That. However that works just fine for ICBMs and the like…

The future is more likely to be quantum accelerometers and quantum gyroscopes, as they have no “external dependency”.

More likely image-based navigation, where you just upload the entire imagery of the route and then use it to correct your inertial references.

Encrypted positioning information from low-orbit satellites is another option.

That doesn't work well in some conditions, it's not new either. Some cruise missiles that have TFR (Terrain-following radar) and actually do this already.

It also is not really applicable when you are on a balistic course at *very* high altitude, course correction has to happen early in these case given the reentry speed/constraints.

I presume radio signal or certain frequencies of thermal would be viable for adverse weather conditions.

The frequencies used in GPS: Yes. The frequencies used for celestial nav: No.