Can characters besides Navigator mutants take/use this Skill? Is that in keeping with the fluff?

From THE NAVIGATOR HOUSES section on page 313.

"Renegades dedicated to the Ruinous Powers utilise both rogue
Navigators and sorcerers with analogous powers to steer their
vessels through the shifting tides of the Empyrean, steering not
by the sickly illumination cast by the Astronomican, but by other,
more powerful beacons only they can look upon."

So you can navigate the warp if you are a psyker of a sorcerer (although the book doesn't say so, just like with psyniscience, it was propably because in these skills could be bought only for specyfic careers before and ffg just copy/pasted from previous books)

Hiyas!

(If memory serves me right)

There's a highly chaotick/heretickall device which lets mostly anyone navigate, described in Rogue Trader's Hostile Acquisitions (I believe) which I'm 'porting to BC .

HtH

L