Space Cadet is a 1948 science fiction novel by Robert A. Heinlein about Matt Dodson, who joins the Interplanetary Patrol to help preserve peace in the Solar System.

They find it, but all aboard are dead, the unlucky victims of a fast-moving object that punctured the ship when the armored outer airlock door was open.

Before the accident, a researcher on the Pathfinder had found evidence that the planet which blew up to form the asteroids was inhabited by an intelligent species, and that the explosion had been artificial.

The captain of the Aes Triplex transfers half the crew to the repaired Pathfinder so that they can take the ship and the news of the startling discovery back to Earth quickly.

To their amazement, the matriarch takes the stranded humans to the carefully preserved Astarte, the legendary first ship to set out for Venus over a century before and thought to have been lost en route.

Later, Matt's mentor in the Patrol makes him understand that if such an unlikely dilemma should arise, his commanding officer would lock him in his room rather than expect him to participate in the attack.

Written almost a decade before the American Civil Rights Movement, and at a time when non-white characters were almost entirely absent from science fiction, the book also explores the theme of racism, both literally, in discussions about the cosmopolitan racial makeup of the (all-male) Patrol, and metaphorically, in its description of conflict with the Venerians.

Discouraged by the intellectual demands of his Patrol training, and attracted to the glamor and esprit de corps of the Marines, Matt requests a transfer, but is dissuaded by his mentor.

In contrast, the Marines, the service branch which deals with ordinary military affairs, are trained to prize unquestioning loyalty and bravery as the highest ideals, and are deliberately recruited from the type of person who seeks glory and excitement.

The novel contains an early description of a mobile phone: Matt dug a candy bar out of his pouch, split it and gave half to Jarman, who accepted it gratefully.

"[2] P. Schuyler Miller gave the book a favorable review as "a first-rate historical novel of the near future," saying "So subtly has the scientific detail been interwoven with plot and action that the reader never realizes how painstakingly it has been worked out.

Greene had originally submitted a radio script for "Tom Ranger and the Space Cadets" on January 16, 1946, but it remained unperformed when Heinlein's novel was published.

Both the "trainee astronaut" and "person regarded as being out of touch with reality" entered the Oxford English Dictionary, though by 2014 Oxford noted that, in American English, the phrase had also recouped the positive connotations originally meant by Heinlein and Joseph Greene, the Tom Corbett, Space Cadet writer: "An enthusiast for space travel, typically a young person."