Let's just use big lasers! As a side benefit, we'd have some big honking lasers for other...ummm...uses!
Aeneas couldn't see the launching mirror below the capsule, but suddenly the spacecraft rose and there was a blinding green beam, a solid rod of light over a meter thick extending from the capsule to the ground. The sound rolled past: two hundred and fifty explosions each second as the laser expanded the air in the parabolic chamber below the capsule, and the air rushed out to propel it upward. The two hundred and fifty-cycle note was oddly musical, but very loud at first, then dying away. The spacecraft soon vanished, but the light stayed on for half a minute, tracking the capsule; then it vanished as well.
The mirrors at each blockhouse pivoted slightly, and a second capsule rose from another launch station. The green light tore through roiled air, and there was a humming roar that vibrated the glass of the observation room until the spacecraft was gone and there was only the silent power of the green light. In the half minute that the second capsule absorbed power, a new spacecraft had been placed on the first launch station. The mirrors pivoted again, and it rose; then another, and another.
The laser launchings had been impressive on TV; live they were unbelievable. The long lines of capsules moved toward the earth and concrete emplacements protecting the launching mirror; they reached them; and seconds later, each capsule vanished at 300 gees, shoved upward by a meter-thick column that was nothing more than light, but which looked like a great green growing plant.
"About a thousand kilograms each?" Aeneas asked.
"Exactly a thousand kilos total weight," she said. "We lose fifty kilos of ablating material. The rest goes into orbit, and that's all payload. Any mass is payload. That's what we need up there, Aeneas, mass, any mass—metal, fuel, gases, tankage, even human wastes. We can convert and modify if we have something to start with."
"And you can launch eighty thousand kilos in one hour . . ."
(Jerry Pournelle, High Justice)
At first it looked like a field of mirrors. Over a hundred lasers were scattered across the brown Baja desert sand. Each sent its output into a mirror. The mirrors were all arranged so that they reflected onto one very large mirror nearly a kilometer beyond the balcony.
A rail track ran onto a platform above the final mirror. Squat capsules, like enormously swollen artillery shells, sat on cars on the track, a long line of them waiting for launch. As he watched, one of the capsules was wheeled along the track until it stopped over the launching mirror.
The field became a blaze of blue-green light as the lasers went on. Somewhere nearby, Kevin knew, were two large nuclear power plants. They poured their entire output into the lasers below him, enough electricity to power a city, all turned into laser light. The mirrors pivoted slightly so that all their energy went to the one large mirror at the end of the field.
The capsule rose, suddenly and silently, as if pushed into the sky by a rapidly growing giant blue-green beanstalk. It vanished in seconds, but the laser beam continued to follow it, moving from vertical to an angle toward the east. Finally all the lasers went out together.
"My God," Kevin said aloud. "I'm going up like that?"
He heard a laugh behind him and turned quickly to see the girl who'd been in the altitude chamber with him. She smiled as he looked at her. "Yes, we are," she said. "Scared?"
"Me too. I wish I'd taken the shuttle."
Another capsule was in position, and rose silently from the platform, vanishing into the clear blue sky, followed by the silent beam of intense light. If he listened carefully Kevin thought he could hear the hum of the beam. It was pulsed at something like two hundred times a second.
The laser system worked like a ram jet. Under each capsule was a bell-shaped chamber, open at the bottom. The laser energy entered the chamber and heated the air inside. The air rushed out, pushing the capsule upward. Then the beam was turned off just long enough for more air to get into the chamber, to be heated by the next pulse of the beam.
"I'm still not sure I believe it works," Kevin said. "It looks like black magic."
"Green magic," Ellen said.
(Jerry Pournelle; Exile to Glory)