The Phantom Planet (1961)

Starring Dean Fredericks, Coleen Gray, Anthony Dexter, Francis X. Bushman, Richard Weber
Directed by William Marshall
(actor & director credits courtesy IMDB.com)

In the distant future, an Earth astronaut is stranded on a mobile asteroid, home to a tiny race with advanced technology who are in a war with the fearsome Solarites.

An independent science fiction film impressively mounted on a limited budget, the picture presents some unique visuals against the background of an eerie and otherworldly musical score.  Although per IMDB the score was assembled from stock music, it seems integrated and well-suited to the picture.  The visuals include rocket ships, Fredericks shrinking within his space suit, an unusual alien makeup for giant actor Richard Kiel in one of his earlier roles, spaceships encased in a fiery exterior, a pre-Star Trek detention cell with a powerful forcefield, gravity plates that disintegrate whatever touches them, and more.  Fredericks makes a fine leading man for this adventure, and Bushman, a prolific actor with work going back to the silent era, is distinguished as Sessom, the leader of the tiny aliens.  It may not stand on the same level with the more polished sci-fi productions of the era, but it does bring a unique new tale to the screen and one that's entertainingly presented.