A space-based superconducting microwave oscillator clock

Superconducting Cavity Stabilized Oscillators, SCSO, have produced the most stable clocks to date, achieving an Allen variance of 3×10−16 for integration times between 102 and 103 seconds. Cavity frequency variations are mainly caused by acceleration effects due to gravity and vibrations, temperature variations, and fluctuations in the energy stored in the cavity. We describe the status of a project aimed at building an improved cavity system suitable for use on the International Space Station, ISS. Primary experimental applications include the measurement, in conjunction with other types of clocks, of the dependence of fundamental constants on the gravitational potential, gravitational redshift measurements, and the measurement of the anisotropy of the velocity of light. A major secondary application is as a flywheel for the atomic clocks co-located on the ISS.