There&#x27;s plenty of aviation navigation methods aside from GPS, some of which will fit on a small processor.  We&#x27;ve been doing optical&#x2F;radar terrain map following for decades in cruise missiles for example.  There&#x27;s also inertial, celestial, VOR&#x2F;NDB&#x2F;TACAN, ADF and others.  A smart navigator will use multiple methods; if one of its methods begins to disagree from the others, it can be downweighted.