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…"

"Yes. We lose some. Each one of those capsules has to be picked up, somehow. That costs mass. We guide some into rendezvous with Heimdall, but they have to go after most. Still it's cheaper this way-once we start launching, the power scheduling's such that it's better to go on for a full hour."

The lines of capsules had ended; now new ones were brought up. These were longer and slimmer than the others; and when they took their places over the launching mirrors, they rose more slowly.