Another interesting possibility would be to use a Star Tracker[1][2] for absolute fixes to sanity check GPS / recalibrate the INS periodically. And it has a lon

Another interesting possibility would be to use a Star Tracker[1][2] for absolute fixes to sanity check GPS / recalibrate the INS periodically. And it has a long and storied naval tradition! [1] https://en.wikipedia.org/wiki/Attitude_control#Star_tracker https://en.wikipedia.org/wiki/Attitude_control#Star_tracker [2] http://opci.com/ocns.htm http://opci.com/ocns.htm