Astronav systems have expensive moving parts that aren't very githubbable. There was an SDR software defined radio passive radar project that got taken down. https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
If you restrict the domain to nighttime or exoatmospheric, a high-resolution wide-angle camera paired with an offline astrometry database has the makings of a strapdown astronav.
Widening the domain again, the natural motion of the vehicle is probably enough, when combined with inertial sensors to aid pixel-shift image stabilization, to achieve the same kind of processing gain as the older systems got with shutter-synchronous detection.