"When is it?"
"Half an hour, maybe less," the Federation soldier said. "You couldn't stop them. You'll never get there in time."
"Is there another tank?"
The soldier nodded, pointed across the pumice to a squat green vehicle with caterpillar treads. Alan was already running for it and calling over his shoulder. "Stay here. If the remaining Federation ships try to come down, use the dome-guns on them. Stan, you come with me."
The pilot sprinted after him. Together they entered the moon tank, which was not airtight. They found Terra Mines spacesuits inside, the ancient, long-unused type that looked like deep sea suits. The tank's rocket engine sputtered and caught. The tank lumbered toward the domelock and through it while they donned the spacesuits.
Then they were bouncing soundlessly across the airless surface of Tycho crater, leaving the dome far behind them. Earth was above them in the sky, in the quarter-phase. You could see part of North America reflecting sunlight. Blue-black, the Pacific Ocean was in shadow.
Ahead loomed the central mountains of Tycho crater, biting into the black sky, saw-toothed, for fifteen thousand feet. On labored the moon tank, climbing now, its old engine whining a protest against the steep grade, the sound echoing strangely inside the vehicle because outside in the luna vacuum it could not be heard at all. They crossed the first peak of the range, looked down on a great cauldron in the rock, a crater within the crater, a mile across.
At one end was a Federation spaceship, standing on its tail rockets and pointing up at the sky like a gleaming needle.
At the other end was the launching platform, massive, indistinct in the gloomy shadows of the mountains. On the platform, partially out of shadow, rested the cobalt bomb, big as a small spaceship.
Another tank sped toward them across the uneven moonscape. Two men were perched atop it in red spacesuits, firing already although they were still out of range.