Relativistic robots and the feasibility of interstellar flight
The Valkyrie Antimatter Rocket
Begun at Brookhaven National Laboratory brainstorming sessions in 1984, Project Valkyrie, like the neutron telescope, dating the Shroud of Turin, exploring the Titanic, and most other ‘officially non-official projects,’ turned out to be, in explorer’s parlance, ‘the best bar in town.’
The subject of a 1986 American Association for the Advancement of Science symposium (‘Interstellar Travel and Communication’), Valkyrie papers tended to be filled with tongue-twisters – ‘matter-antihydrogen annihilation propulsion device’ – studded generously with equations.
Valkyrie’s chief designers were James Powell and Charles Pellegrino, with vital inputs from particle physicist Hiroshi Takahashi on the initial ‘water pulse’ engine design (60 bursts per second). Isaac Asimov (who is best remembered for his science fiction, but he was also a scientist and , at that, a brilliant theorist) corrected some serious errors in what became known later as the Asimov Array. In 1994, shortly before comet Shoemaker-Levy 9 struck Jupiter, Pierre Noyes joined Valkyrie from the Stanford Linear Accelerator facility. According to Pellegrino, when he and Powell worked together, they often finished each other’s sentences, leap-frogging ahead as if Charlie and Jim were not merely one-plus-one-equals-two, but as if a new entity were formed, larger than the sum of its parts: Charlie and Jim squared. What they had completed during those first two months of 1984 should have, according to some observers, taken a ‘normal’ team ten years. When Pierre Noyes joined, they were -all three together- cubed.
In what Pellegrino describes as ‘one of science’s more magical moments,’ sentences were spoken in but fragments and hand motions, and over the course of a single afternoon Valkyrie’s engine core was simplified enormously, and became steady burn, rather than pulse.
Two simpler, downscaled versions quickly emerged, the Mark II and the Mark I (neither of which can be discussed her in any great detail).
The ancestral Valkyrie, called Vasmir, is presently being developed independently (as a test engine with a conventional power source) at NASA’s Johnson Space Center. Like Valkyrie, Vasmir will propel charged particles at relativistic velocity through magnetic fields (‘ion propulsion’); but it will be powered in space by fission-electric reactors and, while putting Jupiter and Saturn only months away, and Mars only weeks from Earth, it will be practical for Solar System use only.
About 1997, following the advice of his professorr and mentor Edward I. Coher, who had said, ‘English is a perfectly respectable language. Why not use it?’ Pellegrino subsequently broke all the technical Valkyrie language down into a tribute to Star Trek’s creator, Gene Roddenberry:
Project Valkyrie: Making Star Trek Real
By Charles Pellegrino
The human race is a remarkable creature, one with great potential, and I hope that Star Trek has helped to show us what we can be if we believe in ourselves and our abilities.
– Gene Roddenberry
About the same time Gene Roddenberry was coming up with his idea for ‘a Wagon Train in space series,’ I was learning an important lesson in nuclear physics – or the thermonuclear inverse to the Golden Rule- call it what you will; and let me tell you something: I was scared to death.
I was eight years old, then, and the Cuban Missile Crisis was in full bloom. At P.S. 23, in Flushing, the teachers had given us dog tags, and one of those diabolical ‘bomb wardens’ seemed to delight in telling us that the dog tags could withstand very high temperatures, meaning that we would be identifiable among the dead if we misbehaved, and failed to duck and cover in time, and became carbonized shadows on the school walls.
My best friend at that time was a Cuban refugee named Carlos – who had seen half his family killed personally by Fidel Castro. And as we practiced our duck and cover skills in the halls of P.S. 23, a life-sized bronze statue of none other than Fidel Castro stood watch over us, stood beside the American Flag, near the principal’s office. It stood there because two of Castro’s nephews were attending the high school across the street. (Or something like that. Something strange.)
‘Castro is coming,’ my friend said. ‘He has big guns. Big guns and big bombs.’
What I will never forget, what I will take with me as long as I live, is how high and squeaky his voice became as he said it. I was only eight years old. And I was scared to death. And yet I laughed.
‘Who is laughing over there?’ shouted the teacher with the unhealthy interest in dog tag vaporization points.
I filed this away for future reference- RULE: There must be no laughing during a nuclear holocaust. And I began to believe that one probably had to go really, really nuts in order to become a grownup.
Into that nutty world (thank whatever gods my be) came Gene Roddenberry with his off-beat T.V. series. I remember having bad dreams (and even worse daydreams) about a day in the not too distant future when my grandmother’s granite tombstone would glow ghostly red under the firestorm, and I envied her for having grown old and died before she could become witness to the death of her entire civilization. I suspected that if any of my generation survived, our children would inherit a radioactive wilderness. And then came this visionary this Roddenberry showing us an alternate future in which Russians and Americans and other ‘modern day antagonists’ would live and work together in space, a future in which it was possible to believe that our civilization, if it was wise and paid attention, might not merely survive, but might actually excel.
Years later, Jim Powell, Hiroshi Takahashi (both of Brookhaven National Laboratory), Pierre Noyes (of the Stanford Linear Accelerator), and I had designed the world’s first practical antimatter rocket. Rather than flee the world of sub-atomic particles and high-energy physics. I ultimately embraced it. I think the hopeful future Gene Roddenberry pointed to had more than a bit to do with putting me on that path: and in homage to him, I gave some of the ship’s components names that were already familiar to viewers of Star Trek. Hence, the antihydrogen containment units became ‘antimatter pods.’
The Valkyrie, as our rocket is called, will have a maximum cruising speed of 92 percent lightspeed which is a nice speed at which to be traveling because the crew (a maximum of four to each spacecraft, though most likely two) will be aging at only one-third the rate of stay-at-home observers on Earth. While this can mean six years of back taxes for every two years of flight pay, it also means that the nearer stars will be reachable in travel times comparable to those already experienced by Charles Darwin aboard the Beagle, and by Charles Wayville aboard the H.M.S. Challenger.
At this time, we have seen no hints of a universe that will allow anything so large as a molecule of water to achieve lightspeed (the real-life equivalent of warp speed, at which light itself becomes ageless), and to survive the journey. But the fact remains that relativistic rockets – actual starships – can be built without having to climb over the hurdle of inventing a new physics. The Valkyries should be flying by the year 2070. If our civilization really is wise, and really does pay attention, then something very much like the voyages of discovery envisioned by Gene Roddenberry will begin in our lifetimes. We can build a future that anyone living today would be proud of. Human beings are perfectible, and I do believe we are moving (albeit slowly, albeit painfully) in that direction.
Now, about that starship. Let me show you how it is done, and why it should be done, and why the near future may be even more fantastical than most science fiction writers have imagined.
Until very recently, most scientists simply dismissed the notion that crewed spacecraft would ever be able to cover interstellar distances and return in a reasonable amount of time. To most people (even to scientists) the distance across the Atlantic Ocean, from New York to London, seems large. That’s nearly 6560 kilometers, but it can be traversed by a beam of light in just under one forty-sixth of a second. The ocean, for all its frightful majesty, reaches barely one-sixth of the way around the Earth’s almost 41,000 kilometer circumference. The distance from the Atlantic Ocean to the Sea of Tranquility on the moon is nearly ten times the circumference of the Earth, about 410,000 kilometers, or one-and-a-half seconds away at the speed of light. Mars, on its closest approach to Earth, is almost five light minutes away, or two hundred times the distance to the moon. The distance to the nearest star system, the Alpha Centauri trinary, is 41 trillion kilometers about four-and-a-half light years, or a half million times the distance to Mars. And that is the nearest star system.
As I write, a new generation of telescopes is revealing what the creator of Star Trek seemed to have known all along: Earth is not unique, for almost every star in the sky appears to be orbited by planets. Even if almost all of those planets are as lifeless as the sands of the moon and Mercury, then across the span of a galaxy 25000 times as wide as the distance separating Earth from Alpha Centauri, the existence of other Earthlike worlds is, given enough throws of the cosmic dice, statistically inevitable: and beyond our galaxy, at a distance only twenty times the diameter of the Milky Way; lies the Andromeda Galaxy – another island of 600 billion stars and beyond Andromeda, for more than eight billion light years, upward of 300 billion galaxies fill the visible universe. And that is the visible universe.
Take this, therefore, as a mathematical certainty: we are not alone.
And strangest of all to think that we may soon be able to go out there – to ‘go that away,’ and to finally answer the question, ‘Who goes there?’
Failing the discovery of something akin to ‘sub-space’ we will be forced to obey, in our exploration, the seemingly unbreakable laws of relativity – which gives us a universe limited by the speed of light. It is now, and probably forever shall be the case, that the universe, and we, must play within the bounds of the chessboard discovered by Albert Einstein.
Most of the equipment for the rocket itself can be assembled using today’s technology. Providing the fuel, however, becomes problematic. We would require an array of solar powered linear accelerators (‘atom smashers’) girdling the moon’s equator. Mega-engineering projects require, in their own turn, miniature self-replicating factories that draw building materials directly from the lunar soil. Current advances in robot technology teach us that we should be able to climb this technological hurdle by about 2040. The brains of ants and wasps, working far more efficiently than today’s chess champion computers, are already capable of performing all of the essential analyses and motions that make possible the production of self-replicating machines. Within those microscopic bundles of insect nerves lie the keys to a technological advance that will make very large lunar arrays (named Asimov Arrays, after the scientist/author who corrected a major mathematical error the week we invented them) as feasible and inexpensive as the cost of developing the first thirty machines which can then be sent to the construction site, somewhat like a viral infection.
(We can probably do this, and we probably should, but . . .)
Pierre Noyes, who worked with Freeman Dyson on Project Orion (an interplanetary ancestor of Valkyrie that utilized fission bombs), cautions that once humanity instills an antlike intelligence into its machines, mutations among their replicants and an evolutionary process far more rapid than anything the Earth has seen in biological organisms may commence. ‘We may be unable to prevent it,’ he says. ‘Try to imagine a million years of evolution taking place in very smart ants overnight.’
Why is it that science fiction doesn’t seem quite so strange anymore?
What makes it possible for the realities of scientific achievement (Valkyrie rockets) to catch up with the fiction (starships) is that Valkyrie is the ultralight of rockets, consisting mostly of naked magnetic coils and pods held together by tethers. Indeed, it can best be summed up as a kite (with magnetic field lines instead of paper sheets) that flies through space on a muon wind of its own creation. Earlier starship designs by space scientists Donald Goldsmith, Tobias Owen, and others yielded estimates that a journey to the nearest star would require 400 million tons of matter-antimatter fuel and would be barely capable of reaching ten percent lightspeed, leading to flight times of several decades. Such estimates arose from traditional rocket configurations (huge, reinforced towers, with engines welded to their feet), which resulted in prohibitively heavy, slow-moving vehicles. Thus did more than 99.7 percent of their mass become fuel. Our stripped down Valkyrie’s fuel stores (both matter and antimatter combined) are estimated at slightly less than half the mass of the rest of the spacecraft, or about one hundred tons.
The engine is simply a magnetic coil, which generates a magnetic field, against which particles from the matter-antimatter reaction zone are bounced. The magnetic field (and hence the coil), is propelled forward by the bounce. The coil then pulls the rest of the ship along on a string, much as a motorboat pulls a water skier. A pulling rather than a pushing engine eliminates most of the structural girders that would not only, by their mere existence, add unwarranted mass, but would multiply that mass many times over by their need for shields and cooling equipment, and by added fuel to push the added fuel . . . leading to a chain reaction of design complications. . .and to an engine that burns hotter, but which cannot afford to push the giant to even a significant fraction of lightspeed. By contrast to what has traditionally become known as the large, slow-moving ‘space ark’ approach to interstellar flight, Valkyrie becomes a low mass speedboat.
The primary propellant for Valkyrie, the antiproton, is not merely a figment of the science fiction writer’s imagination; though, as is often the case, science fiction writers seem to have discovered it long ahead of the scientists (Gene Roddenberry is the first person, to my knowledge, to have anticipated antimatter’s practically in spacecraft propulsion).
At this time, small numbers of antiprotons are routinely produced in physics experiments. In atomic accelerators, they are magnetically confined (or bottled), cooled, and stabilized by combination with antielectrons (called positrons), to produce antihydrogen atoms.
An antihydrogen atom is the antimatter twin of the more familiar hydrogen atom, but its electron (positron) is positively charged and its negatively charged proton (an antiproton) also has a charge opposite that of a normal hydrogen nucleus. Since matter and antimatter annihilate each other on contact, each converting 100 percent of its mass into energy and near-lightspeed particles (at which point even a tiny chip of protons can deliver a force equivalent to being struck by a New York City taxicab), and since each, on contact, releases enormous bursts of energy from literally microscopic amounts of propellant, one cannot simply fill a space shuttle’s tanks with several tons of liquid antihydrogen and let it slosh around inside (Note: this would be bad).
The only storage method that has a hope of working is solid antihydrogen, supercooled within one degree of absolute zero (within one Kelvin of –273 degrees C). At very low temperatures, antihydrogen condenses into ‘white flake,’ with an extremely low vaporization rate.
Particles of solid antihydrogen can be suspended and held away from the ‘pod’ walls by electrostatic forces and/or magnetism. Within 0.0005 degrees K., antihydrogen appears sufficiently stable to allow storage and mixture, as microscopic fuel wafers, with actual matter, and although this manner of storage was once considered as the basis for a potential engine design, visions of outward bound starships blossoming into red-shifting novae raised too many hairs on the backs of our necks and led us to decide: ‘Don’t go there.’ This, despite the fact that in 1984 we were discovering, to our surprise, that matter-antimatter reactants quickly flew apart, once the reaction began, making the reaction itself seemingly impossible to sustain.
An almost identical problem faced colleagues trying to sustain controlled fusion: it worked only if one wanted to create a short, powerful burst. The universe seems to delight in handing civilization such cruel jokes. Turning a new energy source into a bomb is easy, a no-brainer. If you want to build an engine, or an accident-proof reactor, you have to think a lot harder. Our problem led to a very complex Valkyrie Mark II engine design, in which micro-wafers had to be assembled from matter and antimatter immediately prior to use, then fired – up to sixty wafers per second – into a laser-warmed reaction zone. This led to a new problem, almost identical to one encountered by World War One aircraft engineers trying to figure out how best to fire bullets through the propeller of a plane without shooting off the propeller (except that antimatter multiplied this problem a hundred fold). As the engine grew more complex, so too did its safety systems, so too did its mass, meaning more fuel and more firings per second, meaning more complexity, and so on, and so on. Our physics was clearly leading us in the wrong direction.
By 1993, the Brookhaven National Laboratory Valkyrie sessions had led me and Jim Powell to a few items we had never intended to invent (two of which are described in various technical reports, and in the novels ‘Flying to Valhalla’ and ‘The Killing Star.’ Along the way, we were nicknamed ‘the Salvador Dali and Pablo Picasso of nukes.’ Then, in 1994, ‘Rembrandt’ asked if he could join us. Powell and I, when we worked together during a Valkyrie jam session, seemed to communicate in the kind of shortspeak often said to occur between identical twins. The result was not Jim plus Charles (one plus one) equals two – but, rather, ‘Jim and Charles squared.’ When Pierre Noyes joined the sessions, something even more magical occurred: We were cubed.
Cutting one another off in mid-sentence and completing our sentences for one another, we managed to simplify the Valkyrie’s antimatter core by a factor of a hundred, in a single afternoon. Along the way, Pierre began to wonder what would happen if we aimed the world’s most powerful laser directly into the path of gamma rays shooting out of a proton-antiproton reaction zone. When he went back to Stanford, the collision was arranged: photons of light (massless units which, while traveling at lightspeed, manifest simultaneously and self contradictorily as both particles and waves) collided with photons of light, their power sufficient to spin photons off as electrons and positrons. The world’s first absorbic reaction, the conversion of energy to matter, is no longer science fiction (oh, goody – another brave new bomb, if we are unwise, and fail to pay attention).
One result of ‘Dali, Picasso, and Rembrandt cubed’ has been the Valkyrie Mark III engine – about which we are finally able to release some details.
Mark III is quite simple, actually. Temperature regulation in the antimatter pods will control how fast or slow antihydrogen white flake is permitted to evaporate. As the evaporated antihydrogen leaves the magnetic bottle, and is guided toward the magnetic gun barrel of an atomic accelerator, the atoms are ionized and stripped of their positrons. The positrons are simply ejected into space (for, if allowed to react with electrons, they will produce powerful gamma rays while providing essentially zero thrust). The antiprotons are accelerated to approximately 750 kilometers per second, and when they arrive at the reaction zone, behave somewhat like slow relativistic bombs (mark this as an oxymoron, albeit an essential one). At this velocity, the antiprotons pass like ghosts through beryllium windows, hardly noticing that they have passed through anything at all. They detonate when they reach (‘and stick to’) the hydrogen nuclei behind the window (including deuterium, and possibly traces of tritium), and by carefully controlling the number of antiprotons reaching the hydrogen (by regulating evaporation rates in the antimatter pods), and hence controlling the temperature of the hydrogen target, the result becomes a finely tuned fusion reaction – in effect, an antimatter triggered hydrogen bomb that, instead of exploding, merely glows, at any rate one wants it to glow.
That glow is in fact a spray of (for our purposes) reasonably massive charged particles, among them helium nuclei. Just as the antiprotons shooting in through the beryllium window fail to notice that a container wall exists, any fusion products shooting out (at the still relatively slow velocity of 12 to 20 percent lightspeed), depart like beams of light exiting glass. The particles then bounce off the ship’s forward magnetic field, giving away their energy as thrust.
As the ship’s speedometer begins to climb above twelve to twenty percent the velocity of light, fusion ions, though more massive than the products of straightforward proton-antiproton annihilation, decline significantly in propulsion efficiency. To push the Valkyrie to a higher fraction of lightspeed, higher exhaust velocities are needed. At this point, the Mark III reaction mix depends less and less upon fusion, until ultimately it shifts purely to proton-antiproton pairing. At this point, the less efficient reaction (which sheds low mass particles at high speed), has become the more efficient reaction, if for no other reason than it is our only choice.
The reaction products, traveling at high relativistic speed (the speed we want to get our rockets up to) consist of elementary particles called mesons. Each meson has a mass intermediate between a proton and an electron. It is essentially a proton fragment gone so relativistic (read ballistic) that it is at once a particle and a wave, and some of its quarks and gluons have dispersed into the universe as energy (read, massless photons and neutrinos). The matter-antimatter spray produces three varieties, or ‘flavors,’ of pi-mesons.
1. Neutral pi-mesons comprise thirty percent of the proton-antiproton reaction products. They decay immediately into gamma rays.
2. Positively charged pi-mesons, traveling near the speed of light, decay into positively charged mu-mesons (muons) and neutrinos after flying, on average, only twenty-one meters. The muons last several microseconds (almost two kilometers) before decaying into positively charged electrons and neutrinos.
3. Negatively charged pi-mesons behave the same way positively charged ones do, except that the resulting muons and electrons are negatively charged.
The charged pions and muons are the particles we want, and preferably we want the innermost fringes of the engine’s magnetic field (or magnetic pusher plate) to reach within twenty-one meters of the reaction zone, so that it can steal whatever thrust the pions have to contribute before a significant fraction of them have decayed and shed some of their energy as useless neutrinos.
One reason for our ship being built from a tether system is that the engine sheds lethal doses of gamma rays. Riding an antimatter rocket is like riding a giant death ray bomb: you want to put as much distance as possible between yourself and the engine. Suspending the crew compartment, antimatter pods, and other major, radiation-sensitive elements on the end of a ten kilometer-long tether allows the engine to dissipate most of its rays directly into space, and shaves off many tons of shielding.
Further protection is gained by strapping a tiny block of (let us say) tungsten to the tether, about one hundred meters behind the matter-antimatter reaction zone. Gamma rays are attenuated by a factor of ten for every two centimeters of tungsten they pas through. Therefore, a block of tungsten twenty centimeters deep will reduce the gamma dose to anything behind it by a factor of ten to the tenth power. An important shielding advantage provided by a ten kilometer-long tether is that, by locating the tungsten shield one hundred times closer to the engine than the crew, the diameter of the shield need only be one-hundredth the diameter of the gamma ray shadow (or eclipse) we want to cast over and around the crew compartment. The weight of the shielding system then becomes trivial (except for a gamma “sky shine” effect, which can probably be handled by the crew compartment’s cosmic ray shielding, combined with clever placement of droplet coolant and water supplies).
Gamma rays will, however, knock atoms out of position in structures near the engine, making coils, tethers, and maintenance equipment stronger, yet brittle. This will probably require additional tungsten plugs and rings (called shadow shields, these gamma ray eclipsers are already being used in certain very advanced nuclear reactors). Another supplemental solution is to weave most structures residing within four kilometers of the engine from hundreds of filaments, heating them, one at a time, to several hundredths of a degree below their melting point. Gamma ray displacements in the wires are thus rearranged, and the atoms can reestablish their normal positions. (This “cure” is being made more practical by the development, in Japan, in 2002, of ‘smart titanium composites.”)
There appears to be nothing we can do, however, to prevent the occasional transmutations of atoms into other elements. Fly far enough with your engines burning at full throttle, and your ship will slowly turn into gold, plus lithium, arsenic, chlorine, and a lot of other elements that were not aboard when you left. These new substances will be concentrated around the antimatter reaction zone, and it is important to note that advanced composite materials already coming into existence dictate that Valkyrie, even at this early design stage, will be built mostly from ceramic and organic composite materials, rather than from metals.
It is likely that expanding knowledge of composites will be taken into account by the time relativistic spacecraft are actually being built, so that the ships will incorporate any transmuted elements into their filaments in a manner that ultimately results in structural improvements for vessels designed (by aid of sophisticated tether relays and robot technology) to essentially rebuild themselves as they fly. Exploiting what seems at first glance to be a disadvantage (transmutation) is simply a matter of anticipating the ‘disadvantage’ before you begin to build. It’s the disadvantages unforeseen ( the questions unasked) that threaten to jump up and pull you down.
Valkyrie’s tether system requires that elements of the ship be designed to climb ‘up’ and ‘down’ the lines, somewhat like elevators on tracks. There is an irony involved in this configuration. Our ‘inside-out’ rocket – with its engine ahead of the fuel tanks and its fuel tanks ahead of its payload – is nothing new. We have simply come full circle and rediscovered Robert Goddard’s original rocket configuration. Nor is the engine’s magnetic field nozzle an entirely new creation. It guides and focuses jets of subatomic particles in the same way that the tool of choice among microbiologists guides streams of electrons through magnetic lenses. Valkyrie, in essence, is little more than a glorified electron microscope.
Flying through space at a significant fraction of lightspeed is like looking down the barrel of a super particle collider. Even an isolated proton has a sting, and grains of sand begin to resemble torpedoes. Judging from what is presently known about interstellar space, such torpedoes will certainly by encountered, perhaps as frequently as once a day. Valkyrie does not have the Enterprise’s force shields, nor can we dump energy harmlessly into ‘subspace.’ Add to the interstellar dust problem, the fact that as energy from the engine (particularly gamma radiation) shines into the shadow shields and other ship components, the heat it deposits must be ejected.
Jim Powell and I have a system that can perform both services (particle shielding and heat shedding), at least during the acceleration and cruise phases of flight. We can dump intercepted engine heat into a fluid (chiefly organic material with metallic inclusions) and throw streams of hot droplets out ahead of the ship. The droplets radiate their heat load into space before the ship accelerates into and recaptures them in magnetic funnels for eventual re-use. These same, heat-shielding droplets will ionize most of the atoms they encounter by stripping off their electrons. The rocket itself then shunts the resulting shower of particles – protons and electrons – off to either side of its magnetic field, in much the same manner as a boat’s prow pushes aside water.
When an interstellar dust grain impacts against the droplet field, far ahead of the ship, the particles from which the grain is made simply behave as individual particles, ‘unaware’ that they are part of anything else. Hence, as dust penetrates the droplet, each proton, electron and neutron will scatter, their angle of scatter increasing as the particles pass through more and more droplets in their approach to Valkyrie’s magnetic field. We need only worry about neutrons or other uncharged particles that plunge through the magnetic field lines and impact the coil and other engine parts on the nose of the ship, where they will deposit heat – which we expel on a spray of reusable droplets.
One of the great advantages of a droplet shield is that it is consistently renewing itself. Put a dent in it, and the cavity is immediately filled by the outrushing spray.
Valkyrie is designed to carry a spare engine, located at the aft end of its ten-kilometer tether. The forward engine pulls the ship along during the acceleration phase of flight. It also fires during the cruise phase (with the ship essentially in a 92% C freefall), but only at one thousandth of a gravity, keeping the tether taut and permitting recapture of the forward-flying droplets. At the end of the cruise phase of flight, the crew compartment, antimatter pods and shadow shields are rearranged along the tether, and the aft engine begins its (months-long) deceleration burn. The spare provides a rescue capability, and eliminates the difficulty of swinging a ten-kilometer-long ship broadside to relativistic bombardment, in order to turn the engine around and fire in reverse.
At this stage, empty fuel pods, weighing several tons and no longer in use, will consume fuel if they are decelerated with the rest of the ship. Since new pods and return propellant (at least the matter component – which is in fact the lion’s share of the ship’s fuel reserve) can be manufactured and replaced at the destination solar system, the pods will be ground up into ultrafine dust and dumped overboard. At up to ninety-two percent the speed of light, the dust will fly ahead of the decelerating ship, exploding interstellar grains and clearing a temporary path. (Trajectory must be such that relativistic dust streams will dissipate and fly out of the galaxy without passing near stars and risking detonation in the atmospheres of planets.
This fist of relativistic dust is the first line of defense against particles encountered during final approach. With the aft engine firing into the direction of flight, fields of droplet spray will become useful only for expelling heat from the aft engine, because, along the tether, ‘up’ has now become ‘down,’ and the droplets can only be sprayed ‘up,’ behind the engine, where, traveling at uniform speed, they will fall back upon the decelerating ship. To shield against particles and grains ahead of the ship, ultrathin ‘umbrellas,’ made of organic polymers similar to Mylar and stacked thousands of layers deep, must be lowered into the direction of flight.
This is the second line of defense – against particles drifting into the ever-lengthening column of space between the ship and the ‘fist.’ The umbrellas will behave much like the droplet shield and, in like manner, they will be designed with rapid self-repair in mind.
During the cruise phase of flight, pseudogravity is produced by rotating the entire crew compartment (which is also the landing vehicle, with living accommodations approximately equal to a one bedroom apartment) on a harness (counterbalanced with supplies) to produce a force equivalent to one Earth gravity (or one g). The two-crew members (presumably husband and wife) will probably have to weigh in at or below 55 kilograms, in order to best endure the two g acceleration required to reach the 92 percent cruising speed, and then to decelerate down from it. Both the acceleration and deceleration phases of flight last for six months, as experienced by outside observers (slightly less for the crew: at 70 percent lightspeed, the crew are already aging nearly one third slower than the rest of the universe; at 92 percent c, they age only one day for every three days experienced on Earth).
This may sound grueling to some, but there are many people (myself included) who would be willing to make such journeys, to worlds we would already know (given the current rate of advance in long-range planetary observation) to be worth exploring. And, given an on-board storage capacity for the accumulated art, music, history, film and literature of our entire civilization, we will be traveling with luxuries Charles Darwin and the librarians of Alexandria would have envied.
And there you have it. In our lifetime: interstellar flight, Star Trek – call it what you will; and we shall have it too, if only we are wise, and pay attention.
There will be differences between the reality and the fiction, to be sure. Slower travel times? Almost certainly. Transporters? Not likely. But we may find that we are not troubled by Einstein and Hawking’s travel restrictions. Sometimes reality has a way of sneaking up on us and surpassing fiction. Gene Roddenberry imagined futuristic medical facilities that begin to look more familiar each passing year, yet he did not foresee how soon we would (Khan aside) reach the genetic frontier, where we have begun, now, to find hints that the aging process can be slowed significantly, perhaps stopped, perhaps even reversed. Jim Powell, my partner on the Valkyrie (and the man who first suggested turning my ‘clones-from-amber recipe’ into a dinosaur theme park), believes that there is not theoretical limit to how long humans can live. Even sooner, we may be able to artificially boost human intelligence. Power and peril. Promise and responsibility. This is the world we are coming to, and it is not for the timid.
I know of a place where the lava is water, and where lakes are gasoline. It orbits Saturn with tides that put the Bay of Fundy to shame. In a few years, we shall drop a flock of robot helicopters into its atmosphere.
I know of volcanically-warmed oceans, hidden beneath the ice of Endeladus and Europa, and we should not be shocked, when our robot submarines finally penetrate the ice, if we find crablike and fishlike creatures there.
I know of a bacterial consortium, interconnected by a circulatory system more than a city block long, that has begun, at a furious rate, to mine sulfur and iron from the Titanic’s hull plates, turning the ship’s minerals into the substance of biology, and turning the ship itself into one of the largest organisms on Earth (second only to the fungus that underlies a good part of Michigan). Through this strangest of all living fossils, we can look back across four billion years and see that the phenomenon we call multicellular life appears to have been pulled from a disarmingly simple bag of tricks, and we can look outward and outward from our Earth and see that the universe must be teeming with creatures that breathe and swim and perhaps even talk.
I know that electrons coursing through our neural grids make it possible to read these words. They are the basis of every thought we have, somehow producing a mind that, as it asks questions about the universe and designs computers to help answer them, feels quite separate from the nerve cells and electrons themselves. The electrons are working in our best interest, supposedly; but perhaps it is they, and not you, not me, who are really thinking about these words.
Maybe our bodies are little more than vessels serving their interests, and as we set forth to design increasingly advanced artificial brains (ancestors to Data, perhaps), it becomes possible to believe that the sine qua non of our existence is to build faster, less bulky, more mobile electron vessels, perhaps even to eventually clear the decks for them, as dinosaurs once cleared the decks for us.
I know of particles that appear to tunnel backward, over very short distances, through time; and beyond them I (or ‘merely’ the electrons in my head, trying to understand were they came from) have peered with Stephen Hawking, Sir Arthur C. Clarke and the Jesuit Mervin Fernando into the basement of the universe – peered beyond quarks, beyond gluons, to an absolute limit of smallness, at one million billion billionth of an inch. ‘Physics,’ the Jesuit said – ‘It is our destiny to know the universe.’ But . . . ‘I don’t think that physics tells us how to behave to our neighbors,’ the physicist replied. ‘Ah,’ quipped Arthur Clarke, ‘but physics may determine who our neighbors are and on what planets they live!’
I know of apparent paradoxes in the age and structure of the universe (hopefully more apparent than real) that have revived the idea of multiple quantum dimensions, and brought to life hypotheses about ‘quantum subspace’ and a ‘pretzel universe,’ in which light from a given object has so many different paths through which to reach us that it can propagate as multiple copies. If these paradoxes turn out not to be mere mathematical aberrations, then the universe may be smaller and stranger than we have been led to believe and, in principle, we could look out to the very edge of space and see our own solar system.
There are wonders, out there, of which you and I have scarcely begun to dream; and some of them are closer than you think.