The World of Ptavvs by Larry Niven

voice. The loudness, hopefully, would carry over Masney's screaming. "You can feel it but it doesn't hurt. Anyway, you have enormous courage, more than you have ever had in your whole life." Masney stopped screaming, but his face was a mask of suffering. "All right," said Kzanol/Greenberg. "Sleep." He brushed Masney's face with his fingertips. Masney collapsed. The car continued weightlessly across the concrete, riding its cushion of air, aiming itself at the cylindrical shell that was the Lazy Eight III. Kzanol/Greenberg let it go. He couldn't operate the controls from the back seat, and Masney was in no shape to help. He could have cut the air cushion, by stretching, but only if he wanted to die.
    The mental scream ended. He put his hand on Masney's shoulder and said, "Stop the car, Lloyd." Masney took over with no sign, physical or mental, of panic. The car dropped gently to the ground two yards from the outer hull of the giant colony ship.
    "Sleep," said Kzanol/Greenberg, and Masney slept. It would probably do him good. He was still under hypnosis, and would be deeper when he awakened. As for Kzanol/Greenberg, he didn't know what he wanted. To rest and think perhaps. Food wouldn't hurt him either, he decided. He had recognized the mind that screamed its pain over hail of Kansas, and he needed time to know that he was not Kzanol, thrint, lord of creation.
    By and by there was a roar like a fusor exploding. Kzanol/Greenberg saw a wave of flaming smoke pour across the concrete, then gradually diminish. He couldn't imagine what it was. Cautiously he lowered his mind shield and found out.
    Jato units. Kzanol was going after the second suit.
    ***
    Ships and scopes and Confinement Asteroid-- by these you may measure the Belt.
    A century ago, when the Belt was first being settled, the ships used ion drives and fission batteries and restarting chemical attitude jets. Now they use fusion tubes, based on a method of forcing the inner surface of a crystal-zinc tube to reflect most forms of energy and matter. The compact air converter has replaced tanked air and hydroponics, at least for months-long hops, though the interstellar colony ships must grow plants for food. Ships have become smaller, more dependable, more versatile, cheaper, far faster, and infinitely more numerous. There are tens of thousands of ships in the Belt.
    But there are millions of telescopes. Every ship carries at least one. Telescopes in the Trojan asteroids watch the stars, and Earth buys the films with seeds and water and manufactured products, since Earth's telescopes are too near the Sun to avoid distortion by gravity bend and solar wind. Telescopes watch Earth and Moon, and these films are secret. Telescopes watch each other, recomputing the orbit of each important asteroid as the planets pull it from its course.
    Confinement Asteroid is unique.
    Early explorers had run across a roughly cylindrical block of solid nickel-iron two miles long by a mile thick, orbiting not far from Ceres. They had marked its path and dubbed it 5-2376.
    Those who came sixty years ago were workmen with a plan. They drilled a hole down the asteroid's axis, filled it with plastic bags of water, and closed both ends. Solid fuel jets spun S-2376 on its axis. As it spun, solar mirrors bathed it in light, slowly melted it from the surface to the center. When the water finished exploding, and the rock had cooled, the workmen had a cylindrical nickel-iron bubble twelve miles long by six in diameter.
    It had been expensive already. Now it was more so. They rotated the bubble to provide half a gee of gravity, filled it with air and with tons of expensive water covered the interior with a mixture of pulverized stony meteorite material and garbage seeded with select bacteria. A fusion tube was run down the axis, three miles up from everywhere: a very special fusion tube, made permeable to certain wavelengths of light. A gentle bulge in the middle created the wedding-ring lake which now