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 space 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?" [Illustration: "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 assemble 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 mass, 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 mass would fission in a slow chain reaction and no explosion would result. Rip was trained in scientific analysis. 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 mass. 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.