Developments and Prospects in Temperature Control Technique of Loop Heat Pipe for Spacecraft

With the development of space-based remote sensing and deep space exploration technology, higher standards for temperature stability and uniformity of payloads have been proposed to spacecraft thermal control systems. As an efficient two-phase heat transfer device with active temperature control capabilities, the loop heat pipe (LHP) can be widely applied in spacecraft thermal control systems to achieve reliable temperature control under various operating modes and complex space thermal environments. This paper analyzes the fundamental theories of thermal switch-controlled, reservoir temperature-controlled, and bypass valve-controlled LHPs. The focus is on the theories and methods of achieving high-precision and high-reliability temperature control via active reservoir temperature control. Novel control techniques in recent years, such as non-condensable gas (NCG) control with a temperature stability of 0.01°C, are also briefly introduced as promising approaches to improve LHP performance. The on-orbit performance and characteristics of various LHP temperature control methods are provided and ranked in terms of control precision, energy consumption, complexity, and weight. Thermoelectric cooler (TEC)/electrical heater, as the foundation of reservoir temperature control, can achieve a temperature stability of ±0.2°C in space applications under a wide range of heat load. Microgravity model, control strategy, and operating mode conversion are three optimization directions that would hopefully further expand the application scenario of reservoir temperature control. Specific design principles and challenges for corresponding directions are summarized as guidance for researchers.