quickly. They had accelerated for six and a half hours. Now,
ten minutes after brennschluss, they were going to start deceleration.
That meant they had really high-vacked it to get somewhere in a hurry. He
calculated swiftly.

"I don't know exactly," he admitted. "But from the ship's actions, 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 over 100,000. Most of them
were only a mile or two in diameter. Others, much smaller, had never been
charted by anyone. One leading astronomer had estimated that as many as
50,000 asteroids filled the belt.

"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 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