A Solar-Diver Spacecraft Carrying Inertial Sensors Through a Close Perihelion Pass as a Strong-Field Frame Test

This paper presents a space mission design, computed from stated assumptions and not measured, built to measure one quantity: the inertial-sensor precession attributed to the strong-field frame term under test at perihelion, for which the design case adopts 125 milliarcseconds per year equivalent. The instrument is a heat-shielded spacecraft on a highly elliptical heliocentric orbit with perihelion at eight solar radii, carrying a compact gyroscope package and a three-axis accelerometer behind the shield, operating its precision observing plan during the weeks around each perihelion when the field is strongest. It operates from a heliocentric orbit with perihelion at 0.037 astronomical units and aphelion near Venus, period about 150 days for 4 years. The one-day measurement uncertainty is 310 milliarcseconds per year equivalent; averaged over the full mission of 1461 days it falls to 8.11 milliarcseconds per year equivalent, giving a signal-to-noise ratio of 15.4 for the design case and a five-sigma detection limit of 40.6 milliarcseconds per year equivalent. The spacecraft has a dry mass of 670 kilograms, a wet mass of 930 kilograms including propellant, and a total electrical load of 891 watts supplied by a solar array of 0.411 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.