1991-07-01

The Thermal Control of the European Retrievable Carrier, An Example of Flexible Thermal Control System 911448

The intensive endeavor of the human, to do research work and to test in the low earth orbit, results in complex orbital platforms. These space based platforms are either permanent or retrievable. This is the case of the European Retrievable Carrier (EURECA), a free-flying reusable platform that is launched and retrieved by the NSTS Orbiter. The first EURECA mission will be primarily a microgravity mission specifically for material processing and life science payloads.
The thermal control system of EURECA has to ensure the correct environment for the carrier and the payload, throughout all mission phases, by means of passive and active means. The passive means consist of various multi-layer insulations, surface finishing, conducting straps. Electrical heaters work, in conjunction with the active cooling loop, to keep the spacecraft temperature at adequate level. The cooling loop consists of a single phase Freon 114 pumped loop, with two radiators in parallel. The possibility to accommodate different payload heat dissipations is ensured also by the capability of the system to bypass one of the two radiators.
The degree of on-board autonomy required for EURECA, mainly due to the very short ground contact periods, necessitates a sophisticated control of the thermal functions performed by a dedicated on-board computer.
The thermal control of EURECA is believed to be a good example of the System Thermal Control of today, which means a maximum of flexibility in the development, manufacturing and operation. This is required for the high density, complex structure, different mission profiles, considerations of retrieval capability, adaptation of future payloads and take over of non-thermal related tasks of today's spacecraft's.
This paper deals both with the development and verification of the thermal control system design and with its operational aspects.
In addition examples are given to show how the model development, the implementation of the different requirements and the design solutions are made, in case of problems not solvable by the affected subsystems alone, namely:
  • Missing power interface for a payload in some mission cases
  • Electronic design problem of the 20 N thruster chamber temperature monitoring
  • High temperature of the battery due to specification problems
  • Power shortage during operational phase
The paper is completed by a critical review (lesson learned) of the performed System Thermal work, in which the authors give also some suggestions for improvements.

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