A Space Academy tournament, consisting of sports, a written exam, and a space race, pits the Polaris unit in competition against other Cadet units at the Academy. The chief competition is the Vulcan unit led by Eric Rattison. Controversy cast a shadow over the Polaris unit when evidence indicates that a member of the Polaris crew has stolen an examination paper from Dr. Dale's office.

Astro is believed to have contracted "Space Fever" a disease which could result in having him permanently grounded from space travel, and thus, out of the Polaris Unit. During his narration, Frankie Thomas defines for the viewers just what a 3-man Space Cadet unit, like the Polaris, really is.

The Space Cadets, along with Captain Strong, Commander Arkwright, and Dr. Joan Dale, seek an Academy scientist lost on a distant planet in an uncharted solar system. Their search takes them to the legendary Rocket Graveyard, where dozens of lost ships have accumulated over the past 200 years. The graveyard appears to be otherwise deserted, but there are unknown foes waiting -- not all of which are human.

A clue provided by a youthful stowaway provides the only hope of preventing Roger and Captain Strong from making contact with an anti-matter asteroid and instantaneous annihilation.

The Cadets are menaced by a weird, near-mute visitor from Alkar, the legendary black planet lying beyond the orbit of Neptune. But a much more deadly threat comes from an old and very dangerous enemy, that could lead to an attack against the entire Solar Alliance.

An adventurer calling himself the "Ace of Space"- stows aboard the Space Cadets' ship (the Ventura on this occasion) with the aid of the impulsive Roger. But "Ace" thereupon commandeers the ship and forces the Cadets to fly to Venus and help him search for the legendary Lost Colony. They do find it, amidst the Venusian jungles, but they also encounter the very same menace that wiped out the original Colony, established by the first colonists from earth 200 years ago!

The Polaris, on a mission to destroy a dangerous contra-terrene asteroid, is crippled by a split in the servo-gyro and forced to land on Jupiter for repairs.

Cadets Astro, Roger Manning, and Eric Rattison, out on space maneuvers aboard the Polaris, run into trouble when the Servo unit (which controls the automatic steering unit) on the space ship goes out of commission, and they are forced to make an emergency landing on Jupiter. Problems with Jupiter's intense gravitation field and ammonia storms threaten the ships' survival, and also hinder the efforts of Tom and Captain Strong to come to their aid.