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?”
“Who, me? Why, I’ve got everything lined up, I guess. Both radars are right on the beam. I’ve got a couple wrinkles I’d like to try with the FM circuit.”
“Is it all right the way it is?”
“Good enough, I guess.”
“Then don’t monkey with the radios. I can keep you busy.”
“Oh, sure.”
“How about the radar screen Art was going to rig?” Morrie inquired.
“Eh? Oh, you mean the one for our friend the prowler. Hm. . . .,” Cargraves studied the matter. “Ross thinks and I agree that the best way to beat the prowler is to get out of here as fast as we can. I don’t want that radar out of the ship. It would waste time and always with the chance of busting a piece of equipment we can’t afford to replace and can’t get along without.”