Dead Men Flying

by Bill Patterson

  “Who's Scott?” asked Niall.

  “My second in Engineering. You can argue with him about the pollution angle, if you insist. Let me get through the rest of the jobs. We're going to use RTGs to vaporize the ice. They have to be self-loading and remotely controlled. It's fine if they're on all the time, I just want to be able to control the mass flow through them. This will get our comet stopped. Next, we're going to drill a channel through to the center of propulsion of this lumpy thing.

  “Harlan, we're going to ask you to line that channel to reduce ice erosion. Use whatever you can lay your hands on, but I suspect a combination of aerogel with an overlay of sprayed-on aluminum with a carbon nanotube woven lining would work best. We've got all that from the Moon, but you can design whatever you think up to the task. Within reason, we're not really under mass limitations. An iron pipe with walls a third of a meter thick would never pass the first review committee back home, but is perfectly fine here. Your only limit is what we've got on board, and no cannibalization!”

  “Clear, Jeff. I look forward to working on it.”

  “Good. Lima is going to machine whatever we send his way. Harlan, as soon as you get that exhaust pipe laid, we're going to need you to design and build the feed pipes. That's a lot more straightforward.

  “Niall, I want you to help Ivan with the physics of the nuclear reactors, both the thorium one and the NERVA one. But if you're really opposed to it, I'll recommend to the Commander to pop you back in the LN2 bath and keep defrosting physicists until we find one we can trust to help us get back home. You don't have to make up your mind right now, but do you think you can help us at least get the RTGs up and running? They're not going to spread any pollution, because when we're done with the attitude thrusters, we'll just take out the radioactives and throw them back into the thorium reactor to be burned up. Can you do that, at least?”

  “Yeah, sure. But you don't have to put it that way. I'll help, but I want to hear what this Scott person says. I really don't want to spread a plume of radioactive crap across space where it's going to screw up science for decades in the future.”

  “Save it, I don't need to know,” said Jeff. “Look, I've been killing myself—we all have—since The Event, and it's been wearing us down. I shouldn't take it out on you. I know you've just woken up, but believe me, the alternatives have all been hashed out, and this is what needs to be done. That's why I've called for Scott—he's just getting up and I've been awake for fifteen hours already. Scott? Take over.”

  “Greetings, gentlemen,” Scott’s voice said over the intercom. The slam of the hatch had to be audible in the microphone. “Jeff's gone?”

  “Uh, yes,” said Niall. “I take it he's running on fumes.”

  “You could say that,” said Scott. “There's an incredible number of things that need to be done before we will have a chance to even think about going home. Earth isn’t talking to us because we refused to accept suicide, and the Moon, while giving us as much support as they can, has troubles of their own.”

  “I really find that hard to believe—that Earth would just cut us off like that,” said Harlan. “I also can't believe that Subby would hit the power relays for the Control Room, either.”

  “I know you read the flight logs. We heard the whole thing ourselves. Believe it,” said Scott. “Earth has its own problems. That debris that is keeping us from going straight home is also slamming into the Earth’s surface at random times. How'd you like to be walking hand-in-hand with your sweetie, then a blast of wind hits you, and the only thing you have left of her is blood stains on your coat? Actually happened. Earth news is really depressing.”

  Niall and Harlan were silent, thinking over the implications.

  “But back to things we can actually do something about. Let's talk about radiation plume you're so worried about, Niall. Talk to me, tell me what you think is going to happen.”

  “We build a big, unshielded reactor in the heart of the comet and pump water through it. That's how the first NERVA rockets were designed, right?”

  “Close enough. So, water flows past the rods. Then what?”

  “Well, the uranium puts out fission products of all kinds. At the very least, it makes some portion of the water itself radioactive. Tritium and O-17. Radioactive water, actinide wastes, strontium-90, cesium-137, iodine-131, do I really have to go down the whole list? All of this gets blasted into space with our exhaust plume.”

  “Of course it does. Keep going,” said Scott.

  “Keep what going?”

  Scott remained patient. “Follow the plume outbound. What happens to it?”

  “It spreads out and starts interacting with other objects and chemical species in the area.”

  “What is its speed?”

  “How should I know?” asked Niall. “So much of that is a function of the engine design, particularly the mass flow rate and the geometry of any engine bell.

  “I agree,” said Scott. “But let's keep thinking. How many half-lives have to pass before something decays down to don't-care status? Seven to ten, right?”

  Niall was slow to answer. “Something like that. Eight is the usual number.

  “Right. Take tritium. Eight half-lives of about twelve and a third years is just shy of one hundred years. You know the status of space exploration when you left—there wasn't much at all. The only reason we were headed to Mars in the first place was that the head of the UN decided that would be a great goal to shoot for, just before he got blown up by those terrorists. It was just like JFK back in 1963——the goal of sticking the blue flag on the Red Planet became a quasi-religious thing. Huh…maybe that’s why Earth cut us off for ditching mission objectives.

  “Now, the Earth is getting pounded to death by Lunar debris. They're setting off nukes, for God's sake, right there in Low Earth Orbit, trying to push the rocks aside. Suppose we were able to snap our fingers and get rid of all the debris impactors. How long would it take the Earth to be able to send a probe towards Jupiter? Ten years from now? Twenty?”

  “Probably not for at least forty years.”

  “So they might pick up a little tritium. Fine, we've still got a problem. Let me ask you this, Niall: Suppose we set off the biggest plume of tritium. Suppose we rupture a few fuel rods from too much water pressure or not enough, or something equally bad, and the plume is loaded with everything, not just tritium. Doomed, right? We’re going to open up a huge sheet of silvered mylar out here in space at some point. What happens to it?”

  “It will blow away. Solar wind and radiation pressure. Everyone knows that.”

  You could almost hear the smile in Scott's voice. “Exactly. Now, consider this plume of radioactivity, from every possible nucleon in our reactor and coolant. Most decay in the first thirty years, but some are very long-lived—hundreds of thousands of years for some isotopes. They're the ones most people worry about. Except you don't have to. How much lighter is a radioactive technetium atom than a whole sheet of mylar? Doesn't it stand to reason that the plume will be immediately accelerated by the solar wind and blown away into interstellar space?

  “Huh. Never thought about that,” said Niall.

  “Yeah, we had to go wrestle with this exact chain of reasoning before we hit on the solar wind. We don't worry about releasing this little bit of radioactivity, because it will contaminate things about as well as the chimney of a wood-burning stove contaminates the backyards three blocks away during a hurricane. If you got directly downwind, you might get the smallest whiff of smoke. Everywhere else, it's as if the plume never existed.”

  “I feel like an idiot,” said Niall.

  “Don't worry, I didn't think of the solar wind, either. You know who nailed me on it? Mickey Donovan, our radioman. It's called being human. Now, I know Jeff is really looking for one thing: the willingness of everyone to perform the tasks we ask of you. When we get to the NERVA implementation, can we count on you, Niall?”

  “Sure,” he said. “No reservations.”
>
  “Good,” said Scott. “Any other objections by anyone else?” He paused. “Nobody? Then go get some rest, we'll reach out to you with some preliminary things, get your head into the game. Welcome back to the land of the living, men—I, for one, am tired of seeing the same old faces at dinnertime.”

  Ride 'em Cowboy

  Vicinity of Comet C/2082 D4 (PanSTARRS), October 6 2083, 1003 GMT

  Eighty-two was not just tumbling in space. It had a complex motion that consisted of rotation around all three axes: It was moving head over heels, but also spinning like an ice skater and rolling across the floor like a baby.

  It presented the crew with a difficult choice: just how did one board the thing in the first place?

  There was not going to be any nice, sedate docking procedure like linking up to the Chaffee. Whoever was going to be going over first was going to have a very dangerous task: grab hold and hang on, in vacuum, without tearing their suit or smashing their faceplate.

  Jeff floated well clear of Eighty-two. “I still think we should send over a drone first,” he said. “But anything large enough to do something useful is also large enough to damage us if it were to get thrown off.” The ships had moved off to a two-kilometer safe distance. Jeff was riding a two-seated broomstick, and in the rear seat was Mickey Donovan.

  “Good times, Jeff,” he said, as he unstrapped. He had small gas-powered thrusters on his wrists and ankles, and a larger one in the small of his back. He had tested them and refilled the cold LOX tanks before leaving the ships.

  “Don't be fancy,” said Jeff. “Get on board and set the mini-mitt. We don't have a lot of time to dick around out here.”

  The mini-mitt was a scaled down version of its larger cousin that inhabited the iron ring during the outbound flight. It projected a vast web of magnetic force that would attract anything sent its way. When any package got to within a hundred meters of Eighty-two, the mini-mitt would seize the package with a strong magnetic field, while at the same time, it would direct the package to a two-stage braking field. Ideally, it would be holding a package in the center of the small ring until a human turned off the fields—causing the mini-mitt to drop the package—and retrieved it.

  It wasn't very gentle with the package.

  “I'm thinking the best thing I can do is aim for the center of the pitching rotation just after the yawing end sweeps past us. When I get close, I'll fire the crossbow and hope the quarrel sticks in the ice deeply enough to hold me. Then I ride the line in until the roll rotation wraps me up.”

  Jeff looked at the comet like he had never seen it before, instead of having given it the intensive study everyone in the crew had given it for the weeks they had been floating beside it. “Sounds good. If you have any doubts, turn and blast down the length of the long axis and away. I'll come get you.”

  “Bet,” said Mickey. “Here I go!” He gave a blast on his thrusters just before the end of the comet swept by them, following the long axis to the center of rotation, marked with a handy spot of fluorescent paint.

  “Good thing we marked the centroid,” said Mickey. “You get up close to the crust here, you start losing your orientation.”

  “You're doing fine,” said Jeff, following the drifting body with a dim green spot glowing on the life support backpack. “Coming up on centroid.”

  “Yeah, I got it,” said Mickey. “First shot.” He grabbed the preloaded crossbow and tried to aim it. “Impossible to aim, with the helmet's visual aberration. Plus, I'd rather not have this thing recoil into my faceplate.” He aimed it as best as possible, then tripped the handle. The quarrel raced away to embed itself firmly in the crunchy crust of the comet.

  “Damm it,” said Mickey as he spun around like an ice skater in reaction to the arrow shot. “Fired from the side.” He had seconds to act. As he spun, the line attached to the arrow was wrapping around him, but the arrow itself was receding around the bend of the comet as it spun on its long axis. Mickey aimed a wrist thruster in the opposite direction of spin and fired a burst of cold oxygen gas. He slowed, but the amount of line left in the crossbow's spool was getting dangerously low. He triggered the thruster again, this time stopping dead. He still had two turns of line around his middle. The line suddenly tightened and he was whipped around in the opposite direction. He held the other wrist against this new direction of spin and canceled that rotation.

  “Remind me not to do that again,” he said. He quickly clipped the reel from the crossbow to a D-ring on a harness he wore over his spacesuit. “Okay, I'm at spin zero, clipped on the line, and I am reeling in.”

  “Watch your angular momentum,” reminded Jeff. “Things will get violent when you get closer. Don't run dry trying for a smooth ride.”

  Mickey acknowledged, then began to reel in the line attaching him to the bolt. Because he had hit the comet in the center of rotation for the head over heels rotation, he didn't have to worry about one type of rotation. He was still being spun around the comet as it rolled around its long axis, but that would resolve itself by pulling himself in closer to the bolt.

  What was driving him nuts was the spin of the comet around the vertical axis. It was just like the flat spin of an aircraft. It made his line vary from taut as the ground with the arrow in it receded from him to very slack as the arrow approached him.

  He experimented with the reel and discovered with a deliberate varying of the reeling action, he could ensure there was enough slack in the line when the arrow was at its furthest distance from him to avoid being jerked towards the comet, but continue his approach to the madly cavorting ground.

  “You look like you do this all the time,” said Jeff. “You're about one hundred meters to the ground.”

  Mickey concentrated on these last few dozen meters and was able to touch down, boots first, on the ground next to the arrow. He held the line at maximum tension until he felt himself at rest. “Touchdown on Eighty-two,” he said. “That's another small step for man. Now, let's get this show on the road.”

  ***

  The first item of business was to set up the mini-mitt by anchoring its legs solidly into the icy ground next to the comet. Mickey unreeled a cable from the small RTG at its base and turned on the unit. Jeff fired a test package and the mini-mitt neatly captured it.

  Mickey then strung a series of self-anchoring pitons across the landing area. He laid the flat boxes, resembling a lunch box, on the ice and triggered them. A small gun drilled a pilot hole into the ice, down which a piece of memory metal was fed until it hit bottom. A high-density battery heated the memory metal to its transition temperature, turning it into a helix. Like a red-hot corkscrew, a powerful motor drilled the helix into the frozen crust until it ran out of metal. Then a yellow light illuminated on the external box, changing to green when the ice refroze around the helix. A ring atop the external box rated five hundred kilograms; one more hold-down, complete.

  “All right, I've got the lines strung, the Mitt set up. Where's the RTG crew?” asked Mickey. “I really don't want to leave until I get the attitude thrusters at least secured on the surface.”

  “Hold your horses, Mickey, they're getting out here now.” Another broomstick approached, this one with three other astronauts clipped to it and a long line of cargo strung behind it. The pilot punched the broomstick laterally ten meters, spun it one hundred and eighty degrees until it was pointing back the way it came, and began a slow backing up of the stick as the cargo flew past and below it.

  The broomstick suddenly thrust backwards as the cargo line straightened and the cargo flipped on the reciprocal course. The pilot was really smooth, slowing the cargo and astronauts down until they were at rest about twenty meters from Jeff.

  He looked at the pilot, and was not surprised to see Commander Standish at the controls. If anyone was an accomplished pilot on the little scooters, it was Mike. Five years at the orbital shipyards that built the Bradbury was not mandatory in order to become the Commander, but Mike Standish wanted to know his ship
inside out, and the best way to do that was to crawl all over it while it was being built. Along the way, he became a stellar broomstick pilot.

  “Smooth, sir,” he called. “I couldn't do any better myself.”

  “Not such a high bar, Jeff,” Mike said, provoking laughter from the astronauts. “Just kidding. Okay, you pogues, everybody off. Take those rad cans with you, too.” The RTGs were not yet loaded with radioactives, just to make installation safer. But they didn't want the radioactive RTG fuel to be hanging around the Bradbury either, so the answer was to store it in lead casks attached to the line. Their job was to securely tie the casks to the comet until it was time to fuel the RTGs.

  The men piled off and untied the line from the broomstick. Ferrying this load down to the comet was going to require a little bit more than a wrist thruster. The Collins had sent along about a dozen MoonCans and fuel for the Expedition to use, just in case they needed to ferry something massy or bulky. The lead casks fit perfectly into the cargo hold of one MoonCan, and the guidance engine was sophisticated enough to be able to land the 'Can wherever it was needed on the surface.

  Harel volunteered to go down and help Mickey wrestle the MoonCan into a secure position once it landed. He had trained with the little thrusters in the space around the ships until he felt confident in their use. His descent and touchdown were significantly less artistic than the first one Mickey did, but he was undamaged when he clipped his suit to one of the holddowns.

  At a signal from the duo on the comet, Jeff triggered the first MoonCan. It moved off slowly and smoothly. Then it did some kind of pirouette using three thrusters, and it was almost ready to ground. Mickey could only marvel at it. As soon as it grounded, the small upright cylinder began leaning crazily. Harel tried to grab the 'Can, and Mickey yelled at him to get away from it. Harel jumped away just in time, and the small but massive vehicle actually dented the ground when it fell.

  They both bounded towards the vehicle as it began a slow roll. They wrapped aluminum cables through a series of tiedowns on the vehicle, and a number of the five-hundred-kilogram-test pitons set on the comet. The MoonCan quivered slightly, but held. Importantly, the hatches were facing outward so they wouldn't have to roll the 'Can to open it up.