Sentinel-1 SAR instrument improved flight predictions based on measured in-orbit data

Abstract

The Sentinel-1A SAR mission was launched in April 2014, followed by the Sentinel-1B Spacecraft in April 2016. Since then, several sets of in-orbit data have been evaluated to correlate the thermal model for being able to provide more detailed in-flight predictions. The need for detailed in-flight predictions is justified by the fact that the imaging performance of a SAR instrument depends mainly on the thermal performance of its high dissipative units. Components reaching their temperature limits during operational time define the end of the imaging phase, and thus the timespan during which and how often imaging operations can take place. An STM (Structural/Thermal Model) test correlation is standard throughout all missions, which usually delivers a very reliable model for further in-flight predictions. Nevertheless, this correlation does not give information about thermo-optical property degradation or environmental influences, because the effects in space on the thermally active surfaces are very hard to predict. For this reason, thermal engineers use relatively conservative values for in-flight predictions and End-of-Life thermal performance assessments. This might lead to mission performance limitations which predict a too short feasible imaging time of the Radar instrument. For this reason, the first approach was to evaluate the early acquired in-orbit data and to correlate the thermal model with the thermal configuration at Begin-of-Life to assess the maximum possible high dissipative imaging time possible for the Begin-of-Life situation. Then the flight data over a longer timespan were evaluated to determine potential temperature trends which could be caused by thermo-optical property degradation as well as seasonal-related influences. These two assessments combined, allow a thermal performance prediction for Mission End-of-Life, and thus a reliable determination of potential SAR imaging performance over the full mission time. The paper will present the correlation results of the initially measured in-flight data, the determined long-term in-orbit data over 3 years, and the combination of both assessments including its impact on SAR imaging performance over the full mission.