Reliable, low mass rotating heat transfer joints using heat pipes have many potential on-board spacecraft applications including hinges, rotating platforms and moveable radiators. These joints require a high thermal conductance and low outgassing and fluid leakage rates to prevent spacecraft contamination. This paper describes two concepts: the first has the joint in the heat pipe envelope; the second utilizes a high thermally conductive fluid in a gap between two separate heat pipes, one located inside the other.The second concept has been pursued through the testing of a developmental heat pipe-to-heat pipe joint. Thermal performance up to 1500 watts showed a joint thermal resistance of 0.008 to 0.01 C/watt (thermal conductance of 100-125 watts/C) in the temperature range of 25-50 C. Theoretical calculations show the gap fluid leakage to be less than 1 × 10−5 grams of NaK in five years. Extended rotary life test, seal design, fluid leakage measurement and improved heat pipe performance are areas of future development.