Lifetests of the telecommunications satellite heat pipes

Test results obtained during lifetests of heat pipes throughout a period of three years are described together with the instrumentation and the test setup. Bendable 7 mm O.D. artery heat pipes have been developed for satellite applications. Four of these heat pipes subjected to a stationary lifetest were operating with a heat load of 15 watts at a temperature of 60 C, and another one, the accelerated lifetest heat pipe, was operated in reflux boiler mode at a temperature of about 100 C. A sixth heat pipe underwent a thermal shock test consisting of 3000 cycles between 5 C and 80 C. During the lifetests gas generation within all of the heat pipes was detected, resulting in a steadily increasing length of blocked condenser section. Due to the degrading longterm performance of the Al/SS/NH3 heat pipes, some of these were replaced by one-metal heat pipes made from stainless steel. The lifetest of three heat pipes was discontinued prior to the planned lapse of 3 years. These heat pipes were cut open to analyze working fluid and any deposits on the inner heat pipe surfaces.