Rob moved to the chair that the old man indicated. His weight on the seat was barely perceptible, no more than a fraction of a kilogram. He looked at Regulo, shocked again by the sight of the ravaged face with its seamed and corroded features. Then he pushed that thought to the back of his mind. Regulo had a big pile of documents sitting in front of him, and a curious expression of suppressed glee shone in his bright eyes.
“Got your work on the beanstalk design,” he said gruffly. “Ready to talk about it, or do you need time to settle down?”
Apparently Regulo didn’t intend to indulge in social patter about the length of the trip from Earth. That suited Rob. He wanted to get to the real meeting as much as Regulo. He nodded. “I’m ready.”
“Good.” Regulo patted the stack of materials in front of him. “I pulled my old work out of the files. All done a long time ago, back before we could even mass-produce high-load graphite whiskers, never mind the doped silicon stuff that we’ve got now. You’ll see it soon enough” — Rob was leaning forward in the seat — “but first I’d like to hear what you have to say. Do you think you could build me a beanstalk?”
“I can build it.” Rob’s voice was confident as he pulled out his own design notes. “That’s the least of my worries. First of all, I can speed up the Spider. Two hundred kilometers a day of extruded cable will be no problem; maybe we can do a bit more than that. I can make it work with doped silicon instead of graphite, that’s a minor change. That gives us a load-bearing cable that can take over two hundred million newtons per square centimeter. I used a design diameter of two meters for the bottom end, but you can make that any value you choose. There will be a little bit of a taper as you go up, but it’s very small. The cable is only five percent thicker at geosynchronous altitude than it is at the ground tether.”
Regulo was nodding, his eyes fixed on Rob’s. “What load will it take with that diameter?”
“More than I ever see us needing. About two-thirds of a billion tons at the bottom end. I wouldn’t expect that you’d ever want to haul anything more than a few hundred thousand tons up to orbit at one time, or bring it down to Earth. Actually, I can’t see us needing even a tenth of that, but I’m following your advice and thinking big.”
Darius Regulo was nodding happily, drinking in Rob’s words and numbers. He was in his element. “I started out my design with a one-meter base diameter when I did it. Either way, it ought to give us more capacity than we’ll expect to use; but I’ve found that whenever you build in a capacity, you somehow get to use it.” His eyes seemed to capture and focus the dim light of the room, shining cat-like at Rob through the gloom. “So far, our thinking matches. What problems have you found?”
“Four main ones. Only two of them are really engineering.” Rob consulted his notes, then leaned back and began to tick off points on his fingers. “First of all, where do you construct it? The obvious way would be to start out at synchronous orbit and extrude cable up and down simultaneously, so you keep a balance between the cable above and below you, with gravity and centrifugal forces matching.
“But I suspect you know as well as I do that you can’t operate that way. The structure is unstable until you actually get it tethered down on Earth at one end, with a thumping great ballast weight pulling it out beyond synchronous orbit at the other end. If you start building from geosynch, once you have a good length of cable extruded the structure becomes unstable. Small displacements in position grow exponentially. So that’s problem number one: you can’t build it at synchronous orbit, the way you’d like to. And that leads to question number one: where do you build it?”
“Do you have an answer?”
“Of course. But let me go on. Problem number two raises another question of how you build, but it involves different issues. Where do we get the power and the materials? I calculate that we’ll be putting something together that masses about three billion tons. It would only be a quarter of that if we went to your design of a one-meter bottom diameter, but either way it’s a huge amount of material. I don’t think you realize how much power it takes to operate the Spider. So where will we get it?”
Regulo stared down at the desk in front of him. “Are you asking me? I hope not. I could tell you, but I’m hiring you to give me solutions, not tell me difficulties.”
It was hard to know how serious he was in that comment. Rob nodded and said, “I’ll give you answers. But first let me finish the statement of the problems. There’s one more engineering question. We have to tether the beanstalk at the lower end, and we’ll need something like a billion tons to give it the tension that we need. So what do we do about earthquakes? We need some way of making sure that the tether can’t be shaken loose by a natural disaster. We have to include storms, too, though I’m convinced we can handle that with local weather control. I checked with Weather Central, and they would be willing to take responsibility for that one; but earthquakes are another matter.
“One more problem, then I’m done. We’ll be stringing a few billion tons of cable up from the equator out beyond synchronous orbit, and we’ll be putting drive trains, passenger cars and cargo cars all the way along it, going up and down. Add all that together, and you have a hefty piece of work. What would we do if the beanstalk were to break, way up there near synchronous orbit?”
“We can build in ample safety factors.”
“Against natural events, maybe.” Rob shook his head. “That’s not what worries me. What about sabotage? Suppose some lunatic gets on the beanstalk with a fusion bomb? We’d have a three-billion-ton whip, cracking its way right round the equator. You can imagine what that would do when it hit the atmosphere. It would have more stored elastic energy than I like to think about, and it would be falling from thirty-odd thousand kilometers out.”
Rob paused and looked at Regulo, who seemed not in the least disconcerted by the prospect of a collapsing beanstalk. He was staring up at the ceiling now, and thoughtfully tapping his pile of papers. “Are you proposing that as an engineering problem, Merlin?”
“No.” Rob leaned forward. “We both know there’s no good engineering solution to sabotage. But I still think that this is the issue that decides whether or not we can ever build your beanstalk. We have to convince other people that the risks are worth taking. How do we sell them on the idea that the benefits outweigh the risks?”
There was a smile of pure pleasure on Regulo’s face. Rob’s words seemed to delight him.
“You’re the right man for this job,” he said. “You’ve got your finger on the real problem. The engineering is the fun, eh, but the real problem is going to be the permits? Is that what you’re telling me?”
“Of course. It’s the same with every big engineering project. Somehow we have to persuade them back on Earth that they should let us go ahead, even with a small risk of sabotage.”
Regulo had leaned over the desk and rubbed his hand at one part of it. “If I didn’t have an answer to that one, I’d never have called you in the first place. See that sign?”
He tapped the glowing desk top with a thin finger, where the familiar sign ROCKETS ARE WRONG gleamed red on the surface.
“That’s a true statement for four or five different reasons. You just have to pick the argument that serves your purpose at the time. I talked over the risks of this with the environmental control people back on Earth. I told them that we have a basic choice to make. We can go on with chemical and radioactive pollution, year after year, from the rockets that we are using now. That’s not a risk of damage to Earth and the environment, it’s an absolute stone certainty. And they know they don’t have the clout to stop it. Or we can switch to a system that’s completely non-polluting, with a tiny and controllable chance of having an accident.”