Heat pipes are simple, reliable, light-weight and highly efficient components for thermal control and protection, which will find growing interest in the context of manned space flights and future space stations.Despite extensive testing requirements for satellite heat pipes, the crucial data on their zero-g behaviour can only be obtained on actual space flights. For this reason a heat pipe test platform was flown twice on a retrievable satellite (SPAS-01) on board Space Shuttle. Among various other heat pipes, two standard IKE constant-conductance heat pipes and a heat pipe diode based on the liquid trap principle were tested on this platform.The paper compares ground test data and flight data from the first and second flight. The power profile in the second flight was slightly changed in order to gain additional information about heat pipe behaviour under zero-g. The final results from the first flight and first results from the second flight show good agreement with the ground test results. The heat pipes operated very well, even better than predicted.