Flight results of a new GEO infrared Earth sensor STD 15 on board TC2

In the frame of the Telecom 2 and Hispasat spacecraft programs, Matra-Marconi Space (France) entrusted SODERN in 1988 for the development of an accurate version of the Earth sensor designed to operate on three axis stabilized satellites at geosynchronous altitude. This new sensor, called STD 15, is a versatile one directly derived from the STD 12 already used on board the SPOT/ERS satellites. Two STD 15 were launched for the first time in December 1991 on board the TC2-A satellite, followed by a second launch in April 1992 on board TC2-B and a third one in September 1992 on board HISPASAT 1A. After a few months of successful operation, the telemetry data have been analyzed by SODERN in order to draw conclusions about the STD 15 behavior. The aim of this paper is to descrbe the latest version of the sensor, then to carry out a preliminary analysis of the available in-flight data. After a short presentation of its operating principle and associated algorithms, the equipment is briefly described and its main features are shown with special attention to the error budget for the various operating modes: transfer orbit (classical or super-synchronous), Earth acquisition, antenna mapping attitude control and station keeping in GEO. Then the main performance results of on ground testing and computed theoretical results are discussed and compared with the in-flight results.