A Tall Tail Read online

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  Contents

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  This is true, I swear:

  I was in Orlando in October, staying in one of those big, bland conference hotels. DARPA, the Pentagon department tasked with nurturing Mad Science in all its most speculative forms, had decided to throw a brainstorming conference on the 100 Year Starship—a mind-meld to try and figure out what research they’d have to conduct in order to have a hope of beginning to build a starship some time in the twenty-second century. And for no reason I clearly understood, they decided to fly in a bunch of SF authors from all over the world. I’m not sure why the Pentagon might want a starship, but I was glad someone was paying for me to go to Orlando and kibitz on their conference, and I was happy to bloviate about such things from a hard SF point of view.

  The 100YSS conference exceeded all my expectations—and everyone else’s. But the sheer amount of information on tap made the experience feel a bit like trying to drink from a fire hose. It turns out there’s a lot we don’t know about how to build a starship, but also a lot that we do know, and this was the mother of all networking opportunities for folks with an interest in the field.

  Like all networking sessions, a lot of the interesting stuff happens among small groups by the poolside bar, or over a dinner table in a nearby restaurant. You get talking to some interesting-sounding folks who ply you with beer, and the next thing you know you discover you’ve been drafted into some kind of DARPA-funded think tank, or wake up with a hangover in a North Korean labour camp, doomed to spend the next two years coaching the Great Leader’s son through writing the Nobel Prize–winning SF novel that daddy expects him to produce.

  Luckily that’s never happened to me, but I have had an eye-opening experience or two. Like the chat I had on Sunday evening by the swimming pool.

  The Orlando conference center where they held the 100 Year Starship event had a resort-grade outdoor water attraction. Not only were there hot tubs and a regular swimming pool and a water slide, this hotel had an artificial river about a quarter of a mile long, down which you could drift along on a truck tire, propelled by aquajets and drenched by fountains. On a muggy October evening, after a long day of listening to talks about liquid indium ion drives and aneutronic boron fusion reactors, this was exactly the right place to hang out if you wanted to bump into inebriated floating rocket scientists. Like Greg Benford’s twin brother, Jim.

  You probably know Greg Benford best as a physicist and hard SF writer, one of the “Killer B’s” who dominated the field in the 1980s and who is still actively writing novels and research papers. But you might not be aware that Greg has an identical twin, or that his sibling Jim is a card-carrying rocket scientist. Back in 2011, Jim was doing impressive things with microwave sails, and Greg was talking up the applications of a lot of recently declassified Russian research into nuclear thermal rockets: “They built this underground test complex near Semipalatinsk, so that they could capture the exhaust. And then they ran their motor for nearly five hundred hours. That’s about a thousand times longer than Project NERVA managed, in total—in one burn! It’s safe, and it’s reliable, and it’s the best way of getting to the outer planets.” His tire spun slowly round as he drifted under one of the fountains, and because we were orbiting near opposite sides of the artificial river, our paths diverged. Intrigued, I paddled to catch up.

  “Don’t you think launching a nuclear reactor might be a bit problematic?” I asked, as I closed to within hailing distance. “I mean, the antinuclear protests when Cassini launched…”

  Jim waved dismissively. “It’s safe as houses,” he assured me. “You’re looking for safety, right? Nuclear thermal, you launch the reactor fuel piecemeal in Soyuz or Dragon capsules with a man-rated launch escape system, then fuel the reactor once it’s in orbit. No, nuclear-thermal is fine. Not very efficient, but it’s not going to kill anyone. If you want efficient propulsion technology, you’ve got to look elsewhere. But unfortunately the best rocket tech we know of is far too dangerous to use.”

  “How dangerous?”

  Jim winked at me. “Let me introduce you to Leonard,” he said as we drifted toward the poolside cocktail bar. “He’ll fill you in on it…”

  Leonard Hansen—not his real name—is a tanned seventy-something rocket scientist who spent the 1950s in California and New Mexico, as a graduate student researching rocket fuels under John D. Clark and then as a fuels scientist working on various missile programs. Today he lives in semiretirement in Florida, but he retains a keen interest in the field of rocket fuel design.

  “What you need to understand is that in order to go faster, you need to increase the exhaust velocity,” he explained. “You can do this by making it much hotter, or by using lighter exhaust particles. If you want to make it hotter, however, you need to pump more energy into it. So if you’re using chemical rockets, you need to use very energetic reagents—fuel and oxidizer.”

  He paused for a mouthful of lime margarita. “Take the space shuttle,” he said wistfully. “With just two tweaks, we could have put a hundred tons into its payload bay!”

  “Two tweaks?” I asked doubtfully. A hundred-ton payload (in a vehicle already massing close to a hundred tons) would have put the shuttle in the same bracket as the Saturn V.

  “Yes.” He smiled sourly. “They could have stretched it, given it a bigger thermal protection system as well—the Columbia disaster wouldn’t have happened. But they rejected my proposal. The first part, to upgrade the SRBs, would have been trivially easy! Although the alternate oxidizer for the space shuttle main engines would have presented certain handling difficulties, that much is true…”

  “Tell him about the SRBs first,” Jim suggested. He leaned forward expectantly; at a guess, he’d heard this before.

  “All right. First, the solid rocket boosters. Regular SRBs run on a mixture of ammonium perchlorate—the oxidizer—and finely powdered aluminum, suspended in a rubbery polymer that holds everything together and provides additional reaction mass. When they ignite you get aluminum oxide and ammonium chloride and lots of energy. But it’s not really enough! We could make them about twenty percent more efficient if we just replaced the aluminum with powdered beryllium. It’s a lighter atom and the redox reaction is more energetic—”

  “Hang on!” I stared at him. “Beryllium is really poisonous. Wouldn’t that—”

  Leonard shook his head. “Nonsense.” A small smile. “You see, then there was my second proposal. If you replace the oxidizer in the space shuttle main engines with liquid fluorine, you could also get an extra twenty percent out of them. And I know what you’re going to say next: wouldn’t that give rise to an exhaust plume of extremely hot hydrofluoric acid? You’re absolutely right: it would! But hydrofluoric acid reacts with beryllium oxide to give you beryllium fluoride—which is almost inert in comparison—and hydrochloric acid, which is neither here nor there.” A shadow crossed his face. “It’s totally safe, compared to some of the other projects I’ve worked on. But NASA took one look at the environmental impact statement and, and…” His shoulders began to shake; whether with laughter or tears, I couldn’t tell.

  Now, I have a background in chemistry. And I thin
k I should explain at this point that liquid fluorine is not your friend. Fluorine is the most active elemental oxidizing agent in the periodic table, and liquid fluorine makes liquid oxygen look inert and unreactive. It likes to oxidize things we don’t usually think of as oxidizable, like water—which it reacts with to product hydrofluoric acid, which is in turn nasty enough that sane people avoid working with it because if you forget for one second what you’re dealing with it’s liable to dissolve your bones.

  Back in the nineteenth century, chemists used to joke that you could tell who had just discovered elemental fluorine by reading the obituary columns. But liquid fluorine and hydrofluoric acid are themselves not the worst oxidizing agents out there. Elemental fluorine may be the thuggish hit-man of the halide world, but if you torment it with chloride ions you can turn it into the chemical equivalent of Hannibal Lecter: chlorine trifluoride, an oxidizing agent so malignant that it will set fire to water and burn explosively on contact with sand, asbestos, or rocket scientists.

  Jim Benford smiled. “Now why don’t you tell him about the proposal for NAIL SPIKE?”

  “What?” Leonard looked confused for a moment. “I thought he’d be more interested in D-SLAM—”

  “Wasn’t that Project PLUTO?” I asked. I’m enough of a crazy cold war projects geek to have heard of the atomic powered cruise missile—a device that only Dr. Strangelove could have loved—from the 1960s.

  “Yes, D-SLAM was PLUTO,” said Jim. “But it’s not that interesting, unless you want a power source for a drone that can explore the atmosphere of Jupiter for years at a time. NAIL SPIKE, on the other hand—”

  “NAIL SPIKE was a CIA project.” Leonard polished off his cocktail and put the glass down on the bar, just loudly enough to get my attention. He caught my eye. I sighed, and waved at the bartender.

  “Are you supposed to be talking to me about it, then?” I asked. “Me being a foreigner, remember?” Not that I wasn’t curious, but I wasn’t particularly enthusiastic about unintentionally having my stay in the US extended by a few years due to someone else’s loose lips.

  “Oh, it’s old hat.” Jim waved my question away. “We’re talking about 1970s projects here. It was declassified in the 90s, after the end of the cold war.”

  “The CIA were into rocketry?” I couldn’t help myself.

  “After a fashion.” Our new round of drinks arrived. Leonard took a cautious sip of his. “Who was that writer friend of yours, Jim, from California…?”

  “Larry, Larry Niven. ‘Any reaction motor is a weapon of efficiency proportional to its efficiency as a rocket.’ That’s what you were thinking of?”

  “Yes, that’s the one. He was spot-on, you know. NAIL SPIKE was about building a really efficient rocket motor and then marketing it to the opposition.”

  “Wait, what?” (I can’t easily describe the experience of involuntary nasal irrigation with a lime margarita, so I won’t bother. Just try not to do it.)

  When I stopped convulsing Leonard continued: "The idea is quite simple. During the 1940s and 1950s we experimented with a number of really quite unpleasant substances before settling in the 1960s on a handful of slightly less unpleasant stuff as our propellants of choice—liquid oxygen, liquid hydrogen, kerosene, and solids based on powdered aluminum. Of course, there were exceptions; Titan ran on dinitrogen tetroxide and a hydrazine/UDMH mixture, for example. Hydrazine isn’t just explosive, it’s corrosive and poisonous too. There’s a reason the EPA-bullied wimps at NASA won’t use it for launch vehicles these days. Dinitrogen tetroxide is explosive and corrosive. But we more or less stopped using really nasty stuff like red fuming nitric acid—we leave that to the Russians these days.

  "But during the 1960s some bright spark at ARPA got a bright idea and handed it to the CIA: why not pretend we were using some extremely high reactivity oxidizers and fuels in our latest missiles, and leak plans and blueprints to the bad guys’ spies? Obviously this wouldn’t play with the Soviets, but small fry like East Germany or North Korea or Iraq might fall for it. Worst case, it would send them on a wild goose chase; best case, they might really damage themselves trying to build and fly this stuff.

  “So we brainstormed the most suicidal rocket motor we could come up with. And you wouldn’t believe just how mad it was.”

  I grabbed another mouthful of iced alcohol; being slightly numb seemed like a good idea under the circumstances. “So what did you come up with?”

  “Well, there’s the stuff we ruled out first. Leaking Project Orion—” the nuclear bomb–powered pulse-detonation space drive “—was a nonstarter; the test-ban treaty put the kibosh on that. The PLUTO nuclear ramjet likewise wasn’t an option. We had to stick to chemical rockets. But it turns out there are chemical rockets as nasty as anything nuclear. Nastier, even.

  “First, there’s an oxidizing agent that’s even nastier than chlorine trifluoride.” Dr Hansen grinned. “It’s called FOOF, dioxygen difluoride. You make it by reacting liquid fluorine and liquid oxygen in a cryogenic steel reaction vessel under X-ray bombardment. I say ‘you’ make it because I’m not stupid enough to go anywhere near the stuff myself. I hear they cancel your life insurance if they catch wind that you’re working with it. FOOF is unstable and tends to explode if you let it get much warmer than the boiling point of liquid nitrogen, or if you look at it funny. It’s mostly used in producing uranium hexafluoride from—” he coughed. “Well, anyway, it’s a great oxidizing agent!”

  Jim nodded wisely. “Happy fun stuff. But you’d need a fuel to burn in it, right?”

  “Yes! And we had just the stuff sitting on the shelf in the glove box, so to speak. Dimethylmercury.”

  “Di—” That’s when I figured out that they were pulling my leg.

  Mercury is nasty stuff, but organic mercury compounds are even nastier, and dimethylmercury is one of the worst. It’s not merely poisonous; it’s about the strongest neurotoxin we’ve got. In fact, just about its only use is as a reference test for toxicity. It passes through latex, rubber, and plastics as if they aren’t there and it can pass right through your skin as well, killing you slowly and painfully, like it killed Professor Wetterhahn in 1997. Chemical warfare suits won’t save you. And unlike the happy fun nerve gases everyone knows about, Sarin and VX and so on, dimethylmercury doesn’t go away. It hangs around for years, like long duration fallout from a nuclear weapon, only much, much nastier.

  “That’s nonsense. Nobody would use that stuff as rocket fuel! For one thing, the mercury would corrode any aluminum components in seconds, and for another, if you spilled even a couple of drops on the launch pad you’d have a permanent no-go zone! Why not just use liquid methane or something?”

  But they were shaking their heads at me. “You want mercury because it’s a heavy atom; you can make your fuel really dense and if you pump enough energy into a mercury ion to make it go really fast you get more momentum from your exhaust stream. That’s the theory, anyway. We managed to talk the Navy and Air Force out of using the stuff decades ago, but figured, why not leak it to someone we don’t like?” Jim explained. “Which is what NAIL SPIKE was about. Len?”

  "Yes. That’s where the guys in Langley came in. Now you’ve got to understand, this was after the Church Committee in the midseventies blew the lid off a lot of crazy stuff—Operation Acoustic Kitty, the Castro assassination attempts, the elephants-on-LSD thing. During the late 1970s the CIA was under the oversight of a suspicious congressional committee, who took most of their toys away from them. But they were still expected to do stuff to…impair…the Soviets’ war-fighting capability. Stuff like providing covert funding for radical Islamic insurgents in Afghanistan, which was in danger of going communist. Or, well, trying to get them to poison themselves.

  “Now, you probably know already that the Soviets were at least even with us in rocketry—possibly even a bit ahead of us on the liquid fuel side during the 1950s. So fooling them into playing with NAIL SPIKE was going to be a tall order. On the other hand, there
’s a special genius at Langley who came up with the bright idea of making the NAIL SPIKE leak look incomplete—of hinting that there was a secret missing stabilizer ingredient in the fuel. So we faked up a few dummy test firings on a stand at White Sands, and we made sure that all the paperwork crossed the desk of a known GRU mole in Los Alamos; ever since the whole Atom Bomb Spies fiasco we’ve kept a couple of Soviet spies on hand, wrapped in cotton wool, for just such a leak. It’s much better to keep them in a box than to arrest them immediately; if you haul them in, the KGB will just send some more and you’ll have to figure out who they are all over again.

  “So. We leaked the design for the FOOF/dimethylmercury test motor to the Soviets, claiming it had an insanely high specific impulse—” the measure of a rocket’s efficiency “—and was ideal for anti-shipping missiles because the fuel’s extremely dense, so your missile can have a smaller frontal cross-section, which is good when you’re pushing through dense air at sea level. And we made sure to salt the documents with references to a special additive that made it all stable and safe to handle. And then we sat back to wait for the exploding chemical plants to show up from orbit, and the reports of dissolving scientists and platoons of technicians dying in neurology units.”

  It made a horrible kind of sense, for Cold War values of sense: not a real rocket motor, but a vile way of getting your enemy’s best and brightest to kill themselves by trying to reverse-engineer an impossible nightmare. So I swallowed another mouthful of my drink and waited for Jim to nudge Len into continuing his horror story.

  "Well, you’ve got to understand that this was 1979. The commies had just invaded Afghanistan, the Cold War was hotting up, the Iranians had taken our people hostage in the embassy in Tehran. So they had high hopes for NAIL SPIKE. But it seemed to sink without a trace.

  “Then, two years later, we got wind that they’d taken the bait. In fact, there was an industrial research unit working on trying to reverse engineer the special additive! That evening in Langley there were high fives all round, I can tell you. We didn’t know much about it, just that it was known as Atom City Number Nine, and it was somewhere in the Ukraine, not far from Kiev, and there was some kind of big engineering complex nearby.”