A Three-Spacecraft Gyroscope Constellation at the Sun-Earth L2 Point for a Direct Reading of Spin-Sourced Torsion

This paper presents a space mission design, computed from stated assumptions and not measured, built to measure one quantity: the additional spin precession attributed to a torsion coupling, for which the design case adopts 0.85 milliarcseconds per year. The instrument is three drag-free spacecraft, each carrying two counter-rotating superconducting gyroscope rotors read out by SQUID magnetometers, with the spin axes of the three craft pointed along three mutually inclined directions so that a genuine geometric precession separates from a torque acting on one rotor alone. It operates from a halo orbit about the Sun-Earth L2 point for 3 years. The one-day measurement uncertainty is 0.14 milliarcseconds per year; averaged over the full mission of 1096 days it falls to 4.23e-03 milliarcseconds per year, giving a signal-to-noise ratio of 201 for the design case and a five-sigma detection limit of 0.0211 milliarcseconds per year. The spacecraft has a dry mass of 850 kilograms, a wet mass of 1030 kilograms including propellant, and a total electrical load of 1065 watts supplied by a solar array of 3.13 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.