“Finally, we won’t need anything like full atmospheric pressure for this to work. If we use pure oxygen at one thirtieth of a standard atmosphere, that will do nicely.
“The bad news is something that I didn’t realize when I first thought of using heat to clean the inside of the smelter. When you melt a metallic asteroid by electric inductive heating, there is good conduction through all parts of it. In other words, heat travels easily to everything you want to melt. But we are dealing with just a thin layer of residue, too thin in places to conduct much of anything—heat or electricity. That means induction is inefficient, and so is conduction. Instead, we have to make the whole interior of the smelter into a radiating enclosure at a uniform temperature—a black body, that’s called in physics. Unfortunately I don’t know anything about black bodies—regardless of what some people around here might think.”
It produced a laugh, as Polly had intended. Rumors of her affair with Vido Valdez, darkest-skinned of all the apprentices, were widespread.
“I still don’t understand black body radiation,” she went on. “Chick Teazle did all the work for me, and I want to give him credit.”
“Credit for me if it works,” Chick said cheerfully. “But Polly’s fault if it goes wrong.”
“It had better not go wrong.” Now Polly was not joking. She had too much riding on this. “I’ve worked up the inspection schedule that has to be done before we begin, and the assignment for each of you will show on your suit’s interior display. If anybody doesn’t know what to do, or has trouble when they start doing it, come back to me. I’ll be standing right here.”
Rick’s assignment was straightforward: inspect the power supply for four of the inductive heating units on the periphery of the smelter. As he moved to do it, he realized that Polly had the worst job of all. She would just hover in space with no assignment, waiting and worrying until everyone else was finished.
On the other hand, he wasn’t going to skimp his own task for the sake of Polly’s peace of mind. He checked the power supply, slowly and systematically, then the transformers, and finally the inductive coils themselves. Beside him, Gladys de Witt did the same thing for four other units. In the well-lit interior he could recognize her by the color coding bars on her suit.
“Sure beats scraping,” she said, as they finished the job and moved together back to the exterior of the smelter. “Wish I’d thought of it.”
Polly and Barney French were waiting for them with half a dozen of the apprentices. Others came drifting back, in ones and twos, while Polly kept an audible head count. Last of all were Vido Valdez and Alice Klein, appearing together around the outside of the smelter.
“Right,” Polly said. She sounded breathless, although she had not moved for the past half hour. “All in working order. Time to pressurize. I’ll give the command, but you’ll all be receiving the same displays as I will.”
Status monitors flashed their reports onto Rick’s suit display. There was nothing to see at the smelter itself, where both ends were now closed and airtight. The internal gas pressure crept slowly up to one thirtieth of an atmosphere.
“Now we’re going to begin heating,” said Polly. “Before we start, we’ll all get well out of the way.”
She led them away from the smelter and away from the main body of CM-26, to where the cluster of small co-orbiting asteroids waited.
“I don’t see how anything can go wrong,” she said, “but just in case, we will use one of these as shielding masses. Get close to it, so you can see the SM but if you need to you can duck out of the way.”
As the apprentices moved into position, Rick noticed that Barney French was doing her own head count and assessment of position. She moved one person—Rick thought it was Lafe Eklund—back a little, so that he was better shielded by the asteroid’s bulk. Finally she nodded to Polly.
“Here goes.” Polly’s words sounded more like a prayer than a statement. Again there was nothing to see at the SM, but the suit displays showed a massive drain on the central power supply, and almost at once a rapid rise in ambient interior temperature.
Five hundred degrees—eight hundred—eleven hundred.
Rick, like everyone else, stared in fascination at the smelter. He realized that it was another of the million facts he did not know about this sort of mining. How high a temperature did a body have to reach before it turned red-hot? How high before it was orange or white-hot? Twelve hundred degrees, read the display. Shouldn’t the heated SM be glowing now against its background of stars?
“We don’t like to waste power,” Barney French said suddenly, as though she was reading Rick’s mind, “so there is excellent thermal insulation between the SM’s interior and exterior. You won’t see a thing from here. But if you were inside—and managed to survive—you would find the walls starting to glow red at five hundred Celsius. If you were inside now, at twelve hundred degrees, they would be white-hot.
“We still have a way to go. To give you an idea of what we’re dealing with here, iron and nickel both melt at about fifteen hundred and boil at twenty-seven hundred in a standard atmosphere. Silicon boils at twenty-three fifty, silicon oxide at twenty-two hundred. We don’t have any platinum or iridium in the dross, which is just as well, because platinum doesn’t boil until thirty-eight hundred and iridium at over forty-one hundred. Mining can be warm work.”
The temperature had been climbing fast. It was up to eighteen hundred degrees. Rick tried to imagine the inferno inside the smelter. The oxygen would have gobbled up any pure metal into compounds, and the dross would be beginning to vaporize. The internal pressure had gone up, to more than a fifth of an atmosphere, and it was still rising.
The inside pressure and temperature were now increasing in unison. There must be a simple explanation for that, if only he could think of it.
“Twenty-two hundred,” Polly said nervously, although every apprentice could see that on the suit display. “Three more minutes, and we’ll hit twenty-seven. I’m going to cut power then and hold it for another two minutes, then give the command to open the big end as wide as it will go.”
“And what will happen then?” Barney asked the question in—for her—an oddly gentle voice.
“The gas inside will blow out. The inside will be left clean.”
“True. But something else will happen that we have to worry about. I wanted you to have the first chance with this, Polly, but now I’m going to open it up. Anybody. What do we have to do when we let the gas inside blow into space?”
There was a long silence. “Stay out of the way?” Chick Teazle said, in a let’s-try-anything voice.
“That, certainly. What else?”
It was a real-time contest, the worst one yet. Rick struggled to visualize the operation. The gas inside was superheated, but there was no way it could damage anything when it came out through the opening aperture at the end of the smelter. It came out hard, because the inside pressure had increased to a third of an atmosphere. Jetted out.
“Rocket!” he shouted, afraid that someone else would beat him to it.
“Be more specific, Rick.”
“The gas that comes out will be in a jet, it will produce a rocket effect just like the drive on a ship. The smelter will be driven in the other direction.”
“So what do we need to do?”
“Balance it.” That came as a shriek from Polly, not Rick. “Use the little thrusters on the outside of the smelter to equal the push from the escaping gas. But I don’t know how to work out the thrust!”
“Nor does anyone else in the group,” Barney said. “But I do! You’re feeling crushed, Polly, but you shouldn’t. This exercise makes two points. First, you all have a way to go before you look like mining engineers. Second—and more important—what you do when you work for Vanguard will almost never be a solo effort. You are part of a team, and no matter how much you want to succeed you should never forget that. Here’s the information for the impulse correction.”