I read the question wrong, disregard the part about the Astronomican in >>23086730
. I was thinking of the Great Crusade-era.>How did the Navis Nobilite work in the Dark Age of Technology?
Probably quite similar to the Navigators in 40k, except using advanced technology to compensate for the lack of the Astronomican.>How could they navigate the warp without an Astronomicon?
With considerable difficulty, and many terrible, terrible fatalities, I would assume.