"I know the usual stuff about them," he told O'Brine. "I haven't any special knowledge." O'Brine blinked. "Then why did they assign you? What's your specialty?" "Astrophysics." "That might explain it. Second specialty?" "Astrogation." He couldn't resist adding, "That's more advanced than the simple space navigation you use, Commander." O'Brine started to retort, then apparently thought better of it. "I hope you'll be able to carry out your orders, Lieutenant," he said stiffly. "I hope, but not much. I don't think you can." Rip asked, "What are my orders, sir?" O'Brine waved in the general direction of the wall. "Out there somewhere in the asteroid belt, Foster, there is a little chunk of matter about one thousand yards in diameter. A very minor planet. We know its approximate coordinates as of two days ago, but we don't know much else. It happens to be a very important minor planet." Rip waited, intent on the commander's words. "It's important," O'Brine continued, "because it happens to be pure thorium." Rip gasped. Thorium! The rare, radioactive element just below uranium in the periodic table of the elements, the element used to power this very ship! "What a find!" he said in a hushed voice. No wonder the job was Federation priority A, with Space Council security! "What do I do about it?" he asked. O'Brine grinned. "Ride it," he said. "Your orders say you're to capture this asteroid, blast it out of its orbit, and drive it back to Earth!" CHAPTER FOUR Find the Needle! Rip walked into the squad room with a copy of the orders in his hand. After one look at his face, the Planeteers clustered around him. Santos woke those who were sleeping, while Rip waited. "We have our orders, men," he announced. Suddenly he laughed. He couldn't help it. At first he had been completely overcome by the responsibility and the magnitude of the job, but now he was getting used to the idea, and he could see the adventure in it. Ten wild Planeteers riding an asteroid! Sunny space, what a great big thermonuclear stunt! Koa remarked, "It must be good. The lieutenant is getting a real atomic charge out of it." "Sit down," Rip ordered. "You'd better, because you might fall over when you hear this. Listen, men. Two days ago the freighter _Altair_ passed through the asteroid belt on a run from Jupiter to Mars." He sat down, too, because deceleration was starting. As his men looked at each other in surprise at the quickness of it, he continued, "The old bucket found something we need--an asteroid of pure thorium." The enlisted Planeteers knew as well as he what that meant. There were whistles of astonishment. Koa slapped his thigh. "By Gemini! What do we do about it, sir?" "We capture it," Rip said. "We blast it loose from its orbit and ride it back to Earth."