Microwave components carrying medium or high powers in the space environment may suffer from multipactor breakdown. The resulting discharge can seriously affect the performance of communications equipment, so effective multipactor detection is essential in the development and qualification stages of flight hardware. This paper presents an extremely sensitive method of detection by means of a travelling wave resonant ring which provides high power levels without the need for costly high power amplifiers. The principle of the ring is presented together with design examples for systems at C-band and Ku-band frequencies presently in use at Spar Aerospace. Measured results on a variety of components are reported together with examples of induced multipactor which demonstrate the effectiveness of the ring technique.