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The Thermal design of the ENVISAT-1 ASAR Active Antenna has provided many engineering challenges. The selection of the Thermal Control has been complicated by the need to dissipate the high power (1300 watts) generated by the active equipments that are mounted on the Antenna Tile Sub-System directly behind the radiating surface. This high power has to be dissipated from the Antenna whilst minimising heater power consumption. The final design uses passive Thermal Control for dissipating the heat from the equipments during operating modes, via radiation from the Active face of the Antenna towards the Earth. This has required evaluations of possible Thermal finishes and resulted in a black painted Earth facing Active radiating face. Heat loss by conduction to the ENVISAT-1 platform has also been minimised in order to ensure that ASAR has negligible impact Thermally on the platform.

The ENVISAT ASAR antenna is 10 meters in length in the deployed configuration and consequently thermal balance testing was impossible due to TVAC chamber size and MGSE limitations. Therefore the verification of the ASAR active antenna thermal design was based mainly on analysis complemented, when necessary, by thermal balance tests at subsystem level on key components. This approach called up for extensive sensitivity analyses, taking into account the fact that all of the design, orbital parameters, operational scenario and mathematical simulation are subject to uncertainties. Special emphasis was put on assessing the impact of uncertainties on albedo and earthshine for low time constant components of the ASAR antenna which is facing the Earth.

This paper describes the thermal vacuum (TVAC) through conductance test and model correlation results performed on the protoflight Mobile Satellite (MSAT®) L-Band Transmit (Tx) feed assembly. Very good correlation was obtained between the model and the measured results. Specifically, the correlated average temperatures for the feed array components, were all within +/- 5°C of the measured test results for all three (3) plateaus. Similar results were also obtained at 10 feed panel locations for each component. In addition, the differences in temperature gradients through the feed assembly from the cup walls to the Beam Forming Network (BFN), comparing the modelled and measured results, were less than 3°C for all three plateaus. The correlation results for the Tx feed assembly were subsequently used to update the spacecraft (S/C) L-Band antenna model.

Radarsat is a Canadian remote sensing satellite designed to gather earth resource data from a low earth orbit. The spacecraft consists of four major entities: the payload module, the bus module, the SAR antenna and the solar arrays. The main features of each subsystem's thermal design are presented, emphasizing the different design challenges encountered in maintaining all components within acceptable limits so that all performance requirements are met. Special reference is given to the difficulties experienced in accommodating the Antarctic coverage.