The side engines seem to be regular atmospheric jet engines (at least they have that sort of intake), but is there any statement in any of the side material (RPG, comics, etc.) what the main "firefly tail" engine is?

I know the Firefly verse ships aren't FTL, but is it a fusion drive? A nuclear lightbulb? Some kind of super-powered ion drive?


1 Answer 1


According to the (officially sanctioned) Serenity Blueprints Reference Pack, Serenity's main propulsion is provided by an radion accelerator core:

The pack itself does not seem to be available for purchase, but you can browse some of the pages on the site I linked above.

River says the same thing in "The Train Job":

Midbulk transport. Standard radion accelerator core class-code 03-K64. Firefly.
River quotes on BrownCoats.com

Radion, in physics, is a

hypothetical particle that emerges as an excitation of the metric tensor (i.e. gravitational field) but whose physical properties are virtually indistinguishable from a scalar in four dimensions, as shown in Kaluza–Klein theory.

Which may be the [pseudo-] science explanation for Serenity's propulsion in-universe. Also, to quote this answer:

Firefly class ships used a fusion explosion to propel it and that glow is the explosion causing the ship to gain a burst of speed.

On the other hand, there is also Radon (symbol Rn, atomic number 86), which is a noble gas, which, according to this answer could be used in real life for ion propulsion engines. The reason it's not used is because it's radioactive, but the Firefly 'Verse is able to shield radioactivity (except Reavers).

Maybe (speculation here!) the name of the engine was supposed to be a reference to this, as the Firefly 'Verse is not that far away in terms of propulsion (no FTL drives, for instance). One argument against that is the real-life ion drives are very slow - they provide constant but minuscule acceleration, as opposed to one huge burst we see in the series.

  • I've read the comics, but I don't remember an explicit mention of the type of the engine or its working principle. Jun 5, 2017 at 7:57
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    "fusion explosion" tends to argue for something like pulsed nuclear propulsion, but the design doesn't look like that. I think the bottom line here is that Firefly is more about the rocketmen than the rockets. Jun 5, 2017 at 10:41
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    @ChrisB.Behrens And yet, I would argue that Serenity herself is a major character in the series—every other of the main characters has a deep, personal relationship with the ship. But yes, the show is very much about the personal and the characterization, not the engineering.
    – KRyan
    Jun 5, 2017 at 12:13
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    The reavers can shield, they just don't care. Jun 5, 2017 at 21:30
  • Interesting. I admit that I don't understand that article, but it seems like radions have something to do with speculative theories of gravity, which could actually make sense - the Verse seems to have some kind of artificial gravity, as the ships aren't "spin" designs. @ChrisB.Behrens: also, I wouldn't think a ship propelled by nuclear pulses could take off as close to people & buildings as we see Serenity do. (though maybe the atmospheric propulsion is all jets?) Jun 7, 2017 at 9:14

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