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.

Hopper Drives

Hopper drives―more formally Morvan Drives (named after Dr. Andre Morvan, 2288 - 2336, who first hypothesized their feasibility) or antigraviton pulse generators―were the first working “FTL” engines created by humanity. The early prototypes appeared late in the 22nd century.

We've already described how gravity distorts space. This is true not only of normal gravity, generated by massive physical objects, but also true of large concentrations of antigraviton particles. Such concentrations very seldom occur in nature (see p. 52), but they can be created. A sufficiently large matter/antimatter reaction, taking place in space far removed from any strong gravity fields, will create a local and very temporary “space warp” in its immediate area.

To visualize how this fits in with the “dimpled sheet” analogy for space-time, imagine that space is a strong but very flexible rubber sheet covering a liquid medium. Drop a small but very heavy object on the sheet, and you will get a deep, narrow dimple in the sheet. Because the sheet is rubber, it will eventually return to its original position (or close to it), but because it's stretched over a liquid medium (scientists refer to this medium as “subspace,” and its existence is still highly theoretical), until the sheet returns to normal that medium will simultaneously try to flow into the “well” created by the dropped object. If the “well” is deep and narrow enough, the pressure of the liquid will actually cause the mouth of the well to close for an instant, allowing an object at the precise correct spot on the sheet to move instantly from one point to another via the closed-off mouth of the well. To “hop” across, as it were.

The hopper drive involves setting a powerful, but tightly focused matter-antimatter reaction, generating enough antigravitons to create a temporary space-time “well.” If a ship is correctly positioned at the very edge of the reaction's event horizon, it can hop across space instantaneously. This “warp” is localized, so the amount of space that can be crossed by it is strictly limited ― most hops involve a distance of 20% to 35% of a light-year.

Obviously, it takes many such hops to transit the distance between even relatively close stars. Nonetheless, the hopper ship can move across space at an average effective rate of up to 10 times the speed of light (that is, if two star systems are 10 light-years apart, an efficient hopper ship can move between them in about a year). Although hopper technology makes star travel possible, voyages still take a significant time in relation to the human lifespan. Therefore, hopper-ships are sometimes called “sloships”

Hopper drives are extremely dangerous. If the ship is positioned even a tiny fraction too close to the reaction, it will be “in the well” when the warp closes, confined with the full force of the reaction―which will certainly annihilate it down to the subatomic level. (This same principle is used offensively to create gravitic mines. Furthermore, the reaction must be triggered far from any large, gravity-generating objects. Otherwise, gravitic distortion from these objects will prevent the well ever closing at all, once again exposing the ship to the force of the reaction. (The safe distance from Sol system for a hop, for example, is about 1.25 times the outer limits of Pluto's orbit, assuming Pluto, Uranus and Neptune are all at points in their orbits well away from the chosen point.)

Hopper drives are “slow,” because time must pass between each hop. Hops can not be ventured less than 18 hours apart, and most captains will not try more than one per standard day. (Local conditions might delay hops much longer.) Lengthy intervals between hops are necessary because of the time it takes to place a reaction-charge and calculate the event horizon, because of the time needed for a ram scoop to generate the energy needed for a hop, but most importantly it's necessary because hops disturb space time. Once a hop takes place, both time and distance are necessary to get to a place where space is sufficiently “quiet” to hop again.

The earliest interstellar colonists and traders used hopper drives because that was the only technology they had. Today most star-traffic uses the less dangerous and more economical jump drive―hopper drives are reserved for explorer and deep-space patrol craft.

Jump Drives

The jump drive is the basic medium of modern interstellar commerce. It allows instantaneous transit between star systems. It is both safer and more powerful than the hopper drive, because it uses natural, stable jump points between the stars instead of creating dangerous and temporary local distortions in space-time―the “grooves” in space-time produced by powerful gravitational fields.

Not every jump point is useful. Since heavier objects naturally produce more jump lines, most jump lines run or between super-heavy stars, far too massive to support any sort of planetary system. (These stars, however, are often used as “way stations” on trips between systems.) One additional advantage that jump drives have over the hopper drive is that jump points often exist relatively near stars―jump points are typically far closer to the orbits of habitable planets than the nearest approach possible via hopper drive.

The jump drive is formally known as the “Akwende drive.” after Sheri Akwende, the discoverer of antigraviton drift. It is this drift that allows us to detect, locate and ultimately transit jump points. The first jump drives were created by Pilgrims about 150 years ago, but they kept its existence secret from the Confed government. The first working Confed prototype was installed on the Haile Selassie, which made a successful jump-transit from Sol to Polaris on 2588.315, returning on .323.

A jump-ship has three essential components. The first is an Akwende drive itself. The drive is usually mounted in the center of the ship, securely braced. The second is a set of fusion engines, for maneuvering to and from jump points. The third is a containment vessel of antiprotons, fuel for the antigraviton generator. Most large ships also carry the equipment to create more antiprotons and recharge the tank, but this isn't strictly necessary.

To begin a journey, the jump ship must first find the jump point. In settled systems, the jump points are carefully charted and tracked―a ship will know what section of space to search, but it must search nevertheless. To find a jump point, the drive is switched on at a very low level, producing a slow trickle of antigravitons. Sensing equipment around the edges of the drive determines where the antigravitons are leading. All jump ships are fitted with this equipment, but most civilian craft can only home in on jump points when they're already within a few hundred thousand kilometers (i.e., they have to know―very exactly, by the scale of interstellar space―where the jump point is before they can head for it.) Military or exploration vessels can plot jump points across many millions of kilometers.

Once the location of the point is determined, the ship starts its fusion engines and heads towards it. As the ship gets closer to jump point, the attraction of the antigravitons toward the point becomes stronger and stronger. When the ship is close enough to the point that the antigravitons can actually arrive at the point itself before decaying (a distance of about 500 meters), the jump drive starts to produce real thrust, though at this point that thrust is very small.

The ship stops at the edge of the jump area to get a precise bearing on the jump point, including its drift rate. It then kicks in the engines, gets as close as possible to the jump point, and activates the jump drive at full power. The high thrust provided by the jump drive drags the ship to the exact jump point. Once the source of the antigravitons coincides with the jump point, an antigraviton field is created with a roughly 500-meter radius. (The radius is a constant, based on the half-life of anti-gravitons.) If the intensity of this field is sufficient, based on the mass contained within the field and the speed with which that mass is moving, then everything in the field vanishes at the point of departure and arrives at the point of arrival, keeping all its original momentum.

All parts of the jump-ship must be subjected to roughly the same amount of antigraviton flux. Because of the short lifespan of these particles, this effectively translates into a maximum ship radius of about 500 meters. Since particles have a half-life, this radius is not fixed, and to a certain extent the power of the drive determines the radius of the sphere. Ships bigger in radius than 500 meters take vastly more power than ones smaller than this threshold. If a ship is too big for its antigraviton flux, then only the parts that are within the field complete the jump―meaning parts of the ship may be left behind, with potentially disastrous results.

Since thge speed of the ship affects the amount of antigravitons required to initiate the jump, a ship can reduce the jump's energy needs by carefully maneuvering to the exact location of the jump point, and matching vectors with the jump point's drift, before turning on the drive. This results in the minimum-energy jump for a given mass, but can take quite some time to achieve. However, for ships that are close to the maximum size, this is the safest way to make a jump.

Each jump draws energy out of the jump line used. This energy is proportional to the energy required to initiate the jump. Thus, a minimum-energy jump takes less energy out of the jump line. Reducing the energy of a jump line may make it connect to a new destination, or it may disconnect it entirely. When a ship attempts a jump that depletes the line's energy, it will either arrive at the wrong destination, or it will simply disappear. No one knows where ships that vanish this way go; they are presumed destroyed.

When a ship generates more antigraviton energy than it needs for the jump, the excess is dissipated in a burst of light and neutrinos at both ends of the jump. This burst is easily detectable from long range. If the ship takes time to calculate the exact amount of energy required, and is equipped with a “variable-flux engine,” it can make a “stealth” jump, eliminating the flash at both ends. Under normal circumstances, ships seldom bother with this; in fact, few civilian ships are even equipped with the gear necessary to calculate the antigraviton flux.

As has been mentioned several times, the jump takes no time at all, in either the frame of reference of the jump ship or that of an outside observer at either end. The only time required for jump travel is that of traveling to and from jump points.

Between Scylla and Charybdis

Ancient mariners told tales of a strait passage guarded by two mythical monsters. Scylla was a huge, many-headed monster that liked to pluck hapless sailors off the decks of their ship, while Charybdis was a great, all-devouring whirlpool. If you tried to navigate the straits to avoid the arms of Scylla, you would be sucked into the maw of Charybdis, while if you tried to sail around the whirlpool, you came within reach of the monster.

The modern Scylla and Charybdis don't guard some ancient Aegean trade route, they guard the final leg of the Ulysses corridor―the longest, and most dangerous, currently charted jump line, which stretches from the outer Sol system to the remote edge of Vega Sector. And they're not monsters of legend, they're two of the universe's most exotic natural phenomena.

In the remote out skirts of the Vega Sector not far from the Kilrathi border, Charybdis is actually the more normal of the two. It is a quasar, a rapidly expanding star that emits light as lasers, and the most spectacular light show in the known galaxy. Quasars and pulsars (i.e., rotating neutron stars) are notoriously prolific generators of jump points. Their agitated movements (the pulsar's rotation, the quasar's expansion) cause dramatic distortions in the space-time fabric, distortions that are the structural basis of a jump line.

The difference between a pulsar's jump points and a quasar's, is that the pulsar's are shifting constantly according to laws of quantum indeterminacy. Theoretically you can get to (or at least close to) anywhere in the universe from the pulsar. The drawback is that it's impossible to predict where you'll end up. (Pilgrim legends say that they had navigators who had the mystical power to jump pulsars, but most Confed scientists dismiss the accounts as simple myth.) Pulsar jump points also tend to appear at an inconvenient depth in the pulsar's massive gravity well.

A quasar, like Charybdis, also has thousands of distinct jump points, but they're more stable than a pulsar's. Once a quasar jump point comes into existence, it tends to remain in existence, and online to the same spot. This makes it theoretically possible to jump quasars, but that doesn't mean doing so is either safe or easy. Most stable jump points lie a convenient, sensible distance from the star that created them, and drift lazily about in a predictable fashion. Quasars, however, are constantly expanding. This has the effect of keeping their jump points dangerously near the corona of the star (and quasar coronas, with their constant laser emissions, are even less safe than the coronas of most stars). Also due to the quasar's rapid expansion, as well as to the sheer number of jump points around the star, the points tend to “jostle” each other constantly, making them hard to find and impossible to predict. It's a matter of historical record, however, that Pilgrims have jumped quasars, and Confed scientists are still trying to uncover the navigational secrets that made this possible.

As quasars go, Charybdis is not a particularly exceptional specimen. Its companion, however, is a true enigma. The Scylla anomaly is one of the most mysterious phenomenon in all of explored space, and it lies almost within reach (astronomically speaking) of humanity's birthplace, in the Oort cloud of Sol system, beyond the reaches of Pluto, where comets make their slow preparations for their long fall inward. Like one of the great monsters of horror fiction, Scylla is a Thing That Should Not Be. Scientists call it a “gravitic anomaly,” but that just explains what it does. Nobody knows what it really is.

Scylla is a compressed field of gravity as strong as the largest star. An object that dense, that close to the sun, should behave like a second, dark sun, turning Sol system into a binary star system (and ripping most of the system's planets and moons apart). However, Scylla has little if any effect on surrounding space (although some feel it may be responsible for the irregularity of Pluto's orbit). In fact, like the Scylla from myth, it's almost undetectable until you're already in its grip. Even if you are 100,000 kilometers from Scylla, you won't know it's there (unless you are looking with some extremely specialized equipment), but pass within 30,000 k of the beast and you'll be in her clutches, sucked down into the singularity at her core and reduced to your component sub-atomic particles.

Work-in-progress, expect frequent changes. Help and feedback is welcome. See discussion page.