Tunnel in the Sky by Robert A. Heinlein

Paperback. Condition: Good-. 1955. Ace. 1st printing.

It was just a test . . .

But something had gone wrong. Terribly wrong. What was to have been a standard ten-day survival test had suddenly become an indefinite life-or-death nightmare.

Now they were stranded somewhere in the universe, beyond contact with Earth . . . at the other end of a tunnel in the sky. This small group of young men and women, divested of all civilized luxuries and laws, were being forced to forge a future of their own . . . a strange future in a strange land where sometimes not even the fittest could survive!