space cadet n.

That hatch may open again, however, at your word, to return you to Earth. I rest it on your honor as space cadets that if it should, what I say to you now will remain within the hull of the Aldebaran.

[Editorial blurb for ‘Mr. Zytzyz Goes to Mars’, by Noel Loomis:] Mr. Zytztz, however, is one of several score of plant men, the only form of life discovered on Mars when the first expedition gets there. He is befriended by a young Space Cadet, Healey, and the attachment between these two utterly different forms of life with utterly different origins, becomes ultimately one of the epics of early space travel.

Space Cadet.

Above all, space cadets must be physically fit. A sick man, or even a weak man, might crack up under the rigors of space flight.

The hatchway hissed open and all the Junior Space Cadets stopped throwing zero-gravity spitballs at each other.

He’s not there anymore. He’s always someplace else. I mean, he’s always been a space cadet, but he'd have his moments, you know? He’d let me in. He paid attention.

There’s no one else left, Captain Kime. You’re the last space cadet left in the galaxy. We need you.