It was far into the usual rest cycle and Rick was tired out, but the idea of sleep while in a two-gee field sounded like pure fantasy. The slightest movement made you aware of your body. Even breathing was an effort.
“Here is CM-31,” Barney went on, “as it was when our original prospecting team arrived and confirmed the nature of the find.” Her face vanished, and was replaced by the image of an irregular and pock-marked lump of rock. Rick knew that the Belt held billions of similar mountain-sized boulders. Without knowing this one’s composition there was no hint that it might have unusual value.
“Now for a few basics,” went on Barney. “Gravity is the force that defines the whole shape and movement of the solar system—the galaxy, too, if it comes to that—but for objects the size of the one you are looking at now, gravity is a very weak force. It is just strong enough to pull small particles of material into contact with each other, but if gravity was all that held CM-31 together, you’d be able to mine it and the other asteroids with a spoon. But when the dust and grains of sand and pebbles meet, a different form of bonding takes over. The little particles sinter, which means that they all stick together to form a single mass. And that mass doesn’t come apart easily. You can think of CM-31 as we discovered it as a ball of iron, with some rock and small fractions of other metals. It’s solid, and it’s hard, and if you want to break a bit off you have to do it with a chisel.
“It’s strong enough that it would still hold together if you started to rotate it around its principal axis of inertia, which is the most stable way to make it spin.”
The lumpy surface of CM-31 now showed dozens of bright points of light all around it. They were drive units. Rick could not tell if this was a simulation or the real thing, but the body began to turn, slowly at first and then gradually faster.
“You can rotate it pretty fast, and the body will still hold in one piece,” Barney’s voice said. “But that’s not true if you also heat it. We use electric induction, which will produce internal currents to heat the body all the way through. If you did that until CM-31 melted, and it was also spinning, it would just fly apart.”
The image on the screen showed the dark planetoid beginning to glow a dull red. It slowly deformed to the shape of a thick plastic disk, then suddenly disintegrated and was gone, parts flying away in all directions.
“Obviously, that’s no way to mine an asteroid. You’d lose the asteroid itself, and you’d lose valuable drive units. It’s also not what people imagine, when they think of the word ‘mining.’ You might ask, what’s the point of heating and spinning a body, when you could just as well mine CM-31 the way most of the mines, like CM-2, were done? Remember the tunnels in CM-2? Mining machines made those, dug ore, and brought it out from the interior.
“The answer to my question, in one word, is economics. It’s far less expensive if you can melt and refine and process a whole asteroid, in one swoop.
“And you can. Here’s how.
“First, you place a cylinder in position around the whole body.”
CM-31 reappeared, just as it had been at the time of discovery. Now a huge silvery cylinder appeared from nowhere and gradually swallowed the whole asteroid into its open end. When the body was totally engulfed, the open end of the cylinder irised shut.
“There’s a couple of things to notice about that cylinder,” said Barney. “First, if you look very closely you’ll see drive units spaced at intervals around the curved part. On the cylinder, not on the asteroid. They will make it spin around its central axis. Second, you can’t see them but there are also hundreds of induction field generators on the cylinder. They will heat anything inside by induced eddy currents. They will also, if the cylinder is rotating, make the asteroid inside start to rotate through an electromagnetic dragging effect. Keep that up long enough, and the material inside will melt. When it melts, it will be thrown outward to the wall of the cylinder.
“One other thing, and this you can’t see: the cylinder is made of the strongest material we know, dislocation-free carbon filaments. It remains strong at high temperatures. It will contain the materials inside it, even when everything is spinning around the cylinder main axis at high speed.”
Rick could see what was coming next, he had known it the moment that the cylinder appeared. The fact that he really owed his knowledge to Deedee did nothing to lessen his pleasure. He could imagine her, tucked away in her own bunk, hugging herself in satisfaction. She had got it exactly right.
“I assume you can all see what’s coming next,” said Barney’s voice, taking away Rick’s sense of superiority. “As everything rotates, the liquid metals press outward on the cylinder wall, the heavier ones toward the outside and forcing the lighter ones closer to the axis of rotation. Actually, it’s not quite as simple as that, because some metals form eutectic alloys that don’t separate by centrifuging, but the general principle is valid. The heaviest metals are tapped first, from spigots on the outer circle of the circular ends of the cylinder. Then we run out the lighter ones. Finally all that’s left behind is a low-density layer of melted rock and sand. With a really high metal content asteroid, that’s not much more than a froth. We empty that, too, and leave it behind in space, all that remains of the original asteroid. At that point, the empty cylinder—after a bit of scrubbing and servicing—is ready to move on and tackle the next mine.
“I’m sure you’re asking, what went wrong in processing CM-31 ? If I could answer that, I would tell you. But I don’t know. We’re moving closer as fast as we can, and a few hours from now we’ll be able to take a look. Until then I suggest that you all rest, even if you don’t think you can sleep.”
Barney French stopped speaking. The projection unit remained alive, throwing onto the ceiling an image of the cylinder, drive units flaring, spinning hypnotically. Rick watched and watched, until at last he slipped into a half-trance. He was neither asleep nor fully awake. He was aware of a time of freefall, when the Vantage turned end-over-end and began its deceleration, but he could not have given an estimate as to how long it lasted. It seemed long after that when the thought came into his head that it should not be necessary to watch a simulation. By now it might be possible to see the real CM-31.
He roused himself and tapped the code for Barney French’s cabin. There was a risk that she was sleeping, but somehow he doubted it.
“Yes?” The answer came at once.
“This is Luban.”
“I know. I can see your call ID. Why aren’t you sleeping?”
“I can’t. I want to ask your permission to climb up to the front of the ship and use the scope there to look for CM-31.”
“You may not be sleeping, but your brain is turned off. We passed turnover a while ago, so we are now decelerating—which means that the front of the Vantage is pointed directly away from our destination. You’d see nothing.” And, while Rick was feeling like a prize buffoon, “You are the fourth person to call and ask me that, so I suppose it’s a general concern. There is no observation port down toward the stern, but there are imaging sensors. Stay where you are. I’m going to hook the output of the rear-pointing sensors into the terminal display. You’ll have a chance to see CM-31 at the same moment as the pilots. Don’t expect anything for a while.”
The projection on the ceiling above Rick flickered through a kaleidoscope of random color swirls, then settled to show a stationary star field. A blue icon at the upper left of the image blinked “target zoom.” There was an impression of impossibly fast motion as stars moved toward the scene edge and disappeared. The image became increasingly grainy, until at last the words “maximum magnification” replaced the first icon.