An Earth-Mars Laser Ranging Transponder Constellation for a Direct Interplanetary Test of Signal Transit Times

This paper presents a space mission design, computed from stated assumptions and not measured, built to measure one quantity: the round-trip range anomaly predicted over the longest Earth-Mars geometry, for which the design case adopts 38 millimetres of range. The instrument is two laser transponder terminals, one on an Earth-orbiting platform and one on a Mars-orbiting platform, exchanging phase-coherent pulse trains at 1064 nanometres so that the interplanetary range is measured by an active transponder rather than by reflection from a passive target. It operates from an Earth platform in high orbit and a Mars platform in areostationary orbit, ranging across distances up to 2.5 astronomical units for 5 years. The one-day measurement uncertainty is 55 millimetres; averaged over the full mission of 1826 days it falls to 1.29 millimetres, giving a signal-to-noise ratio of 29.5 for the design case and a five-sigma detection limit of 6.44 millimetres. The spacecraft has a dry mass of 620 kilograms, a wet mass of 940 kilograms including propellant, and a total electrical load of 872 watts supplied by a solar array of 5.65 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.