Star Trackers
Star trackers are used in a number of applications for navigation, space craft, missiles, and the now ancient SR-71 which had a ten hour accuracy of .3NM with its 1960's technology.
Was wondering its effectiveness in the airline industry in as much as you need a clear sky, that is no cloud cover. Obviously no good if you are in IMC, so the question is, how much of your time at altitude is spent in IMC, a figure plucked out of the air I realise ie a wild guess. Not much, a lot, as a pax who has done a fair share of international and domestic travel cruise in IMC seemed an extreme rarity.
Question due to the GPS issues thread in R & N.