Celebrating 20 years since it beamed into UK cinemas, “Galaxy Quest” remains the finest “Star Trek” movie made since 1991 and probably has almost as good a claim to siring “The Orville” as “Star Trek: The Next Generation”.

Eighteen years after its abrupt cancellation, the cast of the cult TV series “Galaxy Quest” are glumly schlepping from convention to store opening to convention, strip-mining…