ns, I'd
say we were aiming for the far side of the asteroid belt. Anyway, we'll
fall short of Jupiter."

There was a glimmer of respect in O'Brine's glance. "That's right. Know
anything about asteroids, Foster?"

Rip considered. He knew what he had been taught in astronomy and
astrogation. Between Mars and Jupiter lay a broad belt in which the
asteroids swung. They ranged from Ceres, a tiny world only 480 miles in
diameter, down to chunks of rock the size of a house. No accurate count
of asteroids--or minor planets, as they were called--had been made, but
the observatory on Mars had charted the orbits of thousands. A few were
more than a mile in diameter, but most were great boulders of irregular
shape, from a few feet to several hundred feet at their greatest
dimension.

"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. Santo