ESA Document - Emits - ESA

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3.3.3.1 Requirements and design drivers
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 167 of 422
The thermal requirements are mainly driven by the presence of humans on-board and by the
complexity of a vehicle leaving Earth orbit. A particular robustness and reliability are therefore
expected for the thermal control system (TCS) and required during the complete mission
duration.
Mass shall be optimised, especially considering the significant contribution of the TCS to the
overall budget (thermal protection in particular). Trade-offs of TCS performance against safety
appear as an important driver for such study.
The main requirements are the following:
• The TCS functions are to maintain air temperature and humidity in the habitable zone within
preset limits, and to thermally control the on-board systems. Therefore, TCS shall be
designed:
• to maintain the habitable zones in a certain comfort zone (temperature, humidity) but
respecting also safety requirements (touch temperature, condensation avoidance).
Standard figures are a medium temperature between 18 and 27 ºC and a relative
humidity from 25 to 70%.
• to maintain a uniform environment for a crew up to six members. The volume of the
habitable zone is a particular constraint on the sizing of the TCS elements.
• to maintain elements and/or dedicated zones within temperature requirements
(electronics, propellants, valves, …). To optimise the thermal budget, a certain
rationalization of space and grouping of elements shall be carried out. Ideally, all
equipments are within a single dedicated enclosure.
• to maintain the interfaces of all modules within temperature requirements, for all
possible configuration (THM separated from MEV for example). When decoupled,
heat leaks of these interfaces can be severe if not thermally accommodated (large
surfaces).
• The candidate TCS architecture shall be also capable of :
• Guaranteeing adequate flexibility and reliability of the system for a long duration
mission (2.6 terrestrial years)
• Guaranteeing the performance of the system for any spacecraft attitude and for all
thermal loads derived from the mission requirements. This severe constraint for the
heat rejection capability guaranties a decoupling with attitude control reliability.
• Optimising the heat management system in term of efficiency versus penalties to the
system (mass, energy consumption)
• Guaranteeing safety by adequate provision of thermal hardware for the whole mission
(necessary autonomy of the crew)
• Fully verifying and testing TCS on ground.