COMPASS: Applications of VLBI Beacons in Cislunar Space

The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, in Lunar o rbit, and in the vicinity of the Lunar Gateway) require new solutions for positioning and navigation. COMPASS (Combined Observational Methods for Positional Awareness in the Solar System) is a spacecraft navigation system being developed to provide cost-effective techniques for the positioning of large numbers of spacecraft in cislunar space. COMPASS will use beacons that emit noise at 0.5-1.0 GHz bandwidth at several bands within the 2-14 GHz range and is designed to be interoperable with the routine modes of the new VLBI Global Observing System (VGOS). COMPASS +VGOS should be able to provide rapid determination of interferometric observables ( phase delay and plasma dispersion with picosecond level accurac ies ) during routine VGOS observing sessions. Multi-baseline phase-referenced COMPASS-VGOS observations with simultaneous calibrator observations should thus enable decimeter accuracy transverse position ing with small (credit-card sized) beacons and a few seconds of observations . While COMPASS technology will be applicable to a wide variety of exploration missions and commercial endeavors, a combined COMPASS beacon and Lunar Laser Ranging (LLR) laser retro re flector on the Lunar surface would provide an immediate and strong scientific return , directly tying the Lunar reference frame into the International Celestial Reference Frame (ICRF) and providing independent estimates of Lunar orbit and librations, providing complementary data useful in tests of General Relativity and in determining the internal dynamics of the Moon. Surface beacons would also provide phase reference sources for orbiting beacons in support of time-critical Lunar operations, such as during landing navigation.