Thermal Design Aspects of EURECA during Shuttle Cargo Bay Parking Phases 851361
Although the Shuttle cargo bay parking phase is only a transition phase for ESA's European Retrievable Carrier (EURECA), it can last long enough (up to five days) to be the determining factor for the spacecraft thermal design.
Both the thermal behaviour of safety critical (e.g. avoidance of hydrazine freezing and subsequent thawing, which might cause rupture of lines and valves) and temperature sensitive items have to be determined under consideration of hot and cold conditions for EURECA.
Because the configurations of the Shuttle co-payloads are not known at the present time, hot and cold locations of EURECA within the cargo bay were identified. The position of EURECA in the middle of an otherwise empty cargo bay was determined as the cold location, whereas a sandwiched position of EURECA between two co-payloads was identified as the hot location.
The aim of the thermal control design is to keep all spacecraft components within specified temperature limits and at the same time minimize the required heater power by definition of particular attitude constraints. However, due to the different non-operational temperature level requirements in particular of safety critical items (low temperature sensitivity of hydrazine and high temperature sensitivity of batteries), Orbiter attitude sequences have to be selected where an overheating of the batteries is precluded, which in turn implies that a decrease of the hydrazine temperature is to be accepted.
Because a variety of Orbiter attitude sequences exists, which create the same thermal environment, a decision tool was developed which allows the user to identify potentially favourable Orbiter attitude sequences without detailed thermal analyses.
However, even under consideration of most favourable Orbiter attitudes, a minimum amount of heater power (100 W) is needed for both pre-deployment and post-retrieval phases. This amount grows up to about 300 W, if no dedicated Orbiter attitudes are provided.