Space Propulsion
Imperial Database > Space Propulsion

Article over the methods for space travel, propulsion and maneuvering.

Propulsion

Hyperdrive

The only known way to travel the vast distances between star systems at fast than light speeds. Hyperdrive is a very old invention, which is said to have been first developed (some rumours says bought from an alien race) by the Corellians, although a few other races developed it simultaneously. This was more than 25,000 years ago. It's invention lead to massive space exploration, human colonization and trade over the galaxy. The first hyperdrives were very slow compared with modern drives, but still fast enough to cover hundreds of light years in mere days or weeks.

Hyperspace is sometimes described as another dimension, sometimes as normal space, only viewed from a tachyonic (faster than light) perspective. In a sense, both these descriptions are correct. The only technological means to enter and exit hyperspace is with a functioning hyperdrive. Entering hyperspace is typically referred to as a "jump".

The speed of hyperdrive travel is without limit. Only two factors enter the equation which limits the actual speed with hyperdrive - one, how much energy you put into your hyperdrive (which also has an upper limit depending on the drive), two, navigational hazards. Every object in real space has a mass shadow in hyperspace. If you hit a star or an asteroid while travelling in hyperspace, you are gone. Fortunately, hyperdrives also have a built-in safety cut-out which activates if hyperwave sensors pick up something in your path, and drop you back into realspace, hopefully safe and well.

On the negative side, this means you are now in a location that you weren't expecting, so you will have to use your navigational computer (navicomp), to establish where you are and then plot a new course to a destination. What's worse is that sometimes this emergency break can have serious effects on your hyperdrive, and essentially burn it out. For this reason, and because no one wants to be stuck lightyears into deep space without a functioning hyperdrive, practically all spaceships larger than a one-man fighter also has a backup hyperdrive. A backup drive is inavariably much slower than the primary hyperdrive, because it will then use up less energy and is also smaller in mass to carry aboard, taking up less space on a small ship. A backup drive is also usually only good for one use, after which it needs to be serviced and recalibrated. Larger spaceships can afford larger and better backup drives, of course.

To recap, this means that your speed in hyperspace is limited by your hyperdrive's rating and how empty the space you travel is. This is where hyperdrive "routes" or "lanes" enter. There are long corridors over the galaxy with few objects to disturb hyperflight - along these routes, you can keep a much higher velocity than if you are simply jumping from system to system. For example, jumping directly from Coruscant to Tatooine with a class 1 hyperdrive would take 22 days and 14 hours, while you can jump from Coruscant to Dantooine in 19 hours, and from Dantooine to Tatooine it only takes 20 more hours, a total of less than 2 days compared to over 22 days. A class 2 drive would take twice the time for the same trip.

The other limit is your hyperdrive rating. A higher classed hyperdrive can handle more energy per jump and as a result you will travel faster. But higher classes of hyperdrives are typically also larger and more expensive. Smaller models exist, but are even more expensive. Development of modern hyperdrives means that even one-man ships can fit a class 1 hyperdrive, a feat practically unheard of only a few decades ago. Naturally you will use up more fuel the faster you go as well. Today's military standard is class 2, with a modernization program working towards class 1 for all military ships. Civilan ships usually have class 3 or slower. It is possible to obtain a faster drive with the proper licenses, but very fast ships are often suspected of being used in smuggling and other illegal activities, which may result in more often, and more thorough, customs checks.

Interdiction

A hyperdrive has safety cut-outs that prevents hyperflight while within a gravity well. Interdictors are ships that mounts gravity well projectors, capable of creating an artificial gravity well in space on command. These gravity wells vary between the mass shadow of a planet to that of a star.

Since interdictors prevent hyperspace flight, they are often used by military forces to stop enemy forces from escaping. They are also highly popular with the pirates that has them, since they can ambush a space lane and force merchant vessels out into realspace, where they can attack and sized their cargoes.

There are only three known ways of escaping an interdiction field (or real gravity well). The first way is to run on sublight propulsion until you are outside the gravitational field. The second is to override the hyperdrive's safety cut-outs, but this procedure is highly dangerous - you can end up anywhere in space, and quite likely with a ruined hyperdrive.

HIMS

The third way to escape an interdiction field is to employ a device known as HIMS, Hyperwave Inertial Momentum Sustainer. HIMS was invented by the human population of Bakura, and is so far only used by them. When the device detects a false mass shadow, such as that of an interdiction field, it cuts off the hyperdrive but immediately creates a static hyperwave bubble around the ship which keeps the ship within hyperspace. The bubble provides no thrust, but allows the ship to coast on momentum within hyperspace. Once the bubble runs out, the ship returns to real space. If the ship is still within an interdiction field, another generator immediately fires and creates a new bubble, and the procedure continue until HIMS runs out of bubble generators or the ship finds itself outside of the field. A ship with HIMS activated will appear to flicker in and out of realspace. After HIMS burns out, the ship must continue on sublight propulsion. It should be noted that most weapons cannot be used in hyperspace, which means that a ship within a hyperwave bubble is safe from turbolasers, ion cannons, lasers and common missiles.

Thruster

Since hyperdrives can't be used near a gravity well without considerable navigational risks, ships typically drop out of hyperspace in a system outside of any major gravy wells, and use sublight propulsion to take them the rest of the way to their destination. These sublight engines are known as thrusters. Nearly all thrusters are clean and effective ion engines, but there are a few alien and outdated designs that use chemical propulsion, which have dirty exhausts, are very noisy, and have very short range. But they have one advantage. Chemical thrusters are usually not radioactive, while ion engines give off a lightly radioactive exhaust. For this reason, the use of ion engines within a planerary atmosphere is prohibited on all major worlds (although some may allow a low output). One other use of chemical thrusters is as a means of stealth - while it is easy to detect the trails of a chemical thruster with spectroscopic analysis, most sensors are designed and set to detect the ubiqtous ion engines.

All thrusters can reach near lightspeed velocities given enough time and fuel. How long time it takes depends on their acceleration. Sublight acceleration is measured in MGLT, where 1 MGLT equals about 4000 km/s2. That is, for every second, the ship will increase its current relative speed by 4000 km/s. Typical sublight ratings go from 20 (very slow) to 100 (very fast), but both lower and higher ratings exists.

Repulsorlift

As previously mentioned, use of ion engines are prohibited within atmospheres. This means that spaceships can't land unless they have repulsorlifts. Another reason is that most ships are designed to fly vertically, with the thrusters at the rear. This means it doesn't have any thrusters on the underside, so it can't land (one notable exception is the Nebula-class Star Destroyer, which employs lateral thrusters). Repulsorlifts, however, can easily propel in any direction without any exhaust. It does so by anti-gravity manipulation. One side effect of this is that repulsorlfits can only be used in a gravity well, with something to push against - they can't be used for propulsion in deep space. The distance within you can use repulsorlifts is referred to as antigrav range, which is typically six planetary diameters (around 80000 km).

There are three main types of repulsorlifts. We are going to call these types stable, hovering, and flying. Stable repulsorlifts are designed to maintain a static altitude and a static position at all times. This is often used for landing platforms, sky cities and the like. Hovering repulsorlifts are very common on all forms of speeders. They allow minor change of altitude (often as little as 2 m) to traverse terrain fast, but are otherwise stable. Finally the flying type is built to go in any direction at any time. The drawback of the flying lift is that it's not nearly as stable as the other types, basically you lose stability for each type. Starships always use the flying repulsorlif to land and take off.

Another limitation of repulsorlifts is that they can generally not exceed the speed of sound, though a few high powered versions can barely do so. For this reason, racing swoop and other very fast vehicles have to use additional engines, jets or rockets.

Jet

The most common type of jet engine is the turbojet. Sometimes these are fitted on atmospheric fighter craft or racing vehicles such as podracers, swoops, and speeders, to achieve supersonic velocities. Jet engines use chemical fuel and have relatively dirty exhausts (and very noisy). Another type of jet is the more effective ramjet, which can only be started when you are already travelling at about 300 kph.

Rocket

Rocket engines are thrusters that rely on chemical propulsion just like jets, but rockets carry with them their own reaction mass (usually oxygen), and doesn't rely on air intakes like jets do. Therefore, rockets can also be used in deep space, although they are much slower than ion engines (which propels an ion stream at near lightspeed). Some civilizations with a technological level below galactic standard still use rockets for space propulsion.

Gravitic Engine

Unlike repulsors which use anti-gravity and rely on the presence of gravity, a gravitic drive projects an artificial gravity well outside the ship, which then "falls" into the "well" in space. To slow down, reverse, or change direction, you move the gravity well around the ship.

A gravitic drive cannot be used close to a planet - it would cause hazards and accidents on the surface, and it would also pull in objects towards the gravity well, which can be a hazard for the ship itself. It could however possibly be used at relatively low velocities at high altitude, so that the gravity "suck" doesn't get too powerful, and there are no objects to pull in. The problem may not be as large with smaller ships as well.

Because of its limitations, gravitic drives are generally not used. While one might think that a drive without exhaust would be very stealthy and as such have military applications, a strong gravity well is easily detected at great distances.

Maneuvering

Etheric Rudder

This is a term for a "space rudder". It consists of bending the ion streams from one or several engines with electromagnetic forcefields, so that the force will be applied in a different direction, even completely reversed for deacceleration (breaking). This is by far the most common way to maneuver a spacecraft. "Fire retro thrusters", usually means to reverse the ion stream of the main engines, as few ships are actually fitted with special retro thrusters.

Strike Foils

Strike foils, or S-foils for short, is a set of mechanical wings that can move. When they move, they can change such things as the gravitational centre of the spacecraft, the atmospheric profile, the weapons configuration, or position the thrusters for angled thrust, like a mechanical version of the etheric rudder. S-foils are common on many types of starfighters.

Stabilizer Fins

Are found on most small shuttles and fighters, and all atmosperic craft. Stabilizers help direct the air streams so the craft flies more stably in air. Stabilizers are often fixed and cannot move (though they may have to fold for landing), but some stabilizer fins are also designed to move (with the whole fin or partial fin) in order to help with atmospheric flight, as the moving fins can direct the air current around the craft. Fixed stabilizers are often called wings. Stabilizer fins sometimes have another function, since they would otherwise be useless when in space. For example, TIE fighter wing panels also function as radiators and solar power collectors.

Gyroscope

Small ships often have a gyroscope with which to rotate. A gyro consists of two balanced, rotating rings, one within the other. When they spin, they will transfer rotation in the opposite direction to the ship's hull. Spinning gyros also help to stabilize the craft if they are rotating at level, for example during atmospheric flight.

Maneuvering Thrusters

The same thing as regular thrusters, except these are located over several spots along the hull. Sometimes they can move to point in a specific direction before firing. Maneuvering thrusters are more precise than the etheric rudder, but not as powerful.