Modern spacecraft are using Loop Heat Pipes (LHP) more frequently. However, there are no practical guidelines to help LHP users know how and when to use the active temperature control. Most spacecraft payloads and instruments must operate in a required, sometimes-narrow temperature range. Outside this temperature band the instruments either operate poorly or cease to operate. Radiator (sink) sizing can set the maximum permissible operating temperature, and active temperature control devices (TCD) provide lower margin of operation temperature. The LHP is a component of the spacecraft thermal control system, which, in most cases, functions as a system; therefore, LHP operation requires special consideration when using TCDs.
It is shown that two major groups of TCD devices exist. The classification is based on the mechanism TCDs use to control the LHP temperature. A simple classification of different ways to control the temperature of LHP is presented. Basic physical principles and modes of operation for different types of active temperature control devices are discussed in the paper. Pros and cons of different types of TCD devices for different practical applications are highlighted and discussed.
The detailed explanation, description and examples of the LHP temperature control approaches are presented in the paper. Some basic equations that allow prediction of power consumption for control are given for the thermal TCD approach.
In conclusion, this paper presents the easy-to-use criteria for estimating the efficiency and quality of a LHP control approach.