And then whatever compound we'd designed we'd need to synthesize. In those tank-car lots.
Alternatively, maybe we could base our propellant system on another substance with a hair-trigger reputation that, however, is probably somewhat undeserved: hydrogen peroxide, H[2]O[2]. It decomposes spectacularly to steam and oxygen:
H[2]O[2] (right arrow) H[2]O + 1/2 O[2] + 54.2 kJ/mol.
All by itself it's not a bad monopropellant (I[sp] = 163 sec).
But look at all that lovely oxygen released! Adding some fuel to the mixture could (in theory, anyway) really boost the I[sp] by providing something for the oxygen to oxidize.
Well, let's see. In many ways H[2]O[2] is similar to water. Like H[2]O, it's a “polar” molecule, meaning it has an uneven distribution of electric charge. The oxygens are slightly negative, while the hydrogens are slightly positive. Polar molecules are good at dissolving ionic substances, such as AN, because the solvent molecules can glom onto the ions with simple electrostatic attraction. (Chemists say “coordinate” rather than “glom,” however.) The upshot is that essentially anything that dissolves in water dissolves in H[2]O[2] and typically to about the same degree.
So maybe we can dissolve fuel into H2O2: alkylammonium ions, for example. One problem, though, is that most oxidizable things you can dissolve react immediately. In fact, concentrated H[2]O[2] inflames most organic compounds when spilled on them.
The other problem is that lots of the things that dissolve are excellent catalysts for H[2]O[2] breakdown. Many metal ions in particular are highly effective at very low concentrations. They are no doubt responsible for the terrible reputation of concentrated H[2]O[2]. There have been many accidental explosions involving H[2]O[2] over the years. I've been told, though, that if the tankage and plumbing is kept scrupulously free of such contaminants, H[2]O[2] can be handled with little more fuss than water.
So what we really have here is the “molecular barrier” problem again. We need to shield the H[2]O[2] molecules from the fuel until all is ready.
Now let's think about soap and detergents—"surfactants,” technically. Not as cleaning agents—as a way to make dispersed nanodrops of fuel. Surfactants have a long hydrocarbon tail and a “head” of some molecular group that likes to dissolve in water. In ordinary soaps that “hydrophilic” ("water-loving") end is a carboxylic group, COO-. Because of its negative charge it likes water, while the hydrocarbon tail ... well, it acts like a hydrocarbon. Oil and water are legendary for not mixing, after all. So soap molecules, when they find themselves in a water environment, try to arrange themselves so that their ionic heads are in the water and their hydrocarbon tails away from it. One thing they can do is form a film on the surface of the water, their hydrophilic heads poking into the water and their hydrocarbon tails sticking up into the air. Indeed, it's not hard to make surfactant films a molecule thick—an almost laughably low-tech approach to nanometer-scale structuring(7).
[FOOTNOTE 7: And yes, surfactants are getting a lotof attention as approaches to nanoscale fabrication.]
Or the surfactants can make little balls—"micelles"—withinthe solvent whose outer surface is formed by the hydrophilic heads, while all the hydrocarbon tails poke into the interior of the ball. This is how soaps and detergents work as cleaning agents—oily matter on the object to be cleaned ends up encapsulated in micelles and so can be washed away. A dispersion of micelles in an aqueous (or similar) solution is called an “emulsion,” by the way. They're vastly important both biologically and technologically.
So what about dispersing fuel into H[2]O[2] as an emulsion? We could even make the emulsion out of a high-tech, rocket-fuel surfactant, with its hydrocarbon tail containing triple bonds or cubane blocks or other energy-rich molecular groups.
One problem is the hydrophilic group, which is on the outside of the micelles and thus in direct contact with the H[2]O[2]. Obviously it mustn't react with H[2]O[2]. This rules out ordinary soaps, as their carboxylic heads wouldreact easily.
Detergents provide an alternative. Most detergents have a sulfur-oxygen group instead as the hydrophilic head—either a sulfate ester, such as the sodium laurel sulfate found in many shampoos, or a sulfonate, like the alkylbenzene sulfonates used in many detergents. (In sulfate esters, the sulfur atom is hooked to the hydrocarbon chain through an oxygen link; in sulfonates, sulfur is directly bonded to carbon.) Of course, in such cases sulfur would be another “deadweight spacer” atom, as it wouldn't contribute to the energy of the combustion, but since it's a small part of the overall molecular mass that probably isn't a big problem.
A bigger problem is mixing the emulsion into the H[2]O[2] in the first place without everything blowing up! Once the micelles are established they should be stable, but making them in the first place is a challenge. In water, you simply disperse the surfactant and the micelles form automatically, via self-assembly(8). That won't work in H[2]O[2]—the hydrocarbon “tails” will have lots of time to react before they can get tucked into the micelles. Somehow the micelles are going to have to be made elsewhere (in an aqueous solution?) and injected into the H[2]O[2].
[FOOTNOTE 8: Anotherset of techniques that's getting lots of attention for nanoscale fabrication.]
So we need yet more nanoengineering...
* * * *
Conclusion
Of course, better catalysts, nanoscale synthesis, and so on will have vastly more applications than just high-tech rocket fuel. So there are lots of other economic incentives to develop them—which is good, as I don't see rocket fuel as being nearly enough incentive by itself! It also means we probably don't need a Dedicated NASA Program or some such boondoggle.
Perhaps, in fact, all those old stories about the dedicated, eccentric inventor devising a new fuel in his back yard, with or without the assistance of his trusty sidekick and beautiful daughter, may not be so far off the mark after all....
Copyright (c) 2007 Stephen L. Gillett, Ph.D.
[Back to Table of Contents]
A BRIDGE IN TIME by JOSEPH P. MARTINO
Wherein ‘detour’ takes on a whole new meaning ...
The phone rang. He picked it up.
"Maintenance. Carson speaking."
"Tom, this is Sandy."
"Yeah, boss, what's up?"
"The grocery job finished?"
"Yeah. There was a bad module in the controller. I swapped it out. When I left, they were getting a shipment of fresh-picked apples from next October."
"Thanks for the tip. I'll stop and get some on the way home. Be sure to send the module to the lab. We need to find out what went wrong."
"Done already, boss."
"Good. Got another job for you."
"What this time? Another warehouse?"
"No. This is out on Highway 297, about ten miles west of town."
"What's the problem there?"
"I don't have details. We just got a call. We have two units at a bridge out there. I figured you'd be the best guy to tackle it."
"Thanks for the confidence, boss. I'm on my way."
* * * *
Highway 297 turned out to be a two-lane rural road that twisted and turned through alternate farm and woods. Carson finally reached a bridge.
This must be the place, he thought.
There was a sign beside the road:
BRIDGE CLOSED NIGHTLY 1 AM TO 2 AM.
Beyond the sign he could see one of the company's time gates, both doors raised so cars could drive right through. At the other end of the bridge another gate was visible, its doors also open.
A knot of people stood near the bridge ramp. He pulled off the road near the fence that blocked anyone from bypassing the time gates, and approached them.
A guy in a hard hat, he thought. Must be the construction foreman. A guy in a Highway Patrol uniform. A guy in plain clothes, who has “cop” written all over him. FBI maybe?
As he approached, he introduced himself. “I'm Tom Carson, with the Maintenance Division of Time Gates. You have
some kind of a problem here?"
The man in plain clothes said, “I'm FBI Special Agent Arthur Hamilton, with the Time Crime Division."
Bingo!
FBI held up a copy of the Wall Street Journal, folded so only the date was visible. The date was for three months ahead.
Hardhat chimed in. “We inspect the bridge every morning. One of my guys found this newspaper. We called the highway patrol."
The trooper spoke up. “The bridge is under our jurisdiction, but Time Crime isn't, so we called the FBI."
"And we called your company,” FBI added, “because there may be a flaw in your equipment."
"Look,” Carson said, “I'm used to working with time gates in warehouses. What's going on here?"
Hardhat spoke up. “Starting in just over two months, this bridge'll be closed. We'll tear it down and replace it. It's scheduled to be reopened eight months after that. We're trying something new. Instead of detouring people all over hell's half acre while the bridge is out, we're using your time gates. We shunt people down-time from when the bridge is out, let them cross here while the bridge is temporarily closed, then shunt them back up-time to where they came from. If it works here, we'll use it on bridges with more traffic."
"So that's why you're closing this bridge in the wee hours every morning?"
"You got it."
"But why not shunt them up-time, to when the new bridge is in?"
"This way we know the bridge is here,” Hardhat answered. “We can't be sure when the new bridge will be open. Might be construction delays. A flash flood might wipe out the bridge."
"Or terrorists might blow it up,” FBI added, “like they tried to do with that bridge up on I-70."
"But can't the highway department send back messages every day, confirming that the bridge is open?"
FBI frowned and shook his head. “Besides being illegal, it's a bad idea. With all that message traffic, no one could scan it all. It'd be too easy for someone to slip in something illegal. Stock prices. Horse race winners. Basketball scores. You name it."
"But groceries send messages all the time,” Carson protested.
"Not the same,” FBI said. “They don't use the time gates for messages. They place an order for future delivery, specifying a time and date. If it's a regular order, the supplier loads it on a truck. If it's for an out-of-season product, the supplier sends it through a time gate. No message traffic either up-time or down-time through the time gate."
"Okay, I see what's going on. But how do you protect against criminal activity here?"
Hardhat said, “We photograph every car, including the license plate, when it enters the time gate up-time. A computer stores the picture, along with the time and date it entered the up-time gate, and the time and date it was shunted to the bridge here. We take another picture here of every car that arrives from up-time, storing time and date. And likewise for when the car crosses the bridge and is shunted back up-time. Eventually we can match the records from now and up-time, if there's any questions."
"Do you video the car as it crosses the bridge?"
"No. Just a single photo."
"Then any of the cars could drop something off while they're crossing the bridge, couldn't they? And you wouldn't know it?"
Hardhat and FBI looked at each other.
"Looks like we have a hole in security,” FBI finally said.
"I'll have somebody check the bridge at two A.M. every morning,” Hardhat finally said.
"Okay,” FBI said, “but if anything more happens, we may need additional security."
"Right now,” Carson said, “I'll check both units, just in case something's wrong with them. But I think your problem is with the traffic, not with my equipment."
* * * *
The dew lay heavy on the grass. The sun, half a diameter above the horizon, shone red through the morning haze. Ahead of Carson, the crushed stone jogging track curved around some trees.
Carson held his head high, sucking huge drafts of cool morning air deep into his lungs. He was into his second mile. He had his second wind, his legs were swinging as regularly as a metronome, and endorphins were flooding his bloodstream. He felt on top of the world.
As he leaned into the turn, another runner, a woman, came out of a side trail. Her long blond ponytail swung in time with her pace.
Nice legs under those running shorts, he thought. And she's obviously got a jogging bra under that tank top.
The woman dropped back and fell in step with him.
"Mind if I run with you?” she asked. “I do better when I have someone pacing me."
"Not at all."
They ran in silence for a while, then between breaths she asked, “How far are you going?"
"Just over three more miles. That'll make five for me."
"Okay, I can stay with you that far. I usually stop at four miles."
"You ought to try for five some day."
"I'd either have to start earlier or be late for work."
"What's your job?"
"I'm a stock analyst. And yours?"
"Maintenance engineer for Time Gates, Inc."
"That sounds interesting. But engineering was always beyond me. I was good at numbers, but not at things."
They continued in silence until they finally reached the bathhouse.
The woman untied her ponytail and shook her head. Her hair cascaded down below her shoulder blades. “Time for a shower and then off to work,” she said. “Thanks for letting me run with you. The woman I've been running with was transferred out of town, and I've missed having someone to pace me."
He paused a moment, then said, “You want to try for five miles tomorrow?"
She cocked her head to one side, then said, “Okay, I will. By the way, I'm Jennifer Campbell.” She held out her hand.
He shook her hand. “I'm Tom Carson. I start running at five thirty."
"Good. I'll see you then."
* * * *
As Carson arrived at the bridge, Hardhat and FBI were already there.
"I got your call,” Carson said. “What's up?"
"We caught the guy who was throwing out newspapers,” FBI said. “We've had the place staked out the past three nights. Last night a car came through. It slowed in the middle of the bridge. The driver threw a copy of the Wall Street Journal over the side of the bridge. This time it went down into the ravine.
"There was a guy standing down there waiting for it. We caught him with the paper in his hands. We checked the license on the car. It's registered to the same guy who caught the paper. He was passing information down-time to himself. Open and shut case of time crime."
"So what'll happen to him?” Carson asked.
"Depends on whether he accepts a plea bargain,” FBI replied. “Minimum of five years in jail. Up to twenty-five years if he goes to trial."
"But if he's in jail, how can he throw a paper to himself?” Hardhat asked. “And if he doesn't throw a paper to himself, what's he guilty of?"
"Look,” Carson said. “Don't ask me to explain time travel paradoxes. All I do is fix the time gates when something goes wrong. Paradoxes are argued over at a much higher pay grade than mine."
"Doesn't matter,” FBI said. “The crime's already been committed when he receives information from up-time. Even if he can no longer send it to himself. Anyway,” he turned to Carson, “we're going to put nets on the sides of the bridge, so this can't happen again. We called you out here to make sure that whatever we do with the nets doesn't interfere with your time gates. Can you check that?"
"Sure. I have my instruments with me. Put up your nets and I'll run a set of diagnostics on the time gates."
* * * *
It took Carson three days to muster enough nerve to ask Jennifer for a date. As he picked her up at her apartment he asked, “Any preferences? Chinese? Mexican? Italian?"
She smiled. “Italian sounds good. I had egg rolls for lunch anyway."
"Fine. Franco's, down on Fifth Street, is one of
my favorite places."
After they had placed their orders, Carson said, “You told me you were a stock analyst. Just what's that?"
"I work for Consolidated Insurance. We underwrite almost any kind of insurance. Life, auto, fire, and so on."
"What's that got to do with stocks?"
"The premiums our policy holders pay don't fully cover the losses we have to pay out. Instead, we invest the policyholders’ money in stocks and bonds. The income from that allows us to reduce the premiums below the true actuarial value."
"Hmmm. I never thought about that. I just figured I paid money in, and if I had an accident or a fire I got some of it back."
"That's only partly true. You'd be paying in more if we didn't invest your money well. But what do you do with time gates?"
"Fix them when they go wrong."
"Does that happen often?"
"It doesn't happen often. Our failure rate isn't as low as, say, airliner jet engines, but it's much lower than that of the telephone system."
"What happens if someone gets caught going through a gate when something goes wrong?"
"That hasn't happened yet. We haven't lost even a shipment of apples, let alone a person. There are enough interlocks and safeties that if something does go wrong, the gates are supposed to shut down rather than shunt anything through.” He rapped his knuckles on the tabletop. “I hope they always work."
"This bridge-out thing you're working on. Doesn't that mean that somebody is in two places a once? Home, say, and also in a car on that bridge?"
"To my simple mind, it does. However, the quantum mechanics guys say all the atoms in the two people are in different states, so they're not really the same person. Same thing with cars or anything else."
He described the incident involving the Wall Street Journal. “There was a case where a guy was on the bridge and down below it at the same time. All I can say is, it seems to work."
Analog SFF, October 2007 Page 9
