Cargraves pretended to be asleep that night long before he was. Thus he was able to note that Morrie and Art stood alternate watches all night, armed and ready. He refrained from offering any advice.

The boys both went to bed at sunrise. Cargraves got painfully but quietly out of bed and dressed. Leaning on a stick he hobbled down to the ship. He wanted to inspect the damage done by the bomb, but he noticed first the case containing the thorium, bulking large because of its anti-radiation shipping shield. He saw with relief that the seal of the atomics commission was intact. Then he hunched himself inside the ship and made his way slowly to the drive compartment.

The damage was remarkably light. A little welding, he thought, some swaging, and some work at the forge would fix it. Puzzled, he cautiously investigated further.

He found six small putty-like pieces of a plastic material concealed under the back part of the shield. Although there were no primers and no wiring attached to these innocentappearing little objects he needed no blueprint to tell him what they were. It was evident that the saboteur had not had time to wire more than one of his deadly little toys in the few minutes he had been alone. His intentions had certainly been to wreck the drive compartment—and kill whoever was unlucky enough to set off the trap.

With great care, sweating as he did so, he removed the chunks of explosive, then searched carefully for more. Satisfied, he slipped them into his shirt pocket and went outside. The scramble, hampered by his game leg, out of the door of the rocket, made him shaky; he felt like a human bomb. Then he limped to the corral fence and threw them as far as he could out into the already contaminated fields. He took the precaution of removing them all from his person before throwing the first one, as he wanted to be ready to fall flat. But there was no explosion; apparently the stuff was relatively insensitive to shock. Finished, he turned away, content to let sun and rain disintegrate the stuff.

He found Ross outside the cabin, turning his bandaged face to the morning sun. "That you, Doc?" the young man called out.

"Yes. Good morning, Ross."

"Good morning, Doc." Ross moved toward the scientist, feeling the ground with his feet. "Say, doc—I said some harsh things last night. I'm sorry. I was upset, I guess."

"Forget it. We were all upset." He found the boy's groping hand and pressed it. "How are your eyes?"

Ross's face brightened. "Coming along fine. I slipped a peek under the bandage when I got up. I can see-"

"Good!"

"I can see, but everything's fuzzy and I see double, or maybe triple. But the light hurt my eyes so I put the bandage back."

"It sounds as if you were going to be all right," Cargraves ventured. "But take it easy."

"Oh, I will. Say, Doc..."

"Yes, Ross?"

"Nnnn... Oh, nothing. Never mind."

"I think I know, Ross. I've changed my mind. I changed my mind last night before I got to sleep. We're going through with it."

"Good!"

"Maybe it's good, maybe it's bad. I don't know. But if that's the way you fellows feel about it, I'm with you. We'll go if we have to walk."

"THAT SOUNDS MORE LIKE you, Doc!"

"Thanks. Are the others up yet?"

"Not yet. They didn't get much sleep."

"I know. Let's let them sleep. We'll sit out in the car. Take my arm."

When they had settled themselves Ross asked, "Doc, how much longer will it take to get ready?"

"Not long. Why?"

"Well, I think the key to our problems lies in how fast we can get away. If these attempts to stop us keep up, one of them is going to work. I wish we would leave today."

"We can't do that," Cargraves answered, "but it shouldn't be long. First I've got to install the drive, but it's really just a matter of fitting the parts together. I had almost everything prepared before I ever laid eyes on you guys."

"I wish my blinkers weren't on the fritz."

"It's one job I'll have to do myself. Not that I am trying to keep you out of it, Ross," he added hastily, seeing the boy's expression. "I've never explained it because I thought it would be easier when we had all the gear in front of us."

"Well, how does it work?"

"You remember Heron's turbine in elementary physics? Little boiler on the bottom and a whirligig like a lawn sprinkler on top? You heat the boiler, steam comes up through the whirligig, and makes it whirl around. Well, my drive works like that. Instead of fire, I use a thorium atomic power pile; instead of water, I use zinc. We boil the zinc, vaporize it, get zinc ‘steam.' We let the ‘steam' exhaust through the jet. That's the works."

Ross whistled. "Simple—and neat. But will it work?"

"I know it'll work. I was trying for a zinc ‘steam' power plant when I hit on it. I got the hard, hot jet I wanted, but I couldn't get a turbine to stand up under it. Broke all the blades. Then I realized I had a rocket drive."

"It's slick, Doc! But say—why don't you use lead? You'd get more mass with less bulk."

"A good point. Concentrated mass means a smaller rocket motor, smaller tanks, smaller ship, less dead weight all around. But mass isn't our main trouble; what we've got to have is a high-velocity jet. I used zinc because it has a lower boiling point than lead. I want to superheat the vapor so as to get a good, fast jet, but I can't go above the stable limit of the moderator I'm using."

"Carbon?"

"Yes, carbon-graphite. We use carbon to moderate the neutron flow and cadmium inserts to control the rate of operation. The radiations get soaked up in a bath of liquid zinc. The zinc boils and the zinc ‘steam' goes whizzing out the jet as merry as can be."

"I see. But why don't you use mercury instead of zinc? It's heavier than lead and has a lower boiling point than either one of them."

"I'd like to, but it's too expensive. This is strictly a cut-rate show." Doc broke off as Morrie stuck his head out the cabin door.

"Hi, there! Come to breakfast, or we'll throw it out!"

"Don't do that!" Cargraves slipped a leg over the side of the car- the wrong leg- touched the ground and said, "Ouch!"

"Wait a minute, and lean on me," Ross suggested.

They crept back, helping each other. "Aside from the pile," Cargraves went on, "there isn't much left. The thorium is already imbecided in the graphite according to my calculations. That leaves just two major jobs: the air lock and a test-stand run."

The rocket, although it had operated on the trans-Atlantic run above the atmosphere, had no air lock, since it's designers had never intended it to be opened up save on the ground. If they were to walk the face of the moon, an air lock, a small compartment with two doors, was necessary. Cargraves planned to weld a steel box around the inside of the present door frame, with a second air-tight door, opening inward.

"I can weld the lock," Ross offered, "while you rig the pile. That is, if my eyes clear up in time."

"Even if they do, I don't think it would be smart to stare at a welding arc. Can't the others weld?"

"Well, yes, but just between us chickens, I run a smoother seam."

"We'll see..."

At breakfast Cargraves told the other two of his decision to go ahead. Art turned pink and got his words twisted. Morrie said gravely, "I thought your temperature would go down over night. What are the plans?"

"Just the same, only more so. How's your department?"

"Shucks, I could leave this afternoon. The gyros are purring like kittens; I've calculated Hohmann orbits and S-trajectories till I'm sick of ‘em; the computer and me are like that." He held out two fingers.

"Fine. You concentrate on getting the supplies in, then. How about you, Art?"