“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.”
Regulo chuckled and shook his head. “They weren’t sure, but you know that the safest thing for a bureaucrat to do is to say no to everything. If I’d left it there, they’d have vetoed us. So I told them that the chance of an accident went up or down, depending on the level of the monitoring operations. They would need to create a new security department, one with a high level of funding. New jobs, new facilities, new equipment. Naturally, the money for that would come from the builders of the beanstalk — us. And naturally, the funds would go to them. Did you ever see a bureaucrat when he sees a chance for a little empire-building? Anyway, here’s your permit.”
He pulled a document from the pile in front of him.
Rob stared at it in amazement. “A permit to build a beanstalk?”
“To build three of them, if we choose to. If you’re going to ask at all, why not ask for a lot? I suggest we think of the first one as having a Quito tether point. That’s where I have the best franchises.”
Regulo suddenly stared sideways at the TV cameras pointed toward the desk. He seemed satisfied with what he saw, and turned his attention again to Rob. “Now then, I’ve given you help on that one. What about your solutions for the others? How do you propose to build it?”
“Let’s start with where.” Rob glanced briefly at his notes, then tucked them away into his pocket. “We have to perform the construction well away from Earth, and we ought to choose a stable point that’s not too far away. I’m proposing that we go to L-4, where we have an existing labor pool to draw on if we need it. There’s a decent-sized solar power satellite there, too, and we’ll need the SPS to run the Spider — unless you have other ideas?”
Now he looked at Regulo, deliberately waiting a moment before he went on, “All right, so we extrude the whole thing up there at one go: load-bearing cable, synchronous drive motors all the way along it to move the cars up and down, and superconducting cables to feed power into those.”
“The Spider can do all that?” Regulo showed surprise for the first time since the conversation had begun.
“That, and more.” Rob felt easier. Up to this point of the meeting Regulo seemed to have thought of and improved on everything that Rob could suggest. Now at last there was something Rob could do that the other man couldn’t.
“Maybe Corrie already mentioned to you that the Spider has a biological component,” he went on. “It’s a lot more adaptable than any ordinary piece of hardware, so changing the fabrication plan as the materials are extruded is no big trick. Originally, I wanted it flexible to handle things like tapering supports for bridges without my needing to re-program. Now it turns out the versatility will come in useful here.”