1970L. NivenRingworld 105
The Ringworld is a compromise, an engineering compromise between a Dyson sphere and a normal planet. Dyson was one of the ancient natural philosophers, pre-Belt, almost pre-atomic. He pointed out that a civilization is limited by the energy available to it. The way for the human race to use all the energy within its reach, he said, is to build a spherical shell around the sun and trap every ray of sunlight.
1968L. NivenSlowboat Cargo in Worlds of If Feb. 10/1
The ship began to drag a little, a very little, as the cone scooped up interstellar dust and hydrogen. She was still accelerating. Her insystem tank was idle now, and would be for the next twelve years. Her food would be the thin stuff she scooped out between the stars.
1971L. NivenFourth Profession in 1972 Annual World’s Best SF (1972) 23
You don’t have to depend on sunlight, not if you’re launching from a civilized system. Every civilized system has a moon-based launching laser. By the time the sun is too far away to give the ship a decent push, the beam from the laser cannon is spreading just enough to give the sail a hefty acceleration without vaporizing anything.
1967L. NivenJigsaw Man in H. Ellison Dangerous Visions 220
If the odds broke right, if the right people came down with the right diseases at the right time, the organlegger might save more lives than he had taken.
1970L. NivenRingworld 106
There wasn’t even a theoretical basis for faster-than-light travel. We never did invent hyperdrive, if you'll recall. We'd never have discovered it by accident, either, because we'd never have thought to do our experiments out beyond the singularity.