Children of the Lens by E.E. Smith

Twenty-odd years before, when the then _Dauntless_ and her crew were thrown out of a hyperspatial tube and into that highly enigmatic nth space, LaVerne Thorndyke had been a Chief Technician. Mentor of Arisia found them, and put into the mind of Sir Austin Cardynge, mathematician extraordinary, the knowledge of how to find the way back to normal space. Thorndyke, working under nervebreaking difficulties, had been in charge of building the machines which were to enable the vessel to return to her home space. He built them. She returned.

He was now again in charge, and every man of his present crew had been a member of his former one. He did not command the spaceship or her regular crew, of course, but they did not count. Not one of these kids would be allowed to set foot on the fantastically dangerous planet to which the inertialess _Space Laboratory XII_ was anchored with tractors and pressors.