Lost in Transmission

Appendix A. In which an appendix is provided engineering issues

On the subject of his engines, Money Izolo waxed loquacious. “Deutrelium burns clean, sir—only charged particles are produced, so we can steer them out the back with electric fields. Meaning there's no radiation hazard to the crew, in theory. But there's impurities, yah? Teeny little bits of the ship that get mixed in with the fuel slurry. These cause side reactions, releasing stuff like high-energy neutrinos, which convert some fraction of the electrons in the exhaust plasma into pions, which are harder to stop. That's a problem, a danger, that never goes away. I could use a whole person full-time, just monitoring the pion flux.”

Conrad smirked. “A true pioneer, eh?”

But Money missed the pun and just looked at him blankly for a moment before continuing. “When we're nonpropulsive, the demands on the reactor will be a lot less, and a lot steadier. Lighting, heating, life support . . . Those are predictable loads. Still, data processing can take a lot of power when the hypercomputers get large enough. Working on a tough problem they can fill this whole wall, with the heat sinks glowing red from dissipated information, which is the same thing as heat. And we expend about one hundred watts continuously on waste management, mostly dust.”

Conrad's eyebrow went up. “Dust?”

“Yah, there are mechanical parts on this ship: fans, bearings, hinges, and seals. Stuff like that. It's all subject to mechanical wear. And the stuff that rubs off winds up mostly in the atmosphere, as a nanoparticle smog which settles out on surfaces. And to the extent that we have people onboard, out of fax storage, there are always shed skin cells, and hair, and what have you. People shed an incredible amount of mass over the course of a month. Almost half a kilogram per person, which is more than the weight of your hand. Yah, I know, it's disgusting.

“Anyways, the wellstone bucket-brigades that stuff to the nearest fax machine for disposal, but it takes a certain amount of energy and computing to do that, see? And inside the fax there's a sorting penalty. We're fighting entropy itself. To turn a kilogram of dust into a kilogram of buffer mass sorted by atomic number, you need as much energy as you'd get from burning a thousand birthday candles. On a planet, that process happens naturally, powered by sunlight, and the fact that it's wickedly inefficient doesn't matter. But here it's a part of our daily maintenance. Like holding back the tide with a mop.”

“I thought entropy always increased.”

“It does, yah. All you can do is push it off somewheres else. With enough energy, you can reduce it locally, but there's a larger increase in the rest of the universe. It has to be that way, right? Or else life and machinery wouldn't be possible at all. But entropy is the great bill collector; it always catches up, oozing around every barrier. It'll find us in the end.”

“How comforting.”

“Isn't it? And then there's the occasional juking maneuver—we'll be in Sol's Oort cloud for another thirty years, and later on we'll be in Barnard's for ten. Juking takes energy, and requires a minimum reactor temperature. But yah, I think most of that can be handled automatically.”

Conrad ran his hand along the wall, feeling the flat, smooth texture of the wellstone. He tried to imagine the electrical potentials in there, dancing as oversized pseudoatoms flexed their orbital “arms” to pass a dust grain along. “That's interesting about the sorting penalty,” he said. “I've never heard anything like that before.” Return to text.

astrogation issues

Said Robert M'Chunu on the subject of getting lost: “You remember the term ‘drunkard's walk'?”

“No,” Conrad answered.

“Really? I thought you were one of the navigators on Viridity. Drunkard's walk is where you get random, quantum-level noise on a rate sensor. This is inevitable; no sensor is free of it. So you've got multiple rate sensors, each with its own random noise. This is fortunately very small, but you add up your rates over time to get your orientation, and suddenly you're accumulating and then squaring those errors. So they grow exponentially. If we let ours drift for six months, then the orientation we compute is complete gibberish. Six months is a long time for a planetary voyage. A really long time. But out here, it's nothing.

“Our Cartesian location—the XYZ of it—is even worse, because there you're integrating from acceleration to velocity to position, which cubes your errors. Of course you can always get a fixed reference for orientation, from the stars themselves. There are bright ones, distant ones, with close to zero proper motion. They're fixed against the sky, even though we're moving very fast. Those make excellent references, and they keep our attitude numbers sane. Downrange velocity we can get from the reference pulsars, which are neutron stars with very precisely known rotation rates. They flash like beacons, and we can measure the Doppler shift to obtain a fairly accurate velocity.

“But cross-range, perpendicular to our direction of travel, our references are poorer, and our precision is a lot lower. Just about the only lateral references we have are Sol and Barnard themselves. We're running a straight-line course between them, so their proper motion should be zero. They shouldn't drift against the background stars, not at all. So we look for very tiny motions, and compensate when we see them. But even on a good day that leaves us with velocity errors of walking speed or higher. And those errors are integrated to get position. You see the problem? Garbage in, garbage-cubed out. That's navigation for you.” Return to text.

pressing problems

“Pressing neubles isn't so easy,” Money said to Conrad against the backdrop of the hypermass. “If you just wrapped a blob of neutronium in an ordinary diamond, you'd get an explosion. The sad truth of it is, those neutrons would slip right through the diamond lattice, because there's nothing to hold them in. Pull this mass away from the black hole and you'd have the same problem: no confinement.”

“Well how do you make a neuble then?” Conrad objected. He had seen it done. He'd seen a neuble with his own two eyes: a two-centimeter sphere of diamond with . . . something inside. The color was difficult to describe: somewhere between light gray and mother-of-pearl and shiny silver superreflector.

Money chuckled. “It's one of those things, sir, that seem really simple until you try 'em. At the kind of pressures we can achieve industrially, we get only slightly past the drip line, which is the point where the neutrons start to condense. Where the electrons and protons are squeezed into neutrons, you see? They don't want to lose their identity that way. They fight it.

“I don't know about a neutron star or anything, but the neutronium we make is only about fifty percent neutrons by mass. Mixed in with that you've got superfluid protons and ordinary conduction electrons moving close to lightspeed, which is equivalent to a very, very high temperature. They want to fly energetically off into space, yah? This creates a phenomenal outward pressure, over and above the density of the neutronium itself. So the first thing you've got to do is pull the electrons out, and isolate them from the protons with a superinsulator.”

“Which diamond is not,” Conrad said. Because he did know some things about the behavior of materials.

“Which diamond is not, right. Actually, the insulator isn't a physical substance at all, or not precisely one. It's more like a quantum state which forbids the electrons from being on the other side of the barrier. Anyway, once you've got protons and neutrons on the inside, and relativistic electrons whizzing around on the outside, you've got what amounts to a gigantic atom. But it's unstable, yah? The attraction between the protons and electrons has a tendency to hold the thing together, but it's powers of ten weaker than the outward pressure of all those neutrons, which desperately want to fly apart. It's the mother of all atomic nuclei, and large nuclei are always unstable.”

“Meaning what?” Conrad asked. “That neubles can't exist? You're not making sense, Money.”

“Oh, they can exist, all right. But they've got to be a particular size. An atom is just a really small piece of neutronium, yah? Most potential atoms don't exist in the real universe, because they'd be unstable. Too big, too squishy. But stability islands occur all up and down the periodic table, and there's a strong one centered on atomic number 10³⁸. That's a billion-ton atom, you see, and its mass equates to the Schwarzchild radius of a proton-sized black hole, which is a magic number. Gravitic engineering is full of numbers like that. Anyway, ‘stability island' is a relative term, because the thing still wants to decompose in a couple of picoseconds. It still wants to explode. But we've brought the pressures down into the realm that diamond can withstand. That's how a neuble is made.” Return to text.