Speaker
Description
Heat pipes are conventionally used for spacecraft thermal control. A well-designed heat pipe provides a reliable thermal link that transports large quantities of heat at nearly isothermal conditions, varying its working temperature and pressure within its design range to adapt to the conditions of the heat source and sink. However, heaters are often used in the cold non-operational phase to compensate for this efficient thermal link and ensure the survival of sensitive hardware in the extreme cold, which consumes part of the spacecraft power budget.
Planetary rovers and deep space missions experience large fluctuations in environmental conditions, including long periods of extreme cold (e.g., lunar and Martian nights, or long cruise phases) with limited available spacecraft power. Thus, it becomes beneficial to implement variable thermal links that can passively adapt to maintain stable spacecraft equipment temperatures. This includes passive thermal switching, where the link is terminated during long cold phases, maintaining acceptable equipment temperatures with minimal heating power.
The variable conductance heat pipe (VCHP) presents a potential solution. Variable conductance can be achieved in several ways. Most commonly, the active area in the heat pipe condenser is partially blocked by flooding with a non-condensable gas. Other control schemes include condenser blocking with excess working fluid, or the control of vapour flow to the condenser, or liquid back to the evaporator.
In this presentation, the various design schemes for VCHPs are discussed. Emphasis is placed on the hot reservoir VCHP, which builds upon flight heritage from the cold reservoir VCHP previously flown as part of the European SIGMA instrument. The improved hot reservoir design eliminates the need for heating during cold phases, making it particularly suitable for planetary rovers and deep space missions. The current TRL for this technology, along with its strengths, limitations, and design challenges, are examined. Additionally, a potential thermal modelling approach using ESATAN TMS is suggested, focusing on capturing the physics of variable conductance within the TMM.
