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NOAA-4 was launched in November 1974 and was one in a series of reconfigured ITOS satellites launched with new meteorological sensors onboard to expand the operational capability of the ITOS system. The primary objective was to provide global daytime and nighttime direct readout real-time cloudcover data on a daily basis. The sun-synchronous spacecraft was also capable of supplying global atmospheric temperature soundings and very high resolution infrared cloudcover data for selected areas in either a direct readout or a tape-recorder mode. A secondary objective was to obtain global solar-proton flux data on a real-time daily basis. The sensors were mounted on the satellite baseplate with their optical axes directed vertically earthward. The nearly cubical spacecraft measured 1 by 1 by 1.2 m. The satellite was equipped with three curved solar panels that were folded during launch and deployed after orbit was achieved. Each panel measured over 4.2 m in length when unfolded and was covered with approximately 3500 solar cells measuring 2 by 2 cm. The dynamics and attitude control system maintained desired spacecraft orientation through gyroscopic principles incorporated into the satellite design. Earth orientation of the satellite body was maintained by taking advantage of the precession induced from a momentum flywheel so that the satellite body precession rate of one revolution per orbit provided the desired 'earth-looking' attitude. Minor adjustments in attitude and orientation were made by means of magnetic coils and by varying the speed of the momentum flywheel. The primary sensors consisted of a Very High Resolution Radiometer (VHRR), Vertical Temperature Profile Radiometer (VTPR), and a Scanning Radiometer (SR). __________ Taken from the NSSDC System for Information Retrieval and Storage (SIRS). For more information contact the NSSDC Coordinated Request and User Support Office, 301-286-6695 (NASA Goddard Space Flight Center, Code 933.4, Greenbelt, Maryland 20771, USA, "http://nssdc.gsfc.nasa.gov/).
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