"Astrophysics."
"That might explain it. Second specialty?"
"Astrogation." He couldn't resist adding, "That's what scientists call space navigation, 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!"