Book 4: Preparation
BOOK 4: PREPARATION / CH. 1:SHEEP-DOG TRIALS
TEN YEARS EARLIER
Mars had water, but not enough for farming. Not enough to make it livable.
So, a decision had been made, once the energy issues had been solved with
fusion reactors, that a few thousand small icy asteroids would be delivered to Mars from the Kuiper belt. Small, since people were nervous about the idea of throwing dinosaur killers around the solar system, plus of course it was much easier to move the small ones.
It took a strange sort of person to coax asteroids from the inner edges of the Kuiper belt into an orbit that would intercept Mars. You were a long way from home, not quite as far as Neptune, but almost, and there wasn't exacly much opportunity to pop over to a friend's house for a chat and a cup of tea. Or of visiting Mum on her birthday. It took at least three months each way, and normally far more.
All the actual orbital manouvers, of course, were done by the robotic probes, which gave the lumps of dirty ice a push here and a nudge there, grouping them into line to send “down-hill “. Someone once said they moved around like sheepdogs, and so sheepdogs they became, even in official communications. But the sheepdogs needed instructions, checking over and occasional repair. So the Martian terraforming (water delivery division) service corps were formed. Since they 'fed and watered' the sheepdogs, everyone called them shepherds. Their job was important, but left them a lot of free time, so much so that it was a requirement that they have something else time-consuming and mentally challenging to do. Many used the time to write books, or study theoretical subjects. They tended to be philosophers, mathematicians, theoretical physicists or religious hermits. Anyone who had at least repaired their own bicycle at an early age, was capable of using a torque wrench properly and replacing a circuit element the right way up, who was also mentally suited to the task and needed a few years of thinking time was welcome. There were often vacancies, but not many. The job paid well, but there just weren't many people interested. The only face to face meetings the shepherds had while on the job were with the crew of the supply ships, who called once every eight months.
The computer bleeped an alert and crackled. “Shepherd six, shepherd six, Supply four here, are we interrupting anything, Jack?”
“Yes, but it's not as important as visitors. Nice to hear your voice, Wilma.
I don't suppose you've got any extra chocolate have you? I ran out much too soon last time.”
“Well you did only order twenty bars for eight months, that wasn't much compared to your normal dose.”
“I was planning to exercise self control, and cut down to half a bar a week. I found I didn't have enough will-power though.”
“I see. Well, we've got plenty. I don't suppose you want a lift home do you?” this was a key question that was always asked. There were forms to fill in to request a transfer home, but they were rarely used. Filling out a form asking to be relieved felt very very different to having company turn up and offering you a choice between a lift home and another eight months of isolation.
Jack hesitated. “You know, Wilma... I think I do. I'm not finished yet, not by a long shot, but I think I'm close enough that I probably wouldn't need more than four months to get there. I'd hate to have to make someone make a special journey to fetch me, and lets face it, I'd need to ask them to come about now if my guess about how long it'll take is at all
right.”
“Well, you're welcome to come aboard, once we've docked. Any problems with the dogs?” Wilma asked. Of course there had been, that was why Jack was out here. There were always problems with the dogs that the automated systems couldn't cope with.
“Not much. Sheepdog four is getting a bit slower than it used to be, but it's still in spec. It'll probably need its lines scrubbed in a few months. Oh and I had to replace dog eight's power board again last week. I'm sure that's not right. Two failures in two years with the same problem?” Changing the power board was a fairly simple procedure, once you'd taken practically all the other boards out. It didn't need to be done very often, fortunately.
“But it could limp back home OK?” Wilma asked. If it hadn't been able to then Jack would have had to ride another sheepdog out to it, hook them together and then bring it back, quite a risky task.
“Oh yes. No problem there. But why should two main rectifiers fail? They're not exactly complex, or even highly stressed — you know how over specified those things should be. I wonder if there's some other fault.”
“Maybe there was just a bad batch?” Wilma suggested.
“Perhaps. That's what control said, but no one else has had any failures so I'm not convinced. I was thinking about it when you called and really, I think it should be given a complete checkup. It wouldn't take more than a couple of weeks, I think, put everything through its paces with a few thermal cycles and the odd bit of vibration.”
“You mean kick it around a bit, don't you Jack?”
“Standard field vibration test, yes.”
He was right. It wasn't in the service manual, but it did seem that the best way to check that everything in the three tonne robotic probe was up to nudging rocks around was to give the circuits a good kick or three and see if it glitched. Sometimes people missed, or kicked too hard and broke things, so Wilma wasn't allowed to encourage it.
“Well, if you want to stay to kick your dog in its sensitive bits then I guess you can, Jack.”
“No, I'm coming. Running out of chocolate was my own silly fault, but it helped me decide. I need to see civilisation again.”
“Maybe your replacement can give it a good kicking then, Jack.”
“I've written them a note about it.”
“We'll be docking soon Jack, then I can introduce you to him.”
“What?”
“Your replacement. Philosophy student by the name of Dan, came out with me on this run for the fun, excitement and in case anyone wanted to swap.”
“I'll tell him just where to kick them then.”
“I'll pretend I didn't hear that, Jack.” Wilma had heard it all before, of course. She'd been piloting the six month long supply runs for almost two decades now, visiting the different shepherds in one segment or another. Jack was actually a rare type of shepherd, this was his second tour. All told he'd been a shepherd for fifteen years, and had come out for his first tour just before Wilma had started. If Jack thought the dog was starting to fail then it probably was. And he knew all about where to kick them to check for different failure modes. She'd try and make sure Dan paid attention.
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Hand-over took a day, just like restocking might have, so it didn't put Wilma's schedule off at all.
At the airlock, Jack turned to Dan.
“Well, Dan, the station's all yours now. If you find any of my missing socks, just incinerate them. They're not worth the postage. Do check on those dogs soon, like I said. Oh, and keep a watch on the spectroscope for those diamonds. They'd just burn up if you sent them to Mars, which'd be a real pity.”
“Jack!” Wilma warned “Don't you go filling Dan's head with nonsense! There's no such thing as space diamonds.”
The dogs were fusion powered of course, and early on a bright spark in the design department had asked why anyone should bother shipping purified hydrogen out to them for fuel when they were constantly bumping into icebergs?
A heated probe could easily be deployed to suck in a few hundred liters of comet whenever the tanks were getting low. Certainly that then needed to have the contaminants filtered out, and the filters needed cleaning every now and again, but that was a small price to pay for not needing to bring out tonnes of hydrogen to refuel the sheepdogs. The high purity water used to supply the hydrogen also provided the shepherds with their drinking water and oxygen, and allowed the shuttle to refuel at both ends of its journey, increasing the cargo capacity and reducing the transit time at the same time. The project would probably have never happened without it.
Of course, there were contaminants, hydrocarbons mostly, pure carbon as graphite, nanotubes or fullerines was possible too. Different authors had even postulated ways that diamonds might be formed, but mainstream scientists couldn't really believe they made any sense outside of the gas giants. And the gas giants were notorious for not letting things get out of their atmospheres at orbital velocities. So,
proto-comets with diamonds on didn't make any sort of sense. That didn't stop rumours.
“Oh Wilma! You cut me to the quick. Do you really think the rumours would persist if there weren't any?” Jack replied as they closed the hatch on his ex-home and made their way to her cargo ship.
“Yes, I do, and you know it. They're a myth!”
“Wilma, in view of the fact that you've been a supply pilot for twenty years now, I think it's time someone let you in on a secret.”
“Oh yes, Jack? What's that?” Wilma asked, sceptically.
Bracing himself against the airlock door, he rummaged in his pack for a bit, and pulled out a little bag. He carefully opened it and took out one of the fifty or so rough crystals that were in it. “Rumour has it that it was your birthday the day before yesterday, Wilma. Have a very very happy birthday, and don't spend it all at once.” And with a curious twisting motion of his hand he sent the crystal spinning slowly towards her. It was roughly octahedral, and transparent. It hadn't been cut and polished of course, but it certainly looked like it might be a raw diamond to her untrained eyes. It felt cold to her skin. Diamonds conducted heat well, she knew.
“It's real? They exist?” was all she could say.
“Took them from dog five's filter with my very own hands,” he replied. “Happy birthday, but don't tell the others.”
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Their route would take them relatively close to the next 'sheep' which would be added to the 'flock'. It was Jack's last chance to watch this strange dance first hand, and he decided he'd rather not miss it. There was something he saw on the radar and out of the window that struck him as odd. The asteroid was about normal size, and the dogs were working well together, but there was something odd about how it was reacting to the pushing of the dogs, or about the way the dogs were pushing it.
All asteroids tumble through space and since a dirty snowball sixty metres or so across weighed quite a lot more than the three ton dogs, there wasn't much point in trying to stop that. So it was that a dog would make contact, stay for maybe a minute and then back off, once its angle of thrust had been turned more than a certain amount by the rotation of the asteroid. As it backed off, another dog would take its place, or approach in another direction to correct the trajectory. As it got closer to its intended course they'd mostly leave it alone.
The dogs had been working on this one for long enough by now that there should have only been occasional contacts needed. That was it, Jack realised: the dogs were still working hard on it.
“Wilma, I think maybe Dan's first sheep is looking like a goat.”
“Pardon? I've never heard that term before.”
“Oh. Maybe it's my own. Sometimes you get odd ones round here. Look just perfect until the dogs try to move them, and they act like they're made of rock rather than water. I call them goats. I'm sure the astronomers have a nice scientific name for them, but I forget it.”
“Would Dan know about them?”
“Yeah. I told him he mustn't go sending any goats down with the sheep. He just needs to watch the mass estimates from the flight data.”
“Well I'm sure he'll do OK.”
“Yeah. He's probably doing some cleaning or something.”
In fact, Dan was looking through the telescope at the dance. It was hypnotic. The little flares from the manouvering jets, as the dogs lined themselves up, then the great tail that the main engines produced, tens of kilometres long, and multiple colours, depending which elements were in the mix at a given time — there was no need to filter the reaction mass nearly so well as the water that fed the fusion core.
It was entrancing and he was entranced. Everyone was for their first few sheep. It was against regulations not to check the mass readings, but perfectly normal to be entranced. Dan should have told the dogs to pick another sheep. Jack could have reminded him, but he didn't think it would do any harm, and would teach Dan an important lesson if he realised the mistake himself.
Dog eight was working hard. That was its purpose, so there was nothing unusual there. The unusual thing was the little place on its throttle limiting circuit where there wasn't a perfect connection. When it got really hot, say, when there was a heavy asteroid to move, which took longer than usual, there was a chance that the connection would stop conducting at all. That had happened twice now, and the surge in power of the engine turning on full from cold had killed the main power board. This time it didn't, since there wasn't a surge. The throttle was already at
full thrust. The fault just meant that when the dog's computer tried to disengage its drive, it couldn't. The computer signalled the power board to enter emergency shut-down mode. There was a dedicated signal wire for this. Unfortunately an inept field vibration test had broken it before Jack had started his most recent tour, and an oversight in the diagnostic program meant that it was never checked properly. The plasma engine burned, and the asteroid turned. Dan realised there was something wrong just as the computer signalled mayday.
Jack looked on in horror as the dog's main engine flare, still burning
at full throttle, disappeared behind the asteroid. It should have turned off long before. The way the asteroid was turning, it'd be aiming straight at them in about ten minutes, and they were too close.
He swore. “Wilma, If we don't get out of the way, and Dan can't turn that dog off, we're about to get roasted.”
Wilma had been reading, but took in the situation quickly. “How far, which way, how long have we got?”
“Six, seven minutes or so, I'd guess. I'm pretty sure it's tumbling right in the same plane as our flight-path, so I don't care if it's up or down as long as it's at ninety degrees. As for how far, the further the better. We're what, fifty kilometres from it? The cone will be at least three kilometres wide out here, but it could be more. If you can get us five kilometres up or down in ten minutes then we're probably safe. Make it that far in five and I'm fairly sure we are.”
“What do you think this is, a sports car? Wake up everyone, we're doing things this ship wasn't designed for, emergency manoeuvres about 10 seconds.”
Stolen story; please report.
She turned to Jim, the navigator, then Nancy, the engineer: “Jim, say we've got five minutes and want distance, maximum OMS or turn and use the main engines? Nancy, If Jim wants main engines, we'll want full fusion power available immediately when Jim says so. Once we're not aiming at anyone, squirt it out raw until we're ready to blast.” She'd just given the command to use pure fusion products as thrust. Really long-range missions were configured that way, it was highly efficient in terms of reaction mass, but the thrust was very low. In the present circumstances, it was just a good way to make sure that full power was available instantly, all Nancy would need to do was add reaction mass to the plasma jet and they'd get noticeable thrust.
Everything depended on mass. Their main engine was flexible: it could eject more reaction mass for extra thrust and shorter journeys, or it could eject less reaction mass faster and keep thrust up for years. With their
current load of cargo and reaction mass, the main engines could accelerate them at a fiftieth of a gravity, but the main engines couldn't steer. The orbital maneuvering system could accelerate them at one twentieth of an earth gravity in pretty much any straight line, or if they needed to turn quickly on the spot, it could could turn them ninety degrees in about a minute. But the fuel was limited, and individual rocket nozzles weren't meant to make long burns. Everything is a compromise, and no one had expected the cargo ship to need to dodge quickly.
The safe limits were set at a minute per nozzle at full power, followed by a cool-down period. They could over-stress them, twenty, thirty percent longer was probably fine in an emergency, but more than that was risky. They really needed those OMS engines and damaging them would mean they couldn't turn or dock properly, and would put all their lives at risk.
Knowing those numbers, it wasn't a particularly complex calculation to know how far each system could take them in a certain amount of time. If they only had three minutes it would have been easy: there was no way the main engines would be able to make up for the time lost in turning the ship round. But ten minutes was plenty of time. With nine minutes of full thrust, they could have been almost thirty kilometres off their present course, the longer acceleration was like that. But, in between, it was less clear, especially when you added in options like starting to accelerate before the ship was fully turned.
Jim, at the navigator's desk, didn't have time to do the maths, but got it almost exactly right for the parameters he'd been given: “A thrusting OMS turn is probably best, Wilma. Just front thrusters for a minute with no reciprocal at the rear, then start the main engines and eventually straighten us up with a burn from the rear OMS.”
The combined thrust pattern would give them some speed from the initial OMS burn, and then the continuous thrust from the main engines could take over.
He could have specified that the main engines turn on earlier, and they would have helped a bit more. Of course, if they'd turned them on immediately they would have been blasting Dan with a higher energy plasma beam than the one they wanted to escape. That wouldn't have been polite.
Dan, in the dog control room, tried what he knew, to no effect.
He didn't realise it was a wiring fault, and thought the computer had got stuck somehow. He instructed the computer to reset itself. It didn't have any effect, except to prevent him from issuing more instructions while it did that. A full computer reset like Dan had commanded took a minute. The dog kept burning on full; Dan watched on in horror as the accident unfolded.
Jack's guesses turned out to be wrong in all the wrong directions. The path of the dog's plasma tail hadn't been exactly along their flightpath, but two kilometres above it, so in fact they spent the first two and a half minutes getting to its centreline. Also, the plasma tail thrusters pointed roughly at them after only four and a half minutes. If Jim had told Wilma to use the OMS, they'd have been 6.3 kilometres from their previous path, as it was, they were just over five kilometres. If Jack had been right, or had said to go down, they'd have been safe. The tail was eight kilometres wide. Three kilometres from its center line just wasn't enough. The tail was diffuse, of course, spread over such an area it wasn't going to cut through the cabin or anything like that, but it was still a hot plasma which can do all sorts of damage in its own right, and also included dust particles up to the size of grains of sand. Just like a comet tail. Unfortunately, cargo ships aren't designed to fly through comet tails. The dust and sand, travelling at more than ten times faster than a bullet, exploded through the outer thermal insulation layers and sent a shower of debris through the cables beneath them, and the plasma shorted out exposed circuitry. High voltages and currents burnt along microscopic circuit paths and electronic components were destroyed. The communication antennae were the first to go, then the navigation cameras. The computer took the only step it could to protect itself and the crew, and triggered the electronic crow-bar circuits; for a few milliseconds every input and output lead went straight through them, harmlessly bypassing the computer. Then the fuses blew and the circuit breakers tripped. The fusion reactor shut itself down, and all electrical power died with it, apart from the emergency lamps. Jack hadn't moved from his place at the window, transfixed by their approaching doom. Ten seconds later, the tail had passed. The light surrounding the ship was gone, and there was silence.
Jim, having seen what was likely to happen, hadn't been so passive. Even before the tail hit, he'd sent the mayday signal and then started going towards the emergency store. He got out the oxygen masks, and in the silence and gloom, he handed them out. “Just in case.” he said. “We don't know there's no leak.”
“My ears aren't popping.” Jack replied.
“So, it's not fast.” Wilma said. “Unfortunately, we don't have a pressure gauge which doesn't depend on there being some electricity around. Unless you do, Jack?” He shook his head.
“We can bodge something if we've got an airtight bag.” Nancy offered, trying to think of something that would work.
“Good thinking!” Jack complimented her.
“We must have something.” Wilma replied.
“Food packs and tape?” suggested Jim, handing her the pack from his lunch and the ubiquitous space emergency supply: a spool of tape.
“Excellent!” Nancy said and started constructing. “Jim, did I see you'd hit the mayday?”
“Yes. I hope it went out.”
“I'm sure Dan saw what happened.” Jack said.
“Yes. But how able is he going to be, without someone to talk him through it?”
“He should do fine. But he's now got two problems to solve — us and that mad dog. He's going to have to work out a solution to both, that thing's blasting away between him and us and we don't want him to get hit on the way to get us.”
“What's gone wrong with it do you think?” Jim asked.
“I'd guess the throttle's jammed on full.”
“And the emergency shut-off?” Nancy asked.
“Not working somehow.” Jack shrugged, “It passed full diagnostics, but then that should have caught the throttle too.”
“So, what's going to stop it?”
“The filter will probably block in about 3 months, if nothing else.” Jack offered. “It's a shame I cleaned it out recently, or it'd be that much sooner.”
“Could he command the refueling not to happen?” Wilma asked.
“Yes. That'd at least mean it'd calm down a bit in, what, a day or two?” Jim asked.
“Hmm. The dog's engine's not going to like that.” Jack considered. “It doesn't eject the reaction products like you guys do, it's another system altogether: heat exchanger makes superheated steam and then that feeds the plasma jet.”
“So, if there's no reaction mass, what happens?” Wilma asked.
“The reactor probably melts. The reaction mass acts as coolant.” Nancy supplied.
“So stop the plasma jet without engine shutdown, and the dog will die a messy death?” Jim asked
“I expect so.” Jack confirmed. Then, indicating the Oxygen-rebreather pack he'd been handed, he asked “How many of these do we have?”
“Two more rebreathers, total of fifteen oxygen tanks, including the ones we're holding.” Jim replied. “Each one should be good for twelve hours if we do lose pressure.”
“So, with four of us, and four and three quarters of a tank each, however we manage to share, then we've got two days. What if we don't lose pressure?”
“Then, if we can get some power to life support, we're fine for a year or more, and if we can't then it'll be more like a week before the scrubbers are full...”
“Did I hear a 'but' there?”
“But if we don't have any heating then it's all going to be a bit irrelevant anyway. Four bodies is not enough to keep this ship warm. Temperature will be dropping at about half a centigrade per hour. With all the water on board it'll slow when it gets to freezing point for a while.” Nancy answered. “By the way, I've finished this pressure sensor. If this bag starts looking full then we've got a leak.”
“At least the dog's not going to blast us again.” Wilma said.
“Is there some kind of light we can point out of the window?” Jack asked “Really, we should try letting Dan know we're still alive out here.”
Jim handed him a flash-light. “Don't suppose you know any Morse code?”
“S is three short flashes, O is three long ones, E and T are a short and a long respectively. Can't remember any more I'm afraid.”
“Good job it's all printed on the handle then.” observed Wilma.
“Ooh, what a good idea someone thought of that.” Jack whistled appreciatively. “I think I'll start with `Save Our Sausages'.”
“Souls, Jack, souls. S.O.S. means save our souls.” Jim pointed out.
“I know. Now, since we seem to be spinning, Mr navigator, can you look out of that window to tell me which way to flash?”
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When he'd seen the ship get blasted and apparently go dead, Dan had relayed his version of the mayday, along with the telemetry data from the dog's computer, to Jupiter control. Not that that would help much; given the distances involved, it would be roughly two hours until they even received the message. After that, he'd set the station's telescopes to point at the cargo ship. He was just working out the boost calculations to call most of the other dogs home without them getting fried by the mad dog's rocket when the computer announced there might be a signal from the departing ship. In terms of space travel, the ship was still moving slowly. It had separated from his station and had originally been drifting away at about twenty kilometres an hour. Even that was because one of the dogs had given it a nudge. There was no point in wasting the cargo ship's OMS fuel, and they couldn't turn on their main engines so close to the station. Their attempt to escape the blast had given them some more velocity, of course, but they where still within easy reach, or would have been, without the mad dog.
He checked the telescope image. Deliberate-looking flashes from one of the windows. Morse code, probably. He'd never seen it in real life before. He told the computer to decode it for him.
“S.O.S. All alive, no power, no leak. S.O.S. All alive.” the message repeated. The problem was, he couldn't exactly send a message back to them, if they didn't have a telescope. Or could he? Yes! He realised that he could instruct one of the dogs to pulse it's engine. That would certainly be visible to them, but given what had happened to dog eight, he wasn't going to risk it just yet.
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“Think he's seen it yet?”
“Probably. No reply yet though.” Jack answered, keeping on with his pattern.
“What could he reply with?”
“Well, he's got a laser ranger we ought to be able to see. Maybe he hasn't thought of that though.”
“Why don't you suggest it?” Jim asked.
“Because, it's taking all my concentration to not get lost in sending this message, without having to talk to you, yet alone try to work out how to send anything that complicated.”
“Fair enough. Happy flashing.”
“Just stop, Jack. He's sure to have noticed by now, and if he hasn't then he's not likely to for a while. Is there anything happening?”
“I think he's calling the dogs home. Not a bad idea. Oh, it looks like one is coming this way.”
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Dan was growing and more worried about that mad dog. The tail wasn't following a precise arc, but the spin seemed to be precessing. The computer estimated he had about 3 hours before it aimed at him. The station should be better protected than the ship was, but still, he was concerned. He forwarded that data to Jupiter too, but any reply would be too late. What could he do with it? If at least he could stop it spinning then he'd be able to route the others around it's tail, and the dog would go away from him too. He set the computer to see if that was possible. It indicated that it was; the spin could be stopped by three dogs pushing on just the right lumps and ridges on the asteroid. It would take about an hour of thrust. He sent one dog after the ship, to bring it back to the station, and sorted out the instructions for the other dogs.
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“Any news, Jack?” Wilma asked. Jack was still in position at the window. He'd developed a system. Every minute he'd send “S.O.S.” then every five he'd repeat the full message. He really wanted Dan to know they were alive.
“We're too far to see much, now.”
“Get some rest. I'll take over.”
“No, I'm fine. The dog's going to be getting close soon though. It's coming nice and slowly, which I'm perfectly happy about.”
“Me too.” Jim agreed,
“Oh, I might be imagining it, but I think the mad dog isn't spinning as quickly.” Jack added.
“Is that good news?”
“Probably. It'd help us get back there without another roasting.”
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Jupiter control to Dan:
Accident summary: Computer control of rocket motor and reactor has been lost. Exact sequence of events unknown, further tests in progress.
Analysis: Malfunctioning sheepdog is navigation hazard. Robotic repairrecovery not feasible. Manual repairrecovery too perilous while motor firing.
Mitigation: Shutdown of motor may be achieved by reaction-mass starvation. Reactor shutdown or destruction will follow. Either is preferable to continued hazard.
Instructions: 1. Command computer to disable reaction mass refueling and withdraw refueling probe. 2. Use other sheepdogs to rescue shuttle. Advise on damage and repair schedule. 3. Plot final course of asteroid for eventual recovery.
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Nancy meanwhile, had been refreshing her memory of the circuits. She'd put the relevant data-crystal, normally kept in a special protective case, into her wrist unit, unfolded the screen to maximum size, and was scrolling around, trying to follow the lines on the complex diagrams. It would have been much easier on a screen bigger than ten centimetres across.
Judging by how many of the circuit breakers had triggered, it was clear that something significant had happened. If the computer had triggered the crowbar circuits itself, then it was probably OK, and so was the reactor. Other conditions — she was just checking which ones, could also trigger the crowbar circuits. If
that had happened, then that meant there was a chance that something vital in the reactor had seriously broken. The other possibility was that the crowbar circuits had not been triggered. That would mean that all those broken fuses and triggered circuit breakers had failed because those currents had gone through the computer itself. There wasn't actually a single board that they all connected to except the power supply. Optical fibres — lighter than copper — joined some sub-systems together. Such a catastrophic failure was unlikely, but if it had happened then it would indicate that the generator had done something seriously nasty. It was her job to make sure it hadn't before she reconnected it. Meticulously she pulled the circuits and checked for signs of damage.
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Ten hours after they'd been hit, and three hours after the dog had coupled onto them and started to push them towards the station, Nancy spoke to Wilma. It was getting chilly.
“Wilma, your call: I've checked everything I could. As far as I can see the computer threw the crowbars across the power lines, so I should be able to restore power safely, at least to some circuits.”
“Well done! Which ones?”
“Heating, lighting, life-support certainly. Once they're up, I can test other circuits better. Based on what I know, I could probably start the computer too, but I'm pretty sure we've got some dead circuits out there, so it'd just be the main computer, until I can do more tests. I don't want to connect a bad circuit that'll trigger another forced shutdown.”
“Of course not. And you're tired and might make a mistake too. What about radio? It'd be good to be able to talk to Dan.”
“Someone decided to save a few grammes and made that a computer function. That's one of the circuits I suspect the most, actually, along with the outside cameras.”
“Oh great. So, no radio. But life-support and heat would be nice. Any benefits to starting up the computer?”
Wilma was hesitant. “Maybe. I'd need to talk to Jack. We've got the dockyard acoustic interface on the coupling, I don't know if the dog has one. If it does then we might be able to get the computer to talk to the dog, and use its radio.” Jack had finally fallen asleep an hour ago.
“Remind me what a `dockyard acoustic interface' is please. I don't know if I've ever heard about it.”
“It's built into the coupling: a little ultrasonic transmitter-receiver that lets the dockyard talk to the computer even before they'd built most of the ship. Its also used when we're docked. Saves having data cables going through the airlocks, and it still works if they've disconnected the radio.”
“Sounds wonderful. Why would you need to talk to Jack?”
“I don't know if the dogs have one. If they don't then there's no point in bringing up the computer, which is a slight risk.”
“Ah. Well, I think you should just restore life support and heat and leave it at that then. Then get some sleep, you've been alert for almost twenty hours.” Then, seeing Wilma's expression, she added “I will too, soon, Jim's watch starts in half an hour.”
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The end of dog eight's existence was more spectacular than had been expected by anyone.
In the two days since the refueling probe had been disconnected, the constant thrust had given it and the asteroid an appreciable speed, and it was a long way from the station now.
But the reaction fuel was running out, and pressure in the reservoir reduced below where the regulator that fed the reactor was set. Constrictions which had previously been swept clean by the flow of water and steam started to clog up with silt and debris. The flow in them reduced further and became erratic, and eventually they were blocked entirely. Had the reactor temperatures got closer to the softening point of the encasing metals, then automatic shutdown would have occurred. No one had expected there to still be water in the system at elevated temperatures, however. The pressure of the water rose and rose further, eventually something had to give, and it did. The water exploded as though it had been high explosive. The dog split in two; one half hurtled into space, the other half gave up most of its momentum to the asteroid, altering its course a small but critical amount, before spinning off in the other direction. The explosion also released a cloud of dark debris which eventually settled back over the asteroid. The albedo dropped to almost nothing, even darker than most comet's nucleii. Camouflaged, and no longer on the orbit expected, the asteroid went on its way. It had been aiming at where Jupiter would be in eight years. Now, it was going to miss.
The telescopes on the station reported the explosion to Dan, who duly passed that fact, along with the last orbital data and telemetry from the dog to Jupiter control. They decided that the risk of the dog hitting anything manned was roughly zero, and there was obviously nothing to be gained by visiting where the dog had exploded from.
The darkened asteroid dropped down the gravitational well towards the inner solar system, gathering speed with every kilometre.
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JANUARY 2270
Scientists based on Europa who were studying Jupiter looked for the asteroid a week before it was due to hit. They'd hoped it would give them a nice collection of data as it impacted the gas giant, but they failed to find it where the data-set said it should be. That wasn't particularly unusual, so they searched the sky for it, half-heartedly, but didn't find it. In fact, it had passed the other side of the moon to where their telescopes were pointing. It had just been a potential data-source to them, and they had plenty of other sources of data, and a conference to prepare for. It didn't occur to them to wonder where it might be going if it had missed Jupiter. In fact, having swung past Jupiter, it was now on a collision course with the third planet. Ambrose Bierce wrote that an accident was an inevitable occurrence due to the action of immutable natural laws. Unfortunately, the laws of human forgetfulness and laziness played their part. When it was early enough to make a difference, no one cared enough to look at all the data in order to refine the orbit, and thus find out where the asteroid was going.