Impulse Engines (Star Trek Lore)

The Impulse drive is the standard form of sublight locomotion in Star Trek ships from Starfleet and beyond.
They are basically fusion reactors with a more traditional exhaust to produce thrust in space, but let's take a look at them in detail.

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This Video is for critical purposes with commentary.

[maverickjsmith]

As a small pedantic note, in the TNG tehcnical manual, subspace driver coils were added to impulse drives with the ambassador class project when simulations projected that the vessel's mass was too great for then current impulse drive designs, taking minutes to reach full impulse. A subspace driver coil, powered by the impulse exhaust, was added to reduce the apparent mass of the ship when powered. This solved the ambassador design problem and became the standard for all impulse drives moving forward. This improvement is so powerful a single impulse engine on the galaxy class can drive it's enormous mass of 4.5 million metric tons to 0.25c in seconds.

tl;dr ships got too big and they made a better impulse engine that cheats physics and now it's the standard

[NimbleTack]

My starship kept jumping to half light speed even when I was trying to go slowly. Turned out I'd accidentally installed Impulsive Engines.

[CZtuner]

Impulse Power is based on the 1930's Subatomic Impulse Postulate, whereby cold fusion could be achieved by synchronising the subatomic impulse of hydrogen atoms via a yet to be perfected contraption called a Synchroniser. (Scotty mentions a Synchroniser a few times in TOS episodes). Experiments were last conducted, during the 1950's, ending in failure due to spurious detrimental magnetic fields. TOS writers assumed that humans would have solved the problem by the time of TOS.

I had this explained to me by a physicist, back in the mid-1980's.

[ptah]

In Balance of Terror, when Scotty says the Romulan ship was simple impulse, I took it to mean that it used fusion reactors rather than matter/anti-matter reactors. If it had a singularity drive, it's likely Starfleet didn't know about it. That's my little retcon

[josephmassaro]

Impulse speed is all over the place in Trek. In Star Trek III, Both Kirk and Styles call for 1/4 impulse power...in space dock. I'm sure thrusters is the most you want to use in space dock, but that's what they called for.

[logicplague]

You should do one on how Stardates work, I bet subspace is easier lol.

[bipolarminddroppings]

If Full Impulse is only 1/4 lightspeed, time dilation isn't an issue. You have to get significantly closer to lightspeed before time dilation becomes noticable, at 1/4 lightspeed 20 minutes of measured onboard time will be 21 minutes as measured by an outside observer.

So you would need to be at full impulse for many days before it really matters.

[liljenborg]

In spite of how much we (the fans) love the technobabble and figuring out how all the tech works, "Impulse Drive" is a sign that the makers of the show don't really care about realistic movement of ships in space.
"One quarter impulse" makes sense to your normie audience because they either are familiar enough with the throttle on a boat to grasp the concept or they can simply figure out that it means something akin to "a quarter of how fast you can go before you have to go to warp". And the "one quarter impulse" is consistent no matter the power of the engine or the mass of the ship, even though anyone familiar with boating would quickly grasp that "one quarter throttle" on my son-in-laws little putt-putt fishing boat is a VERY different thing that "one quarter throttle" on my brother-in-law's "if I can just get a a hundred more RPMs out of this baby, she could break the SOUND BARRIER" ski boat.
But nowhere in the literature do you actually get a "g" value for how much acceleration the engines actually pull. (At least the RCS thruster pages give you the thrust value in Newtons.) In fact almost NEVER is impulse thrust referred to as "acceleration" (which is how a "hard" sci-fi setting would measure ship's speeds). Starship movement is always treated as a "speed" (if the engine is on and set for "one quarter impulse" the ship is moving about a quarter of lightspeed - which would be between 45 and 50, 000 miles per second - not that most of your normie audience knows that that would get you to the moon in five or six seconds or to Mars in less than an hour, and is about 120 times faster than the Apollo rockets to the moon could travel). Even "Warp Speed" is a speed level, not an acceleration level. But you can still use "one quarter impulse" INSIDE spacedock without blowing a starship shaped hole through the outer hull 0.0005 seconds after throttling up. It also means the script writers never have to worry about ships having to spend an hour (or a day or two) to SLOW DOWN (space travel works like a car, right? If you stop holding the gas pedal, you start slowing down, right?) Once the engines are off, the ship practically stops instantly (that what that acceleration compensator field thing is for, right?).
In terms of Star Trek, these sorts of things don't matter to the STORY they're trying to tell. It just has to LOOK good on screen (hence starships with phasers and photon torpedoes that have ranges measured in light seconds shooting at one another at less than a kilometer as if they were sailing ships broadsiding one another with seventeenth century canons - heck, even in STO max range is TEN klicks) and make sense to a "normie" audience who doesn't know that what they're watching doesn't make sense in terms of actual physics.

[MathewRenfro]

@3:00 if full impulse is 1/4 speed of Light, (approx. 186, 000 miles/second) then its 46, 500 miles/second.
then 1/4 impulse (standard solar cruising speed, ) then that is 11, 625 miles/second.

[gideonsiete]

Even if full impulse is only 0.25c, that is still ridiculously OP. With that much kinetic energy simply crashing a 100, 000 ton starship into Earth would be an extinction level event.

[VulpisFoxfire]

I would note that 'impulse drive' is probably a catch-all term, covering *any* drive system designed for sublight travel.

[HrLBolle]

0:35
Vessel movement at a speed greater than maneuvering at close range or the holding position before executing certain maneuvers, such as docking to a space station or a space dock

[rubaiyat]

I believe the TNG tech manual basically described it as a Mass Effect drive without the branding. There was a fusion reactor and rocket, but in between a component that could lower the effective mass of the ship so it could nearly instantaneously accelerate a ship to high fractions of light speed like hitting full impulse from a stop would require.

[nixboox]

I think you missed the biggest part of how the impulse engines work. Their subspace fields super-accelerate the propellant so that the ship can move quickly and nimbly, but the inertial dampeners also alter the mass distribution of the ship so that it moves like a much lighter vessel. This is why the ships never need months to get up to speed, and no one ends up splattered against the rear bulkhead when they start moving.

[mutanix]

I always wondered how ships did impulse in reverse as we never see forward facing impulse engines.

[philipfahy]

I like how handwavium led them to basically create a more complex torchdrive as an impulse engine. Like fusion reactor heating up exhaust propellant is pretty realistic torch drive, and then ya had to go and add in subspace.

[stephenconnolly]

Waaaay back in the say, one of the old Star Trek novels described it as Internally Metered PULSE Drive. You contain and compress the energy of the impulse reactors so it has nowhere to go, leading to waves of distortion in space, and the ship rides the waves.

[unarealtaragionevole]

I'm glad you brought up time dilation at full impulse. It's something I remember from the books but never the shows. I always thought a good idea for a show would be if a ship lost warp ability and communications. Unless someone rescues them, they have two options: 1) travel at less than full impulse and die of old age in space...or 2) risk full impulse for long periods and time travel into the future with time dilation.

[lucasbachmann]

1:44 I'm not sure warp drives came before impulse has a source. Everything in TOS would imply otherwise and note on TOS Earth had interstellar colonies - Khan's ship for example. It would also make sense just as a starship has chemical rockets for thrusters it would maintain the legacy impulse drives too.

[stevengalloway]

Great explanation of the "slower" engines of Star Trek that we sort of overlook in favor of the "more glamorous" warp.... 😆