When the USS Enterprise first appeared, its warp nacelles looked like this from the rear:

At some point in The Original Series, the ship seems to have enjoyed a mild refit, resulting in ball-like attachments at the rear ends of the nacelles that weren't there before:

When exactly did the Enterprise receive these balls and what is their precise function with respect to the ship's warp drive?

  • 190
    The moment Kirk stepped aboard
    – Gaius
    Jul 1, 2015 at 7:17
  • 11
    At least it wasn't Michael Bay adding them.
    – user16696
    Jul 1, 2015 at 13:21
  • 8
    Judging by the extremes its crew is willing to put the vessel through, and its generally consistent ability to survive them with reparable damage, I'd say it's always had balls.
    – talrnu
    Jul 1, 2015 at 13:56
  • 28
    I think you mean, "boobs," since, you know, she.
    – Lexible
    Jul 1, 2015 at 18:13
  • 9
    Someone just tried to edit the title to replace balls with port nacelle spheres... Not a chance!!
    – Daft
    Jul 2, 2015 at 16:22

3 Answers 3


Out-of-universe, this was due to the existence of more than one Enterprise model, and to footage being reused:

The second configuration, used in the second pilot (and throughout the rest of the series, due to footage being reused) was similar to the first version, with the addition of running lights, additional markings, and a grille pattern on the rear of each engine nacelle.


In-universe, we have the following observation:

Sometime between 2265 and 2266, the old deflector dish was replaced by a significantly smaller model, the spikes on the Bussard collectors were removed, a smaller bridge dome of flatter curvature was installed, the aft caps on the warp nacelles were each equipped with a spherical attachment, and the impulse drive now had only two large exhausts.

Memory Alpha also notes that:

It is unclear whether the warp nacelles were merely modified or completely replaced.


As pointed out in Thaddeus' answer, there are two refits documented where modifications to the warp nacelles occurred. However, I am of the opinion that the second refit is the one that we are interested in:

A second, more extensive refit occurred at some point after her encounter with the "galactic barrier" in 2265. It involved replacing the bridge module, a newer, smaller deflector dish, and refinements to her warp nacelles

In other words, the first refit happened between 2264 and 2265 but the modifications to the warp nacelles occurred between 2265 and 2266.

As to what these "ball" attachments are, here's a blueprint:

Enterprise Blueprint

(View larger image) (Source)

You will note that the "balls" are referred to as the space matrix restoration coils. The Memory Alpha article I've linked to is pretty useless, but this site has something more to say:

While the exact function of this component is unknown, it can be surmised that the device in some way alters the state of particles that interact with the warp coils. It is generally believed that the device in some way keeps the Coils in phase with the normal universe and prevent them from slipping into subspace as a result of the massive energy fields that they generate.


As the article above goes on to say, this is a pretty important aspect of warp travel! I can't actually find a blueprint of the Enterprise prior to its 2265 refit where the "balls" were added, but looking at the below blueprint of the Enterprise after its major refit, you can see in this aft view that it doesn't have any balls, but still incorporated the space matrix restoration coil as referred to in the Memory Alpha page because we hear it mentioned in The Motion Picture :

Enterprise refit aft view

Furthermore, when we look at the Enterprise NX-01 blueprint, we also see that there it too had a space restoration matrix coil, meaning the Enterprise prior to refit probably also had it:

Enterprise NX-01 Blueprint (View larger image) (Source)

The important thing to note from this image is that there are no "balls" for the space restoration matrix coil, so the parts on the rear of the nacelles on the pre-refit Enterprise were probably also part of this coil.

Consequently, I conclude that why the Enterprise got balls, in-universe, was due to improvements in the space restoration matrix coil.

  • 3
    Nice answer! :-)
    – Praxis
    Jul 1, 2015 at 8:16
  • 4
    Or maybe they just wanted to spice up the flagship's appearance, nacelle-balls being the 22nd century equivalent of truck nuts.
    – Schilcote
    Jul 3, 2015 at 4:43
  • 3
    @N_Soong : Great updates! The blueprints are very helpful and your conclusions are reasonable. :-)
    – Praxis
    Jul 4, 2015 at 4:51
  • 1
    Now that the bounty is over, I just want to say that it was a tough decision regarding which answer to award it to. Thaddeus' answer is wonderful (the illustrations and video are great), and it provides an excellent answer to the first part of my original question. After the bounty was placed, N_Soong added a lot more material to his already superb answer, enough to produce an answer that completely answers all aspects of the question, in my opinion. As a result, I have decided to award the bounty to N_Soong's answer...
    – Praxis
    Jul 11, 2015 at 0:31
  • 2
    ...In a sense, I feel that both answers have been recognized for their merits: Thaddeus' with many well-deserved upvotes and N_Soong's with the bounty. I thank both of you for your interest and hard work!
    – Praxis
    Jul 11, 2015 at 0:35

There were two versions of the Enterprise used in production.

  • The first one was used in the original pilot and for all of the original introduction shots.

enter image description here

December 29, in 1964: Craftsmen Richard Datin, Vern Sion, Mel Keys, and Volmer Jensen pose outside of Jensen's Los Angeles model shop with the just-completed original 11-foot version of the starship Enterprise.

enter image description here

  • The second Enterprise design was seen in all of the original series episodes and had several changes including changes in painting, additional lighting and the spheres added at the rear of the nacelles.

enter image description here

Here is some footage from the Smithsonian talking about the history of the original Enterprise model used in the series.

  • The sphere shape object at the end of a Constitution Class starship's nacelles is part of the warp drive field manipulators. They were supposed to help stabilize the warp field but as to their efficacy, or why the design changed in-universe, it was never established.
  • The USS Enterprise's first documented refit occurred sometime between 2254 and 2265. Minor changes were made to the ship's exterior (most notably the impulse engines, warp nacelles, running lights, and hull markings). More substantial changes were made to the interior color scheme and layout of the ship.

  • A second, more extensive refit occurred at some point after her encounter with the "galactic barrier" in 2265. It involved replacing the bridge module, a newer, smaller deflector dish, and refinements to her warp nacelles.

  • Who's the guy in the first image that looks like Stan Lee? Jul 1, 2015 at 14:18
  • 5
    @MasonWheeler: Umm, since can't decide which of the three you mean, none of them. Jul 1, 2015 at 14:41
  • 5
    -1 for referring to them as "spheres" :) Jul 1, 2015 at 22:37
  • 1
    Does anybody know why the original photo was manipulated to make it look like there were only 3 people? (See revision history; the first photo is clearly shopped!)
    – Mr Lister
    Jul 2, 2015 at 14:08
  • 4
    I don't agree that it was photoshopped, just two different pictures that are close to identical. If you look at the edit of the text, when the picture change, the text "(not pictured)" was also removed from one of the names. If it was photoshopped, great care was taken to the shadows of the guys on the sidewalk, the detail of the two cars in the background that have portions obstructed by the heads of 2 guys and a slight rotation of Mel Keys (gold shirt).
    – dave k
    Jul 2, 2015 at 18:02

Here is a copy of a memo sent to Robert Justman. Apparently the balls in the back were supposed to have the same light effect as the bussard collectors.

To: Robert H. Justman cc: H. Solow, M. Jefferies, B. Heath, Anderson Co. Date: April 7, 1966 Subject: SPACESHIP MODEL

Bob, here is a resume of our discussion of changes in the large model as per the Anderson Company drawing and cost list:



FILLIGREED PANELS ON TWIN POD STRUTS. We see this marked as "painted". We were of the impression we were going to use some applique which gave the illusion of something like solar cells. We're willing to go any intelligent way here, but wonder if this is an error.

ROUNDED DOMES ON REAR OF TWIN NACELLE PODS. We see no estimate for eliminating them. What is the minimal cost of putting a steady light source illumination in them? Incidentally, we do feel they should be somewhat the same color as the front pods, carrying out a feeling of the same power engines running through the whole pod.

HANDLES ON TWIN NACELLE PODS. We wanted these handles improved to look less like "handles", but wonder if it cannot be accomplished in some way at less cost than $180.00. Or, understanding that this is an estimate, could we review the cost of this shortening? At any rate, let's assume this is one of the last things we'll do, something which could be cut if our cost gets too high.




LIGHT SOURCE ON INSIDE AREA OF BOTH PODS. We'll omit this item and cost of $300.00, discuss with Matt Jefferies an applique metal grid overpaint or something else which will require no structural change. And we'd like to have some sort of estimate on this or whether it can be included in the overall detailing figures. Incidentally, this eliminates Anderson's next quote about possible rebuilding of pod, an item for which he was going to give us a price later if it becomes necessary.

SMALLER QUARTER SIZE MODEL. Does the price of revamping this smaller model include some lights in the pods? it seems to us this is one change, since it involves elimination, that would affect any shooting of the smaller model, even if it's flashing by. Would like Anderson to tell us if, perhaps, we could do away with the fluctuating aspect of the lights here since it most often will flash past us very fast. Or, if we do need the fluctuation here, possibly we can do with a standard fluctuation and do without any change of intensity.



STEP BY STEP REVIEW AND APPROVALS. This U.S.S. Enterprise is terribly important to us -- if the audience does not believe it, they are not going to beleive a multimillion dollar series investment. Therefore I want to suggest and emphasize that I am making myself available to come by and review, discuss, and approve all these changes as they are going on. (....)


  • 1
    Welcome to the site. Do you by any chance have a source for this??
    – Rogue Jedi
    Apr 11, 2016 at 14:13
  • No sorry Rogue I don't. I found this years ago on the interwebs. I'm fairly certain it is legitimate however. It would be both bizarre and completely pointless to fake a document like this. Anything is possible however. :)
    – Spockboy
    Apr 13, 2016 at 16:54
  • 4
    The memo above is accurate. A photograph of it appears (including the text skipped over with ellipsis points above) in this rather terrific little book by original Enterprise model maker Richard C. Datin and his daughter: The Enterprise, NCC 1701 and The Model Maker
    – user267998
    May 5, 2016 at 2:44
  • They're worried about their "multimillion dollar series investment" being believed by audiences yet cheaping out with the crafts shop over $180 non-handle-looking handles....
    – davidbak
    Feb 11, 2021 at 22:52

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