By Lisa Schwarzbaum
Updated October 17, 1997 at 04:00 AM EDT

Pity the poor moviegoing children of an earlier generation who had to make do with boring belching scenes before more thrilling on-screen flatulence became the rage. The gas gags in this coarse, space-travel kidcom are long and audio-enhanced, but they’re not enough to make up for a lack of real humor or filmmaking imagination in a story about what every kid dreams of: blasting off. With more than a little credit due to the screwball hyperactivity of Pee-wee Herman, comedian’s comedian Harland Williams (a fave of Jim Carrey) plays dorky scientist Fred Z. Randall — a traditional Disney wise-fool boy-man — who, through one twist and another, makes his way to Mars with a NASA crew. And once freed from his earthly klutziness (when he goofs or smashes things up, he reflexively announces, ”It wasn’t me!”), Fred saves the mission from disaster and wins the heart of the nice girl astronaut (Jessica Lundy). William Sadler plays the disdainful team commander who treats Fred shabbily (i.e., Bad Dad); Beau Bridges plays the older astronaut who recognizes Fred’s very special spirit (i.e., Good Dad). C-