S3·E23 Ambush in Space

Roy Cowan, a former solar guard Captain, escapes from the Asteroid Prison and sets out to ambush the Polaris. His aim: to destroy Tom Corbett and his crew mates who twice before foiled his bid for fame and glory. Two convicts, including the treacherous Roy Cowan, escape from the Prison Asteroid by hijacking a space freighter. Cowan and his accomplice lure the Polaris Cadets into an ambush using their hijacked freighter as bait, which they themselves have abandoned, but not before starting a wildcatting reaction in the freighter's reactors, which will cause the ship to explode as the Cadets approach.