Hyrst shifted his attention to space. There was a ship in it, heading toward the asteroid, and coming fast. Hyrst frowned, doing in his head without thinking about it a calculation that would have required a computer in his former life.
"Twenty-three minutes and seventeen seconds," he said, "inclusive of the four remaining."
He finished getting the weights off his boots. He handed one to Shearing. Then he half-climbed, half-floated up the wall and settled himself above the entrance, where there was a slight concavity in the rock to give him hold.
"Shearing," he said.
"What?" He was settling himself beside the mouth of the crack, where a man would have to come clear inside to get a shot at him.
"A starship implies the intention to go to the stars. Why haven't you?"
"For the simplest reason in the world," said Shearing bitterly. "The damn thing can't fly."
"But—" said Hyrst, in astonishment.
"It isn't finished. It's been building for over seventy years now, and a long and painful process that's been, too, Hyrst—doing it bit by bit in secret, and every bit having to be dreamed up out of whole cloth, and often discarded and dreamed up again, because the principle of a workable star-drive has never been formulated before. And it still isn't finished. It can't be finished, unless—"
He stopped, and both men turned their attention to the outside.