Part 22 (1/2)

”Not quite, Pederson,” Rip corrected. ”Koa is on the right track. The pull of the sun is pretty strong. But I don't think it's strong enough to capture boats.”

He had figured the asteroid's...o...b..t to pa.s.s as close to the sun as possible while maintaining a margin of safety. He had wanted to use the sun's gravity to pick up speed. His regular star sightings had told him several days before that the sun was dragging them.

But Koa had started a train of ideas running through Rip's head. If they could get close enough to the sun so small boats would be unable to break free of its gravity, the Connie wouldn't dare send a landing force. The powerful engines of a cruiser could break loose from Sol's pull, but not the chemical jets of a cruiser's boats.

Rip got his instruments and pulled out a special slide rule designed for use in s.p.a.ce. He had Koa stand by with stylus and computation board and take down figures as he called them off.

He recalculated the safety factor he had used when deciding how close to put the asteroid to the sun, then took quick star sights to determine their exact position. They were within a few miles of perihelion, the point at which they would be closest to Sol.

Rip tapped gloved fingers on his helmet absently. If they could blast out of the orbit and drive into the sun ... he estimated the result. A few miles per second of extra speed would put them so far within the sun's field of gravity that, within an hour or so, small boats would venture into s.p.a.ce only at their peril.

He reviewed the equipment. They had tubes of rocket fuel, but the tubes wouldn't give the powerful thrust needed for this job. They had one atomic bomb. One wasn't enough. Not only must they drive toward the sun, they must keep reserve power to blast free again. If only they had a pair of nuclear charges!

He called his Planeteers together and outlined the problem. Perhaps one of them would have an idea. But no useful suggestions were forthcoming until little Dominico spoke up. ”Sir, why don't we make two bombs from one?”

[Ill.u.s.tration: ”Sir, Why Don't We Make Two Bombs From One?”]

”Sir, Why Don't We Make Two Bombs From One?”

”I wish we could,” Rip said. ”Do you know how, Dominico?”

”No, Lieutenant. If we had parts, I could put bombs together. I can take them apart, but I don't know how to make two out of one.” The Italian Planeteer looked accusingly at Rip. ”I thought maybe you know, sir.”

Rip grunted. If they had parts, he could a.s.semble nuclear bombs, too. Part of his physics training had been concerned with fission and its various applications. But no one had taught him how to make two bombs out of one.

The theory of nuclear explosions was simple enough. Two or more correctly sized pieces of plutonium or uranium isotope, when brought together, formed what was known as a critical ma.s.s, which would fission. The fissioning released energy and produced the explosion.

But there was a wide gap between theory and practice. A nuclear bomb was actually pretty complicated. It had to be complicated to keep the pieces of the fissionable material apart until a chemical explosion drove them together fast and hard enough to create a fission explosion. If the pieces weren't brought together rapidly enough, the ma.s.s would fission in a slow chain reaction and no explosion would result.

Rip was trained in scientific a.n.a.lysis. He tackled the problem logically, considering the design of a nuclear bomb and the reasons for it.

Atomic bombs had to be carried. That meant an outer casing was necessary.

Probably the casing had a lot to do with the design. Suppose no casing were required? What would be needed?

He took the stylus and computation board from Koa and jotted down the parts required. First, two or more pieces of plutonium large enough to form a critical ma.s.s. Second, a neutron source-some material with the type of radioactivity that produced neutrons-to start the reaction. Third, some kind of neutron reflector. And fourth, explosive to drive the pieces together.

Did they have all those items? He checked them off. Their single five KT bomb contained at least enough plutonium for two critical ma.s.ses, if brought together inside a good neutron reflector. Each ma.s.s should give about a two kiloton explosion. And they did have a good neutron reflector-nuc.l.i.te. There wasn't anything better for the purpose.

”What have we got for a neutron source?” he asked aloud. He was really asking himself, but he got a quick answer from Koa.

”Sir, some of the stuff left in the craters from the other explosions gives off neutrons.”

”You're right,” Rip agreed instantly. A small piece from one of the craters, when combined with half of the neutron source in the bomb, should be enough. As for the explosive, they had exploding heads on their attack rockets.

In other words, he had what he needed-except for a method of putting all the pieces together to create a bomb.

If only they had a tube of some sort that would withstand the chemical explosion-the one that brought the critical ma.s.s together!

He told the Planeteers what he had been thinking, then asked, ”Any ideas for a tube?”

”How about a tube from the snapper-boat?” Santos suggested.