Future space stations and platforms will require a centralized thermal utility to provide temperature control of various heat sinks or sources. Its purpose is to transport large amounts of energy over long distances towards a heat rejection system, with very small temperature differences.The present paper deals with the heat rejection system. A concept of a multi-tubes condenser has been selected and designed, using ammonia as the working fluid. In order to support and confirm the modelization software, an experiment is set up with a one-tube condenser uniformly cooled, involving limited heat power, but representative of thermo-hydraulic conditions.This paper presents the test programme. Objectives are first to confirm the selected technology, and to assess internal operation from the measurements of the external temperature along the tube, and differential pressure drop. The experiment which is thought out from an industrial viewpoint also has for purpose to enable simplifications in the modelization, without going into the condensation phenomenon. A description of the test apparatus is also given.A second condenser tube with asymmetrical cooling, more representative of the space concept (Og), will be tested to quantify the influence of the cooling device on the condensation of the fluid, and adapt the modelization to the space case.