Every Citizen's Guide to Practical Science
STARSHIP DRIVES
There are three basic types of modern starship drives. Impulse drive is the standard motive system for slower-than-light maneuvering for all star vehicles. The hopper drive is used to explore uncharted regions of space. The jump drive is used for instantaneous travel along pre-charted interstellar trade routes.
Impulse Drive
The earliest spacecraft were solid-propellant ballistic rockets. These behemoths needed tremendous quantities of fuel and were extremely limited in maneuverability. For space travel (even within a system) to become safe, practical and economical, a drive was needed that allowed a full range of maneuverability, used cheap, light and plentiful fuel, and could efficiently accelerate to speeds sufficient for regular inter-planetary travel. This need was answered by the developement of a practical fusion engine in the mid-21st century. Both “hot” and “cold” fusion had been used in power plants for the cities of Terra for several decades by the time the technology became efficient enough to produce the first fusion-propelled prototype space vehicles. The first fusion craft, the Sagan, was commissioned by the UN Solar Trust in 2032, built by McDonnell-Douglas engineering, and launched from the L3 station in 2041. The Sagan flew a regular shuttle route between Luna, Mars and Titan for almost 75 years before it was finally decommissioned. (The original Sagan currently stands on Deimos, as part of the Spacefarer's Museum complex.)
Fusion, or impulse, engines get much of their fuel from space itself, by sweeping up the gas that composes the “solar wind”produced by stars.
The impulse engine actually consists of two elements. The first is, of course, the engine itself. This consists of electromagnetic field generators, usually mounted at the stern of the ship. Hydrogen gas is released into the field created by these generators, where it is compressed with the force comparable to that in the center of a star. The compression creates “hot fusion,” the same process that creates and maintains stars. (This is related to, but very different from, the “cold fusion” used by the energy cells that power nearly all modern equipment.) That energy, in turn propels the spacecraft. Large freighters and battleships usually operate under a thrust of one, or at most two, standard gravities, while light fighters and couriers can sustain a thrust of up to 8G. This same fusion reaction also provides power for the ship's life support, communications, weapons, shields, and other systems. (Most ships, small and large, back up these peripheral systems with an array of standard cold-impulse cells, for emergency use.)
The second element of an impulse engine is the ramscoop. This also consists of electromagnetic field generators―in fact, small ships use the same generator to create both fields. The ramscoop field, projected for up to several kilometers around and ahead of the ship, sweeps hydrogen gas into large intakes in the bow of the ship, where it is filtered and stored in the ship's fuel tank. The faster a ship goes, the more fuel gets swept into the tank. At low speeds, the amount of fuel swept up is fairly insignificant. At high speeds, the fuel is enough to maintain the ship's engines indefinitely, without ever “dipping into” the tank. A ship must always use tanked fuel for acceleration but once at speed it can rely on ramscoop intake for operation. A very large ship moving at moderate speeds actually sweeps up more gas than it uses, and can recharge its tanks as it flies; small ships like fighters and shuttles usually run at a slight deficit, and must refuel from their carrier or a tanker.
One side affect of the ramscoop is drag―sweeping up the gas actually acts to slow down the ship. This drag increases the faster the ship goes, and must be countered by thrust. Thus, ships must have a maximum speed based on their thrust and size, and cannot accelerate beyond this speed. The maximum speed of a bulky freighter or a cap ship, for instance, is about 150 KPS; for a sleek fighter, it's up to 500 kps. When a ship shuts off its engines, it slowly loses headway.
Small ships like starfighters and racers, for whom speed is a premium, have “afterburners” that adjust the ramscoop field. The opening of the field is reduced, to reduce drag, and the gas is routed past the ship rather than into the tanks. At the stern, the ramscoop field captures and compresses the gas to fusion, acting like an extra set of engines. The result is 50% more thrust and a nearly doubled top speed. However, no fuel is being swept into the tanks―using afterburners rapidly depletes the small fuel tanks that fighters carry.
If a ship doesn't need to maneuver, it can reduce the size of the ramscoop field while maintaining normal thrust. This reduces drag and drastically increases the ship's maximum speed. However, ships maneuver by manipulating the engines' fields to redirect the exhaust. The higher the thrust (and therefore speed), the higher the maneuvering thrust required. Thus, ships only use reduced-scoop speeds when they do not expect to need to maneuver, such as when traveling between worlds. In this one respect, impulse-drive ships are much like the ancient “rockets” that proceeded them―for maximum speed and efficiency, they must plot out their course in advance, and head for it with a minimum of maneuvering.
The complex electromagnetic fields used by engines and ramscoops are created by “magnetic monopoles.” These are like regular magnets, except that where a normal magnet has two poles (north and south), a monopole has only one pole (either north or south). Most monopoles are very weak; they are used like amplifiers to control and redirect much larger fields produced by standard electromagnets. Monopoles are an artifact left over from the Big Bang, billions of years ago, and can no longer be created in the normal universe; they are thus a very valuable commodity, and the focus of much exploration outside the normal space routes.
The complexity of a ship determines how many monopoles are required; the mass and size of the ship determines how powerful each monopole must be. Thus, a starfighter requires thirty microgauss (30 millionths of a a gauss) monopoles; a cruiser or free trader needs a dozen milligauss (12 thousandths of a gauss) monopoles; a large passenger liner requires four centigauss (four 100ths of a gauss) monopoles.
Gravitic Warp Theory
Hopper and jump drives are still popularly referred to as faster-than-light (FTL) drives, but this is a misnomer. As Einstein predicted, it remains impossible for an object made of normal matter to accelerate beyond the speed of light in this universe. However, gravitic warping―the principle behind both the hopper and the jump drive―makes possible something that's even more incredible . . . the instantaneous transition of matter from one point in the universe to another, far different point.
The Grand Unified Theory, perfected in the late 2000s, led to the development of antigravity vehicles. Unlike modern “antigravity” vehicles, which simply divert and channel gravity, these vehicles actually negated gravity, by projecting a field in which the gravitic mass of every particle was suppressed. This meant that the occupants of the vehicle were weightless, and thus subject to all the inconveniences and discomforts that condition causes. Naturally, there was immense commercial pressure to develop a more comfortable alternative.
In 2214, Dr. Shari Akwende, a subatomic engineer working for Aerospatiale Afrique, was searching for a solution to that exact problem. The Grand Unified Theory implied the existence of antigravitons, counterparts to the gravitons that carried the gravitic force. These antigravitons have half-lives of many microseconds―very short in “real-world” terms, but quite long in the subatomic field. Like many researchers of the time, Akwende assumed that generating a sufficient constant antigraviton flux would push something away, in the same way that graviton flux pulled things toward the generator. This would result in vehicles that were no more weightless than 20th-century airplanes, but that retained all the advantages of antigravity.
Akwende had already made a significant advance, putting her years ahead of competition. She had conclusivelyh determined that matter-antimatter collisions conducted in a suppressed gravity field would produce antigravitons. But so far, her antigraviton generator had produced no thrust whatsoever, in spite of generating what was, in theory, a large enough flux. In the course of trying to detect any thrust at all, Akwende discovered that the antigravitons showed a very slight tendency to head in a single direction. That direction changed over the course of the year, and when correlated with Earth's motion, pointed in the rough direction of Alpha Centauri. Repeating the experiments on an early Plutonian flight enabled Akwende to triangulate on the exact point in space, a small patch between the orbits of Pluto and Neptune, where the antigravitons were heading. It would be several decades before the ability to produce antigravitons would bear fruit, and centuries befor the implications of Akwende's “antigraviton flow” would be realized.
Even today, only a small fraction of the gravitic warp theory is truly understood. There are three competing theories, each of which requires the suspension of a different fundamental law. However, a large body of empirical research has been compiled, and the effect can be described, if not understood. The basic concepts of gravitic warping are usually described as follows.
Stretch a large cloth, like a bedspread, tight. Now put two rocks on it, some distance apart. You'll notice that each rock is sitting at the bottom of a deep dimple in the sheet. If they're close enough together, the two dimples intersect, with a saddle-shaped “ridge” in between them. If you put a marble next to one of the rocks and push it hard enough toward the other one, it will roll up out of the dimple, across the ridge, and down into the other dimple, winding up next to the second rock.
Take the whole assembly and start lowering it into a pool, keeping the cloth stretched tight. Stop when the two rocks are just covered in water. Everything is the same, except that the water slows down the marble, and it becomes much harder to push it up out of the dimples. So, to repeat the marble trick, you'll have to start with the marble out of the water, but still on a line between the two rocks.
Replace the bedspread with deep space, the rocks with stars and the marble with a starship, and you've got a fairly good model of jump travel. The pool is the “antigraviton potential field,” and the water level the “Olivarez equilibrium boundary,” but we'll call it sea level.
Remember that we've replaced the imaginary two-dimensional bedspread with three-dimensional space. Those of us trapped inside that space view it as flat. So rather than seeing “sea level” as some line above our heads, we see it as a sphere enclosing each star at a constant radius. (To picture this, take the bedspread out of the water and take the rocks away. You've got two large wet circles.) If we draw a line from one star to another, we'll find the jump points at the precise intersections of the “sea level” sphere and that line.
Or at least we would, if space had just two stars. But even this one galaxy has billions of stars, and nearly every star has planets, and the gaps between the stars are filled with gas and dust and rocks. Every single piece of matter, right down to a single gas molecule, makes its own dimple in the bedspread―and every piece of matter is moving, so the dimples wander around. What that means is that the line between the two stars is not precisely straight, nor is it constant or even predictable. So the intersections of that line and sea level move around. Plus, sea level isn't constant―the planets have their own, moving dimples that make the sea-level sphere irregular. There's even evidence pointing to the existence of “tides” in the antigraviton sea, adding to the variation in sea level.
Back to our bedspread. The closer together the two rocks are, the closer to the water the ridge is. In fact, if the rocks are heavy enough, and close enough together, the ridge will be underwater. No jump line. On the other hand, if the rocks are light enough, they won't dip into the water at all. Again, no jump line.
This is a place where the analogy breaks down a little. The marble views the water as nothing but a hindrance. The jump ship, however, needs the antigraviton potential―it needs the exact right amount, not too much or too little. That's why the big stars have more jump points than the small ones―they dig deeper into the antigraviton well.
Now we'll mix metaphors. If something large enough to dip below sea level passes between two stations, it sets up a new station. Jump ships will find themselves arriving at an unexpected destination and having to survey out the second jump point to continue. This is why jump flights are occasionally delayed―the jumps themselves are still instantaneous, but the ship has to take time at the “transfer station.” If the intervening body is too close to one of the stations for a jump line, then the jump ship has no choice but to return to port and wait until the “weather” clears.
This phenomenon, called "equipotential eclipsing," happens more frequently than one might expect, since jump lines aren't straight. The lines can twist every which way, following the contours of space. Bodies heavy enough to eclipse a jump line―and something as small as Luna can do it―are also heavy enough to attract the line toward themselves.
Let's change the bedspread a little. Make it out of plastic instead of cloth. Now it returns to its normal flat condition more slowly. When we roll a marble across a ridge, the marble makes its own dimple as it moves. The bedspread takes time to resume its normal shape after the marble has passed.
Our marble analogy has one major flaw. A jump ship doesn't actually move. It doesn't cross the intervening space the way the marble rolls across the ridge. The ridge line is a physical thing that the marble follows. The jump line is a fictional construct that helps us predict where (and whether!) the jump ship will arrive. The passage of the marble warps the bedspread behind it; thus, the marble has no effect on its own journey, but only on the journeys of marbles that attempt to follow it. A jump ship's journey, however, is instantaneous. There is no “before” or “after”―the ship warps the jump line, and if the line shifts its endpoint, then that endpoint is where the ship reappears. And if the line vanishes altogether, then so does the ship.
Jump ships are safe because jump pilots are careful, not because jump travel itself is safe. Quite the contrary, jump travel is almost insanely dangerous. The speed of light is one of the universe's most fundamental physical laws, and it only barely tolerates our violating it. If we push against the limits of jump travel even slightly, we are immediately punished for our temerity.
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