Starship Drives

There are three basic types of modern starship drives:
Impulse drive is the standard motive system for slower-than-light manoeuvering 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.

-- From "Every Citizen's Guide to Practical Science", Practical Science, 1st Edtion, Terra, 2651.

Impulse Drives

Impulse, or fusion, drives are literally powered by the stars. Using simple hydrogen isotopes, impulse drives maintain a "hot fusion" reaction, similar to the fusion reaction in stars, that provides the energy needed to accelerate a spacecraft across interplanetary distances. While "cold fusion" and "hot fusion" technology had been around since the late 20th Century, it was not until the mid-21st Century that practical fusion engines were developed, culminating in the first fusion craft in 2032. Commissioned by the United Nations Solar Trust, and built by McDonnell-Douglas Engineering, the Sagan was launched from the L3 station in 2041, and flew a regular shuttle route between Luna, Mars, and Titan for the next 75 years before it was decommissioned. The Sagan is currently on display at the Spacefarer's Museum complex on Deimos. "Cold fusion" has conversely seen a different use, in the energy cells that power nearly all modern equipment.

While the power that fusion drives can generate is certainly a necessity for space travel, what really makes the fusion drive practical is the fuel that it requires. The hydrogen isotopes hydrogen, deuterium, and tritium are clean (helium is the end product of the fusion reaction), abundant, and easy to obtain in space, being the primary component of the solar winds of stars. Thus in order to refuel, a ship need only sweep up hydrogen as it travels through space. And the impulse drive is designed to do just that.

The impulse drive consists of two basic elements: the engine itself, and the ramscoop. The engine section consists of electromagnetic field generators, usually mounted at the stern of the ship. Hydrogen is released into the electromagnetic field created by these generators, where it is compressed with near-star force to create the "hot fusion" process. The energy released is then used to propel the ship, as well as provide power for the ship's systems, including life support, communications, weapons, and shields. In case of emergency, most ships also back up these critical systems with an array of standard cold-impulse cells. Large freighters and capital ships usually operate under a thrust of around one or two standard gravities, while light fighters and couriers can sustain thrusts of up to eight gravities.

The ramscoop section of the impulse drive is also composed of electromagnetic field generators -- on small ships, these are in fact the same generators as those used for the engine section. The generators project a ramscoop field, up to several kilometres around and ahead of the ship, which sweeps hydrogen gas into large intakes in the bow of the ship, where it is filtered and stored in the ship's fuel tanks. Because the amount of hydrogen swept into the tank is proportional to a ship's speed, a ship moving at high enough speeds can collect enough fuel to maintain its engines indefinitely. Thus a ship must use tanked fuel for acceleration, but once at speed it can rely on ramscoop intake for operation. Larger ships moving at moderate speeds actually sweep up more fuel than necessary, and so are able to refuel its tanks as it flies. On the other hand, smaller vessels usually run at a slight deficit, and must refuel periodically from a carrier or tanker.

One side effect of the ramscoop is drag, caused by the hydrogen collection itself. Because the amount of drag a ship experiences is also proportional to its speed, the drag in fact places a maximum on the speed at which a ship can travel, based on its thrust and size. For capital ships and bulky freighters, this maximum is around 150 kps; For fighters, it is around 500 kps or so. If a ship were to shut of its engines, it will slowly lose velocity, and will eventually come to a complete stop.

Because of the similarities in their basic design with impulse engines, ramscoops are able to offer an additional benefit in the form of "afterburners". This is especially good news for small crafts like fighters and racers, for which speed is a premium. In this mode of operation, the opening of the ramscoop field is reduced to decrease drag, and the hydrogen collected is routed past the ship rather than into the tanks. At the ship's stern, the ramscoop field captures and compresses the gas to fusion, acting like a second set of engines. The result is 50% more thrust and a nearly doubled top speed. However, because no fuel is being collected into the tanks, the ship will quickly run out of fuel if it runs with afterburners for too long. Of course, a ship can simply reduce the ramscoop field while maintaining normal thrust, thereby decreasing drag and increasing its top speed. However this comes at the cost of manoeuvrability. Because ships manoeuvre by manipulating the engines' fields to redirect the exhaust, a higher thrust requires a higher manoeuvering thrust. Thus ships only use reduced-scoop speeds when they do not expect to manoeuvre, such as when travelling between worlds.

Monopoles are used to generate the complex electromagnetic fields used by both impulse engines and ramscoops. Unlike regular magnets which have both north and south poles, monopoles only have one pole, which can be either north or south. Most monopoles are quite weak, and are mainly used like amplifiers to control and direct much larger fields created by standard electromagnets. The complexity of a ship dictates how many monopoles a ship needs, while its mass and size determines how powerful each monopole must be. Thus starfighters usually require thirty microgauss monopoles, cruisers or free traders require twelve milligauss monopoles, and large passenger liners require four centigauss monopoles. Because monopoles are an artifact left over from the Big Bang, they can no longer be created in the normal universe, making them a very valuable commodity, and the focus of much exploration outside of normal space routes.

Since the ramscoop is useful for powering ships at sublight speeds, a different kind of drive is needed for spacecrafts to traverse the huge distances involved in interstellar travel. Currently there are two types of drive in existence: the Hopper Drive and the Akwende Drive. Commonly mislabeled as "faster-than-light" drives -- since relativity does ensure that nothing can in fact travel faster than light -- these devices nevertheless achieve something just as incredible: the instantaneous transportation of a spacecraft from one point in space to another, more distant point. While the operation of these two drives differ in some respects, they both depend on knowledge of Gravitic Warp Theory.

Gravitic Warp Theory

The basis for Gravitic Warp was in fact discovered in 2214 by accident, during an attempt to solve the antigravity problem. During that time, antigravity vehicles worked not by diverting and channeling gravity, as modern devices do now, but by cancelling gravity, which had the unfortunate side-effect of causing sensations of weightlesness in antigrav vehicles. Since the Grand Unified Theory implies the existence of antigravitons -- counterpart particles to gravitons that carry repellant antigravitic forces, instead of attractive gravitic forces -- it was theorised that if enough antigravitons could be produced, one could generate a sufficiently large antigraviton flux that such antigrav vehicles would retain their weight, while possessing all the advantages of regular antigravity.

It was during one such effort to create an antigraviton flux that "Antigraviton Flow" was discovered. By this time it had been conclusively shown that antigravitons could be produced by colliding matter and antimatter in a suppressed gravity field. During the course of the experiment, it was discovered that the generated antigravitons showed a very slight tendency to move in a single direction. That direction changed within the course of a year, and when correlated with the position of the Earth, seemed to point in the rough direction of Alpha Centauri. Further study revealed that the exact position that the antigravitons were attracted to was a small patch of space between the orbits of Pluto and Neptune. However it would be several decades before the implications of Antigraviton Flow was fully understood and harnessed.

Currently much of Gravitic Warp Theory is still clouded in speculation, with three competing theories to explain the observed effects, each of which incidentally requires the suspension of a different fundamental law. But enough empirical research has been compiled that the effects can at least be described.

According to regular physics, all objects of appreciable mass exerts gravity on other objects. This gravitational field also happens to cause warps in space-time. Gravitic Warp Theory postulates the existence of an "antigraviton potential field", which a body of sufficient mass can generate. Such an antigraviton field is generated only if the body manages to exceed the "Olivarez Equilibrium Boundary", a theoretical threshold that determines if a body would actually possess an antigraviton potential at all. Below the Olivarez Equilibrium, a body will not be able to warp space sufficiently to have any antigraviton potential regardless of its mass; conversely once a body has surpassed the boundary point, it will generate an antigraviton field proportionate to the amount that its mass bends space-time. Antigraviton Tropic Anomalies or "Jump points", of which the patch of space between Neptune and Pluto is one example, exist at the very edge of the antigraviton field of an object, at a point between the centres of two antigraviton fields. If two bodies in space are close enough together that their antigraviton fields overlap, no jump point would exist between them. Masses with larger antigraviton potentials also exhibit more jump points than other less massive bodies.

Thus far the situation is fairly simplistic. What complicates the picture (and interstellar gravitic calculations) is the fact that the antigraviton potential of a particular body is influenced by the gravitic influence of all other bodies surrounding it. To put things in perspective, even the field of a star is affected to varying extents by such trivial masses as planets, comets, asteroids, even dust particles and gas molecules. Such influence depends both on the position of these bodies relative to the star, and their mass at each point in time. These bodies also influence the "path" of a jump line, often causing it to curve within space, so that a jump point would not necessarily lie strictly between the centres of two antigraviton fields. In addition, there also exists universal (or at least semi-universal) variations in the antigraviton fields of all bodies. All these factors affect both the size and shape of a star's antigraviton potential field, which in turn affect the size, location, and even the very existence, of all jump points. This is why jump buoys are necessary to both mark and continually track the existence and position of jump points, if only to expedite the jump process for a ship.

All this has a bearing on interstellar jumps. While the jump itself is instantaneous, ships need to spend time travelling between jump points, and getting to the exact location of a jump point. In addition, on occasion a phenomenon known as "equipotential eclipsing" can occur, where a third body interposes itself between two others, attracting a jump line to itself, and thereby creating a separate node along the jump line. Planetary bodies as small as Luna could cause just such an effect, causing a ship to revert to realspace prematurely. The ship will then have to realign itself to its new location, search for the second jump point to its original destination, and then jump again. Very rarely such eclipsing could be close enough or large enough to obliterate the jump line all together, so that a ship has no choice but to wait until the eclipsing ends.

Finally, a ship's journey along a jump line also causes its own gravitic effects on the jump line, thus affecting the jump conditions for ships following it; it's own jump conditions remain unperturbed. There have also been instances where a jump line has vanished during a ship's jump, causing the ship to completely disappear from realspace, into some as yet unknown dimension of space. Thus contrary to popular belief, jump travel is not safe, is in fact quite dangerous, even insanely so. It is only because jump pilots are extremely careful with jumps, that jump travel is even feasible at all.

Hopper Drives

Hopper Drives, more formally known as Morvan Drives (after Dr. Andre Morvan) or antigrviton pulse generators, are the first working "Faster-Than-Light" engines created by humanity. Invented in 2304, it gave humanity the means to finally engage in some practical form of interstellar travel and colonisation.

Hopper Drives take advantage of the space-time warping effect produced by large concentrations of gravitons and antigravitons. While large gravity wells abound in space, concentrations of antigraviton particles occur more rarely in nature. However, they can be created artificially with an appropriately large matter/antimatter reaction, taking place far from any significant source of gravity. A large enough concentration of antigraviton particles is capable of creating a local and very temporary "space warp" in its immediate area. If space-time is warped to a sufficient extent, a "well" in space-time is formed that for an instant can close in on itself -- an effect that is thought to be caused by pressure from "subspace", an as yet highly theoretical concept. A ship positioned at just the right location on the lip of this well could then "hop" across it before it opens up again, in effect traversing the distance of the well in an instant of time.

In order to accomplish this, a Hopper Drive sets off a powerful but tightly focused matter/antimatter reaction that generates enough antigravitons to create a temporary "well" in space-time. A ship correctly positioned on the edge of the well's event horizon would then be able to hop across space as the warp closes. Of course this in itself is an extremely dangerous manoeuvre. If the ship is positioned even a tiny fraction too close to the space-time well, it will be sucked in when the warp closes, and annihilated down to the subatomic level (This same principle is the basis for gravitic mines). In addition, the warp must be done far from other gravity sources, or else the gravity space-time well will never close, and the ship will again be exposed to the gravitational forces of the well. Note that the safe distance for a hop in the Sol system is around 1.25 times the aphelion of Pluto's orbit, assuming that Pluto, Uranus, and Neptune were far away from that point.

Since the Hopper Drive's space-time warp is quite localised, the distance actually traversed by the ship is typically around 0.2 to 0.35 of a light year. As a result, many hops are still required to travel between stars. However, an efficient hopper ship can maintain hopper rates of up to the equivalent 10 times the speed of light. Nevertheless, hopper travel is still quite slow as compared to jump travel, which is why hopper-ships have earned the nickname of "sloships". It does not help that one must allow at least 18 hours (some starship captains might even prefer a standard day) between consecutive hops, or even longer, depending on local gravitic conditions. Since a Hopper Drive causes warps in space-time itself, sufficient time and distance must be allowed to pass before space-time is stable enough to allow another warp. Besides which it also takes time to place a reactionary charge in the matter/antimatter reactor, calculate the event horizon, and collect enough ram scoop energy to fuel the hop.

During the early days of space travel, the Hopper Drive was the only practical means of traversing interstellar distances. Today most spacecraft use the safer and more economical Jump Drive, while the Hopper Drive is mainly used by explorer and deep-space patrol craft.

Jump Drives

Gravitic Warp Theory forms the basis for modern-day Jump Drives. Utilising the jump points of stars to instantaneously travel between them, jump drives are considered safer and more powerful than hopper drives despite the risks involved. Since jump drives rely on natural, more stable jump points relatively near stars, rather than creating dangerous and temporary local distortions in space-time, they allow in-system approaches closer to the orbits of habitable planets than do Hopper Drives, which can only be operated far from other gravity wells. Of course jump drive travel is restricted only to existing jump lines. Since heavier objects produce more jump lines, most jump lines run to or between super-heavy stars, which are incidentally usually too massive to support any sort of planetary system. They are however useful as transit points for travel between inhabited star systems.

The Jump Drive is formally known as the Akwende Drive, after Dr. Shari Akwende who invented it in 2588. The first working Confederation prototype was installed on the Haile Selassie, which made a successful jump-transit from Sol to Polaris on 2588.315, returning on 2588.323. Apart from the Akwende Drive itself, a jump ship must also have a containment vessel of antiprotons, the fuel for the antigraviton generator. Most large ships also have the equipment to create more antiprotons to refuel itself, though this is not strictly necessary.

In order to make a successful jump, a ship must first find the exact location of a jump point. In most explored systems, jump buoys are used to continuously mark and track the location of jump points. However the ship must still pinpoint for itself the precise location of the jump point in space. This it accomplishes by switching on its jump drive at a very low level, producing a slow trickle of antigravitons. Sensing equipment around the drive then track the drift of the antigravitons, and slowly discover the jump point's location. Most civilian craft can only home in on jump points when they're within a few hundred thousand kilometres of them; conversely, military and exploration vessels can plot jump points across many millions of kilometres.

Once a jump point has been properly located, the ship starts its fusion engines and heads toward it. As the ship gets closer to the jump point, the attraction of the antigravitons toward the point becomes stronger. At around 500 metres from the jump point, the ship is close enough that the antigravitons can actually arrive at the point itself before decaying, and the jump drive finally begins to produce real thrust from the antigraviton flow, albeit a very small amount (the 500-metre distance is more or less constant, based on the half-life of the antigravitons). At this point, 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 its engines to get 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 antigravitons coincides with the jump point, an antigraviton field is created. If the intensity of the field is sufficient based on the mass contained within the field and the speed at which the 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.

It should be noted that all parts of the jump-ship must be subjected to roughly the same amount of antigraviton flux. If a ship is too big for its antigraviton flux, then only the parts that are within the field will complete the jump, while the rest of the ship gets left behind, with disastrous results. Standard jump drives are capable of projecting an antigraviton field of around 500 metres in radius, based on the half-life of antigravitons. However, this radius is not fixed, and is somewhat dependent on the power of the drive itself. Larger capital ships require much more powerful jump drives. The most powerful drive every built was able to generate an antigraviton field of some 12000 metres, and was used in the 22000 metre long Kilrathi Dreadnought.

Since the 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 manoeuvering to the exact location of the jump point, and matching vectors with the jump point's drift, before turning on the drive. While this results in the minimum-energy jump for a given mass, it nevertheless takes quite some time to achieve. However, for ships that are almost as large as their antigraviton fields, this is the safest way to make a jump.

When a ship generates more antigraviton energy than it needs for the jump, the excess is dissipated in the now-familiar burst of light and neutrinos at both ends of the jump. Since this jump-burst is easily detectable even at long range, a ship can make a "stealth" jump by taking the time to calculate the exact amount of antigraviton energy needed for the jump, provided it is also equipped with a "variable-flux engine". Under normal conditions, ships seldom bother with this manoeuvre, and in fact very few civilian ships even possess the necessary equipment to calculate the antigraviton flux.

While jumps generally maintain a fairly good success record, there are many inherent risks which constantly remind us of its tenuous nature. Apart from the dangers of drifting jump lines and equipotential eclipsing, among others, one must also contend with the fact that each jump draws energy out of the jump line used. This energy is proportional to the energy required to initiate the jump. Most of the time the amount of energy reduced in the jump line is negligible, but in some rare cases it could be enough for the jump line to connect to a new destination, or even disconnect from realspace entirely. Ships unlucky enough to be caught in these type of disconnections simply disappear. No one really knows where those ships disappear to, and they are presumed destroyed.