The Mercurian Planeteers got into their craft and blasted off, trailing the block of thorium in their exhaust. Rip watched the cruiser take the craft and thorium aboard, then drive toward Mercury, brilliant sunlight reflecting from its sleek sides. The planet was only a short distance away by spaceship. It was the largest thing in space, except for the sun, as seen from the asteroid.
Past the orbit of Mercury, the sun side of the asteroid grew dangerously hot for men in space suits. Rip and the Planeteers stayed in the bitter cold of the dark side, which ceased to be entirely dark. The temperature rose somewhat. They were close enough to the sun that the prominences, great flaming tongues of hydrogen that sped many thousands of miles into space, gave them light and enough heat to register on Rip's instruments.
Mercury was left far behind, and Earth could not be seen because of the sun. There was nothing to do now but ride out the rest of the trip as comfortably as possible, until it was time to throw the asteroid into a series of ever-tightening elliptical orbits around Earth, known as braking ellipses. The method would use Earth's gravity to slow them down to the proper speed. A single atomic bomb and a half dozen tubes of rocket fuel remained.
Then, as Rip was enjoying the comfort of air during his off-watch hour in the boat compartment, Koa beat an alarm on the door.
Rip and the Planeteers got into suits and opened up.
"It's Terra base calling on the communicator, sir," Koa reported. "Urgent message, they said, and they want to talk to you personally."
Rip hurried to the cave. The communicator indicator light was glowing bright red. He plugged in his helmet circuit and said, "This is Lieutenant Foster. Go ahead."
A voice crackled across space from Earth. "This is Terra base. Foster, a Consops cruiser has apparently been hiding behind the sun waiting for you. Our screens just picked it up, heading your way. We've sent orders to the Sagittarius on Mercury to give you cover, and the Aquila has taken off from here. But get this, Foster. The Consops cruiser will reach you first. You have about one hour. Do you understand?"
Rip understood all right. He understood too well. "Got you," he said shortly. "Now what?"
The communicator buzzed. "Take any appropriate action. You're on your own. Sorry. Sending the cruisers is all we can do. We'll stand by for word from you. If you think of any way we can help, let us know."