Vectors (20 page)

His voice was shaky. "There's a bomb on the Beanstalk."

I was off the bunk, pulling on my undershirt and groping around for my shoes. Larry Marston's words pulled me bolt upright.

"What do you mean,
on
the Beanstalk?"

"That's what Velasquez told me. He won't say more until you get on the line. They're holding a coded circuit open to Earth."

I gave up my search for shoes and went barefoot after Marston. If Arnold Velasquez were right—and I didn't see how he could be—then one of my old horrors was coming true. The Beanstalk had been designed to withstand most natural events, but sabotage was one thing that could never be fully ruled out. At any moment, we had nearly four hundred buckets climbing the Stalk and the same number going down. With the best screening in the world, with hefty rewards for information even of
rumors
of sabotage, there was always the small chance that something could be sneaked through on an outbound bucket. I had less worries about the buckets that went down to Earth. Sabotage from the space end had little to offer its perpetrators, and the Colonies would provide an unpleasant form of death to anyone who tried it, with no questions asked.

Arnold Velasquez was sitting in front of his screen door at Tether Control in Quito. Next to him stood a man I recognized only from news pictures: Otto Panosky, a top aide to the President. Neither man seemed to be looking at the screen. I wondered what they were seeing on their inward eye.

"Jack Finlay here," I said. "What's the story, Arnold?"

There was a perceptible lag before his head came up to stare at the screen, the quarter of a second that it took the video signal to go down to Earth, then back up to synchronous orbit.

"It's best if I read it to you, Jack," he said. At least his voice was under control, even though I could see his hands shaking as they held the paper. "The President's Office got this in over the telecopier about twenty minutes ago."

He rubbed at the side of his face, in the nervous gesture that I had seen during most major stages of the Beanstalk's construction. "It's addressed to us, here in Sky Stalk Control. It's quite short. 'To the Head of Space Transportation Systems. A fusion bomb has been placed in one of the out-going buckets. It is of four megaton capacity, and was armed prior to placement. The secondary activation command can be given at any time by a coded radio signal. Unless terms are met by the President and World Congress on or before 02.00 U.T., seventy-two hours from now, we will give the command to explode the device. Our terms are set out in the following four paragraphs. One— ' "

"Never mind those, Arnold." I waved my hand, impatient at the signal delay. "Just tell me one thing. Will Congress meet their demands?"

He shook his head. "They can't. What's being asked for is preposterous in the time available. You know how much red tape there is in inter-governmental relationships."

"You told them that?"

"Of course. We sent out a general broadcast." He shrugged. "It was no good. We're dealing with fanatics, with madmen. I need to know what you can do at your end."

"How much time do we have now?"

He looked at his watch. "Seventy-one and a half hours, if they mean what they say. You understand that we have no idea which bucket might be carrying the bomb. It could have been planted there days ago, and still be on the way up."

He was right. The buckets—there were three hundred and eighty-four of them each way—moved at a steady five kilometers a minute, up or down. That's a respectable speed, but it still took almost five days for each one of them to climb the cable of the Beanstalk out to our position in synchronous orbit.

Then I thought a bit more, and decided he wasn't quite right.

"It's not that vague, Arnold. You can bet the bomb wasn't placed on a bucket that started out more than two days ago. Otherwise, we could wait for it to get here and disarm it, and still be inside their deadline. It must still be fairly close to Earth, I'd guess."

"Well, even if you're right, that deduction doesn't help us." He was chewing a pen to bits between sentences. "We don't have anything here that could be ready in time to fly out and take a look, even if it's only a couple of thousand kilometers. Even if we did, and even if we could spot the bomb, we couldn't rendezvous with a bucket on the Stalk. That's why I need to know what you can do from your end. Can you handle it from there?"

I took a deep breath and swung my chair to face Larry Marston.

"Larry, four megatons would vaporize a few kilometers of the main cable. How hard would it be for us to release ballast at the top end of the cable, above us here, enough to leave this station in position?"

"Well . . ." He hesitated. "We could do that, Jack. But then we'd lose the power satellite. It's right out at the end there, by the ballast. Without it, we'd lose all the power at the station here, and all the buckets too"—there isn't enough reserve power to keep the magnetic fields going. We'd need all our spare power to keep the recycling going here."

That was the moment when I finally came fully awake. I realized the implications of what he was saying, and was nodding before he'd finished speaking. Without adequate power, we'd be looking at a very messy situation.

"And it wouldn't only be us," I said to Velasquez and Panosky, sitting there tense in front of their screen. "Everybody on the Colonies will run low on air and water if the supply through the Stalk breaks down. Dammit, we've been warning Congress how vulnerable we are for years. All the time, there've been fewer and fewer rocket launches, and nothing but foot-dragging on getting the second Stalk started with a Kenya tether. Now you want miracles from us at short notice."

If I sounded bitter, that's because I
was
bitter. Panosky was nodding his head in a conciliatory way.

"We know, Jack. And if you can pull us through this one, I think you'll see changes in the future. But right now, we can't debate that. We have to know what you can do for us
now,
this minute."

I couldn't argue with that. I swung my chair again to face Larry Marston.

"Get Hasse and Kano over here to the Control Room as soon as you can." I turned back to Velasquez. "Give us a few minutes here, while we get organized. I'm bringing in the rest of my top engineering staff."

* * *

While Larry was rounding up the others, I sat back and let the full dimensions of the problem sink in. Sure, if we had to we could release the ballast at the outward end of the Stalk. If the Beanstalk below us were severed we'd have to do that, or be whipped out past the Moon like a stone from a slingshot, as the tension in the cable suddenly dropped.

But if we did that, what would happen to the piece of the Beanstalk that was still tethered to Earth, anchored down there in Quito? There might be as much as thirty thousand kilometers of it, and as soon as the break occurred it would begin to fall. Not in a straight line. That wasn't the way that the dynamics went. It would begin to curl around the Earth, accelerating as it went, cracking into the atmosphere along the equator like a billion-ton whip stretching half-way around the planet. Forget the carrier buckets, and the superconducting cables that carried electricity down to the drive train from the solar power satellite seventy thousand kilometers above us. The piece that would do the real damage would be the central, load-bearing cable itself. It was only a couple of meters across at the bottom end, but it widened steadily as it went up. Made of bonded and doped silicon whiskers, with a tensile strength of two hundred million Newtons per square centimeter, it could handle an incredible load—almost two-thirds of a billion tons at its thinnest point. When that stored energy hit the atmosphere, there was going to be a fair amount of excitement down there on the surface. Not that we'd be watching it—the loss of the power satellite would make us look at our own survival problems; and as for the Colonies, a century of development would be ended.

By the time that Larry Marston came back with Jen Hasse and Alicia Kano, I doubt it I looked any more cheerful than Arnold Velasquez, down there at Tether Control. I sketched out the problem to the two newcomers; we had what looked like a hopeless situation on our hands.

"We have seventy-one hours," I concluded. "The only question we need to answer is, what will we be doing at this end during that time? Tether Control can coordinate disaster planning for the position on Earth. Arnold has already ruled out the possibility of any actual
help
from Earth—there are no rockets there that could be ready in time."

"What about the repair robots that you have on the cable?" asked Panosky, jumping into the conversation. "I thought they were all the way along its length."

"They are," said Jen Hasse. "But they're special purpose, not general purpose. We couldn't use one to look for a radioactive signal on a bucket, if that's what you're thinking of. Even if they had the right sensors for it, we'd need a week to reprogram them for the job."

"We don't have a week," said Alicia quietly. "We have seventy-one hours." She was small and dark-haired, and never raised her voice much above the minimum level needed to reach her audience—but I had grown to rely on her brains more than anything else on the station.

"Seventy-one hours, if we act
now
," I said. "We've already agreed that we don't have time to sit here and wait for that bucket with the bomb to arrive—the terrorists must have planned it that way."

"I know." Alicia did not raise her voice. "Sitting and waiting won't do it. But the total travel time of a carrier from the surface up to synchronous orbit, or back down again, is a little less than a hundred and twenty hours. That means that the bucket carrying the bomb will be at least
half-way
here in sixty hours. And a bucket that started down from here in the next few hours—"

"—would have to pass the bucket with the bomb on the way up, before the deadline," broke in Hasse. He was already over at the Control Board, looking at the carrier schedule. He shook his head. "There's nothing scheduled for a passenger bucket, in the next twenty-four hours. It's all cargo going down."

"We're not looking for luxury." I went across to look at the schedule. "There are a couple of ore buckets with heavy metals scheduled for the next three hours. They'll have plenty of space in the top of them, and they're just forty minutes apart from each other. We could squeeze somebody in one or both of them, provided they were properly suited up. It wouldn't be a picnic, sitting in suits for three days, but we could do it."

"So how would we get at the bomb, even if we did that?" asked Larry. "It would be on the other side of the Beanstalk from us, passing at a relative velocity of six hundred kilometers an hour. We couldn't do more than wave to it as it went by, even if we knew just which bucket was carrying the bomb."

"That's the tricky piece." I looked at Jen Hasse. "Do you have enough control over the mass driver system, to slow everything almost to a halt whenever an inbound and an outbound bucket pass each other?"

He was looking doubtful, rubbing his nose thoughtfully. "Maybe. Trouble is, I'd have to do it nearly a hundred times, if you want to slow down for every pass. And it would take me twenty minutes to stop and start each one. I don't think we have that much time. What do you have in mind?"

I went across to the model of the Beanstalk that we kept on the Control Room table. We often found that we could illustrate things with it in a minute that would have taken thousands of words to describe.

"Suppose we were here, starting down in a bucket," I said. I put my hand on the model of the station, thirty-five thousand kilometers above the surface of the Earth in synchronous orbit. "And suppose that the bucket we want to get to, the one with the bomb, is here, on the way up. We put somebody in the inbound bucket, and it starts on down."

I began to turn the drive train, so that the buckets began to move up and down along the length of the Beanstalk.

"The people in the inbound bucket carry a radiation counter," I went on. "We'd have to put it on a long arm, so that it cleared all the other stuff on the Stalk, and reached around to get near the upbound buckets. We can do that, I'm sure—if we can't, we don't deserve to call ourselves engineers. We stop at each outbound carrier, and test for radioactivity. There should be enough of that from the fission trigger of the bomb, so that we'll easily pick up a count when we reach the right bucket. Then you, Jan, hold the drive train in the halt position. We leave the inbound bucket, swing around the Stalk, and get into the other carrier. Then we try and disarm the bomb. I've had some experience with that."

"You mean we get out and actually
climb
around the Beanstalk?" asked Larry. He didn't sound pleased at the prospect.

"Right. It shouldn't be too bad," I said. "We can anchor ourselves with lines to the ore bucket, so we can't fall."

Even as I was speaking, I realized that it didn't sound too plausible. Climbing around the outside of the Beanstalk in a space-suit, twenty thousand kilometers or more up, dangling on a line connected to an ore bucket—and then trying to take apart a fusion bomb wearing gloves. No wonder Larry didn't like the sound of that assignment. I wasn't surprised when Arnold Velasquez chipped in over the circuit connecting us to Tether Control.

"Sorry, Jack, but that won't work—even if you could do it. You didn't let me read the full message from the terrorists. One of their conditions is that we mustn't stop the bucket train on the Stalk in the next three days. I think they were afraid that we would reverse the direction of the buckets, and bring the bomb back down to Earth to disarm it. I guess they don't realize that the Stalk wasn't designed to run in reverse."

"Damnation. What else do they have in that message?" I asked. "What can they do if we decide to stop the bucket drive anyway? How can they even tell that we're doing it?"

"We have to assume that they have a plant in here at Tether Control," replied Velasquez. "After all, they managed to get a bomb onto the Stalk in spite of all our security. They say they'll explode the bomb if we make any attempt to slow or stop the bucket train, and we simply can't afford to take the risk of doing that. We have to assume they can monitor what's going on with the Stalk drive train."