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Star Trek: Federation Propulsion Technology

Written: 1998.08.01
Last Revised: 1999.10.06

An aft view of the Enterprise-E
The impulse engines (red) and warp nacelles (blue) of the Enterprise-E

Impulse Drive

Impulse drive uses a fusion-powered low-level variant of warp drive to power the ship forward. This allows it to achieve high relativistic speeds in excess of 0.75c (TM pg. 75) although such speeds are normally not used and the TM suggests that combat incidents always occur at low sublight relative velocities. This is supported by the various onscreen combat incidents in the Star Trek canon- we never see any combat in Star Trek where the relative velocities of the combating ships are high (and by "high" I mean "relativistic", rather than fighter-plane speeds).

There is some debate as to whether Federation impulse drives must accelerate a starship in conventional space physics fashion, as opposed to simply initiating the space warpage that allows them to reach high relativistic speeds and bypassing the normal acceleration curve requirements. However, the original TNG TM explicitly stated that the old Ambassador class's acceleration was at least 10 km/s², and the new DS9 TM explicitly states that Bajoran impulse fighters are limited to 15,600 m/s acceleration (this is curious, since the units of acceleration are m/s² rather than m/s, but we can assume that when they say "maximum delta-v" they are actually referring to "maximum delta-v per second"). Impulse fighters can easily outmaneuver capital ships (as seen in "Sacrifice of Angels"), so this allows us to determine that capital ship acceleration is between 10 km/s² and 15 km/s².

The presence of a maximum acceleration limit indicates that impulse drives do require a finite amount of time to accelerate. Some Federation cultists have claimed that this is untrue because the helmsman announces that they are at full impulse almost immediately after the captain orders it, but that only indicates that their engines are at full power. It does not indicate any sort of speed. If the helmsman announced "we are at 0.8c" instead of "we are at full impulse" we might have some idea of its actual speed. But since the helmsman invariably states "we are at full impulse" we only know that the engines are at full power. No speed or acceleration information can be derived from this sort of incident. In conclusion, Federation capital-ship impulse drives appear to be capable of producing accelerations in excess of 1,000g but less than 1,500g.

The stated highly relativistic speeds of Federation starships are at odds with their slow observed speeds in planetary orbit, as seen in STG, "Way of the Warrior", "A Call to Arms", "Tears of the Prophets", and others. In all of those situations, higher speeds would have been useful, but for some reason, they were apparently unavailable. It is therefore surmised that their low-level warp drive, or so-called "mass-lightening effect" must suffer from reduced effectiveness in a planetary gravity well. This is logical because the use of "mass-lightening" technology in a planetary gravity well presents serious Conservation of Energy problems. These problems are briefly discussed in the SW Myths page. The problems with mass-lightening in a gravity well are consistent with the invariably slow speed of starships attempting to enter or leave orbit, although it would theoretically be possible to very quickly circumnavigate a fixed-altitude orbit without running into this problem because no change in gravitational potential energy would occur.


Thrusters use conventional action/reaction physics to drive a ship forward. They do not produce the speed or acceleration of impulse drives, but they appear to be used for combat maneuvering and docking maneuvers. It is possible that impulse drive doesn't allow sufficiently fast direction changes to be used alone in combat maneuvers. They appear to offer precision and flexibility of movement unavailable with the impulse engines- for instance, angled thrusters could theoretically rotate the ship about any chosen axis, which would be virtually impossible to accomplish with impulse engines.

Warp Drive

Warp drive uses a matter/antimatter-powered space-time continuum distortion process to drive a ship forward at many times the speed of light. The warp speed table is as follows (taken from the TNG TM and the Star Trek Encyclopedia):

Warp Factor

Speed in multiples of c



























The TM indicates that the propagation rate of subspace transmissions is "about sixty times faster than the fastest starship, either existing or predicted", and we know that Warp 8 is the highest warp factor that can be maintained for long cruising durations. Therefore, a ship attempting to cross a 120,000 light-year wide galaxy would have to be ready for a 117-year journey, to go from end to end. By dividing the speed of subspace by sixty, we find that the maximum speed of any starship is roughly 3333c. This is consistent with the pilot of Star Trek: Voyager where Captain Janeway said the Voyager would take 75 years to cover the 70,000 light year distance back to the Alpha Quadrant "at maximum warp."

It is noteworthy that in ST5, the Enterprise-A apparently traveled to the galactic core over a fairly short time duration (a few hours, or a few days). This would be a trip of many tens of thousands of light years, which would seem to suggest that the warp drive speed of the Enterprise-A is comparable to an Imperial warship using hyperdrive. However, this interpreted travel speed is completely inconsistent with every single episode of Voyager (which wouldn't even exist as a series if it weren't for the speed limitations of warp drive). Some Federation cultists have chosen to simply assume that ST5 is indicative of true warp speed, and that every other incident of poor speed is due to an anomalous condition. However, this is obviously a ludicrous assumption: if one incident contradicts literally hundreds of other incidents, then the one incident must be the anomaly. However, it still must be explained. There are a few possible explanations:

  1. Sybok knew of a wormhole that led to the galactic core from near their starting location. This wormhole must have been unstable, but it might have remained stationary long enough for Sybok to pass through and for the crew to return to Federation territory afterwards.

  2. Sybok might have been speaking figuratively when he said that they were headed toward the centre of the galaxy. Coruscant is invariably described as the centre of our galaxy and sometimes even the centre of the universe, yet it is thousands of light years away from the physical centre of the galaxy and extremely far from the centre of the universe. The "Great Barrier" that he spoke of was similar to the "Great Barrier" seen in TOS, which was actually at the outer edge of the galaxy. In fact, the physical appearance of the planet, and the barrier itself, indicated that it could not have been the centre of the galaxy. The small planet in ST5 bore no resemblance whatsoever to the massive collection of stellar matter, nebular gases, and antimatter fountains which have been observed at the centre of the Milky Way galaxy.

Regardless of which explanation we choose, it is clear that ST5 cannot be used as "proof" that every other film and episode in Star Trek history is incorrect in its portrayal of warp drive speed.

The Federation DS9 TM specifies that the maximum speed which can be maintained for as long as 12 hours is warp 9.9 for upgraded versions of the Galaxy-class and Nebula-class starships. Maximum 12-hour speeds are listed as warp 9.2 for the Miranda-class, warp 9.7 for the Norway-class and Saber-class, and speeds between warp 9.55 and 9.75 for various other sundry ship classes. Their fastest starship appears to be the Defiant-class, which is rated for a maximum of warp 9.982 for 12-hours. This represents a significant strategic advantage over other groups in the area such as the Romulans, Klingons, Cardassians, Jem'Hadar, etc. According to the DS9 TM, no starship from any of those groups has been observed exceeding warp 9.6.

Using this information, we can conclude that the average Federation, Romulan, Klingon, Cardassian, or Jem'Hadar warship is capable of approximately 2000c cruising speed, with high-end ships being capable of 3000c, and a handful of exceptional vessels being capable of roughly 6000c. This is, of course, insignificant compared to the speed of hyperdrive which ranges into the millions or tens of millions of times c, but it nevertheless represents a significant improvement over previous efforts from the Federation.


Warp drives can be disrupted by strong gravity fields. The gravity well of the Dyson sphere in Relics forced the Enterprise-D out of warp, even though its surface gravity level was no higher than Earth-normal gravity. This was seen when Starfleet officers boarded the derelict, unpowered USS Jenolan, where they were able to move about unimpeded even before they re-powered the ship's systems. This indicates that the intensity of the gravity well is not as important as its sheer size- a passing starship would be influenced by such a large gravity well for an unusually long duration, even though the gravity well is no more intense than a typical planetary gravity well.

Further evidence of warp drive vulnerability to gravity wells is seen in Once More Unto the Breach when Worf used an inverse graviton beam (an anti-gravity beam) to keep Jem'Hadar warships from going to warp. The technique was successful, so this indicates that Jem'Hadar warp drives can be prevented from functioning through the use of anti-gravity beams. It is reasonable to conclude that Romulan, Klingon, and Federation warp drives would be similarly affected, since all of the aforementioned warp drives appear to function on the same basic principles.

The enormous gravity-well projectors can be reversed to project anti-gravity beams in a manner similar to a standard Imperial repulsorlift drive, but on a larger scale (and a much larger scale than Worf's puny anti-graviton beam). In fact, this was actually done in Solo Command, when an interdictor reversed its gravity-well projectors to put a Victory-class Star Destroyer away. This means that Imperial interdictor cruisers can potentially be just as effective on warp-driven starships as they are on hyperdrive-equipped starships, regardless of whether reverse-polarity is actually required.


Federation propulsion technology is similar to Star Wars Imperial propulsion technology in sublight performance, but vastly inferior in superluminal performance. This confers a large strategic advantage to our forces; we can move and attack star systems at will, knowing that their forces cannot possibly intercept us or reach the target before we do.


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