System Study: Radiation Hardened Autonomous Navigation

摘要

The question of whether a beacon tracker, similar to the NRL Rad-Hard Star Tracker, can be successfully used in a Landmark Tracking AutoNav application rests squarely on the accuracies required, the number of beacons available, and their optical characteristics as well as distribution over the surface of the Earth. Basically, we have found that a star tracker can be used in a landmark approach, but only within some rather severe constraints: (1) Beacons can be distributed more-or-less uniformly over the Earth. Restriction to the United States does not seem feasible; (2) Position errors of several kilometers can be tolerated between updates; (3) A very sophisticated orbit propagator is built into the system. There are non-trivial problems associated with this approach to the problem. Most of them stem from the fact that the tracker would be used in a way for which is was not designed nor intended. (1) The beacons 'twinkle'; (2) The light from the beacons is refracted by the atmosphere by varying amounts which can be only partially compensated for; (3) The tracker's field of view is too small; it greatly reduces the number of targets that can be seen, as well as the durations of observations. This results in fewer updates, and necessitates a very sophisticated orbit propagator; (4) There are already too few beacons can be obscured by cloud cover. This is, perhaps, the most egregious problem with this approach. (FR)