Charles Sheffield - Skystalk.pdf - Charles Sheffield - margozap

Skystalk

by Charles Sheffield

Finlay's Law: Trouble comes at 3:00 A.M. That's always been my experience, and I've learned to dread

the hand on my shoulder that shakes me to wakefulness. My dreams had been bad enough, blasting off

into orbit on top of an old chemical rocket, riding the torch, up there on a couple of thousand tons of

volatile explosives. I'll never understand the nerve of the old-timers, willing to sit up there on one of those

monsters.

I shuddered, forced my eyes open, and looked up at Marston's anxious face. I was already sitting up.

“Trouble?” It was a stupid question, but you're allowed a couple of those when you first wake up.

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 outgoing 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 the intergovernmental 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.

Damnit, 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 halfway 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 that 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 if 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 halfway 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 up 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.”

There was a long, dismal silence, which Alicia finally broke.

“So that seems to leave us with only one alternative,” she said thoughtfully. Then she grimaced and

pouted her mouth. “It's a two-bucket operation, and I don't even like to think about it-even though I had

a grandmother who was a circus trapeze artiste.”

She was leading in to something, and it wasn't like her to make a big buildup.

“That bad, eh?” I said.

“That bad, if we're lucky,” she said. “If we're unlucky, I guess we'd all be dead in a month or two

anyway, as the recycling runs down. For this to work, we need a good way of dissipating a lot of kinetic

energy-something like a damped mechanical spring would do it. And we need a good way of sticking to

the side of the Beanstalk. Then, we use two ore buckets-forty minutes apart would be all right-like this...”

She went over to the model of the Beanstalk. We watched her with mounting uneasiness as she outlined

her idea. It sounded crazy. The only trouble was, it was that or nothing. Making choices in those

circumstances is not difficult.

* * * *

One good thing about space maintenance work-you develop versatility. If you can't wait to locate

something down on Earth, then waste another week or so to have it shipped up to you, you get into the

habit of making it for yourself. In an hour or so, we had a sensitive detector ready, welded on to a long

extensible arm on the side of a bucket. When it was deployed, it would reach clear around the Beanstalk,

missing all the drive train and repair station fittings, and hang in close to the out-bound buckets. Jen had

fitted it with a gadget that moved the detector rapidly upward at the moment of closest approach of an

upbound carrier, to increase the length of time available for getting a measurement of radioactivity. He

swore that it would work on the fly, and have a better than 99 percent chance of telling us which

outbound bucket contained the bomb-even with a relative fly-by speed of six hundred kilometers an

hour.

I didn't have time to argue the point, and in any case Jen was the expert. I also couldn't dispute his claim

Charles Sheffield - Skystalk.pdf

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