In-Situ Navigation and Timing Services to Prepare for a Human Mars Landing Site

In a previous paper, we described the system concept of a proposed Mars Regional Navigation Satellite System (MRNSS) that is built upon a number of notional Mars orbiting and surface missions in the human exploration era of Mars.We assume two areostationary Mars relay orbiters that have continuous line-of-sight visibility with the Mars landing site, a Deep Space Habitat (DSH) in an inclined 48-hour circular orbit, and a surface communication lander that could serve as the reference point.These orbiting and surface infrastructure elements broadcast GPS-like ranging signals and other ephemeris information to the mission users.With one or more additional orbiters in areosynchronous orbits that trace around a figure-8 path, a regional navigation satellite system can be realized that provides in-situ course absolute localization and precision relative localization and timing services to the users in the vicinity of a Mars landing site.We also introduced a new geometric trilateration method that simultaneously performs absolute positioning and relative positioning.The relative position is derived from a "differencing" function of two raw-range measurements between a known reference point and of the target from a navigation satellite, thereby eliminating most of the common errors like atmospheric delays, ephemeris errors, and instrument delays in real-time.In the Mars environment, this "error-cancellation" function greatly reduces the need to perform extensive orbit determination (OD) of the navigation satellites like the Earth's GPS, and only requires occasional tracks from the Earth's large-aperture deep space antennas to perform OD's.In this paper, we provide detailed simulations on both the absolute positioning scheme and the relative positioning scheme, and show that the relative positioning scheme provides 200 -400 times improvement in localization accuracy.On the ground side, we discuss new approaches that simultaneously perform 2-way Doppler/ranging, and re-introduce the method of Same Beam Interferometry (SBI) for the Mars navigation orbiters.This helps to further reduce the tracking burden of the ground antennas required to support the OD of the Mars orbiters, making the concept of MRNSS more realizable.