A Pair of Optical Lattice Clocks on Separated Deep-Space Trajectories as a Sensor for a Fifth-Coordinate Frequency Drift

This paper presents a space mission design, computed from stated assumptions and not measured, built to measure one quantity: the fractional frequency offset between the two clocks attributed to motion along a fifth coordinate, for which the design case adopts 3.20e-18 in fractional frequency. The instrument is two spacecraft, each carrying a strontium optical lattice clock with a cryogenic silicon reference cavity, linked by a coherent two-way optical link that transfers frequency between the craft without adding noise above the clock floor. It operates from two heliocentric drift-away trajectories separated by up to 0.6 astronomical units for 4 years. The one-day measurement uncertainty is 1.60e-17 in fractional frequency; averaged over the full mission of 1461 days it falls to 4.19e-19 in fractional frequency, giving a signal-to-noise ratio of 7.64 for the design case and a five-sigma detection limit of 2.09e-18 in fractional frequency. The spacecraft has a dry mass of 680 kilograms, a wet mass of 920 kilograms including propellant, and a total electrical load of 907 watts supplied by a solar array of 3.16 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.