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Based on the film and television events, it seems early shows had Klingon, Romulan, Vulcan, Breen, and Starfleet ships having nacelles placed far away from the hull on struts or wings. On the other hand, Ferengi and Cardassian ships have their warp coils in or near the ship's hull.

Note this question asks about distance, like "why not put nacelles close to the body" rather than the number of nacelles used. Why do most Starfleet ships stick their nacelles out so far. Please avoid answers talking about counting engine parts unless somehow the number of nacelles requires them to be far apart.

Aside from "coolness," why are nacelles kept away from the hull in Starfleet vessels? Some races can incorporate the nacelles within the hull, others agree with Human design. I'm interested if anything in-universe (not extended universes) gives us an explanation for the way we see these ships on screen.

I grant that even in the real world some engineers disregard safety. That would be my blind guess. It just sort of looks vulnerable.

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Apart from simple narrative necessity, I think we can extrapolate from the original Enterprise blueprints (Sheet 11, Paramount 1975) that radiation is the answer.

When we look at the plan for the Support Pylon (where the famous Jeffries Tube is located), we see two safety locks located in the pylon. There are notations for each. The lower safety lock:

Warning: Entry beyond this safety lock permissible only with anti-radiation suits.

The upper safety lock:

Warning: Entry beyond this safety lock permissible only with environmental suits and entire main propulsion unit shut down.

Presumably, if you wander far enough up the Jeffries Tube without proper safety equipment, you're not going to be coming back down again, except in a body bag.

enter image description here

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    @ToddWilcox --- One might conjecture that between the time of the old Enterprise of the TV series and the newer Enterprise of the movie era, they figured out a way of dealing with the radiation issue. Other conjectures abound. – elemtilas Oct 4 at 0:57
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    There obviously remain questions because this configuration is widely used, but not ubiquitous. We can certainly say that Reliant was a warship and it was absolutely necessary to avoid the "big long sticks," so it had some radically unique design features that were impractical on mass-produced long-haul starships. These are all exploration and research vessels, after all. Love this post, do want more! – Vogon Poet Oct 4 at 2:10
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    This is also why the saucer-on-a-stick exists: The Secondary Hull was primarily Engineering, Hangar Bays and the Warp Drive - living quarters (et cetera) were in the Saucer, conveniently distant from the antimatter-based warp drive. – Chronocidal Oct 4 at 8:08
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    @PeterCordes That's not actually true. Particle + anti-particle -> two photons is only one of many ways the annihilation can go, and is only dominant for very low mass particles, like electrons. But Federation ships use deuterium; smashing a proton against an anti-proton makes a decidedly unfriendly mix of particles which very quickly decay further. The fall off is very fast, but something like STENT's warp core would be extremely dangerous in real life, not to mention the effect of all those particles interacting with the casing etc. But yeah, the nacelles are about radiation from warp coils. – Luaan Oct 4 at 11:50
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    @Burgi They hid in the catwalk, and we don't know how far towards the nacelles they ventured (the whole area they used could have been before the "radiation point"). Though, granted, this example came to my mind as well and, if nothing else, I expect the whole radiation thing was just retconned. Also note that the entire catwalk would become fatal to humans when the engines were online so it's kind of a different beast anyway. – Lightness Races with Monica Oct 4 at 14:10
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Not all Starfleet vessels have nacelles far away from the hull (think shuttles), but that main thing that was taken into consideration is that the nacelles needed to "see" each other. This would require the spacing to be farther apart on larger ships.

It seems this was something Andrew Probert (the concept artist for TOS) decided on during conversations with Gene Roddenberry on the matter.

As far as the line-of-sight requirement, that was my edict, that, in order to be codependent, the warp engines had to "see" each other, totally. I'm taking about the power combs, not necessarily the Bussard collectors but the bulk of those combs have an energy path between them. And then for other starships, just like in World War II, where all the nations had fighter aircraft that all looked different -- you know, a cultural distinction between, say, a German aircraft and an American aircraft or a Japanese aircraft -- they all operated in the same way having the same basic components of wings, body, and engine, so I applied that thinking to the alien ships I designed as well, so the Ferengi ships, and Romulan Warbirds, have twin warp engines that have to see each other in order to operate. Even my shuttlecraft having a very shallow clearance, still see each other. That's why designs like the Romulan scout ship, where the engines cannot see each other, aren't consistent. There are also some cool Starfleet designs like the Nebula Class ships, but their warp engines cannot see each other. Even those runabouts ignore that ruling which messes up the continuity. Science fiction in particular NEEDS to be consistent. If you negate that,...it all falls apart.

Source: "An Exclusive Interview with Andrew Probert", Interview conducted face-to-face on May 28, 2005 at Wonderfest, and revised via email in June 2005 (posted on trekplace.com)

This also confirms why "Klingon, Romulan, Vulcan, Breen, and Starfleet ships" have such similar designs. Probert also does not seem to be a fan of designs that break this rule stating science fictions needs to be consistent.

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    Interesting stuff. I'm sure I've seen this elsewhere on the site – Valorum Oct 4 at 16:30
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    :D @Valorum.... scifi.stackexchange.com/a/91888/55637 - weird how there would be two questions with the same answer....there should be a name for that ;) – NKCampbell Oct 4 at 17:25
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    @NKCampbell Opportunity abounds! – Skooba Oct 4 at 17:30
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    I can't help but disagree with the idea that continuity must fall apart. Just hang a lamp on it by having an engineer comment on how they must be using a different propulsion technique. – candied_orange Oct 5 at 1:28
  • Note that this is only a partial answer; it explains why the nacelles have to be away from the hull, but not why the distance between hull and nacelle is as great as it is. Of relevance is that the quote specifically mentions shuttlecraft as still meeting the line-of-sight requirement, despite having significantly less distance between nacelle and hull (as known from their in-series appearances, and hinted at by the "shallow clearance" statement). – Justin Time 2 Reinstate Monica Oct 6 at 21:21
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Gene Roddenberry's concept of the warp field was that it was symmetrical and needed to be in open space. That's why the nacelles are not in direct line with the hull of the ship - it wouldn't be possible to create a stable warp field with bits of ship in the way!

You can see the same design concept in Klingon, Romulan, and Ferengi ships to name a few. This design was not universally followed by all Star Trek ships, but many or most of the ships in the original series and the Next Generation did follow this design principle.

Voyager can't go to warp until the nacelles have direct line of sight with each other. I can only imagine that the Defiant has a big, open space inside the ship for the warp field, which contributed to the ship being so cramped!

From An Exclusive Interview with Andrew Probert:

Tyler: Do you know the origin of what have become known as "Roddenberry's Rules of Starship Design" -- the idea that warp nacelles have to be in pairs, and things of that sort. I understand that there were a set of guidelines. Do you recall the origin of those?

Probert: Gene specified to me, in fact, that starship warp engines operate in pairs... only in pairs because they're codependent. If you had one warp engine, you'd probably go in a circle, I don't know... (laughs) So in the same breath he negated the three-engined dreadnoughts along with the single-engined destroyers, on the edict simply that, to achieve warp drive, you had to have codependent warp engine pairs. As far as the line-of-sight requirement, that was my edict, that, in order to be codependent, the warp engines had to "see" each other, totally. I'm taking about the power combs, not necessarily the Bussard collectors but the bulk of those combs have an energy path between them. And then for other starships, just like in World War II, where all the nations had fighter aircraft that all looked different -- you know, a cultural distinction between, say, a German aircraft and an American aircraft or a Japanese aircraft -- they all operated in the same way having the same basic components of wings, body, and engine, so I applied that thinking to the alien ships I designed as well, so the Ferengi ships, and Romulan Warbirds, have twin warp engines that have to see each other in order to operate. Even my shuttlecraft having a very shallow clearance, still see each other. That's why designs like the Romulan scout ship, where the engines cannot see each other, aren't consistent. There are also some cool Starfleet designs like the Nebula Class ships, but their warp engines cannot see each other. Even those runabouts ignore that ruling which messes up the continuity. Science fiction in particular NEEDS to be consistent. If you negate that,...it all falls apart.

(emphasis mine)

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    "Gene Roddenberry's concept of the warp field was..." - do you have a reference? Genuinely curious about this... – Dai Oct 4 at 11:29
  • @Dai Not offhand. But I do remember it being on something official, or referencing something official and thinking "That makes so much sense now!" – CJ Dennis Oct 4 at 11:31
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    This would be an amazing anwer with a reference, hope someone has it! It seems someone should have mentioned it in character at one point as well, with so many drydock and shipyard scenes. – Vogon Poet Oct 4 at 12:42
  • @VogonPoet I've seen all the episodes of all the shows, and it was never mentioned in-universe. I saw it in an interview with Gene Roddenberry, or one of the other main people, or a direct quote. I'll have to see if I can track it down when I have time! – CJ Dennis Oct 4 at 13:07
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    I always took it that the warp coils didn't need to be on sticks like that, but that their positioning made the Warp System more efficient. USS Defiant is a warship, and the long-term flight efficiency is far less important than armouring up, so it keeps its nacelles compact. Most of the races that didn't put the nacelles on pylons are presumably regarding the tradeoff of structural durability vs efficiency as not worth it. – Ruadhan2300 Oct 4 at 13:18
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One question is why the nacelles have empty space between them. Others have answered because Gene Rodenberry.

A second question is why the nacelles are so far apart. One answer given -- which is excellent -- is safety. The nacelles are far apart by necessity in early starfleet designs because they have to be far apart from the hull.

The raditiation problem is eventually solved. So the question becomes if there is an engineering reason to keep the nacelles far apart. The answer is to use energy efficiently.

The warp nacelles create a subspace bubble. The nacelles are long, so they create elliptical bubbles of nearly constant width in the middle. To create a larger field, it uses less energy to overlap two medium size bubbles to make one to encompass the ship. Consider that two overlapping fields half the width is roughly 1/4 the size of a field with the full width. This suggests to me that there is minimum distance required between the hull and the bubble edge. To achieve this with the least amount of power, you would want the nacelles to be as far apart as possible.

People have commented about the Defiant's unique design. I have a theory, but one that I think may be inconsistent with canon. I don't recall if any characters said "nacelles" (plural) when referring to the Defiant.

It's possible that the defiant uses a single nacelle design; to weather battle a singular set of warp coils could be in the center of the ship. We know the defiant has a power core comparable in size to the Enterprise-D, yet it is much smaller. The loss in efficiency would be a trade off that is of negligible impact.

The warp flash when a ship "accelerates to warp speed" is vented excess energy during start. (I am not sure I am 100% correct on that point.) It makes sense that the warp flash would then come from the sides of the Defiant, as the energy is dumped to space.

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