https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker It's old tech There's also the classic of dead reckoning, which is usual

https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker It's old tech There's also the classic of dead reckoning, which is usually infeasible but modern commercial aircraft have the capability of bounded accuracy in their dead reckoning navigation for several hours at a time if needed, and if you are the US government, you can build fantastical machines to measure your own motion and dead reckon yourself to a very very tight point on the other side of the world. https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_Sphere https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_Sp... That thing still has orders of magnitude better stability than common laser ring gyros as used on those airplanes, and the same for the price tag. GPS was dominant because it's cheapish and high performance and easy for a lot of contexts. However, it is critically easy to jam, for physics reasons. A jamming transmitter will always be thousands of miles closer to you than the GPS satellites are. Jamming GPS is cheap and easy, so all war will involve the denial of precision GPS guidance, so we are looking into alternative guidance again. TERCOM as used in the Tomahawk missile existed to guide them semi-inertially back in the 80s and was functional. In Ukraine, various providers have developed (supposedly) ways of using commodity cameras to watch the scenery pass by under a flying drone to ground medium quality inertial systems, to allow dirt cheap, unjammable navigation over long distances. It will be interesting how this plays out.