A navigation technology known as LiAISON (Linked Autonomous Interplanetary Satellite Orbit Navigation) has been known to produce very impressive navigation results for scenarios involving two or more cooperative satellites near the Moon, such that at least one satellite must be in an orbit significantly perturbed by the Earth, such as a lunar halo orbit. The two (or more) satellites track each other using satellite-to-satellite range and/or range-rate measurements. These relative measurements yield absolute orbit navigation when one of the satellites is in a lunar halo orbit, or the like.

The geometry between a lunar halo orbiter and a GEO satellite continuously changes, which dramatically improves the information content of a satellite-tosatellite tracking signal. The geometrical variations include significant out-of-plane shifts, as well as in-plane shifts. Further, the GEO satellite is almost continuously in view of a lunar halo orbiter. High-fidelity simulations demonstrate that LiAISON technology improves the navigation of GEO orbiters by an order of magnitude, relative to standard ground tracking. If a GEO satellite is navigated using LiAISON-only tracking measurements, its position is typically known to better than 10 meters. If LiAISON measurements are combined with simple radiometric ground observations, then the satellite’s position is typically known to better than 3 meters, which is substantially better than the current state of GEO navigation.

There are two features of LiAISON that are novel and advantageous compared with conventional satellite navigation. First, ordinary satellite-to-satellite tracking data only provides relative navigation of each satellite. The novelty is the placement of one navigation satellite in an orbit that is significantly perturbed by both the Earth and the Moon. A navigation satellite can track other satellites elsewhere in the Earth-Moon system and acquire knowledge about both satellites’ absolute positions and velocities, as well as relative positions and velocities in space.

The second novelty is that ordinarily one requires many satellites in order to achieve full navigation of any given customer’s position and velocity over time. With LiAISON navigation, only a single navigation satellite is needed, provided that the satellite is significantly affected by the gravity of the Earth and the Moon. That single satellite can track another satellite elsewhere in the Earth- Moon system and obtain absolute knowledge of both satellites’ states.

This work was done by Jeffrey S. Parker and Rodney L. Anderson of Caltech; and George H. Born, Jason M. Leonard, Ryan M. McGranaghan, and Kohei Fujimoto of the University of Colorado at Boulder for NASA’s Jet Propulsion Laboratory.

The software used in this innovation is available for commercial licensing. Please contact Dan Broderick at Daniel.F.Broderick@ jpl.nasa.gov. NPO-48736