It doesn’t exactly sound like the casting coup of the year: “Let’s get the comedian from ‘Home Improvement,’ that tough chick from ‘Aliens,’ and the British villain from ‘Die Hard’ and put them all in a sci-fi comedy!” Huh? What were they thinking? Well it turns out someone was actually on to something (and not necessarily on something) because Galaxy Quest, starring Tim Allen, Sigourney Weaver and Alan Rickman, turns out to be a funny little gem that’s even more enjoyable if you have a working knowledge of all things from “the final frontier” and “where no man has gone before.”

Now playing, Galaxy Quest is a cleverly conceived comedy that is light years ahead of the vastly overrated and shamelessly excessive buffoonery of Mel Brooks’ cheesy Star Wars spoof, Spaceballs. Instead of simply mocking Star Trek by creating a space-bound comedy, director Dean Parisot and scriptwriters David Howard and Robert Gordon take a more rich route by mining the more fertile territory of both the classic Trek series itself and Trek fandom as well.

Thus, the movie begins, feet firmly planted on planet Earth, with a frustrated troupe of actors from a failed — yet hardly forgotten — 70s show called “Galaxy Quest.” They have been relegated to endless appearances at packed conventions, repeating tired, creaky lines and answering the same old questions ad infinitum about a show long in their past.

Allen does a great Shatner, without actually doing a Shatner impression, as actor Jason Nesmith, the commander of the show and by far the ego of the cast; Rickman is the cranky “thespian” who bemoans his fate as the show’s resident alien and perpetual second fiddle to Nesmith; and Weaver is the bosomy, blonde shipmate about whom no one is quite sure what her character actually does on the show. Daryl Mitchell (as the show’s helmsman), Sam Rockwell (as the unnamed crewmate who meets an unfortunate, yet forseen end), and the always reliable Tony Shalhous round out this game and engaging cast.

The film kicks the pace up a notch when Nesmith gets visited by some fawning Thermains — peculiar folks whom the actor believes to be starstuck fans but actually turn out to be real aliens from the Klatu Nebula. They’ve sought him out because their people, having studied all the old episodes and mistaken them as “historical documents,” believe the “commander” and his “crew” are their race’s last hope against an evil oppressor. Nesmith, playing along because he thinks it’s just another gig, unwittingly gets caught up in an intergalactic mess and recruits his fellow actors to join in the “fun.”

Galaxy Quest has much going for it, not the least of which is its eager cast, who energetically throw themselves into the lark. Rickman is wonderfully droll as the grouchy ex-Shakespearean who turns surly when constantly asked to repeat his character’s famous line, “By Grabthar’s hammer, by the suns of Warvans, you shall be avenged” and Weaver is fun as she goes against type playing a perky space Barbie instead of her usual dauntless, don’t-mess-with-me roles. Perhaps most surprising are the actors behind the Thermians, who effectively play the aliens as innocents, not quite confident in human behavior but chock full of hero worship for their beloved TV idols.

Rated PG for sci-fi violence, mild language and suggestiveness, Galaxy Quest successfully toes the line between catering to Trek fans, who will enjoy the myriad inside jokes the script has to offer, and pleasing those who know not, nor care anything for it. It’s also the only film I can remember in which its profanity is noticeably toned down instead of inexplicably beefed up for a more “attractive” rating.