I'm absolutely fine with the idea, that a certain angle/position of the nacelles is better than others. And hence it's good (for whatever reason - be it energy efficiency or more speed...) to have them in that position. So my question is less: "Why do the nacelles rise when they go to warp?". The answer is simple: "Because in trek-physics it's better to have them there when going to warp." My question is more: "Why are they lowered when dropping to impulse?"

The nacelles are not involve in the propulsion of the ship when on impulse. Why are they not forged in the favourable position for warp? For some reason it must be better to lower the nacelles when you fly on impulse.

Maybe they are less exposed in combat-situations? Are they easier to access for reparations if they are lowered? Can the Bussard-collectors work more efficiently if they don't have the saucer-section blocking their ways?

Why can the warp-nacelles be lowered? Why are they not fixed in the position which is best for flying on warp?

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    In-universe you should just check out the USS Voyager Technical Manual. It should help as should this Memory Alpha entry on the Intrepid Class starships. Out-universe it was a style design, a way to make the ship look cooler - Here's a snipped from The Art of Star Trek posted on Forgotten Trek. – 22nd Century Fza May 25 '14 at 10:28
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    @Richard No it is not, since I didn't asked why the rotation helps keeping the fabric of space intact. Since [except for some techno-babble] the nacelles could be lowered once reached high warp, the answer provided there is not addressing the question why the nacelles are lowered (at some point [usually when dropping out of warp]) before you go to warp. – Einer May 25 '14 at 11:45
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    @Richard Strictly speaking my question isn't answered yet. You answered (correctly) that they must be raised and I just filled out the blanks in my head that lowering the nacelles while on warp isn't a good idea, so it must be done when dropping to impulse. Still I only speculate, that they are lowering them knowing that soon they will want to go to warp and than they need them to be down to be able to move them upwards again. – Einer May 25 '14 at 11:52
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    @Richard I don't want to be a nit-picker but you can program a computer to do anything automatically you want it to do. But the question remains, why it should do this or that automatically. There should be a reason for that. – Einer May 25 '14 at 12:01
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    @Richard I don't doubt that. But is that answer given in the post you say that this is a duplicate of? – Einer May 25 '14 at 12:27

The Voyager entry on StarTrek.com speaks to the reason for the movable ("variable geometery") warp nacelles. After the events of TNG "Force of Nature" it was proven that high speed warp damages the structure of subspace.

The new 'folding wing' seems to negate this by moving when initiating high warp (or creating a substantial warp field). Notably, when low warp is initiated this same movement doesn't always seem to take place

Voyager's folding wing-and-nacelle warp drive system allows the starship to exceed the warp 5 "speed limit" without polluting the space continuum. Voyager can reach a speed of warp 9.975, but only for short periods.

The TNG Technical Manual also suggests that variable geometry nacelles would provide for greater stability and less shearing stress at high warp speeds

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Out of universe, you can see from this early design sketch that the warp nacelles were intended to have much more dramatic movable portions (referred to as "Warp Field Enhancers") that would flare out from the main ship. This was ultimately scaled back due to studio concerns over lighting and budgets.

enter image description here

  • So it's good to have them up there when going to warp. I acknowledge that. Why not just simply let reside them where they are when dropping to impulse? But why are they lowered for impulse? – Einer May 25 '14 at 10:59
  • @einer - The principle is that by moving during the warp sequence, they somehow remove the subspace damage. If they were up already, that movement wouldn't occur. When the ship returns to impulse, the pylons lower the nacelles back into their "ready" state. – Valorum May 25 '14 at 11:01
  • So what you are saying is: It isn't the actual position that counts, it's the movement of going upwards while going to warp? – Einer May 25 '14 at 11:05
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    @Einer - Yes, they have to move when going to high warp. Notably, they don't move when the ship is going to low warp; chakoteya.net/Voyager/321.htm – Valorum May 25 '14 at 11:12
  • Now that's interesting! Would you mind working it into your answer. I would mark it as right answer then. Though it still seems strange to me that they don't lower the nacelles once they'd reach high warp. But I can live with that - probably something about warp field geometry and being/not being able to change direction at warp and stuff. But I'm satisfied with the "movement counts"-answer you provided. – Einer May 25 '14 at 11:17

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