Star Born by Andre Norton

Raf Kurbi, flitter pilot and techneer, lay on the padded shock cushion of his assigned bunk and stared with wide, disillusioned eyes at the stretch of stark, gray metal directly overhead. He tried to close his ears to the mutter of meaningless words coming from across the narrow cabin. Raf had known from the moment his name had been drawn as crew member that the whole trip would be a gamble, a wild gamble with the odds all against them. RS 10 -- those very numbers on the nose of the ship told part of the story. Ten exploring fingers thrust in turn out into the blackness of space. RS 3's fate was known -- she had blossomed into a pinpoint of flame within the orbit of Mars. And RS 7 had clearly gone out of control while instruments on Terra could still pick up her broadcasts. Of the rest -- well, none had returned.

But the ships were built, manned by lot from the trainees, and sent out, one every five years, with all that had been learned from the previous job, each refinement the engineers could discover incorporated into the latest to rise from the launching cradle.