The Web Between the Worlds

by Charles Sheffield

  “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.”

  “Aye, Cornelia did mention the bio thing.” Regulo rubbed at his face with a thin, veiny hand. “Did she tell you just how much we fooled with that damned design, and never once sniffed at a bio-combine system? Maybe it’s time I went back for a technology refresher course.”

  “You seem to do pretty well.” Again, Rob couldn’t tell if Regulo was being serious. His facial abnormalities distorted every expression. “So far, I haven’t managed to come up with anything better than your designs. But let me keep going. We get to the point where we have a hundred thousand kilometers of load cable, with power cables and drive attached to it, up near L-4. We need one more thing apa
rt from a powersat, and that’s a ballast weight. It has to be a big one. It provides the tension in the load cable and balances the tether. We can’t attach the ballast until we make contact with the tether, so the ballast weight will be flying around the Earth in its own orbit.

  “We fly the beanstalk in, and curve it down to make contact with the tether point — at Quito, if we decide that’s the best place for it. We’ll have to curl in to atmospheric entry along a spiral approach from L-4. The ballast weight swings up and contacts the end of the cable at the same time as the tether end comes in to ground contact — and we’d better not miss that tether, or the whole thing will be off like a slingshot, past the Moon and on its way to God-knows-where. I’ve checked the timing, and I don’t think we have any real problems. The inertia of the system works both ways — you have time to do things. But changing direction or speed is almost impossible unless you have a lot of time to work with.”

  “We won’t miss the catch. I’ll be down there to hold and tether it myself if I have to, and damn what the doctors say.”

  Regulo’s face was full of resolve. Rob wondered suddenly just what the doctors did say. If anything, the old man looked worse than at their first meeting. How much of Regulo’s body was covered with the terrible deformity that marred his face?

  “All right, my lad, what are your other worries?” Regulo broke into Rob’s train of thought. “I agree with you, the fly-in from L-4 or L-5 will get around most of the problems of stability. I’ll always take a situation with dynamic stability over one with static stability, any time. What are you suggesting for the transport system itself? How many cars, how big, how fast?”

  “I’m designing for six hundred; three hundred going up and three hundred coming down. There will be a continuous drive arrangement from a set of linear synchronous motors running up and down the entire length of the beanstalk. I’ve chosen a nominal load for each car of four hundred tons.” Rob pulled out his notes and glanced at them again for a moment. “You might want to think about this, see if you agree with me. If you do, it provides us a carrying capacity of about two hundred and forty thousand tons a day. It sounds a lot, but it’s completely negligible compared with the mass of the beanstalk itself. Long term, we’ll have to keep the upward and downward movements pretty well balanced or that will affect the stability, but we have nothing to worry about on a day-to-day basis. As you’ll see from my numbers, with even spacing of the cars we’ll have a velocity of about three hundred kilometers an hour. That’s respectable for travel up through the atmosphere, and not high enough to cause aerodynamic problems.”

  “Hold it.” Regulo held up his hand before Rob could continue. “So far, we’ve been running along on just about the same design lines. Take a look at my calculations, and you’ll find that they parallel yours remarkably closely. But if you’re wanting a two-meter diameter load cable, then I’d suggest that we go for a bigger shipment rate. Why keep the weight of the cars so low?”

  “It’s your money.” Rob shrugged. “If you’re willing to spend more, that’s no problem for the design. I can increase the load. But I sized the carrying capacity to fit with a fifteen-gigawatt supply system, because that’s what we’ll get with an off-the-shelf powersat. We could use a couple of them, or even a custom-made job, but the total cost will go up.”

  “Don’t worry about that, finance is my department. Let’s have a daily carrying capacity, up or down, of a million tons. That’s a nice round number, and there’s no point in spoiling things for a few riyals. You never know, some day I may want to ship a few million tons of salt up here. Cornelia says she’s getting tired of the taste of freshwater fish.”

  That was a joke, it had to be. Rob looked at Regulo closely, but still the facial expressions offered no clue. After a moment, he shrugged. “A million tons. Fine, I’ll design for that. Everything else stays the same except the size of the cargo carriers. I think we ought to keep the passenger carriers small, that gives us a more flexible service. I’ll just arrange to have more of them, and time them to run more frequently. Let me dispose of one more problem, and I’ll save the tough one for last. Earthquakes. I’m proposing a really simple-minded solution. Instead of any fancy sort of tether, I suggest that we pile a billion tons of rock on the bottom end of the beanstalk. It won’t matter how much the ground moves about, there will still be all the anchor that we need.”

  “No argument with that. Simple solutions usually beat any others.” Regulo again tapped his own pile of papers. “I thought just as you did. No point in making it hard if you can make it easy. All right, what’s your other problem? So far we seem to be doing well.”

  “Materials.” Rob pulled a single sheet of calculations from his notes. “We need a few billion tons of silicon and metals, and we need it close to the L-4 location where we’ll be doing the main construction. Where will we get it? I’m relying on you for an answer, because obviously it can’t come from Earth. An asteroid, of course, and we move it to where we want it. But which asteroid?”

  “Fair enough.” Regulo reached over the desk and took the sheet from Rob’s hands. After studying it for a few moments he turned to the control panel by the side of the desk, and began to touch a pad there.

  “How much did Cornelia tell you about the computer system here on Atlantis?” he asked.

  “Nothing at all.” Rob thought of Corrie’s mysterious comment on the way out. “Unless Caliban is your computer?”

  “Caliban!” Regulo raised his bushy white eyebrows. “Now, there’s a wild idea. Though when I sit here and think about it, perhaps it’s less wild than it sounds.” He laughed. “No, Caliban isn’t the computer. You’ll meet Caliban later. The computer is called Sycorax — that’s Joseph Morel’s damn fool name for it, by the way, not my choosing. But don’t let me get started on that. About forty years ago I decided that anybody who wanted to be a really good engineer ought to have the best computer system that money could buy. I still hold the same view, and I’ve been building the computer capacity that I control from here ever since. I moved the central processor to Atlantis twenty years ago, and there are satellite data banks and peripheral processors in a lot of other places — on Earth, on the Moon, in the Belt, and out on the satellite mining operations in the Jupiter and Saturn systems. But I still don’t like computers; which is why I give Joseph a free hand to do what he wants with them, and call them whatever fool names he chooses.”

  As Regulo was speaking, a long table of data outputs had begun to appear on a big display screen at the side of the room. Regulo stared at it for a moment, then he keyed in more control words and the table rapidly began to change.

  “These are outputs from Sycorax,” he said. “Don’t ask me where the data bank is stored. All I can tell you is that it must be somewhere on Atlantis, or the response time would be a lot longer. The records that we access most often are stored here, the rest are spotted about all over the System. Do you recognize this table?”

  Rob glanced at it for a few seconds. “It seems like a list of the biggest asteroids. I don’t know what the other values are — diameters and orbital elements, maybe?”

  “That’s the first set of entries. Did Cornelia tell you where I made my first money? I started out by mining the asteroids, and Regulo Enterprises is still doing it. You can’t make any money at that game unless you have good information — I learned that fifty years ago, from the first partner I ever had. Sycorax holds records on every known body in the Solar System. Of course, there are things out in the Halo that we haven’t managed to tag yet, but we’re not after those today, anyway. These data files have orbital elements, size, composition and a current position that is continuously recomputed. We can also list the mining costs for each asteroid, and the value of materials delivered to any chosen destination in the System. To stay ahead in this business, you need two things: better information than other people, and a willingness to settle for small percentage profits. How accurate do you think those figures are on the sheet you g
ave me?”

  Rob was watching in admiration as the complex display unfolded on the screen before them. It was his sort of data bank. “Those are my first calculations, so I wouldn’t trust them to better than twenty percent. We should go for the high end of the range — let’s say we’ll need three billion tons of silicon, and about the same amount of metals. We can make do with a lot of variability in the metals’ mix, so long as we have a fair amount of iron and carbon in there.”

  “That’s good enough.” Regulo was busy at the terminal, entering the specifications. “Now let’s see what Sycorax can come up with. It may take a minute or two. The files are still stored in the old way, carbonaceous, silicaceous, metal-rich and mixed composition. We want a mixture, and a particular one, so there has to be a good deal of sorting. I’ve also asked for a lowest cost delivery to L-4, so we won’t get too many things to choose from. We might as well do the mining there, rather than out in the Belt.”

  He leaned back. “Speaking of mining, I’m still very interested in having a version of the Spider that can handle high-temperature materials. Did you take that idea any further?”

  “Yes. It’s easy enough to do. But you haven’t told me why you want to do it.”

  Regulo looked at him slyly. “Just another little idea I’ve been having. You know how we mine the asteroids, do you? We still dig holes in them, like weevils going at a lump of ship’s hard tack. I don’t like that, and I’m looking for alternatives. What would you charge to let me have the use of another Spider on something else for a couple of years?”

  “Five percent of project revenues.”

  “Net?”

  “Gross. You see, I’m learning from you. But I wouldn’t lease one to you at all unless I could be sure that somebody competent would be working with it.”