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The Rosetta spacecraft was re-targeted to a newly selected comet following a one-year launch delay. The thermal control of the spacecraft has to cope with a large Sun distance range - 0.88 to 5.35 AU - and increasing comet activity combined with operational conditions that span from full payload activity to power saving hibernation mode. The new mission stretches the range of solar flux even further than the original mission and some adaptations to the thermal hardware were required. This paper describes how the new demanding mission scenario influenced the thermal design of the spacecraft and its operations. Then, the thermal behaviour of the spacecraft as revealed by the first in-orbit results is evaluated and compared where possible with the response anticipated by the analyses and by the environmental thermal test programme results. Rosetta was injected into an Earth escape trajectory on March 2th 2004 by an Ariane 5 dedicated launch.

This paper describes the processes and evolution of the design and verification of the thermal control subsystem of the Rosetta spacecraft. In particular, it describes the testing, both at component-level and spacecraft-level, that was necessary and the subsequent correlation activities that were required to understand the thermal behaviour of the spacecraft and thus develop a thermal model that portrayed this correctly.

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.