Grumman-581 writes:

I seem to remember some talk awhile back about each star having it's
own electomagnetic signature and the attempt to base a navigational
system upon this... Awh, 'ell, this is probably classified, so just
forget that I said anything... grin

The SR-71 navigated by finding stars in the sky and obtaining a fix
from them. I think it needed only three stars in order to do this.
It could do it even in daytime. It wasn't quite as accurate as GPS,
but it was more accurate than anything other than an INS at the time,
and it had better long-term stability.

I think the details of the system may still be classified. I always
wanted to know how it could see stars in daylight (although it could
not see them through cloud cover).

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