CHAPTER THIRTEEN - PERIL AT PERIHELION
Sergeant-major Koa had made no comment since notifying Rip of the callfrom Terra base. Now he asked thoughtfully, "Lieutenant, can the Connielaunch boats this close to the sun? Won't the sun's pull suck them rightin?"
Corporal Pederson scoffed, "Naw, Koa. If sun's gravity be that strong, itpull us in, too."
"Not quite, Pederson," Rip corrected. "Koa is on the right track. The pullof the sun is pretty strong. But I don't think it's strong enough tocapture boats."
He had figured the asteroid's orbit to pass as close to the sun aspossible while maintaining a margin of safety. He had wanted to use thesun's gravity to pick up speed. His regular star sightings had told himseveral days before that the sun was dragging them.
But Koa had started a train of ideas running through Rip's head. If theycould get close enough to the sun so small boats would be unable to breakfree of its gravity, the Connie wouldn't dare send a landing force. Thepowerful engines of a cruiser could break loose from Sol's pull, but notthe chemical jets of a cruiser's boats.
Rip got his instruments and pulled out a special slide rule designed foruse in space. He had Koa stand by with stylus and computation board andtake down figures as he called them off.
He recalculated the safety factor he had used when deciding how close toput the asteroid to the sun, then took quick star sights to determinetheir exact position. They were within a few miles of perihelion, thepoint at which they would be closest to Sol.
Rip tapped gloved fingers on his helmet absently. If they could blast outof the orbit and drive into the sun ... he estimated the result. A fewmiles per second of extra speed would put them so far within the sun'sfield of gravity that, within an hour or so, small boats would ventureinto space only at their peril.
He reviewed the equipment. They had tubes of rocket fuel, but the tubeswouldn't give the powerful thrust needed for this job. They had one atomicbomb. One wasn't enough. Not only must they drive toward the sun, theymust keep reserve power to blast free again. If only they had a pair ofnuclear charges!
He called his Planeteers together and outlined the problem. Perhaps one ofthem would have an idea. But no useful suggestions were forthcoming untillittle Dominico spoke up. "Sir, why don't we make two bombs from one?"
"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 takethem apart, but I don't know how to make two out of one." The ItalianPlaneteer looked accusingly at Rip. "I thought maybe you know, sir."
Rip grunted. If they had parts, he could assemble nuclear bombs, too. Partof his physics training had been concerned with fission and its variousapplications. 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 correctlysized pieces of plutonium or uranium isotope, when brought together,formed what was known as a critical mass, which would fission. Thefissioning released energy and produced the explosion.
But there was a wide gap between theory and practice. A nuclear bomb wasactually pretty complicated. It had to be complicated to keep the piecesof the fissionable material apart until a chemical explosion drove themtogether fast and hard enough to create a fission explosion. If the piecesweren't brought together rapidly enough, the mass would fission in a slowchain 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 casingwere required? What would be needed?
He took the stylus and computation board from Koa and jotted down theparts required. First, two or more pieces of plutonium large enough toform a critical mass. Second, a neutron source--some material with the typeof radioactivity that produced neutrons--to start the reaction. Third, somekind of neutron reflector. And fourth, explosive to drive the piecestogether.
Did they have all those items? He checked them off. Their single five KTbomb contained at least enough plutonium for two critical masses, ifbrought together inside a good neutron reflector. Each mass should giveabout a two kiloton explosion. And they did have a good neutronreflector--nuclite. There wasn't anything better for the purpose.
"What have we got for a neutron source?" he asked aloud. He was reallyasking himself, but he got a quick answer from Koa.
"Sir, some of the stuff left in the craters from the other explosionsgives off neutrons."
"You're right," Rip agreed instantly. A small piece from one of thecraters, when combined with half of the neutron source in the bomb, shouldbe enough. As for the explosive, they had exploding heads on their attackrockets.
In other words, he had what he needed--except for a method of putting allthe pieces together to create a bomb.
If only they had a tube of some sort that would withstand the chemicalexplosion--the one that brought the critical mass together!
He told the Planeteers what he had been thinking, then asked, "Any ideasfor a tube?"
"How about a tube from the snapper-boat?" Santos suggested.
Rip shook his head. "Not strong enough. They're designed to withstand theslow push of rocket fuel, not the fast rap of an explosion. When I sayslow, I mean slow-burning when compared with explosive. Who has anotheridea?"
Kemp, the expert torchman, said, "Sir, I can burn you a tube into theasteroid."
Rip grabbed the Planeteer so hard they both floated upward. "Kemp, that'swonderful! That's it!" The details took form in his mind even as he calledorders. "Dominico, tear down that bomb. Santos, remove two heads from yourrockets and wire them to explode on electrical impulse. Kemp, we'll wantthe tube just a fraction of an inch wider than a rocket head. Get yourtorch ready."
He took the stylus and began calculating. He talked as he worked, tellingthe Planeteers exactly what they were up against. "I'm figuring out whereto put the charge so it will do the most good, but my data isn't complete.If our homemade bomb goes off, I don't know exactly how much power it willgive. If it gives too much, we'll be driven so close to the sun well neverget free of its gravity."
Bradshaw, the English Planeteer, said mildly, "Don't worry, Lieutenant.We're caught either way. If it isn't the solar frying pan, it's Conniefire."
A chorus of agreement came from the other Planeteers. What a crew! Ripthought. What a great gang of space pirates!
He finished his calculations and found the exact spot where Kemp wouldcut. A few feet away from the spot was a thick pyramid of thorium. Thatwould do, and they could cut into it horizontally instead of drillingstraight down. He pointed to it. "Let's have a hole straight in for sixfeet. And keep it straight, Kemp. Allow enough room for a lining ofnuclite. Koa, pull a sheet of nuclite out of the cave and cut it to size."
Kemp's torch already was slicing into the metal. Rip asked, "Can you weldwith that thing, Kemp?"
"Just show me what you want, sir."
"Good." Rip motioned to Trudeau. "Frenchy, we'll need a strong rod atleast eight feet long."
The French Planeteer hurried off. Rip consulted his chronometer. Less thanten minutes had passed since the call from Terra base.
He went over his plan again. It had to work! If it didn't, asteroid andPlaneteers would end up as subatomic particles in the sun's photosphere,because he had calculated his blast to drive the asteroid past the limitof safety. It was the only way he could be sure of putting them beyonddanger from Connie landing boats or snapper-boats. The Connie would haveonly one chance--to bring his cruiser down on the asteroid.
If he tried that, Rip thought grimly, he would get a surprise. The secondnuclear charge would be set, ready to be fired. The Connie cruiser was sobig that no matter how it pulled up to t
he asteroid, some part of it wouldbe close enough to the charge to be blown into space dust. No cruisercould survive an atomic explosion within five hundred yards, and theConnie would have to get closer to the nuclear charge than that.
Dominico reported that the bomb had been dismantled. Rip went to it andexamined the raw plutonium, being careful to keep the pieces widelyseparated.
This particular bomb design used five pieces of plutonium which weredriven together to form a ball. Rip made a quick estimate. Two were enoughto form a critical mass. He would use two to blast into the sun and threeto blast out again. He would need the extra kick.
There was only one trouble. The pieces were wedge shaped. They would haveto be mounted in thorium in order to keep them rigid. Only Kemp could dothat. They had no cutting tool but the torch.
Santos appeared, carrying a rocket head under each arm. They had wireswound around them, ready to be attached to an electrical source.
Rip hurried back to where Kemp was at work. The private was using acutting nozzle that threw an almost invisible flame five feet long. Inair, the nozzle wouldn't have worked effectively beyond two feet, but inspace it cut right down to the end of the flame. Kemp had his arm insidethe hole and was peering past it as he finished the cut.
"Done, sir," he said, and adjusted the flame to a spout of red fire. Hethrust the torch into the hole and quickly withdrew it as pieces ofthorium flew out. A stream of water hosed into the tube would have washedthem out the same way.
Rip took a block of plutonium from Dominico and handed it to Kemp. "Cut aplug and fit this into it. Then cut a second plug for the other piece.They have to match perfectly, and you can't put them together to try outthe fit. If you do, we'll have fission right here in the open."
Kemp searched and found a piece he had cut in making the tube. It wasperfectly round, ideal for the purpose. He sliced off the inner side whereit tapered to a cone, then, working only by eye estimate, cut out a holein which the wedge of fission material would fit. He wasn't off by athirty-second of an inch. Skillful application of the torch melted thethorium around the wedge and sealed it tightly.
Koa was ready with a sheet of nuclite. Trudeau arrived with a long pole hehad made by lashing two crate sticks together.
Rip gave directions as they formed a cylinder of nuclite. Kemp spot-weldedit, and they pushed it into the hole, forming a lining.
Nunez found a small piece of material in one of the earlier craters. Itwould provide some neutrons to start the chain reaction. Rip added it tothe front of the plutonium wedge along with a piece of beryllium from thebomb, and Kemp welded it in place.
They put the thorium block which contained the plutonium into the hole,the plutonium facing outward. Trudeau rammed it to the bottom with hispole. The neutron source, the neutron reflector, and one piece offissionable material were in place.
Kemp sliced another round block of thorium out of a near-by crystal andfitted the second wedge of plutonium into it. At first Rip had worriedabout the two pieces of plutonium making a good enough contact, but Kemp'sskillful hand and precision eye removed that worry.
The torchman finished fitting the plutonium and carried the block to thetube opening. He tried it, removed a slight irregularity with his torch,then said quietly, "Finished, sir."
Rip took over. He slid the thorium-plutonium block into the tube, took arocket head from Santos and used it to push the block in farther. When therocket head was about four inches inside the tube, its wires trailing out,Rip called Kemp. At his direction, the torchman sliced a thin slot up theface of the crystal. Rip fitted the wires into it and held them in placewith a small wedge of thorium.
Kemp cut a plug, fitted it into the hole, and welded the seams closed. Thetube was sealed. When electric current fired the rocket head, the thoriumcarrying the plutonium wedge would be driven forward to meet the wedge inthe back. And, unless Rip had miscalculated the mass of the two pieces,they would have their nuclear blast. Rip surveyed the crystal with someanxiety. It looked right.
Dominico already had rigged the timer from the atomic bomb. He connectedthe wires, then looked at Rip. "Do I set it, sir?"
"Load the communicator, the extra bomb parts, the rocket launcher androckets, the cutting equipment, my instruments, and the tubes of fuel,"Rip ordered. "Leave everything else in the cave."
The Planeteers ran to obey. Rip waited until the landing boat was nearlyloaded, then told Dominico to set the timer for five minutes. He wonderedhow they would explode the second charge, since they had only the onetimer left, then forgot about it. Time enough to worry when faced with theproblem.
"I'll take the snapper-boat," he stated. "Santos in the gunner's seat. Koain charge in the landing boat. Dowst pilot. Let's show an exhaust."
He fitted himself into the tight pilot seat of the snapper-boat whileSantos climbed in behind. Then, handling the controls with the skill oflong practice, he lifted the tiny fighting rocket above the asteroid andwaited for the landing boat. When it joined up, Rip led the way to safety.As he cut his exhaust to wait for the explosion, he sighted past thesnapper-boat's nose to the asteroid.
He was moving, and the direction of his move told him the sun was alreadypulling. Its pull was strong, too. He cut his jets back on, just to holdposition, and saw Dowst do the same.
Another few miles toward the sun and the landing boat wouldn't have thepower to get away from Sol's gravity. A few miles beyond that, even thepowerful little snapper-boat would be caught.
Below, the timer reached zero. A mighty fan of fire shot into space. Theasteroid shuddered from the blast, then swerved gradually, picking upspeed as well as new direction.
Rip swallowed hard. Now they were committed. They would reach a newperihelion far beyond the limits of safety. P for perihelion and P forperil. In this case, they were the same thing!