t nuclear physics?"

Rip's eyes narrowed. He said cautiously, "A little, sir."

"I'll assume you know nothing. Foster, the designation SCN means Space
Cruiser, Nuclear. This ship is powered by a nuclear reactor--in other
words, an atomic pile. You've heard of one?"

Rip controlled his voice, but his red hair stood on end with anger.
O'Brine was being deliberately insulting. This was stuff any Planeteer
recruit knew. "I've heard, sir."

"Fine. It's more than I had expected. Well, Foster, a nuclear reactor
produces heat. Great heat. We use that heat to turn a chemical called
methane into its component parts. Methane is known as marsh gas, Foster.
I wouldn't expect a Planeteer to know that. It is composed of carbon and
hydrogen. When we pump it into the heat coils of the reactor, it breaks
down and creates a gas that burns and drives us through space. But that
isn't all it does."

Rip had an idea what was coming, and he didn't like it. Nor did he like
Commander O'Brine. It was not until much later that he learned that
O'Brine had been on his way to Terra, to see his family for the first
time in four years, when the cruiser's orders were changed. To the
commander, whose assignments had been made necessary by the needs of the
Special Order Squadrons, it was too much. So he took his disappointment
out on the nearest Planeteer, who happened to be Rip.

"The gases go through tubes," O'Brine went on. "A little nuclear material
also leaks into the tubes. The tubes get coated with carbon, Foster.
They also get coated with nuclear fuel. We use thorium. Thorium is
radioactive. I won't give you a lecture on radioactivity, Foster. But
thorium mostly gives off the kind of radiation known as alpha particles.
Alpha is not dangerous unless breathed or eaten. It won't go through
clothes or skin. But when mixed with fine carbon, thorium alpha
contamination makes a mess. It's a dirty mess, Foster--so dirty that
I don't want my spacemen to fool with it.

"I want you to take care of it instead--you and your men. The deputy
commander will assign you to a squad room. Settle in, then draw equipment
from the supply room and get going. When I want to talk to you again,
I'll call for you. Now blast off, Lieutenant, and rake that radiation.
Rake it clean."

Rip forced a bright and friendly smile. "Yes, sir," he said sweetly.
"We'll rake it so clean you can see your face in it, sir." He paused,
then added politely. "If you don't mind looking