"Half Earth normal."
Libby concentrated for an instant, then looked puzzled. "But look -- This valley is a thousand feet long and better than five hundred wide. At half of fifteen pounds per square inch, and allowing for the arch of the roof, that's a load of one and an eighth billion pounds. What fabric can take that kind of a load?"
"Cobwebs."
"Cobwebs?"
"Yeah, cobwebs. Strongest stuff in the world, stronger than the best steel. Synthetic spider silk, This gauge we're using for the roof has a tensile strength of four thousand pounds a running inch."
Libby hesitated a second, then replied, "I see. With a rim about eighteen hundred thousand inches around, the maximum pull at the point of anchoring would be about six hundred and twenty-five pounds per inch. Plenty safe margin."
The metalsmith leaned on his tool and nodded. "Something like that. You're pretty quick at arithmetic, aren't you, bud?"
Libby looked startled. "I just like to get things straight."
They worked rapidly around the slope, cutting a clean smooth groove to which the 'cobweb' could be anchored and sealed. The white-hot lava spewed out of the discharge vent and ran slowly down the hillside. A brown vapor boiled off the surface of the molten rock, arose a few feet and sublimed almost at once in the vacuum to white powder which settled to the ground. The metalsmith pointed to the powder.
"That stuff 'ud cause silicosis if we let it stay there, and breathed it later."
"What do you do about it?"
"Just clean it out with the blowers of the air conditioning plant"
Libby took this opening to ask another question. "Mister -- ?"
"Johnson's my name. No mister necessary."
"Well, Johnson, where do we get the air for this whole valley, not to mention the tunnels? I figure we must need twenty-five million cubic feet or more. Do we manufacture it?"
"Naw, that's too much trouble. We brought it with us."
"On the transport?"
"Uh huh, at fifty atmospheres."
Libby considered this. "I see -- that way it would go into a space eighty feet on a side."
"Matter of fact it's in three specially constructed holds -- giant air bottles. This transport carried air to Ganymede. I was in her then -- a recruit, but in the air gang even then."
In three weeks the permanent camp was ready for occupancy and the transport cleared of its cargo. The storerooms bulged with tools and supplies. Captain Doyle had moved his administrative offices underground, signed over his command to his first officer, and given him permission to proceed on 'duty assigned' -- in this case; return to Terra with a skeleton crew.
Libby watched them take off from a vantage point on the hillside. An overpowering homesickness took possession of him. Would he ever go home? He honestly believed at the time that he would swap the rest of his life for thirty minutes each with his mother and with Betty.
He started down the hill toward the tunnel lock. At least the transport carried letters to them, and with any luck the chaplain would be by soon with letters from Earth. But tomorrow and the days after that would be no fun. He had enjoyed being in the air gang, but tomorrow he went back to his squad. He did not relish that -- the boys in his squad were all right, he guessed, but he just could not seem to fit in.
This company of the C.C.C. started on its bigger job; to pock-mark Eighty-eight with rocket tubes so that Captain Doyle could push this hundred-mile marble out of her orbit and herd her in to a new orbit between Earth and Mars, to be used as a space station -- a refuge for ships in distress, a haven for life boats, a fueling stop, a naval outpost.
Libby was assigned to a heater in pit H-16. It was his business to carve out carefully calculated emplacements in which the blasting crew then set off the minute charges which accomplished the major part of the excavating. Two squads were assigned to H-16, under the general supervision of an elderly marine gunner. The gunner sat on the edge of the pit, handling the plans, and occasionally making calculations on a circular slide rule which hung from a lanyard around his neck.
Libby had just completed a tricky piece of cutting for a three-stage blast, and was waiting for the blasters, when his phones picked up the gunner's instructions concerning the size of the charge. He pressed his transmitter button.
"Mr. Larsen! You've made a mistake!"
"Who said that?"
"This is Libby. You've made a mistake in the charge. If you set off that charge, you'll blow this pit right out of the ground, and us with it."
Marine Gunner Larsen spun the dials on his slide rule before replying, "You're all het up over nothing, son. That charge is correct."
"No, I'm not, sir," Libby persisted, "you've multiplied where you should have divided."
"Have you had any experience at this sort of work?"
"No, sir."
Larsen addressed his next remark to the blasters. "Set the charge."
They started to comply. Libby gulped, and wiped his lips with his tongue. He knew what he had to do, but he was afraid. Two clumsy stiff-legged jumps placed him beside the blasters. He pushed between them and tore the electrodes from the detonator. A shadow passed over him as he worked, and Larsen floated down beside him. A hand grasped his arm.
"You shouldn't have done that, son. That's direct disobedience of orders. I'll have to report you." He commenced reconnecting the firing circuit.
Libby's ears burned with embarrassment, but he answered back with the courage of timidity at bay. "I had to do it, sir. You're still wrong."
Larsen paused and ran his eyes over the dogged face. "Well -- it's a waste of time, but I don't like to make you stand by a charge you're afraid of. Let's go over the calculation together."
Captain Doyle sat at his ease in his quarters, his feet on his desk. He stared at a nearly empty glass tumbler.
"That's good beer, Blackie. Do you suppose we could brew some more when it's gone?"
"I don't know. Cap'n. Did we bring any yeast?"
"Find out, will you?" he turned to a massive man who occupied the third chair. "Well, Larsen, I'm glad it wasn't any worse than it was."
"What beats me, Captain, is how I could have made such a mistake. I worked it through twice. If it had been a nitro explosive, I'd have known off hand that I was wrong. If this kid hadn't had a hunch, I'd have set it off."
Captain Doyle clapped the old warrant officer on the shoulder. "Forget it, Larsen. You wouldn't have hurt anybody; that's why I require the pits to be evacuated even for small charges. These isotope explosives are tricky at best. Look what happened in pit A-9. Ten days' work shot with one charge, and the gunnery officer himself approved that one. But I want to see this boy. What did you say his name was?"
"Libby, A.J."
Doyle touched a button on his desk. A knock sounded at the door. A bellowed "Come in!" produced a stripling wearing the brassard of Corpsman Mate-of-the-Deck.
"Have Corpsman Libby report to me."
"Aye aye, sir."
Some few minutes later Libby was ushered into the Captain's cabin. He looked nervously around, and noted Larsen's presence, a fact that did not contribute to his peace of mind. He reported in a barely audible voice, "Corpsman Libby, sir."
The Captain looked him over. "Well, Libby, I hear that you and Mr. Larsen had a difference of opinion this morning. Tell me about it."
"I -- I didn't mean any harm, sir."
"Of course not. You're not in any trouble; you did us all a good turn this morning. Tell me, how did you know that the calculation was wrong? Had any mining experience?"
"No. sir. I just saw that he had worked it out wrong."
"But how?"
Libby shuffled uneasily. "Well, sir, it just seemed wrong -- it didn't fit."
"Just a second, Captain. May I ask this young man a couple of questions?" It was Commander "Blackie" Rhodes who spoke.