem (CDHS), Attitude and Orbit Control Subsystem (AOCS), Flight Software, and Reaction and Self-mode Control Unit. Power was supplied by two 5.8 x 2.4 m solar array panels backed up by four NiCd 24-Ah batteries. Attitude and orbit control was maintained by horizon and Sun sensors and gyroscopes. Primary attitude control was provided by a set of momentum wheels and hydrazine thrusters. The ERS 1 thermal control system was of a passive design complemented by an active heater system. The On-Board Computer (OBC) ran the flight software. All instrument computers were linked by the On-Board Data-Handling (OBDH) system. All of the onboard processors were programmable during flight. The spacecraft orbital orientation permitted a 3-day repeat cycle.The Payload Module consisted of the Payload Electronics Module (PEM) and the Antenna Support Structure (ASS). The PEM was a honeycomb structure that facilitated the integration of the ERS 1 instruments. The ASS assembly provided support for the SAR antenna. See "UK ERS-1 Reference Manual",DC-MA-EOS-ED-0001,January 1991.
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