The dynamic behavior of a space radiator that is driven by gas-loaded heat pipes with external reservoirs is dependent on the interactions between the neighboring heat pipes and on those between each pipe and its respective reservoir. To get an insight into these phenomena a thermal vacuum test program with a 3-GLHP radiator was performed with varying gas masses and heat loads and also in the configuration where the radiating sheets were segmented. The heat pipes are axially grooved, with acetone as working fluid and argon as control gas. The test results are contrasted with results from a numerical simulation that is based on a flat front type vapor space model. Special interest is directed to operation near and at overload and to the thermal response to the failure of one outside heat pipe.