Satellite sizes have increased considerably during the last 10 years, which has implied the need for larger solar simulators and sophisticated motion systems in thermal tests. As a consequence some alternative test techniques become more and more attractive, the infrared one in particular.The size of the OLYMPUS S/C (formerly L-SAT) and the presence of heat pipes on both the radiators suggested the use of the Thermal Model of the Spacecraft to assess the feasibility if an IR test at Spacecraft level. Both Solar Simulation and IR tests were carried out in order to allow the IR test validation on the basis of a comparison of the test results.Basic information are provided about Thermal Control Design, Thermal Model and Mathematical Modelling.The IR philosophy is shown including test set-up, power control system, test sequence and IR test peculiarities, i.e. IR sources, flux requirement definition, outer surface property measurements, IR heater Rig design, test predictions and correlation approach.On the basis of the previous Solar Simulation Test, IR test results are discussed and some conclusions are provided concerning the IR test techniques as an alternative which can be validated, by employing two independent campaigns of test prediction and correlation. Possible improvements to IR test effectiveness/performance are identified.