It is important to note that this article and articles like it are written with the Ecumene in mind, and that the diversity of drives far exceeds what can be summarized here.
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Torch drives use some highly-efficient, high-thrust reaction drive to propel a spacecraft. The main downside of a torch drive is that it has no failsafe to prevent it from directing itself at an object and reaching extreme velocities, causing earthquakes or other disasters (and theoretically actual damage to the object itself, but in practice attempts at using torch drives to destroy large asteroids, planetoids, and planets have completely failed for one reason or another).
- Fusion drives use any of the various forms of a fusion reactor to heat and propel exhaust. They are largely hampered by their reliance on fuels, but many early militaries use them in abundance. There are many forms of fusion drive, but most require some form of large radiator to dissipate heat.
- Bomb drives are a weaker cousin to fusion drives. These drives use an uncontrolled fusion reaction- that is, a nuclear bomb- to propel a spacecraft. Several implementations of this exist, but most groups that discover this use of nuclear bombs resign themselves to developing a less horrifying drive to use. In common parlance, many non-bomb drives are referred to as bomb drives because they share the "feature" of extreme radioactivity.
Gravitic drives mess with gravity for huge returns.
- Wing drives are usually one of the first "clean" brachistochrone-capable drives, but the principles behind them are rather complex. Wing drives are mostly used for maneuvering in the modern day, because they work by "sailing" on the border between subspace and hyperspace. This border is strongly influenced by gravity, but crucially is three-dimensional- and such wing drives can "tack" to change direction and maneuver the spacecraft they're attached to. Larger wing drives can work in concert for direct travel, but most modern ships prefer to use many smaller ones.
- Impeller drives are rather simpler in principle than wing drives, but are more difficult to make function. Impellers "push off" from highly gravitic masses, and as such work best near them (although they work rather better than wing drives further out). This means that impellers are very good for going directly between two bodies, such that in-system cargo ships are often built with only two main engines- one facing forward, one facing rearward. They are difficult to make a proper orbit with, but the various solutions to that problem enable the G-Shuttle.
Reactionless drives technically include gravitic drives, but are more specifically any non-gravitic drive which does not produce exhaust and yet produces thrust. They are more difficult to produce than gravitic drives, but tend to have fewer "catches".
- Helical drives use a very specifically calibrated centrifuge to produce a spinning thrust vector that averages out to a unidirectional thrust. These drives are occasionally considered localized fakedrives solely by the principle of "they shouldn't work, but they do".
- Capture drives only work at extremely high speeds, and as such are often treated as engineering or scientific curiosities before they become available for use as a type of fakedrive. These exploit mass-altering relativistic effects to gain thrust.
- Broken drives are reverse developments of fakedrives. These drives either locally break the laws of physics (hence the name) or rely on arcane, barely-understood unconventional laws of physics. They are considerably more useful than many other forms of STL drives, but they wear out extremely quickly due to their odd effects.
- Alternative Space drives are any drive that produces or enters an alternative space where some method of FTL travel can be achieved.
Hyperspace drives include any faster than light drive that functions by entering hyperspace in a "ballistic" manner and using hyperspace's inherent properties to travel between two gravity wells. An object exiting hyperspace is automatically placed into a theoretically circular orbit around the target body (though this varies depending on distance and the presence of other masses). Hyperspace exits can occur in the same location as other dense matter- depending on the refinement of the drive this can mean a non-exit, a "bounce", or simply a "shunt" away from the interfering matter. Particulate matter, and other matter less dense than the arriving matter, will be displaced safely. In-system hyperspace travel is impractical- bounces are too common. Early hyperspace drives were heavily constrained by their slow travel speeds, meaning that where a drive's range extended it was counterbalanced by the difficulty of adding enough mass to sustain a ship's crew for the longer period of time required to travel that longer distance. This is why the Ecumene largely expanded along clusters and mains, even though its scout ships were able to follow traces- small-crew scouts could budget enough mass to sustain their crews without damaging another vital system.
- Hop-family drives (Hop drive, Skip drive, and Jump drive) are some of the first-developed faster than light technology. This style of drive functions via an entry into hyperspace starting at a gravitationally "flat" area within a gravity well and emerging in a similar area for the best results. This means that most safe hop-family drive usage requires the usage of high-power slower than light drives to make full trips in a timely fashion- the safest exit points are beyond most planets in a star system. Depending on the level of refinement of the drive, hop-family drives can take between a month to half a day per one light-year. Hop drives are only capable of "short" travel, up to 1.4 light years; skip drives 3.3 light years; and jump drives 5.6 light years.
- Leap-family drives (Leap drive, Bound drive) function by an almost opposite process to hop-family drives- instead of "positive" hyperspace, where massive objects produce gravity wells, in "negative" hyperspace they produce gravity peaks. Leap drives travel much like hop drives, but move from near a gravity peak to near a similar gravity peak. This means that leap-family drive spacecraft do not require large sublight engines, although these are easy enough to produce that most of them do anyway. Leap-family drives are generally slower than hop-family drives- they take between a month and a half to a day per one light-year. Leap drives have longer range than hop drives- leap drives proper are capable of traveling up to 7.9 light years due to the fact that a gravity peak takes up less linear "space" than a gravity well for the same mass, and bound drives are capable of traveling up to 9.2 light-years.
- Vault drives function as a synthesis of the principles behind leap- and hop-family drives. Before it proved possible, its method of operation was likely to rip apart any vessels attempting it- switching between positive and negative hyperspace mid-flight requires a partial hyperspace exit, which is extremely stressful in any place where a hyperspace exit would not normally be possible. Vault drives gimmick their hyperspace entry very precisely to provide the ability to travel from the "outskirts" of a gravity well to the "bottom" of another, or vice versa. Because of the precise gimmicking of the hyperspace entry, vault drives are also capable of travelling from a gas giant's gravity well within a system to the gravity well of a gas giant in another system, and as well are capable of travelling between systems by exploiting the unstable lagrange points of lower-mass worlds. Vault drives are intermediate in speed between equivalent hop and leap drives. Vault drives also use their gimmicking to travel up to 11.8 light years.
Subspace drives include any drive that functions by entering one of hyperspace's counter-volumes, subspace. Subspace has a different correlation to realspace than hyperspace- where in hyperspace gravity matters only for one's exit point, subspace is rather more navigable than hyperspace (attempts to replicate subspace navigation in hyperspace have mostly just resulted in the loss of the test vehicles). An object exiting subspace can use gravity to tune its exit trajectory, but if it attempts to exit on a course that intersects with (or, for the matter, starts within) a dense body of matter it will be violently shunted back into subspace. Speed in subspace is variable, but if a vessel transiting subspace goes too close to the limits (generally initially established as one-tenth lightspeed and eight hours per light-year, but these can be bent with time and effort) it will leave subspace (though this is often much safer than the equivalent exit in hyperspace). Subspace drives operate on wholly different principles from hyperspace drives, but are difficult to develop without the experience given by the use of hyperspace drives- such that in FTL research projects subspace is often initially discarded as a dead-end technology, with only brief periods of flight at just under one-tenth lightspeed possible before further development.
- Heave drive is one of the simplest forms of subspace drive. It is closely related to wing drive, and uses a similar gravitic maneuver mechanism to travel. However, because of the special properties of subspace heave drives can be entirely contained within the hull. Heave drives have a variable travel speed and distance due to the fact that they have a strong reliance on gravity. However, heave drives are one of the few faster than light drives available within a star system- and as such are commonly used for travelling long distances within star systems. Heave drives can manage speeds of between roughly half lightspeed to roughly seven hours per light-year for up to 13 light years.
- Sway drive is a subspace drive designed entirely with subspace in mind. It relies less heavily on gravity than heave drive, but can just as easily embrace it to perform maneuvers at extreme speed. The main advantage of sway drive is that it can maneuver, though this makes it more likely to drop into realspace. The speed of the sway drive is often coupled to that of the heave drive but is about 1.5 times slower, and its range is approximately 16 light years.
- Surge drive exploits the ability for a specially-modified subspace drive to move another object into subspace. If the "launching" craft is much larger than the "projectile", the subspace bubble that keeps the spacecraft real is likewise much larger. This means it is more stable- and as such a surge drive "projectile" can be launched in such a manner that it stays at the speed of eight hours per light-year for up to three-and-a-half light-years- a full Concord day. This means that the surge drive is often one of the fastest drives available, with the issue that before other drives catch up they can often only be established in already-inhabited systems or else only launch small payloads.
Bubble drives are any drive which produces a "bubble" of alternative space around a realspace object that is itself contained in realspace. Bubble drives can also be applied to alternative space, in which case the object is maintained by a bubble of realspace- this is how subspace drives function. Most alternative spaces, however, are amenable enough to life that bubble drives intended for those spaces can be considerably less complex.
- Warp drives are arguably the most famous type of bubble drive- they produce a bubble of space subject to heavy relativistic effects, then accelerate that bubble. This means that a speed that in realspace would be considerably below the speed of light will produce a bubble moving considerably above the speed of light. Warp drives require considerable refinement to travel at or beyond specific speeds- these are usually designated in intervals of five. The "warp five" barrier requires a second bubble to prevent the ship from tearing apart, with more arcane restrictions required for ever higher speeds. Some warp drives are designed to drop out of warp at a specific travel time, making them less complex.
- The Warp Drive, Derivation 17, requires an assortment of rare types of crystals- and not much else. The proper arrangement of these crystals produces a spherical warp bubble a few hundred metres across, and a prolonged period of time spent within a warp bubble of this type precipitates new crystals- making travel with this drive sustainable. There's just one problem: where these crystals exist, many of them will already be in the proper arrangement- requiring ships hoping to export this warp technology to hunt down chunks of asteroid containing the crystals, all travelling in random directions at varying FTL speeds.
- Real Space drives are any drive which functions entirely in realspace, with no alternative space needed. Some of these involve teleportation, others faking alternative space, some using a faster-than-light particle.
Teleportation drives are any drive which "skips over" portions of realspace without entering an alternative space.
- Stutter drives are any drive that uses many repeated teleports to travel. This category is quite diverse, even if only considered by the rates of teleportation that vary between drives.
- Transdimensional drives are one of the odder interpretations of a teleportation drive- instead of teleporting to a specific location, transdimensional drives attempt to route the teleportation through a known alternative space, such as hyperspace. This makes them considerably faster than normal teleportation drives, at the cost of destination fuzziness- transdimensional drives are most often aimed at a star's outer cometary cloud rather than at the star itself, because this makes them less likely to smack into the star proper. The standard transdimensional drive is instantaneous from an internal perspective, but takes several Concord days from an external perspective. Its maximum range is 24 light years, which it travels in 7 Concord days; half the distance requires 4 Concord days and 1/4th the distance requires 3. This means the most efficient use of the standard transdimensional drive is to travel long distances. Some transdimensional drives can travel further, but require dedicated computers to calculate the correct teleportation route- an uncomputed jump can travel at up to twice the speed, but may well leave the ship without any functioning FTL drives a hundred light-years away.
- Bogowarp is near-universally known as the oddest type of teleportation drive. Some refer to it as an unrefined variant of a transdimensional drive, but this isn't precisely true- it directs its teleportation ability elsewhere. This results in a drive that teleports to a random location in the universe, making it practically useless for any purpose. There is one known civilization that used bogowarp in large quantities- they outfitted an uncountable number of rocks and asteroids with bogowarp systems approximately half a million years ago, then sent them out. By sheer chance, two examples ended up near the same galaxy as the Ecumene, with one located in the Ecumene itself and another approximately one million light-years away. They made first contact 381 years ago, and once confirmation of first contact is recieved in 2400 years both will enter bogowarp again.
Tunnel drives are a major subfamily of teleportation drives, but are widespread enough to warrant their own grouping. They also function counter to some assumptions of standard teleportation drives.
- Ice Cube drives- so named for a famous metaphor used to describe them- are any drive which "melts" a spacecraft, teleports it, then "refreezes" it at the destination. This provides a major advantage over most teleportation drives- they are extremely fast and long-range, travelling at eight hours per light-year for up to twenty light-years. The downside of an Ice Cube drive is that the spacecraft needs to be of a "memorable" shape to refreeze without damage- usually this means looking like something out of a pre-starflight work of fiction ("winged", "nacelled", and "wedge" ships are common), but some progress has been made in using semi-malleable materials.
Railroad drives are a bridge between drives and gates/non-drives. Ordinarily this refers to drives that produce a concrete connection and then travel through it (especially when a prior deployment of a "track-layer" spacecraft is required to produce the connection), but may refer to other implementations.
- Beacon, Lighthouse, or Station drives are three terms for a closely related but quite large family of drives which function by increasing the range or speed of another interacting FTL drive. They are named such largely because the former type needs to be somewhat evenly spaced between destinations, often causing "station towns" to form nearby in the deep space environment where they exist. Technically, each drive can only function with one or two compatible drives- but most stations implementing these drives have large arrays of interactible drives to choose from. The first form of station drive produced often comes soon after the invention of the Surge drive- a "twist" in subspace produced by this drive can extend a surge drive's range without needing it to drop out of subspace, though a more refined variant can enable slightly faster speeds but require a premature stop-and-restart.
- Semi-reactionless drives use principles of gates, teleportation drives, and reactionless drives to produce a railroad drive. A semi-reactionless drive will "steal momentum" from nearby objects and then move using that stolen momentum. Ordinarily this produces an STL drive, but most also connect a fakedrive- allowing the semi-reactionless drive spacecraft to travel faster than light.
Fake drives are any drive which not only functions entirely in realspace, but also uses quirks of physical laws to travel. This can sometimes mean working similarly to a bubble drive by producing a bubble of altered space, but these are different from bubble drives in that the fakedrive bubble is permeable to objects not also using a fakedrive. This means fakedrive ships tend to require quite advanced deflection technology, or have complex multi-bubble arrangements.
Selective drives include any drive that is only capable of going between areas of space with certain characteristics, most often with a higher selectivity than "between lagrange points". Selective drives are special because they are the largest class of drive to violate the rule that no drive can move a spacecraft faster than 6 hours per light-year (though several other types, plus many ancient artifacts, are also capable of this). However, this comes with a catch- nearly all selective drives preferentially select further-away stars from the starting location, though this is often because said stars are the nearest stars that fit the drive's exacting specifications. The first activation of a standard selective drive causes it to "tune" itself with some characteristics of the system it is in, after which it will only go to similar systems. The saving grace of the selective drive is that most refined versions save a "log" of systems they have been to and can return to any of them. The other downside of selective drives is that they are difficult to make work with larger spacecraft, meaning that they are not very useful for inhabiting new places- just exploring. Many alien selective drives have been found, some programmed with networks of varied stars they can go to. Some even get around the restriction of size... but these are often hopelessly arcane and difficult to use. The holy grail of a drive scientist is a less selective selective drive- or more selective, to seek out rare phenomena.
Non-Drives and Gates:
Stargates are any artificial construct built to link two (or more) places in space. There are many types of stargate, often incompatible, but they most often share the limitation that an entering body must be of a specific size to fit.
Wormhole mouths are specific locations that connect to one other wormhole mouth, and are special because- with effort- they can be moved or bound to specific locations. Wormhole mouths are often found paired close together in deep space, but can travel through some types of FTL- making the "warp wormhole tug" a common feature of starfaring societies. Other wormholes connect parts of space that are very far apart, sometimes in an unstable manner- these can often be stabilized to produce two or more separate wormholes. Artificial wormholes are possible to create but difficult, and some theorize that the reason wormholes exist at all is due to an ancient alien civilization's efforts to produce a wormhole network.
Points are specific locations that happen to connect to another point of the same type some distance away. Points are immobile within a specific reference frame- some may be at a specific location in stationary orbit above an object, others at lagrange points, others at some defined distance from an object. This is not to say that they can be moved by outside effort like wormholes- all attempts at moving a planet to reposition its points have ended in failure. Most points require a "trigger" drive aboard the object travelling through to open them.
Indirect Drives aren't FTL or drives at all- they're installations designed to propel other craft to high speeds. These have varied designs, but most often use a LASER of some sort.
Discontiguous drives use a modified drive designed to put another craft into FTL safely. For hyperspace and bubble drives this is unsafe at best, but some subspace and railroad drives rely on it. Those are described in their respective sections- this section specifically describes those that do not belong to another category.