Rip gave directions as they formed a cylinder of nuc.l.i.te. Kemp spot-welded it, and they pushed it into the hole, forming a lining.

Nunez found a small piece of material in one of the earlier craters. It would provide some neutrons to start the chain reaction. Rip added it to the front of the plutonium wedge along with a piece of beryllium from the bomb, 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 his pole. The neutron source, the neutron reflector, and one piece of fissionable material were in place.

Kemp sliced another round block of thorium out of a near-by crystal and fitted the second wedge of plutonium into it. At first Rip had worried about the two pieces of plutonium making a good enough contact, but Kemp's skillful hand and precision eye removed that worry.

The torchman finished fitting the plutonium and carried the block to the tube 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 a rocket head from Santos and used it to push the block in farther. When the rocket 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 the face of the crystal. Rip fitted the wires into it and held them in place with a small wedge of thorium.

Kemp cut a plug, fitted it into the hole, and welded the seams closed. The tube was sealed. When electric current fired the rocket head, the thorium carrying the plutonium wedge would be driven forward to meet the wedge in the back. And, unless Rip had miscalculated the ma.s.s of the two pieces, they would have their nuclear blast. Rip surveyed the crystal with some anxiety. It looked right.

Dominico already had rigged the timer from the atomic bomb. He connected the wires, then looked at Rip. "Do I set it, sir?"

"Load the communicator, the extra bomb parts, the rocket launcher and rockets, 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 nearly loaded, then told Dominico to set the timer for five minutes. He wondered how they would explode the second charge, since they had only the one timer left, then forgot about it. Time enough to worry when faced with the problem.

"I'll take the snapper-boat," he stated. "Santos in the gunner's seat. Koa in charge in the landing boat. Dowst pilot. Let's show an exhaust."

He fitted himself into the tight pilot seat of the snapper-boat while Santos climbed in behind. Then, handling the controls with the skill of long practice, he lifted the tiny fighting rocket above the asteroid and waited 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 the snapper-boat's nose to the asteroid.

He was moving, and the direction of his move told him the sun was already pulling. Its pull was strong, too. He cut his jets back on, just to hold position, and saw Dowst do the same.

Another few miles toward the sun and the landing boat wouldn't have the power to get away from Sol's gravity. A few miles beyond that, even the powerful little snapper-boat would be caught.

Below, the timer reached zero. A mighty fan of fire shot into s.p.a.ce. The asteroid shuddered from the blast, then swerved gradually, picking up speed as well as new direction.

Rip swallowed hard. Now they were committed. They would reach a new perihelion far beyond the limits of safety. P for perihelion and P for peril. In this case, they were the same thing!

CHAPTER FOURTEEN - BETWEEN TWO FIRES

Back on the asteroid, the Planeteers started laying the second atomic charge. Rip selected the spot, found a near-by crystal that would serve to house the bomb, and Kemp started cutting.

The Planeteers knew what to do now, and the work went rapidly. Rip kept an eye on his chronometer. According to the message from Terra base, he had about fifteen minutes before the Consops cruiser arrived.

"We have one advantage we didn't have back in the asteroid belt," he remarked to Koa. "Back there they could have landed anywhere on the rock.

Now they have to stick to the dark side. Snapper-boats could last on the sun side, but men in ordinary s.p.a.ce suits couldn't."

"That's good," Koa agreed. "We have only one side to defend. Why don't we put the rocket launcher right in the middle of the dark side?"

"Go ahead. And have all men check their pistols and knives. We don't know what's likely to happen when that Connie flames in."

Rip walked over to the communicator and plugged his suit into the circuit.

"This is the asteroid calling Terra base. Over."

"This is Terra base. Go ahead, Foster. How are you doing?"

"If you need anything cooked, send it to us," Rip replied. "We have heat enough to cook anything, including tungsten alloy." He explained briefly what action they had taken.

A new voice came on the communicator. "Foster, this is Colonel Stevens."

Rip responded swiftly, "Yes, sir!" Stevens was the top Planeteer, commanding officer of all the Special Order Squadrons.

"We've piped this circuit into every channel in the system," the colonel said. "Every Planeteer in the Squadrons is listening, and rooting for you.

Is there anything we can do?"

"Yes, sir," Rip replied. "Do you know if Terra base has plotted our course this far?"

There was a brief silence, then the colonel answered, "Yes, Foster. We have a complete track from the time you started showing on the Terra screens, about halfway between the orbits of Mars and earth."

"Did you just get our change of direction?"

"Yes. We're following you on the screens."

"Then, sir, I'd appreciate it if you'd put the calculators to work and make a time-distance plot for the next few hours. The blast we're saving to push back to safety is about three kilotons. Let us know the last moment when we can fire and still get free of Sol's gravity."

"You'll have it within fifteen minutes. Anything else, Foster?"

"Nothing else I can think of, sir."

"Then good luck. We'll be standing by."

"Yes, sir. Foster off."

Rip disconnected and turned up his helmet communicator, repeating the conversation to his men. Koa came and stood beside him. "Lieutenant, how do we set off this next charge?"

There was only one way. When the time came to blast, they would be too close to the sun to take to the boats. The blast had to be set off from the asteroid.

"We'll get underground as far away from the bomb as we can," Rip said. He surveyed the dark side, which was rapidly growing less dark. "I think the second crater will do. Kemp can square it off on the side toward the blast to give us a vertical wall to hide behind."

Koa looked doubtful. "Plenty of radiation left in those holes, sir."

Rip grinned mirthlessly. "Radiation is the least of our problems. I'd rather get an overdose of gamma than get blasted into s.p.a.ce."

A yell rang in his helmet. "Here comes the Connie!"

Rip looked up, startled. The Consops cruiser pa.s.sed directly overhead, about ten miles away. It was decelerating rapidly. Rip wondered why they hadn't spotted it earlier and realized the Connie had come from the direction of the hot side.

The enemy cruiser was probably the same one that had attacked them before.