On-orbit Experiment Plan of Loop Heat Pipe and the Test Results of Ground Test

It is becoming increasingly difficult to meet the challenging thermal control requirements of modern spacecraft missions with only existing thermal control devices such as conventional heat pipes. A loop heat pipe (LHP) is an effective method to overcome some of these thermal control constraints. The LHP is a passive two-phase heat transfer device that utilizes the evaporation and condensation of a working fluid to transfer heat and capillary force to circulate the fluid. The LHP can transport much heat for a long distance against gravity and has many other excellent characteristics, such as high controllability of operating temperature and a shutdown function. In this study, LHPs for space application have been developing. As a part of the study, a bread board model (BBM) of LHP was designed and fabricated. As a result of an on-ground test of the BBM, it was confirmed that the BBM fulfilled all requirement (e.g. maximum heat transport rate, minimum required heat load for start-up, operating temperature control and shutdown function). To adopt the LHP as a heat transfer device in practical spacecraft mission, the thermal characteristics under micro-gravity conditions should be examined in advance. An on-orbit experiment of a LHP radiator system is planned. This paper describes the test plan of on-orbit experiment of a LHP radiator system on the International Space Station (ISS) and the results of thermal vacuum test of flight model for on-orbit experiment on ground.