Charles Sheffield: The Web Between the Worlds

“We do. Isn’t that a terrible situation, from the point of view of engineering efficiency? So there’s where we have to begin.” Regulo pressed another key on the control console and the wall display became animated, showing the Earth and Moon rotating together about their common center of mass, with the Earth also rotating on its axis.

“Suppose we don’t use rockets at all,” he said. “Rockets are like ferry-boats, taking materials and people up and down. Suppose that instead of ferry-boats we were to build a bridge to space. The idea is simple enough: we take a cable, tethered to a point of the Earth’s surface, somewhere on the equator. It extends vertically upwards, all the way up to synchronous orbit, where we are now, and on beyond it. At the far end, we have some kind of ballast weight. See the picture? The whole thing hangs there in equilibrium, with the downward forces from all the length of cable below geosynchronous altitude just balancing the outward forces from centrifugal acceleration. The ballast weight wants to fly outward, but the cable prevents that, and the outward tension on the cable is just balanced by the force on the tether point, down on the surface. The whole assembly rotates, at exactly the same speed as the Earth. Like this.”

Regulo pressed another key. The rotating Earth-Moon system now showed a long cable, extending up from the surface of the Earth and rotating steadily with it.

Rob stared at the display, thoughtfully, head to one side and hand rubbing at his black beard. He had not bothered to remove the eleven-day growth before he and Corrie left Suget Jangal. “It sounds nice. But I don’t see how it could work. Every element on that cable wants to move in a different orbit. Every part of it wants to move around the Earth at a different speed.”

“Quite true.” Regulo sounded confident, and it was clear that he was enjoying himself. “Elements of the cable want to move at different speeds — but they can’t. The tension in the cable prevents that from happening. There’s no difference between this situation and a stone swinging around on the end of a rope.”

He reached again to the side of the desk and picked up another listing. “Look, Rob, this isn’t something I’ve just now dreamed up. You can find references to it in the literature — as an idea, not as an engineering reality — over ninety years ago. The first suggestions for a system like this one go back to the 1960’s, maybe even farther. All the orbital mechanics were studied back then. This is a list of some of the references. I told you, I’ve known about the idea and wanted to build it for over forty years. The thing that always held me back was the problem of materials. We never had anything strong enough to support the cable’s own weight, never mind carry other materials up and down. I’ve been watching the progress in materials science, year after year, looking for something like that article I just showed you. Finally, it came.”

Regulo again picked up the abstract that he and Rob had been reading earlier. He tapped the page with a thin finger. “There’s a crucial point about this that you might have missed on a quick read through. These doped silicon whiskers for cable-making can be produced cheaply , and that’s the key to everything. They’re even less expensive than the graphite ones.”

Rob was still staring at the image on the display screen. His eyes were blank as he performed rapid mental calculations. “Regulo, that thing would have to be at least seventy thousand kilometers long, just to keep the ballast weight to a reasonable value. My God, what a project — and I thought the Tasmanian Bridge might be the biggest job I’d ever see.”

Regulo watched approvingly as Rob’s absorption in the display before him increased. “You see now why I’m interested in the Spider,” he said. “You know, I noticed at once when you patented the Spider, three years ago. I thought it was just the thing we’d need if I ever got the chance to build this one. We tried to duplicate the idea for ourselves, thinking we might find a way around your patents once we understood the process. We never came close. That’s when I realized the two of us ought to be talking. It’s one of my basic principles, hire anybody who does something that I can’t. As for your estimate of seventy thousand kilometers…”

He leaned forward and again pressed a key on the control board. The display remained in position, but an additional message appeared at the foot of the screen: CABLE DESIGN LENGTH: ONE HUNDRED AND FIVE THOUSAND KILOMETERS.

“What would it mass to give a reasonable transportation capability?” Rob emerged from a fury of introspective calculation. “Where would you get the materials to make it? Where would you get the power to run it? And where would you assemble it? — I can see problems in that, even now. And I don’t see how you’d get the permits that would let you put it together and bring it down to Earth.” He shook his head. “Regulo, it’s fascinating, but I have so many questions about it that I don’t know where to begin.”

“Excellent!” The other man nodded his gnarled head. As much as his ruined face could show anything, it displayed deep satisfaction. “You’re interested. I was quite sure you would be, once you heard about it. As for your questions, I could probably answer most of them now, but I suggest we do things a little differently. I propose that you go back down to Earth, think about this for a while, read the references, and make your own first shot at an engineering design. If you’re anything like me, you’ll want to do your own design anyway, no matter what anybody else says.”

Rob smiled ruefully. Regulo had put his finger on a key point of the Merlin engineering philosophy — don’t accept a design unless you’ve been over it for yourself. He nodded agreement.

“I thought that might get to you,” said Regulo happily. “Take a look at the design of the Spider, too, and see if it can be speeded up, the way we talked about. You ought to think in terms of a hundred thousand kilometers of cable — see now why I need a capacity of at least two hundred kilometers a day? I’d be happier if you could even double that. And take a look at the old reports on the dynamics of the bridge. You’ll see that it’s often called a skyhook , although to me it always seems more like a beanstalk.” He laughed. “Up from the surface of the Earth, to a new land at the top of it — surely that’s a beanstalk, if ever I heard of one. Pity your name isn’t Jack.”

Regulo reached over and switched off the display. “Come back and see me when you’ve had a chance to get your head around some kind of design and installation plan, and let’s fight it out between the two of us. I’ll warn you, I have my own ideas, and I’ve been thinking about all this for an awful long time. You’ll have to come up with something at least as good, and convince me of it. Of course, I don’t know the real potential of the Spider, and you do, so that gives you one advantage.”

He rose stiffly from his chair, movements labored and clumsy even in the low gravity of the station. “We’ve done enough for the moment. Damn it, I don’t have the stamina I need. Fifty years ago I never got tired, now I’m tired before we even begin. Go on and get Cornelia for me, would you? Tell her that we’re done here, and you’re ready to go back down again. Unless there are other things that you think we have to settle now? Any money questions, for instance — we haven’t even mentioned those.”

Rob shook his head. “Let me convince myself that your beanstalk is feasible. We’ll have plenty of time to talk contracts after that.” He looked curiously into Regulo’s pale eyes. “I do have one question. If I take over the engineering, what will your role be? You started it, and I’m sure you’ll want to be involved.”