Mission Design for the CubeSat OUFTI-1

CHAPTER9THERMAL-CONTROL SYSTEMThe goal of thermal control is to guarantee to all the elements on board thermalconditions that allow them to reach their expected performances: each one ofthem has to be able to work when needed, during lifetime, with the requiredperformances from the beginning until the end of life.Each system has well defined temperature limits. We usually define the workingtemperature limits and the stand-by temperature limits: the former indicatesthe temperature gap where the element can work respecting the requirements,the latter the temperature gap where the elements can’t respect the specifiedrequirements but it doesn’t suffer any damage. For instance, the electronicequipments and the battery have typically as working temperature limits -20 ◦ Cand +40 ◦ C and as stand-by limits -40 ◦ C and +60 ◦ C.The thermal control can be active, semi-active or passive: we call active a systemthat needs power to work and passive a system that doesn’t. The definition ofsemi-active (or semi-passive) control system is more vague. It comes from thefact that an active system can break down, while a passive can’t, even if itcan be degradated by the external environment: we call therefore semi-active asystem that doesn’t require power but that can break down. A typical exampleare all the system with a state’s change (ex. heat pipes).On a CubeSat, because of the limited mass and power, often the only possiblechoice is a passive thermal-control system.85