A Laser Polarimetry Satellite Measuring Vacuum Birefringence in a Long Orbiting Optical Cavity

This paper presents a space mission design, computed from stated assumptions and not measured, built to measure one quantity: the phase retardation between polarisation components attributed to the vacuum term under test, for which the design case adopts 3.50e-11 radians of retardation. The instrument is two satellites flying in formation 1,000 kilometres apart, maintaining a common high-finesse optical cavity along the line between them with a polarisation-modulated laser, so the retardation accumulated over the long baseline is read as a phase difference between two polarisation channels. It operates from two co-orbital satellites in a 1,200-kilometre circular Earth orbit, separated along-track for 2 years. The one-day measurement uncertainty is 1.20e-10 radians; averaged over the full mission of 730 days it falls to 4.44e-12 radians, giving a signal-to-noise ratio of 7.88 for the design case and a five-sigma detection limit of 2.22e-11 radians. The spacecraft has a dry mass of 560 kilograms, a wet mass of 655 kilograms including propellant, and a total electrical load of 940 watts supplied by a solar array of 2.71 square metres at the operating distance. Every performance figure in this paper comes from the deposited computation; the design is simulated, not measured, and no hardware described here has been built or flown.