At the conceptual design stage fundamental trade-offs are made. Firstly all heat sources are identified. Internal heat can be generated by items such as electronic equipment and batteries, whereas external heat is largely due to solar radiation and planet infra-red flux.
Once all heat sources have been identified it is necessary to find means to reject heat or to keep certain components warm. Various architectures are assessed and, broadly speaking, a decision is made on whether to use a passive or an active architecture.
Passive hardware dissipates no electrical power and has no mechanically activated moving parts. For example, radiators, surface coatings, heat pipes and multilayer insulation (MLI).
RAL Space specialises in the design and manufacture of MLI for instruments and small spacecraft.
Active hardware may employ power or moving parts. For example, heaters, louvres, coolers and thermal switches.
In general it is desirable to use a passive architecture wherever possible to minimise cost, mass, power and risk. However, most instruments will require heaters and many will also have thermal requirements which can only be met by the use of advanced active methods. Initial trade-off studies which weigh up the advantages and disadvantages of a range of passive and active options are important in the optimisation of the thermal control subsystem.
Preliminary studies are performed using Microsoft® Excel or specialised thermal modelling software packages such as ThermXL (link opens in a new window) and ESATAN-TMS (link opens in a new window).
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