Starman's Quest

The Lexman Spacedrive gave man the stars—but at a fantastic price. Interstellar exploration, colonization, and trade became things of reality. The benefits to Earth were enormous. But because of the Fitzgerald Contraction, a man who shipped out to space could never live a normal life on Earth again.
Travelling at speeds close to that of light, spacemen lived at an accelerated pace. A nine-year trip to Alpha Centauri and back seemed to take only six weeks to men on a spaceship. When they returned, their friends and relatives had aged enormously in comparison, old customs had changed, even the language was different.
So they did the only thing they could do. They formed a guild of Spacers, and lived their entire lives on the starships, raised their families there, and never set foot outside their own Enclave during their landings on Earth. They grew to despise Earthers, and the Earthers grew to despise them in turn. There was no logical reason for it, except that they were—different. That was enough.
But not all Starmen liked being different. Alan Donnell loved space, and the ship, and life aboard it. His father, Captain of the Valhalla, lived for nothing but the traditions of the Spacers. But his twin brother, Steve, couldn't stand it, and so he jumped ship.
It had happened only a few weeks before, as Alan experienced it. For Steve, though, he knew it would have been nine years in the past. Now, while Alan was still only 17 years old, Steve would be 26!
Thinking about it got under Alan's skin, finally. The bond between twins is a strong one, and Alan couldn't stand to see it broken so abruptly and permanently. There were other things, too. If Alan remained on the Valhalla, he'd have to marry one of the girls of the ship, and the choice of those his own age was pitifully small. And above all else, he was convinced that the secret of the Cavour Hyperdrive was hidden somewhere on Earth—the Cavour Hyperdrive, that would enable man to leap interstellar distances almost instantaneously, and bring an end to the sharp differences between Earthers and Spacers.
These forces worked quietly within him—and suddenly, without really meaning to, Alan in turn jumped ship and remained on Earth!