Star Trek Technical Commentaries

Starship Defenses and Propulsion

The defense field, sometimes described as 'conformal shielding', involves (in its modern form) the replication and projection of a coil of high-strength alloy as an energy layer beyond the ship's outer hull, which in effect became an invisible (and sensor-transparent) layer of armor (the ablative armor generator seen in "Endgame" [VOY] is a variant of this technology). Advances in weaponry and defensive grid technology eventually relegated defense fields to the status of a tertiary line of defense - one that could be raised to full defensive configuration without the calling of a Red Alert or the signaling of hostilities. ("The Wrath of Khan") Nonetheless, as the most adaptive-resistant of the defensive grid's components, the defense field continues to be an important part of a starship's defenses - during the Dominion War, Allied starships were often forced to rely on their defense fields as their primary means of protection against the shield-penetrating Jem'Hadar phased polaron beams.

The deflector screen, often referred to as 'deflectors' or 'screens' ("The Motion Picture"), is projected in a hull-conformal field similar to that of the defense field, albeit in a manner much further away from the hull and less following of the vehicle's form. Consequently, the deflector provides much greater protection than the defense field, though it is more vulnerable to ECCM. During the 23rd century, it was not possible to operate transporters through raised deflector screens ("A Taste of Armageddon" [TOS]) - but by 2364, deflector and transporter technology had advanced to the point where starships could routinely do so, even under less-than-ideal conditions. ("The Arsenal of Freedom" [TNG])

The forcefield shield, alternately known as 'forcefields' and 'shields' ("The Motion Picture"), is the 'bubble shield' that modern Starfleet starships are well known for. It offers the greatest amount of protection against kinetic energy and known weapon attacks - but the simplicity of its geometry also renders it the most easily neutralized by ECCM, and (with the exception of the Sovereign-class starships) the magnitude of its spatial distortion effects prohibits the use of transporters while in defensive configuration. ("The Arsenal of Freedom" [TNG])

The ablative armor generator represents a parallel development of the defense fields that have played a role in protecting Starfleet starships for over a century. (Indeed, just as with transphasic photon torpedoes, the ablative armor generator was almost ready to be fielded by Starfleet when the captain of the USS Voyager used this technology to survive her chosen means of returning to Earth in December 2377.) However, instead of generating a hull-conforming field of energy that behaves as an invisible metal shell, the ablative armor generator materializes a shell of multilayer ablative armor around the vehicle through external emitters that incorporate both replicator and transporter technology. While the generated shell is actually no stronger than the ship's defense fields in terms of its instantaneous directed kinetic energy capacity, the solid armor shell avoids the Achilles heel of frequency windows that are a necessary part of energy-based defensive grids, making the armor particularly efficient in defeating Borg adaptive weapons. In addition, the transient nature of the armor shell enables its generators to repair damage sustained by the shell with relative ease, much as the emitters of a depleted defensive grid can be recharged.

Its successful use by the crew of the Voyager in surviving their journey to Earth in 2377 aside, however, the armor generator concept also has numerous operational shortcomings - many of them inherent - that precludes its replacing of the traditional defensive grid for the foreseeable future. The armor generators are not only significantly less durable and shock resistant than those of a defensive grid, but the former also requires seconds to charge its generators and deploy the shell (as opposed to the microseconds of defensive grids), and thus vehicles equipped with armor generators still require defensive grids in order to ward off weapons fire from surprise attacks. In addition, the armor shell's very lack of a frequency window that prevents Borg adaptation to it also requires that significant physical gaps be opened in the shell when the starship's crew wishes to use active sensors, weapons, transporters, and navigational deflectors. Furthermore, while the shell is deployed, the ship is unable to utilize its defensive grid altogether, making a ship with its armor deployed significantly more vulnerable against a conventional Threat force than if it were to energize its defensive grid instead - especially in the case of Federation warships, which already have permanent installations of ablative armor and extremely powerful automodulating defensive grids (which renders the armor shell's lack of frequency windows redundant). Even the long-term viability of the armor generator in Borg suppression missions is open to question, given that the system installed on Voyager nearly failed under even a significantly understrength Borg attack despite the system having been installed with the assistance of one of its designers. As such, the introduction of ablative armor generator technology - from both Voyager and Starfleet R&&D - is unlikely to significantly alter the nature of interstellar naval combat or the balance of power in the Milky Way, especially given the assimilation of the technology by the Borg Collective.

Note: I am aware that the ablative armor generator was intended by TPTB to be futuristic technology well beyond anything Starfleet had c. 2377. However, the armor's relatively poor performance against the weapons of the small (only twice Voyager's length on a side as opposed to twenty or forty) Borg cubes seen in "Endgame" [VOY], combined with how poorly armed even Borg Cubes are in Voyager (as seen in "Unimatrix Zero Part 1" [VOY]) along with the ease and speed with which the technology was adapted to Voyager, strongly indicates IMHO that the performance of the ablative armor generator technology is much more contemporary than Janeway might think. Indeed, in Christian R�hl's review of "Endgame" [VOY], Mr. R�hl speculated that the armor is only significantly useful against the adaptive weapons of the Borg - indeed, the ability of Admiral Janeway's shuttle to easily resist disruptor fire from a Negh'Var-type starship may be more due to the raw defensive capability of the shuttle itself rather than the armor in particular, and the subsequent lesser performance of the shuttle's forcefield shields may have been due to the shield generator being damaged in the surprise attack that disabled the shuttle's ablative generators altogether.

Unfortunately, it also makes intra-Federation travel impractical. Picard stated in "First Contact" that the Federation's 150+ members are "spread across 8,000 light years," which according to the "official" formula would take even the fastest starships in Starfleet several months to cross, to say nothing of the time needed for far slower civilian ships (whose Cruising speeds are typically Warp 2 and whose Emergency speeds are typically Warp 4). Indeed, it was stated in "Where No One Has Gone Before" [TNG] that 11% of the Milky Way Galaxy has been charted by humanity in the past 3 centuries (which fits Franz Joseph's published TOS-era map that portrays Federation-controlled space as being a circle some 31,000 light years in diameter) - and little more than a year later, Wesley Crusher stated in "The Dauphin" [TNG] that 'only' 19% of the Milky Way had been charted by Starfleet (a figure which is also part of the TNG writer's bible). Another indication of the speeds Star Trek starships are capable of employing to cross such vast expanses of space is that, in 2369, the Enterprise-D undertook a journey to Indri VIII that, as marked in the upper left-hand picture by Graham Kennedy, spanned three-eighths of the galaxy's diameter (37,500 light years) - and Picard anticipated that a two-way (75,000 light year) trip at Warp 7 would be "a few days" at most. ("The Chase" [TNG]) Furthermore, nearly a century before, the USS Enterprise-A made the ~30,000-light year journey from the Federation/Klingon/Romulan border to the center of the Milky Way Galaxy in 6.8 hours at Warp 7. ("The Final Frontier") The original starship Enterprise was expected to make a journey from Earth to Qo'noS in 4 days at Warp 4.5 ("Broken Bow" [ENT]), and even the SS Valiant managed to reach the edge of the Milky Way galaxy in 2065, some two years after Cochrane made his first warp flight in the Phoenix - a journey of 1,000 light years, minimum, and more like 30,000 light years from the intention of the writers. ("Where No Man Has Gone Before" [TOS]) Last, but certainly not least, the Romulans' covert Vulcan invasion force was sent on three ships that crossed the light-year-wide Romulan Neutral Zone at Warp 1 in 2368 - and did so within minutes instead of the year it would require if Warp 1 was actually only the speed of light. ("Unification Part 2" [TNG]) Thus, one must conclude that the official formula is, to say the least, inadequate.

Earth/Starfleet CDP Warp Drive Subtypes

Expanded Name	f	Tested	Initial Platform
Subwarp	0.5	2053	Robot test article
Warp	1	2061	Robot test article
Space Warp	2	2063	Phoenix
Time Warp	3	2151	NX
Transwarp	4	2285	Excelsior
Superwarp	5	~2326	Ambassador
Hyperwarp	6	2366	Defiant
Ultrawarp	7	~2393
Phasewarp	8	~2420
Sidewarp	9	~2460

A better formula was proposed in 1980 by "Star Trek Maps" (detailed in Joshua Bell's Warp Velocities FAQ for rec.arts.startrek.tech). In it, the base formula was multiplied by chi (X), which denoted the local density of matter. This was on average 1,292.7238, and was based on Mr. Spock's calculation that it would take the Enterprise 11.337 hours to cross 990.7 light years at warp 8.4. ("That Which Survives" [TOS] - Although the travel time actually works out to a multiplier of 1,292.4318, the slightly higher figure given by Star Trek Maps allows time for the Enterprise to decelerate from Warp 8.4 upon its arrival.) In addition, the high warp factors that the post-refit Enterprise was capable of relative to TNG-era starships strongly suggests that, as originally intended by the TNG production staff, f for early TNG-era Federation starships was 5 instead of 10/3 (the alternative being that TNG-era ships were significantly slower than their TOS-movie counterparts). As such, f=3+ warp drives have been given several unofficial names in print - the f=4 drives have been called "transwarp" by numerous fan articles in "The Best of Trek" (this would fit with the non-conduit, finite-speed "transwarp" drives that Borg and Voth ships use) as well as "superwarp" by the Star Trek Spaceflight Chronology, while the f=5 drives have been designated "ultrawarp" by FASA. My own take on the types of warp drives utilized by 21st-26th Century Earth/Starfleet ships is shown in the right-hand table (which draws its prefixes from a number of sources such as the Star Fleet Technical Manual, the FASA TNG Officer's Manual, Starfleet Battles, and the Star Trek novel Federation), with other warp navies having warp drives of f=1 through 4 depending on their scope (major intraquadrant powers such as the 24th-Century Klingons and Romulans having drives of f=3 and quadrant-dominating powers such as the Dominion and the Borg using (trans)warp drives with f=4).

Note 1: It has been alleged that Shane Johnson falsified certain Okudagrams in his book "Mister Scott's Guide to the Enterprise" in regards to the Enterprise-A's transwarp capability. Although Shane Johnson states in his interview with Greg Tyler (specifically Question 12) that Mr. Okuda's graphics were indeed altered for the book, he points out that the alterations were not only done with the approval of Paramount's legal department, but also with Mr. Okuda's consent and recommendation - indeed, the captions to the altered images were written and submitted directly to Pocket Books by Mr. Okuda himself. In addition, according to Mr. Johnson, Mr. Okuda had told him that the issue of the Enterprise-A's transwarp capability had simply never been seriously discussed during the production of "The Voyage Home." As such, Mr. Johnson's retroactive inclusion of transwarp drive on certain Okudagrams in his book can be more appropriately described as a correction of what was then officially felt to have been an oversight.

Note 2: The form of Superwarp (f=5) drive developed by Dr. Katherine Ballantine for Starfleet utilized nacelles that each behaved as an integrated pair of warp field generators. Although extremely efficient, this unusual form of warp drive was - in both theory and practice - unable to establish more than nine warp fields simultaneously. Consequently, it followed an asymptotic warp curve where, after Warp 9, f increases to infinity as the warp factor approaches 10 ("Threshold" [VOY]) and, according to Commander William Riker, "in theory, accelerating beyond Warp 10" would result in traveling backwards in time. ("Time Squared" [TNG]) However, Star Trek Art Supervisor Mike Okuda has stated that he drew the "warp curve" by eye only (since he lacked knowledge of calculus), and that he simply picked various warp 9+ speeds off that curve. Thus, there is no "real" formula for calculating what f should be at a given warp factor for Starfleet Superwarp drives (though this hasn't stopped Star Trek fans from trying to devise a formula that would generate Okuda's curve).

The result of the aforementioned adjusted "Star Trek Maps" warp formula is that it simultaneously accommodates every instance of high and low warp speeds found throughout every incarnation of Star Trek - for example, in the aforementioned TNG episode "The Chase," the Enterprise-D could make its 37,500 light year journey at Warp 7 with f=5 and X=1,292.7238 in little more than 15 hours (which fits well within Picard's expectation that a two-way trip, plus time spent at Indri VIII, would only take "a few days"). As for the premises behind DS9 and Voyager, given the way in which travel within a Quadrant is treated as a far shorter prospect than travel between Quadrants, perhaps Quadrants are generally defined - and separated - by stretches of space (each roughly 670 light years wide) that have sub-unity X values (it is possible to have values of X less than 1, or as we saw in "The Omega Directive," even 0). Given the common estimate that it would take 70 years to cruise at warp between both ends of the Bajoran wormhole, if this was done at Warp 6 with f=4 (typical of a Dominion warship, with a speed at which antimatter supplies was not the limiting factor), then this implies an average X value of 0.0077356045 in those "quadrant borders." Of course, similar zones of this low-X space exists "above" and "below" the galactic disc as well as outside of its "rim," preventing a starship from simply flying "around" the low-X zones. (Intergalactic space would have, as one would expect, an average X value of exactly unity.) This would permit travel within a Quadrant to be a few weeks at most, while making a journey between Quadrants an undertaking that could last decades - and how Voyager's destination is often stated to be "the Alpha Quadrant" even though a significant fraction of that journey to Earth would be within the Alpha Quadrant.

Of course, this premise still conflicts with Voyager's generally "slow but steady" journey back to the Alpha Quadrant - it ought to be able to, like its TNG counterparts, cruise the span of the Delta Quadrant in a matter of hours, if not minutes. However, one can rationalize that the immense damage that Voyager took in the pilot episode (in which nearly half the crew and the entire medical staff were killed), as well as subsequent injuries that the ship has taken (at one time, the warp coils themselves had been fused ("Deadlock" [VOY])), with no Starbases nearby to limp to for proper repairs (despite the ship's remarkably pristine interior and exterior appearance - a dramatic testament to the capabilities of modern Starfleet auto-repair systems), has prevented the ship from maintaining very high warp speeds for any appreciable length of time (as seen in "Distant Origin" and "Threshold" [VOY], Voyager's average cruise speed is a modest Warp 6.2 and it risks a catastrophic structural failure at only Warp 9.9), as well as reducing its engines' f from 5 to the "official" 10/3 and effectively reducing the X by one thousand times. This would be a crucial reason why Voyager (and the Equinox) crossed the Delta Quadrant in the direction of the Beta Quadrant (and Borg Space) instead of heading for the Gamma Quadrant terminus of the Bajoran wormhole. Starfleet probably found at least one spaceway across the Beta-Delta border prior to Voyager's abduction by the Caretaker, which would allow the crippled Voyager to cross that border in just over a year - as opposed to the 105 millennia Voyager would need to traverse the unknown Gamma-Delta border - and there was always the possibility that one of the Starfleet starships assigned to charting the Beta-Delta border would be able to find and assist Voyager on its way home. In addition, Voyager was critically short on power throughout its journey (or at least it was supposed to be - Voyager's writers had a penchant for violating previously established rules of holodeck operation, even the ones that they themselves devised to explain their earlier conundrums), with little to spare for its replicators (hence its need for a cook), and had to stop at every inhabited system it could find to obtain supplies (and to attempt field repairs). This theory is reinforced by references to possible "rescue missions" by Starfleet - which would be pointless unless a perfectly functional starship can travel far faster than Voyager can in its current mechanical condition, and with an emergency speed of Warp 9.999, Voyager was one of Starfleet's fastest starships. (Besides, even with the official formula, Voyager could have arrived home after 13 years at its "maximum sustainable cruise velocity of Warp 9.975." ("Caretaker" [VOY])) Just as importantly, it would help explain how races and characters that ought to have been left behind by one or more of Voyager's occasional multi-KLY jumps could still encounter - or even catch up with - the ship (one of the most infamous examples being the former Lindsay Ballard, who in "Ashes to Ashes" [VOY] caught up with Voyager in a shuttlecraft after a six-month search despite Voyager having almost a three-year, 40,000-light year head start).

Note: In 2370, it was alleged by the late Dr. Serova of Hekaras II that repeated use of warp drive damaged the subspace continuum. However, her means of attempting to prove her theory involved her deliberately triggering a warp core breach in the Hekaras Corridor. ("Force of Nature" [TNG]) As Phil Farrand points out in his second volume of "The Nitpicker's Guide for Next Generation Trekkers," Dr. Serova's methodology to prove her hypothesis could be described as erroneous if not outright fraudulent. Given that Warp 5+ speeds became routine again within months of the Hekaras Corridor incident without any explanation (at least in the movies and episodes), it is most likely IMHO that, instead of a complete revision of the centuries-old theories of warp drive and a quadrant-wide refit of all warp vessels, the hasty conclusions drawn from the Hekaras Corridor incident were instead reviewed once the initial panic subsided, found just as wanting as they were in the years prior to the incident, and quietly discarded.

Throughout Star Trek, numerous hints have been given that despite its official description as a Newtonian drive, Impulse Drive is more accurately described as a realspace continuum distortion propulsion system. Granted, given the incredible power densities of Starfleet-grade ZPE-enhanced deuterium - 9*10²⁹ Joules per ton when employed in Starfleet fusion reactors - even the zero-to-warp acceleration of a 400 megaton Galaxy-class starship in less than 10 seconds can be attained on a 13 exanewton, 4 kiloyottawatt propulsion system with 43 kilograms of Starfleet-grade ZPE-enhanced deuterium (out of some 3 megatons that can be carried by that starship). However, impulse flight has not only consistently exhibited decidedly non-Newtonian flight characteristics (often similar to fixed-wing VTOL aircraft maneuvering in an atmosphere), but can also propel a starship in vectors inconsistent with an aft-facing Newtonian drive (such as the direct descent performed by the Enterprise in "The Wrath of Khan" or the backing out of Spacedock in "The Search for Spock"). Second, the impulse drives are described in the TNG Tech Manual as having a top sublight speed irrespective of fuel consumption (0.92c in the case of the Galaxy-class starship) - which is not characteristic of Newtonian space drives. Third, and probably most importantly, are the superluminal capabilities (which would be impossible for any Newtonian drive regardless of power) that have been occasionally demonstrated by impulse drives. In the pilot TNG episode, the saucer section (which does not have warp nacelles) was detached a few light years or so from the Enterprise-D's destination - yet it arrived within hours, albeit after the stardrive section. ("Encounter at Farpoint" [TNG]). Although it can be argued that the saucer employed integrated impulse-warp engines just like the Klingon Bird-of-Preys, when Voyager ran critically short of power in late 2374 and warp drive was directly stated to be unavailable, dialogue clearly implied that, even without warp drive, Voyager would be able to visit at least one other star system in the week it had left before it ran out of power altogether ("Demon" [VOY]) - and with star systems typically 4 light years apart, this would require a non-relativistic speed of at least 200 times lightspeed. Likewise, the 2266 Romulan Bird-of-Prey was stated to have only "simple impulse" for its propulsion, yet it was clearly capable of making interstellar transits within days instead of years. ("Balance of Terror" [TOS]) In addition, at the beginning of "The Undiscovered Country," Captain Hikaru Sulu stated that the USS Excelsior was, as it was passing by the Klingon Empire, "...heading home under full impulse power" from the Beta Quadrant - and it isn't uncommon for warfleets to make interstellar transits under impulse drive only ("Favor the Bold," "Sacrifice of Angels" [DS9]). Furthermore, Voyager was able to hold position and even maneuver at an altitude of its own choosing underneath the event horizon of a black hole ("Parallax" [VOY]) - an absolute impossibility for a drive incapable of superluminal flight.

As such, impulse drive would be, in essence, a sublight-optimized version of the CDP warp drive that can attain superluminal speeds when necessary (such as in the event of warp drive failure or when one wishes to minimize the starship's energy signature). Consequently, the maximum speed an impulse drive is capable of attaining is not measured as a fraction of lightspeed, but as a fraction of Warp 1: Xc, with c representing the fraction of Warp 1 that the impulse drive can attain (as shown by Kirk's order of "Ahead, Warp .5" on impulse power in "The Motion Picture"). As for Sulu's electing to take the Excelsior home under impulse instead of warp, one can theorize that the Excelsior was able to go to and from the Beta Quadrant via a very high-X spaceway - which would also explain why the Excelsior's route back to Earth from the Beta Quadrant took it to the other side of the Federation first. Nonetheless, given that CDP propulsion systems may not be desirable under all circumstances, the impulse drive has an integrated auxiliary Newtonian propulsion system - the "rockets" referred to in "The Cage" [TOS].

Nonetheless, the power and equipment requirements of the CDP hyperdrive places it out of reach for all but the most advanced pre-warp cultures. Consequently, among hyperspace-based interstellar cultures, the typical hyperdrive is one that transitions the ship out of normal space (and thus restricts most of the starship's energy expenditure to the superluminal flight's beginning and ending). Although the classic hyperdrive has a number of subtypes, each with their own advantages and disadvantages, all of them are subject to a number of common limitations (especially those of pre-warp cultures). The nature of hyperspace limits the speed at which pure electromagnetic radiation can propagate to X, which greatly reduces (or even practically eliminates) the effectiveness of non-FTL sensors and communications in hyperspace - a limitation made all the more crippling by the lack of a correlation of distances between hyperspace and realspace. Thus, in unknown territory, the maximum distance of a hyperspace flight is practically limited by the range of the ship's sensors. (Some pre-warp societies have established tachyonic communication networks through hyperspace, which allows - provided the network is of sufficient size - practical real-time communication across even an entire a galaxy, albeit at a cost in both energy and equipment for both the transceivers and the "hyperradio" network itself that even the wealthiest and most powerful pre-warp societies find extremely difficult to sustain.) Furthermore, hyperdrive failure while in hyperspace strands a ship there (likely never to be found due to the chaotic nature of hyperspace), while the failure of a warp drive (or a CDP hyperdrive) will simply drop the ship back into realspace. As such, pre-warp interstellar cultures that are able to address such risks sufficiently (through both innovation and bravery) to use classic hyperdrives for routine (i.e. commercial) purposes are deserving of not only respect, but accolades and admiration, for the magnitude of their achievement.

Note: One common form of the classic hyperdrive is the "hyperdrive motivator," which has the ship "straddle the wall" between normal space and hyperspace. This type of hyperdrive calculates its hyperspace speed relative to normal space by X*1.x, so speeds of the hyperdrive motivator are commonly referred to as "point x beyond lightspeed" (for example, one of the fastest known starships with this type of hyperdrive was a smuggling freighter that could attain .5 beyond lightspeed). While extremely compact and energy efficient (it can even be mounted on starfighters), normal-space objects produce mass shadows in the normal-hyperspace "wall" which not only pose the same risks as realspace collisions, but can force starships out of superluminal flight if strong enough - which renders any superluminal course-change impractical on this type of hyperdrive.

In contrast, a second type of the classic hyperdrive known as the "jump engine" opens a portal directly into (or out of) hyperspace that a starship can enter (along with other ships if so desired). Not only can ships attain speeds of Xg (g being the craft's sublight MGLT rating) when in hyperspace proper, but they are not subject to the mass shadows of realspace, and are thus free to maneuver, change course, and even engage in combat while in hyperspace. The primary drawback of the jump engine, though, is that its demands in terms of hardware and energy are such that not only is a recharge time required between uses, but only the most powerful ships (usually capital vessels) are capable of carrying them. As a result, a network of free-floating installations ("jumpgates") equipped with vortex generators are required for the everyday interstellar transit of most spacecraft. (return)

For maximum cargo capacity and minimal maintenance requirements (and because Star Trek technology doesn't scale linearly), shuttles and commercial ships have limited propulsion systems, and are thus restricted to low warp speeds at best (maximum sustainable cruises of Warp 2 and 3 respectively are typical), with many civilian craft possessing only hyperdrive or even just impulse engines. Nonetheless, it remains desirable for obvious reasons for an interstellar society to minimize transit times for such craft, and to that end, every known warp-capable culture in the Milky Way has mapped out areas of exceptionally high X values (129,272.38 on average) within their territories. As these areas are typically linear stretches of space between individual stars, they can work in much the same way that highways "boost" the speed of land vehicles as opposed to traveling cross-country, and thus enables even a shuttle to cross the 41,000 light years of Federation-controlled space in under 15 days at Warp 2 and f=3. Indeed, the two stars that serve as the termini for the spaceway need not be in the same quadrant - or even the same galaxy (interquadrant spaceways have an average X of 773.56045, while the much rarer intergalactic spaceways have an average X of 10,000). The discovery of such intergalactic spaceways in the Alpha Quadrant during the early 2260s has enabled Starfleet to launch occasional intergalactic exploratory missions to other members of the Local Group since then (Commodore Barstow indicated in "The Alternative Factor" [TOS] that, by 2267, Starfleet vessels not only operated "in every quadrant of the galaxy and far beyond," but that they also had intergalactic communications with minimal time delays as well), one of which involved the USS Magellan journeying to the Andromeda Galaxy in 2285. ("The Wrath of Khan" [TOS Novelization]) Spaceways are also used by pre-warp FTL-capable cultures, as non-CDP hyperdrives are even more dependent on high X values than warp drives (or CDP hyperdrives), to the point where the extremely rare super-high-X value (12,927,238 on average) "hyperspace lanes" are often called "trade routes" by said cultures due to their indispensability for practical intragalactic commerce (and government). Of course, such routes, like highways, represent a means by which users can be easily found by enemy forces, and so they are generally avoided by convoys in wartime. Furthermore, as Graham Kennedy speculates in his article on Warp Speed Anomalies, these "highways" are not necessarily permanent in nature and thus may have to be remapped on occasion - which is why charting is such an importannt mission of Starfleet, especially at the Quadrant and Galactic borders.

Consequently, a few long-established interstellar powers (primarily in the Delta Quadrant) have developed a means of FTL travel based on CDP warp drive physics that can avoid the aforementioned practical limitations of the latter. Although these "subspace conduit" drives each have different names from one another, all work by first utilizing the ship's warp propulsion systems to generate a narrowly-focused warp field 'tunnel' (instead of the usual multi-lobed and -layered geometry) shaped by a dedicated tachyon emitter array (or, for temporary purposes, a tachyon matrix set up in the ship's navigational deflector). The ship then proceeds to fly down the generated conduit with its impulse engines, building the conduit ahead of it as it flies. The conduit is in effect a subspace version of a wormhole, which not only masks the ship from most known realspace sensors, but distorts subspace itself along the conduit's primary axis to such a degree as to reduce the distance for the starship to transit (and thus effectively increases the starship's speed beyond what its warp core would otherwise be capable of sustaining). Since this technology is essentially a variation of warp drive and not an entirely new drive system, its components can be used to provide conventional warp-capable starships with the temporary ability to generate their own conduits with relatively little modification needed for either the ship or its warp drive. Furthermore, because impulse (and not warp) engines are used for actual propulsion while inside of the conduit, non-warp spacecraft (even shuttlepods) are capable of utilizing pre-existing conduits as well (provided they either enter the conduit along with the vessel that generated the conduit, or are able to direct variable-frequency high-energy tachyon pulses to reactivate the conduit prior to its decay). Thus, a starship's equivalent realspace speed within a conduit is measured by Xcm^d, with Xc being the ship's maximum impulse speed, m being the subspace field stress of the conduit as measured in cochranes, and d representing the degree of subspace distortion. The following table lists a few known subspace conduit drives and compares the conduits they can generate:

Nonetheless, despite the effectiveness of the subspace conduit drive at augmenting the speed of a starship's warp drive, it also has a set of significant drawbacks. A ship under subspace conduit drive is not only effectively separated from the rest of normal space, thus precluding its use in FTL combat (except for engaging a ship in the same conduit), but the tremendous subspace distortion generated by the drive renders all known versions unable to use spaceways, thus limiting its usefulness among naval powers that are able to create warp coils capable of fully utilizing the power of a ship's warp core - especially those that have extensive intragalactic spaceway maps (current conduit drives would take at least a hundred times as long to cross the well-mapped Alpha-Beta quadrant border as conventional warp drive). In addition, the inherent instability of the open-ended subspace conduit (especially those with high cochrane and/or d values) can quickly burn out the difficult-to-replicate drive coils, which is why Borg ships not only employ multiple transwarp coils in their drive systems, but miniaturize them so as to allow their employment as a low-speed and -power auxiliary drive separate from the main (conventional) 100-kilocochrane transwarp drive so that the latter may be used for transits between an exit aperture of a transwarp hub's corridor and the ship's destination ("Scorpion," "Drone," "Dark Frontier" [VOY]). (To this day, only a single prototype Borg ship was known to have utilized a transwarp conduit drive as its primary drive system ("Descent" [TNG]), and only the people known to the Borg as Species 116 have succeeded in producing a conduit drive that does not require a replacement of burned-out generator coils following each flight. ("Hope and Fear" [VOY])) Furthermore, conduit generator burnout is greatly accelerated if the ship does not possess a properly configured tachyon emitter array - a problem that is exacerbated if multiple jumps are attempted ("Hope and Fear," "Timeless," "Dark Frontier" [VOY]). Under most circumstances, drive failure within the conduit would result in the conduit's gradual collapse, forcing the ship back into realspace with structural damage - though some failures result in the drive, prior to burnout, "running away" from the navigational controls by intensifying the conduit's subspace distortion until it abruptly collapses at up to 30% above its normal d, resulting in a disastrous loss of navigational control as the ship is ejected from the conduit at high sublight speeds. ("Timeless" [VOY]) Consequently, at least for Starfleet, the subspace conduit drive is simply an idea whose time has not yet come - and, given not only the difficulties in constructing practical high-d conduit generator coils but Starfleet R&D's history of repeatedly advancing the state-of-the-art in CDP warp design in ways unforeseen by others as well, may not come for the foreseeable future.

Note: "Endgame" [VOY] revealed the precise nature of "permanent" Borg transwarp corridors. The Borg use a large free-floating installation known as a "transwarp hub" (of which they currently have six, all of which are inside Borg space proper) to establish a network of intraquadrant transwarp corridors that are each supported by a series of interspatial manifolds inside the corridor. Some time ago, the Borg had embarked on the construction of a seventh hub that would be large and powerful enough to support a galaxy-wide network of 100 kilocochrane, d=2 transwarp corridors that would enable them to place ships anywhere in the Milky Way Galaxy within minutes. However, due to the inherent instability of such powerful, high-d subspace conduits, if at least three sequential manifolds of that hub's corridors were to be destroyed, all of the hub's corridors would subsequently collapse in a cascade reaction that annihilates the entire transwarp network (both the corridors and the installation) of the hub. This is why the shields protecting the interspatial manifolds of that hub had the highest priority in the Collective - and how (thanks to Admiral Janeway), despite that precaution, the uprated Voyager was able to destroy that interquadrant hub just before it became fully operational. ("Endgame" [VOY]). Although the Borg can still generate a temporary interquadrant conduit via the combined efforts of their six remaining transwarp hubs out to 30,000 light years, they can only do so very infrequently and at an extremely high cost in energy and equipment. (return)