The nature of Impulse Power / Drive

[Jedi Marso]

This was turning into a discussion in another thread and I'd throw it here for a tech discussion. How do you perceive impulse drive to work in Trek? Here's my take on it:

My thought on impulse is that there are two facets to it: the 'power generating' facet and a 'gravity drive' facet.

The 'power' aspect of the impulse system is that it is a fusion-reactor power system that operates in adjunct and as the primary backup to the main energizer. The latter is the anti-matter / dilithium channeling power system, commonly referred to as the 'warp engine' or 'warp drive.'

The 'drive' portion of the impulse system I've always thought to be a continuum twister like warp drive, just one that works on a slower-than light level. Sort of like the Alcubierre Drive that resembles warp drive, but on a sub-warp level.

That's why when the warp engines / mains are damaged, they always revert to impulse power first, then auxiliary power, and then batteries at the last. That's the power generating facet of the impulse system at work.

When the captain calls for "One half impulse" when giving maneuvering commands, he is ordering the ship to half of it's max capable 'impulse powered speed.' I don't have the specs right in front of me, but if we assumed that .25c is the maximum speed the ship moves under impulse drive, then 1/2 impulse would be .125c, and because impulse drive is an alcubierre / artificial gravity drive of some sort rather than a Newtonian 'fusion rocket,' the acceleration is smooth and it only takes a few seconds to achieve the desired speed.

When helm commands are being exercised by 'thrusters,' the ship is moving under strictly Newtonian rules through the use of some form of reaction jets. Ship's thrusters provide a tertiary backup for movement, although at infinitesimally small accelerations compared to impulse power. Good for maneuvering out of spacedock or making a fine correction to an orbit, or changing the attitude of the ship when impulse drive is down, but little else.

 

[Crazy Eddie]

It's always been pretty explicit that impulse engines are a combination of conventional reaction engine (e.g. a gigantic thruster) and some kind of subspace fuckery that lowers the ship's inertial mass so that it takes less thrust to actually move anywhere. Support for the latter premise was established in DS9 "Emissary" but was also doubly confirmed in Star Trek Into Darkness, where the Enterprise's maneuvering thrusters cannot even stop it from falling until after the warp core is reengaged. That suggests that those thrusters, while powerful, are not designed to move the full mass of the ship without a subspace field to reduce its inertia. Impulse engines almost certainly take advantage of this feature.

What hasn't been as clear in the reboot films is whether or not they are still thrust-producing engines or using some other kind of trickiness, but evidence strongly suggests a "thrust" component; Sulu's dialog in STXI is almost explicit when he tells Chekov "Give me a five second burst at one quarter impulse, I'll do the rest with thrusters." So while it may not look like it, the impulse engines are still being used almost like a space shuttle's OMS engine, but boosted with subspace magic.



The only thing is, impulse power seems to be much more a measure of relative velocity than of acceleration, otherwise starships would travel interplanetary distances on complicated brachistochrone trajectories that require both very long acceleration and deceleration phases. This doesn't seem to be the case, since starships have been seen to make sudden course correction sunder impulse power or even stop their movement altogether.

On the other hand, Star Trek has never been very good at giving us a realistic depiction of what sublight travel -- or sublight maneuvering -- even looks like; the only major scifi production that does a worse job of this is Star Wars, for what it's worth, and for pretty much the same reason.

 

[Timo]

The only thing is, impulse power seems to be much more a measure of relative velocity than of acceleration, otherwise starships would travel interplanetary distances on complicated brachistochrone trajectories that require both very long acceleration and deceleration phases.

Balancing this against the fact that X impulse explicitly differs in speed value between episodes, it would seem that going for "throttle setting" and implicitly also accepting "complex navigation" is the way to go.

This doesn't seem to be the case, since starships have been seen to make sudden course correction sunder impulse power or even stop their movement altogether.

But it's all relative: if a starship at speed makes a sideways twist, we have no way of telling whether she killed any of her initial forward velocity. Probably she didn't.

Although we could always evoke "subspace anchors" or "drag chutes", things that break the symmetry of Newtonian travel by hooking into an absolute frame of reference underneath the normal structure of space.

Timo Saloniemi

 

[Tenacity]

I like the idea I read several years ago (forget the author) that the impulse engine is basically a version of the warp drive optimized for slower than light travel. This is why when the ship "fires up" the impulse engines we never see any exhaust gases. No matter the angle or light conditions.

A fusion warp drive.

 

[Ronald Held]

Impulse speed as warp speed is plot driven.
Seriously, it must be fusion reactor output with some field to lower the ship's inertial(and Gravitational?) mass

 

[C.E. Evans]

Federation starships may reserve impulse power mainly for sublight travel, but presumably other cultures can use impulse power for FTL flight. That idea would go nicely with the Romulan bird-of-prey in TOS' "Balance of Terror" having only "simple impulse" as a power source.

 

[Timo]

But the Romulans there had a highly capable and advanced power source, because they could fire up their superweapon, their warp drive and their invisibility cloak (or two out of three anyway), while Kirk's ship could only manage a warp drive. Scotty's ridiculing of the Romulan power source thus should be taken as

a) a grievous error, since those do happen at times when one is making wild guesses, or
b) applying to the drive part of the ship only, in which case it no doubt was a grievous error because the power sources of the other two supersystems should provide superior power to the drive as well.

In other words, "simple impulse" as defined by Scotty isn't what the Romulans had. Perhaps "complex impulse", or "supertech that looks like impulse to the ignorant"?

Timo Saloniemi

 

[CorporalCaptain]

It's always been pretty explicit that impulse engines are a combination of conventional reaction engine (e.g. a gigantic thruster) and some kind of subspace fuckery that lowers the ship's inertial mass so that it takes less thrust to actually move anywhere.

This.

 

[Tenacity]

but presumably other cultures can use impulse power for FTL flight

Might explain how the Enterprise got ... well, anywhere in WNMHGB after the "main" warp drive was fried.

 

[C.E. Evans]

But the Romulans there had a highly capable and advanced power source, because they could fire up their superweapon...

Not necessarily. They had a plasma weapon that packed more of a punch than Federation phasers, but even that could have been impulse-powered, taken directly from the engines rather than from a separate distributor.

 

[C.E. Evans]

Might explain how the Enterprise got ... well, anywhere in WNMHGB after the "main" warp drive was fried.

If we go with the idea that impulse engines have subspace driver elements, the saucer could possibly coast at warp for quite awhile, like a surfboard pushed by an enormous wave (or maybe more accurate, like a bullet fired from a gun). At warp 9.5 when the separation occurred, the saucer may have had enough of a push to reach Farpoint Station before its kick off ran out of steam.

 

[Dilandu]

Well, IMHO the solution of impulse drive problems is to assume:

- The warp drive is primarly the auxilary fusion reactor
- Which could also be used as rocket thruster by just letting the plasma out
- And it could be also used to power warp coils. It isn't as cost-effective as matter/antimatter reaction, but could work at least at low warp.

 

[Timo]

Might explain how the Enterprise got ... well, anywhere in WNMHGB after the "main" warp drive was fried.

Why would that require an explanation? We got told exactly how far salvation was: "a few light days". Covering that at STL speeds would be eminently possibly within the constraints of the plot.

The real question goes, why was the ship so close to Delta Vega? And the answer might well be "by design". That is, Kirk would have ventured to the wilderness along a prepared path of camps and supply stashes, and Kirk would fly past the outermost on his way out and then return pretty much where he started when the Barrier didn't welcome him.

(In different timelines, the chain of Project Vega stations would support different pushes into the unknown, so different planets would get to bear the names.)

At warp 9.5 when the separation occurred, the saucer may have had enough of a push to reach Farpoint Station before its kick off ran out of steam.

But that wouldn't explain "Arsenal of Freedom" where LaForge deliberately refused to give the saucer any push. An ability to independently accelerate to warp is likelier (that is, a better way of explaining the evidence) for the E-D saucer.

Timo Saloniemi

 

[Go-Captain]

In TNG, the Q episode where he is depowered, they use the warp field to lower the mass of a moon. That makes it clear what impulse drives do to make for such extreme acceleration and top end speed. Without mass manipulation there is no way the ships could accelerated to near light speed in less than the course of months, but they do it in seconds, or hours at most.

This also explains why non-warp shuttles, like the Type 15 shuttlepod have nacelles. They are called impulse driver nacelles so it further drives the connection. In larger vessels either the impulse engines generate their own warp field, or the impulse engines work in concert with the full blown warp engines. The Galaxy class saucer gives some confusion, because it safely cruises away at warp, but there is nothing saying a ship requires warp power to safely drop from warp, only stay at warp. We might conclude the saucer has warp sustainers like a torpedo, or that the impulse engines do indeed have built in impulse drive units which can also act as warp sustainers. With a sustainer function it could cruise indefinitely once brought up to speed by the combat section, like the manned probe casing used to transport the female Klingon ambassador (Alexander's mother) at high warp from light years away.

The impulse engine itself, the red glowing part, is nothing but some sort of rocket. We assume they have their own fusion reactors, but I am unsure we have ever received a definitive statement or implication within the show concerning that. It does stand to reason though that they have their own reactors since that is the conventional arrangement of fission, fusion, and antimatter engines. Interestingly, the Conastoga class colony ship has conventional rocket cones which look like they are for chemical rockets, so there is an implication that impulse can use any conventional thrust source, assuming the Conastoga even has impulse.

There are also sub-impulse ships, of which the Bajorans had one. These appear to lack any warp system at all, and have a large engine aperture in back. We can assume this means it is purely rocket powered, perhaps by fusion or antimatter rocket sans warp field augmentation.

 

[psCargile]

I guess that the creators used the terms "warp" and "impulse" to denote non-Newtonian, and Newton propulsion, though the impulse seems to function as an inertia drive, and not via reaction. It appears to me that as depicted, TOS propulsion was more advanced than was seen or explained in TMP, TNG, and later, as if it was realised that ships needed maneuvering thrusters because current spacecraft have them, instead of sticking with the original edict that avoided rocket elements.

And the term "impulse" has a meaning in physics, and "specific impulse" is an attribute of reaction propulsion, so it's not like they made up a term. Whether it was used correctly is another issue.

 

[Ronald Held]

Delta Vega was a few crew days away if they cranked the impulse drive to relativistic speeds.

 

[C.E. Evans]

But that wouldn't explain "Arsenal of Freedom" where LaForge deliberately refused to give the saucer any push. An ability to independently accelerate to warp is likelier (that is, a better way of explaining the evidence) for the E-D saucer.

That's not really a given, actually. All LaForge told Logan was to proceed to a starbase, which is really the most logical thing for any evacuation craft to do for a number of reasons (the least of which being where it could be intercepted by other Federation vessels with warp capability). As it was, the stardrive section went after the saucer at the end of the episode to reconnect, likely long before it reached the starbase.

 

[Retu]

That's not really a given, actually. All LaForge told Logan was to proceed to a starbase, which is really the most logical thing for any evacuation craft to do for a number of reasons (the least of which being where it could be intercepted by other Federation vessels with warp capability). As it was, the stardrive section went after the saucer at the end of the episode to reconnect, likely long before it reached the starbase.

Unless the saucer section has some FTL capability, that's equivalent to telling a shipwrecked person: "The nearest coast is 2000 miles that way, better start swimming."

 

[Timo]

We saw that LaForge gave the saucer no boost. He then went on to perform a potentially suicidal attack, supposedly having separated the saucer exactly because he couldn't guarantee he would return - but also because the threat might come after the saucer if the saucer weren't moved away. Why shouldn't LaForge be shot with a squad wielding Varon-Ts when he failed to provide the saucer a boost it supposedly needed to drastically shorten the trip to safety?

We really should assume that no such boost was needed, and it's easy to do so. We know the saucer can move at warp (or at least FTL) and cover significant distances that way. Nobody ever told us she couldn't do that all by herself. So assuming that she has perfectly regular warp engines aboard sounds like a no-brainer.

The impulse engine itself, the red glowing part, is nothing but some sort of rocket.

Or then no sort of a rocket, but instead just this subspace field -manipulating machine. After all, save perhaps for E-nil and E-D, 90% of starship designs place the "nozzle" of this "rocket" so far off the obvious thrust axis that she would only be sent spinning, not moving forward - and the remaining 10% have it placed so that it in fact would blast against the ship's own structures!

Also, there's no correlation between "nozzle" glow and state of flight, suggesting that Uhura had a point in saying that all starships must have a tailpipe. There's some sort of waste coming out of that glowing thing all the time; in TNG, it glows a lot, in TOS-R, it only glows during exceptional peaks of power. But it's not a Newtonian jet.

We assume they have their own fusion reactors, but I am unsure we have ever received a definitive statement or implication within the show concerning that.

Different ship designs might have different power interconnectivity arrangements, but at least "Best of Both Worlds" heavily suggests that impulse engines provide their own power (fusion or otherwise, we don't know) and that this power is useful in combat in applications other than thrust. Whether they really get used that way in the episode is debatable, as their glowing bits are never lit in joined mode. In DS9, comparable ships do have their impulse glowers lit...

Interestingly, the Conastoga class colony ship has conventional rocket cones which look like they are for chemical rockets, so there is an implication that impulse can use any conventional thrust source, assuming the Conastoga even has impulse.

We hear of a breakthrough in sublight propulsion in 2018, and indeed there's a superfast interplanetary spacecraft in VOY "One Little Step", but that one still has prominent rocket engine bells. So the sort of impulse drive that requires no nozzles may be a much later development, perhaps only made possible by the invention of warp.

There are also sub-impulse ships, of which the Bajorans had one. These appear to lack any warp system at all, and have a large engine aperture in back. We can assume this means it is purely rocket powered, perhaps by fusion or antimatter rocket sans warp field augmentation.

We also hear there that this sort of craft performs much better inside an atmosphere than an impulse-powered contender. In open space, the opposite is true. But is this because of the drive systems, or some other differences in the craft?

Unless the saucer section has some FTL capability, that's equivalent to telling a shipwrecked person: "The nearest coast is 2000 miles that way, better start swimming."

And if the saucer has a "sustainer" type warp engine, LaForge's stunt of sublight separation is equal to telling the poor sod "And I can't spare you this helicopter that will take you quarter the way there (and within radio range of rescuers) before you have to ditch it. Just because.".

Timo Saloniemi

 

[C.E. Evans]

Unless the saucer section has some FTL capability, that's equivalent to telling a shipwrecked person: "The nearest coast is 2000 miles that way, better start swimming."

That would be the case if the crew had to abandon ship in escape pods and the nearest M-class planet is 20 light-years away. But after sounding a subspace SOS, Starfleet or Federation-allied ships would be notified for a rescue. We saw at the end of Generations, multiple Starfleet ships coming to evacuate the Enterprise-D's saucer section.