In the 2004 reboot of Battlestar Galactica, many of the spaceships are shown with their engines on for extended periods of time. In space, there is no air resistance to compensate against with thrust, so why have the engines firing unless you are accelerating/decelerating or maneuvering?

This is especially evident with the vipers during gunfights. It would seem that having their main engines constantly on would cause them to accelerate to very high speeds.

There is a point where Boomer mentions that her raptor should have enough inertia to reach her destination, implying that without enough the ship would stop short of the destination.

Is there ever any explanation of this either in-universe or during an interview? Or is this just done for visual effect?

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    "Engine on" may not be the same as "Engine is providing thrust"?
    – Roger
    Mar 17, 2014 at 18:06
  • @Roger In this case, I mean that the engine(s) are providing thrust. The instances I am refering to are when the engine is very clearly thrusting (flames coming out for vipers and raptors, energy of some sort coming out of the engines of galactica/pegasus). Spaceship engines are not internal combustion engines, so they do not have an equivalent to idling like a car engine. They either are expending fuel to create thrust, or they are not. Mar 17, 2014 at 18:09
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    Your last statement may not be necessarily true depending on the way the particular world is defined. I'm thinking of something like Firefly where the engine has to be turning to operate (for instance) the CO2 scrubbers (reference episode "Out of Gas"), but the engine isn't necessarily providing thrust. I don't know enough about BSG to know if they have a separate system that generates power for life support, grav plating, etc., but I take your meaning that you're referring to specific instances where you can see visible thrust.
    – Roger
    Mar 17, 2014 at 18:28
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    WRT Boomer's comment: she may have implicitly meant within a desired/required time frame. With zero other forces acting on a body, any velocity in the correct direction will eventually get you to your destination, but will you get there soon enough?
    – Brian S
    Mar 17, 2014 at 18:37
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    For the record, the canon quote is "I think we have enough inertia to make it to Caprica's ionosphere. Then we power up, find a place to land.". The reality is of course that she means "momentum", not inertia. That said, if she has insufficient speed, she'll miss the planet and sail by without slowing down;
    – Valorum
    Mar 17, 2014 at 19:53

9 Answers 9


Because it looks awesome.

Science fiction is about wonder and awe as much as it's about telling a scientifically-based story. Not having engines always firing is accurate, but it confuses viewers, who know how airplanes look when they work, and wastes the wonderful opportunity for the awesome visual effect.

They're asking for you to suspend your disbelief so they can dazzle and excite you.

EDIT: some answerers have been discussing real orbit-mechanical reasons why you might run your engines for extended periods of time. Those are fun and fascinating discussions for the real world, and I encourage you to pursue them. However, all of them are voided (if you pardon the pun) by the existence of FTL. Almost, if not all, crafts that go any distance in the show do so under FTL power, so the real strategies such as acceleration-deceleration trips aren't relevant.

  • Yeah: there's a million science fiction things that look awesome. Very cool-looking spacecraft that look like super jet fighters -- but it is clunky-looking Borg cubes that are probably how big ships would look. Seeing phaser beams from the side even though unless you are in smoke or fog u can't see a beam that way.
    – releseabe
    Mar 29, 2023 at 21:05

I've also been wondering about this but I have thought that it could be in case they need some rapid acceleration in order to get away from another object its safer to have the engines at 1% thrust at all times. For example say the Cylons suddenly appear in Battlestar, then it will be a lot slower to turn on the engine AND THEN increase thrust rather than just increasing thrust from 1% to 100%. I assume if it is constantly at 1% that they counter the constant 1% thrust every 12 hours with a burst of reverse thrust.


Because the audience expects a visual indication of speed

Your average sci fi viewer isn't going to look at a spaceship in deep space and simply assume it is in motion, especially not assuming that the object is moving really fast relatively speaking - space lacks the visual cues we are use to seeing (clouds, landscapes, by default other vehicles).

It's hard to illustrate, but if you peruse the following compilation of fight scenes:

You'll see that the show uses the following tricks to convey speed:

  1. Speed relative to other ships. For instance, fighters moving past larger vessels
  2. Ships clearly moving past interstellar debris/galaxies/etc
  3. Camera angles and perspectives (IE a first person view in flight, motion blur, sweeping shots)

And of course:

  • Visible engine thrust

Note that the engines aren't always blaring at full thrust. Sometimes you can clearly see that the engines are blasting - usually to indicate they are charging into battles, and other times they're a softer blue glow which helps indicate that they aren't a static unmoving object.

As others have noted, the science on this isn't decidedly against Galactica. It is, after all, a show where the fleet is fleeing about 90% of the time - so they aren't necessarily always trying to get somewhere efficiently as much as they are just trying to get away.


It could be how they generate their artificial gravity. The MCRN Donnager from the TV show The Expanse uses this technique. The decks are alligned perpendicular to the center axis that runs the lenght of the ship so that forward thrust generates the artificial gravity.

Let's not forget that they are constantly under threat of the Cylons that pursue them so it could just be the mentality of "we stop, we die."

  • This is a pretty smart answer that I hadn't though of. Nov 15, 2016 at 20:24
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    Seems unlikely for the galactica at least. The hangar deck is almost definitely arranged that way, as evidenced by the launch tubes and the way that raptor recovery comes down from above (the deck is below the runway). Also, early in season 1, there is a scene with Billy and Dee in an observation deck type room where they see the vipers fly by. The room there is arranged such that the floor is parallel to the direction of thrust and the hallway outside the room is the same. I think it's simply a physics oversight. The way vipers fly is often very similar to aircraft too. Feb 14, 2017 at 20:46

In many sci-fi franchises the engines provide thrust to get to the destination quicker. Although no thrust is needed to maintain a speed in space, the travelling time can be cut down by using thrust to accelerate to approximately halfway then using reverse thrust to slow down for the same amount of time. That would, of course, depend on the reverse thrust being the same as the forward thrust. Not many spacecraft in BSG have big old engines on the FRONT, after all. Maybe there's some form of thrust vectoring in play on the main engines.

It's worth highlighting that there's no real upper limit to speed of an object in motion in a vacuum, and continually applying thrust accelerates a ship according to the engine power levels. Galactica, being the only military ship in the "ragtag fleet", probably has the most powerful engines and runs them at a fraction of max output to allow the others to keep up with it and still be able to decelerate at the end of the voyage.

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    While they were up there no doubt, it is possible that she may not have had the most powerful. It is conceivable that some of the civilian ships might have had more powerful engines simply as a result of being newer, especially some of the ones meant for heavy-lifting... cargo or mining ships. Keep in mind Galactica was, what... nearly a half-century old at the time of the show.
    – eidylon
    Jun 4, 2014 at 22:00
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    There is an upper limit and it's very real - the speed of light. The only way to beat the upper limit is to use the FTL drives and in this universe FTL drives "jump" from point to point.
    – slebetman
    Jul 17, 2014 at 18:56
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    @slebetman: though there is, of course, no upper limit to kinetic energy. Someone travelling through space at .09c is going to have a very different experience from somene travelling at .99c, and a yet different experience from someone travelling at .999c. Adding that decimal place isn't a game of fractions at those speeds. Jul 17, 2014 at 22:33
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    Of course, accelerating to anything even marginally relativistic in less than several years would be enough g force to kill a human without some other means to counteract it. Jul 17, 2014 at 22:34
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    "It's worth highlighting that there's no real upper limit to speed of an object in motion in a vacuum" - Speed of Light. Maybe you've heard of it?
    – paul
    Nov 20, 2014 at 0:52

You answered the question within the question.

"having their main engines constantly on would cause them to accelerate to very high speeds."

The entire MacGuffin Engine of the series is that they are:

  1. Being chased by Cylons
  2. Going somewhere as fast as possible

The only time you see them shut everything off is because they HAVE to (or when they're in orbit). For maintenance repairs, for damage repairs. And then they mumble & stare at each other in fear, hoping that nothing happens while their engines are down.

Compared to many other Sci-fi, Battlestar does a lot of things right. You see the venting of the Vipers for manuvering. You see those with engine damage go streaking off in whatever random direction they were going prior the engine stopping working. You miscalculate the FTL jump, you land inside a mountain.

The initial encounter of the New Vipers vs the Raiders, you see the vipers 'parking' in lines, using their vents to stay "upright"... and when they get hacked, they start slowly spinning, as the vents no longer maneuver them back into place. In every attack from the Battlestar, the vipers have to keep their engines on to not only get from point A to B, but also to get rid of the momentum they gained from the ship, and furthermore to chase down the enemy raiders. Yes - there is something ridiculous about dogfighting in space, but they also touch on that by using projectile weapons of various levels of dumbness. The reasoning of the dumbness & use of 'ancient' weapons at that level of techology is due to the inability to network anything - any smart missiles shot at the Cylons would simply be hacked and turned around against the humans (although you'd think the Cylons would use them... although technically the raiders ARE smart weapons?).

Although there is no mention of conservation of momentum on FTL Jumps - FTL in Battlestar is a point-to-point Teleportation similar to Battlefield Earth, where objects are simply moved, rather than travelling through warped space which WOULD have conservation of momentum, and require deceleration & "internal dampeners". Also, if each FTL jump obliterated all momentum up to that point, that would also explain why the fleet's engines seem to be always running - each Jump requires them to start from 0, and build up the acceleration again.


In real life, as in not in movies, the ideal way to go from A to B in space is to constantly accelerate for 1/2 the journey and then constantly decelerate for the other 1/2. The only reason you don't do this is if you can't afford this (you don't/can't carry enough fuel).

So, assuming advanced technology (with the luxury of not running out of fuel for the duration of the journey) you would never want to turn off your engines and constantly accelerate all the way. This is the only logical strategy if you want to minimize travel times.

In fact, if you do the math, not only would you not want to turn off your main engines but you'd want to run them at 100% all the time.

So, in fact having the engines constantly on is not unrealistic, but very realistic assuming they have the fuel.

The only slightly unrealistic part is the battle scenes where Basestars and Battlestars are essentially stationary. Real slower-than-light space battles would most likely occur at very high speeds and long distances. Obviously if they show that on TV it would be less dramatic, because you wouldn't see much.

Also unrealistic is the concept of fighters in space. In space your speed (acceleration) is a function of how big your engines are. So fighters would be dismally slow compared to Battlestars, which means they'd be mostly useless. The moment they're launched the Battlestar would accelerate so much faster that they'd leave all the vipers behind. The only reason fighters are faster than aircraft carriers on Earth is due to friction. And there is no friction in space.

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    For examples of realistic space battles read "The Mote in Gods Eye" and its sequel.
    – slebetman
    Jul 17, 2014 at 18:57
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    Sorry, but your ideas about speed/acceleration are unfounded. Assuming thrust is proportional to engine size, then acceleration is determined by the fraction of total vehicle mass taken up by the engine. Fighters are stripped-down jobbers with an engine, fuel for a small mission duration, weapons and pilot, so the engine (and acceleration) can be a much larger proportion than a capital ship with living quarters, ammunition stores, maintenance equipment, large fuel stores, etc. Jul 17, 2014 at 21:19
  • @WhatRoughBeast What you said is true, but doesn't invalidate anything in this answer. Constant acceleration will increase/decrease speed until the acceleration is no longer applied or a limit (such as the speed of light) is approached. Ignoring factors such as fuel, increasing speed for first half the journey, then decreasing speed for the second half will minimize total travel time.
    – Izkata
    Jul 17, 2014 at 23:05
  • I was referring to the last paragraph, which I belive is pretty much completely wrong (or at least unsubstantiated). Your claim of constant acceleration for minimum time is correct. However, since fighters would normally be expected to have proportionately much less extra mass (including fuel, since their mission time would be much less than the main ship's) their operational acceleration should be potentially much greater, allowing them to keep up the larger ship. Jul 17, 2014 at 23:17
  • @WhatRoughBeast: Only if the capital ship is badly designed - with a too small engine. For every force deployed with large capital ships with small engines + small fighters with smaller engines I can pit it against an enemy with capital ships manned by 2-5 people with huge engines that would outmaneuver both your capital ships and your fighters.
    – slebetman
    Jul 18, 2014 at 3:20

The engines are reaction-mass type engines. There is a large electrical field in the reaction chamber that sends the reaction mass out the nozzle to create locomotion. The electrical fields would always be on, and are powered by the generators on board the ship (which supply everything power on board, and are always on; they do not move the ship directly). The engines pump reaction mass (fuel) into the electrical field when acceleration is desired. Therefore, even when not accelerating, the engines will glow; when reaction mass is pumped into the engine you'll see the reaction mass ejecting out of the nozzle as visual "thrust."

The engines are always on, and glowing, but not always generating thrust.

I read that the Tylium is used in a fusion reactor, supporting the idea that the engines must be mass-reaction drives.


Just re-watching bsg and the sub-lightspeed engines thrusting also bugs me a bit. The suggestion that this is because it's what people expect is somewhat disproven by the fact that the cylon base stars don't even seem to have such engines although they do seem more space station like and therefore static.

It makes sense for the small craft, but Galactica itself and the fleet that follows don't seem to need such engines most of the time with the exception that sometimes they might need to manoeuvre closer to a planet or similar in a safer fashion than jumping can manage.

  • 1
    Hi, welcome to SF&F. The question was looking for reasons that the big ships would run their engines continually. If you don't have an answer to the question, you should be posting a comment, not an answer. You might want to take the tour to learn how to use the site effectively.
    – DavidW
    Mar 29, 2023 at 20:42
  • Sorry about that, just watching season 3 episode 20 and I believe that I have the answer. When they jump and lose the engines they state that they are on battery power only and need to get the engines restarted. I believe then that the engines are used like an apu for a jet airliner, to provide essential power.
    – Rob
    Mar 29, 2023 at 21:02
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    And that is a reasonable answer; you should edit your post to say that, and if possible include the quote and its source.
    – DavidW
    Mar 29, 2023 at 21:07

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