Impulse Drive: What do we know? (Non-canon speculation)

[Timo]

Sniping from the side galleries:

-Emergency thrusters are probably the same as regular thrusters, the same way Kirk's "Emergency warp!" in "Balance of Terror" is the same as regular warp, only used in an emergency (so that all the knobs can be turned past their soft safeties).

-If vectoring of impulse thrust beyond the glowing bit is achieved by invisible forcefields, then these can give the thrust an S turn in addition to a simple curve. Any desired momentum arm can thus be created in all conditions; the thrust could even be split to create rotation without corkscrewing.

-If vectoring of thrust in S turns is not possible, then Starfleet impulse engines cannot be Newtonian rockets, because 9 out of 10 are way off the thrust axis.

Timo Saloniemi

 

[Santaman]

The idea itself that impulse engines deliver thrust that needs to be re-routed around all kinds of obstacles is totally ludicrous...

Nebula's don't even have impulse exhausts nor do D'Deridex class warbirds and there are more ships without them.

They're coil engines which are powered by the ship's secundary powersource (there's yer redundancy) and then we've got the thrusters which could be newtonian which is system Nr3, 3 systems good!

My 2cts

 

[Ronald Held]

Impulse drive is supposed to be a type of field drive(or field mediated). Where are the large exhausts through the CM of the NCC-1701?

 

[Birdog]

Impulse drive is supposed to be a type of field drive(or field mediated). Where are the large exhausts through the CM of the NCC-1701?

If we assume the warp engines are large nearly solid chunks of machine then the center of mass of the starship is right through the impulse engine on every single iteration of the starship Enterprise with the exception of the NX-01. I'll draw some diagrams later when I have time.

 

[blssdwlf]

Impulse drive is supposed to be a type of field drive(or field mediated). Where are the large exhausts through the CM of the NCC-1701?

If we assume the warp engines are large nearly solid chunks of machine then the center of mass of the starship is right through the impulse engine on every single iteration of the starship Enterprise with the exception of the NX-01. I'll draw some diagrams later when I have time.

You could probably show the impulse engines at the CM for the TOS Enterprise, refit-E. The E-D maybe if you assume the sec hull to be equally massive as the primary hull. The Excelsior/E-B the warp nacelles are too low to offset the primary+sec hulls. The Reliant's impulse are way too high on the CM.

 

[Crazy Eddie]

It doesn't work for Voyager either, and arguably wouldn't work very well on the E-D when the saucer is separated. Although it sort of works on Excelsior if you consider the secondary hull is supposed to be mostly hollow (for the shuttlebay) but the nacelles need to be a wee bit higher in any case.

I tend to go by Timo's "S-tube" theory, mainly, since this best explains how ships are able to maneuver the way they do in a non-inertial fashion even while under impulse. A sublight field drive just isn't going to do all that and still have the ship move bow-first.

 

[Saquist]

I fail to understand how or why that makes any difference.

It makes every difference.
In Trek we are to believe that aceleration and velocity are no longer the issues they are now.

To be sure, the warbird has no "big glowy thing" to correspond to a traditional impulse engine. All the others, do, though, so I'm not sure what your point is.

Defiant's "big glowy Thing in the rear isn't a confirmed impulse engine. (Not according to the Scematics or the MSD. The other ships don't have it either. Especially the attack ship. These are exhaust ports and if there is no exhaust we can't claim impulse is that rocket.

Mentioned by the captain of the Saratoga in TVH and by LaForge in "Disaster." Also, there are visible features on the TMP Enterprise and the Galaxy class that are indicated in blueprints to be emergency thruster ports. On the Galaxy, they're built into the warp nacelles and the back of the spine of the drive section; on the Connie refit, they're below and to either side of the torpedo deck.

I'll take your word for it but the likely hood is that these are standard thrusters.

I can only tell you what shown on screen.

Maybe you should go ahead and do that, then, as the entire following paragraph is utterly confusing.

I mean, unless you're saying the Narada's disruptor blast directly slammed into the warp core, but that's not what I see, so what EXACTLY are you talking about?

...hmm. I didnt know we were talking about the Narada. I don't know that particular bit of the movie.

 

[Timo]

A sublight field drive just isn't going to do all that and still have the ship move bow-first.

Why not? I mean, it can perhaps make the ship go whichever way first, but chooses to point the bow towards the destination or the enemy because the ship is otherwise built to be oriented that way. Or then the subspace field coils of the impulse engine are every bit as "linear" as those of a warp engine, a fact obscured by them being so darn short and internally carried, and there is a vastly preferred direction of motion for them - forward and possibly also backward along the axis of the coil set.

The thrust vectoring thing would be finesse, used on some ships more than on others, and mostly analogous to the way compressor exhaust gases on old Atlas rockets gave their contribution to both propulsion and steering...

In general, we have to deal with the fact that impulse engine glowy bit placement, size and shape varies wildly, down to there being no glowy bits at all. The explicit tailpipe analogy works pretty nicely there, and also goes nicely with the curiously frequent pairing of glowy bits and warp engines (NX-01, Voyager, Defiant, Prometheus, Danube)... Perhaps impulse engines can benefit from the exhaust gases of warp engines as well? And perhaps the ships that have aft-pointing warp engine glowy bits (Daedalus, ENT delta ships, most STXI ships) are actually utilizing those bits for impulse boost?

Timo Saloniemi

 

[Crazy Eddie]

To be sure, the warbird has no "big glowy thing" to correspond to a traditional impulse engine. All the others, do, though, so I'm not sure what your point is.

Defiant's "big glowy Thing in the rear isn't a confirmed impulse engine.

There are very few ships in the Trekiverse for which the impulse engine has been canonically identified in dialog. This usually isn't a problem because "large red glowing thing on the back" is usually sufficient for a visual identification, model makers being as consistent as they are. The designers of the Defiant model obviously included features that were meant to be interpreted as impulse engines and I have no reason to question that choice.

As for the attack ship, the entire rear pod is lined with large exhaust grilles that are clearly not part of the warp drive and just as obviously meant to be interpreted as an impulse engine of sorts. Considering the attack ship is already meant to be something of a diving/swooping speed demon at impulse, what is the reason not to interpret this as a very high-capacity impulse engine?

I'll take your word for it but the likely hood is that these are standard thrusters.

I'm not sure what you mean by "standard" but we have direct dialog references to "maneuvering thrusters" and "emergency thrusters." LaForge's line in "Disaster" implies that the latter uses a kind of exotic chemical propellant that destabilizes when irradiated.

...hmm. I didnt know we were talking about the Narada. I don't know that particular bit of the movie.

Are you talking about Nemesis or STXI? Either way it's the same question: when do we ever see a disruptor blast actually hit the warp core?

 

[Crazy Eddie]

A sublight field drive just isn't going to do all that and still have the ship move bow-first.

Why not? I mean, it can perhaps make the ship go whichever way first, but chooses to point the bow towards the destination or the enemy because the ship is otherwise built to be oriented that way.

Because being a space ship, it isn't built to be "oriented" any particular way. If impulse is a field drive, then there would be virtually no high g-loading on the structure and the engines can push the ship any way you want; you can side-slip, you can jink, you can reverse, you can perform a circular strafe, all at any velocity of your choosing (and we occasionally see starships do some of this, though at very slow speeds). As a thrust-based system, though, this would be a tad more difficult to pull off, enough that thrusters would have to be used to supplement the impulse engines for fine control. This would be the reason why RCS thrusters exist in the first place; they would become superfluous on a field-drive system.

In general, we have to deal with the fact that impulse engine glowy bit placement, size and shape varies wildly, down to there being no glowy bits at all.

What is there to deal with except for variation in engine design? The closest impulse analog we have in the real world--Ion Engines--come with similar variations; NSTAR has a large circular aperture while HiPEP has a rectangular one. Some of the magnetoplasma thrusters and hall thrusters don't glow at all in a vacuum, and this leaves out the fact that ships like the Romulan Warbird would probably want to mask its impulse plume anyway for stealth purposes.

At the end of the day, though, there's still the outstanding issue that if warp-like field drives were capable of the (relatively) slow accelerations we see from impulse engines, then we wouldn't NEED impulse engines in the first place, you could just use the warp engines for both purposes.

 

[Timo]

being a space ship, it isn't built to be "oriented" any particular way

Sure it is. The deflector dish points in only one direction, for starters. Bow and stern torpedo tubes will probably also exist, defining "bow" and "stern" for their part. The ship won't be flying sideways because this would inconvenience or preclude the operation of key hardware, or then call for its mindless duplication or triplication or mounting on a gimballed platform.

you can side-slip, you can jink, you can reverse, you can perform a circular strafe, all at any velocity of your choosing

We do see reverses and (thanks to wobbly TOS VFX) side-slips. Most starships wouldn't benefit from pointing their nose off-axis, though, as their weapons indeed are "gimballed" and don't call for maneuvering, whereas the deflector dish isn't and calls for nose-forward flight.

What is there to deal with except for variation in engine design?

Implied engineer idiocy, of course. If impulse engine glowy bits did produce thrust, it would be a capital offense to install those bits off the thrust axis for no good reason. And it's pretty damn difficult to come up with good reasons for the more exotic placements we see, including the ones that would not only send the ships spinning without the S-shaped forcefield trick, but would also damage parts of the ship itself were the engines to emit a thrust-generating propellant jet.

if warp-like field drives were capable of the (relatively) slow accelerations we see from impulse engines, then we wouldn't NEED impulse engines in the first place, you could just use the warp engines for both purposes.

As already pointed out, tomorrow's rocketplanes will have two or perhaps three types of Newtonian drives for main propulsion, not to mention the Newtonian drives used for reaction control. One design won't work for all flight regimes. Why should subspace field engines be any different? It's a small wonder already that the ships manage with just one type of warp engine through the entire regime from warp 1 to warp 14.1...

Timo Saloniemi

 

[Crazy Eddie]

Sure it is. The deflector dish points in only one direction

And only comes into play at warp speeds. Under impulse power it isn't all that useful; ordinary shields more than suffice.

What is there to deal with except for variation in engine design?

Implied engineer idiocy, of course. If impulse engine glowy bits did produce thrust, it would be a capital offense to install those bits off the thrust axis for no good reason.

The simple "good reason" is that the impulse engines don't need to be anywhere except on the aft end of the ship; if you can vector the exhaust, then it really doesn't matter where you put them at all.

OTOH, under impulse power there is again no special reason for a preferred orientation and the engines can provide on-axis thrust just by angling through the center of gravity. Relative to the plane of the TMP Enterprise, for example, this would have the ship moving "up and forward" at impulse power, while the TNG stardrive section would move down and forward (joined with all three impulse engines, directly forward). Modern spacecraft already do this to some extent; the SpaceX dragon and most versions of the Soyuz have thrusters that fire off-axis, but nevertheless push through the ship's center of gravity to produce a non-torque acceleration. In older Soyuz models, this is because the service module has several different thrusters with different valve configurations. In the Dragon, it's because the thrusters are mounted internally but cannot fire through the heat shield and therefore must be angled at about 30 degrees. Dragon can perform a deorbit burn using only three thrusters, but it has to angle its "nose" slightly to keep the thrusters antegrade.

Starships--REALISTICALLY--could and would do the same thing, especially if impulse is only meant to be used as a maneuvering engine in orbit. But that doesn't look as cool in VFX, so we can maybe take that as artistic license.

if warp-like field drives were capable of the (relatively) slow accelerations we see from impulse engines, then we wouldn't NEED impulse engines in the first place, you could just use the warp engines for both purposes.

As already pointed out, tomorrow's rocketplanes will have two or perhaps three types of Newtonian drives for main propulsion, not to mention the Newtonian drives used for reaction control.

But see, we're not talking about two different types of warp drives, we're basically talking about the SAME warp drive on two different scales. The only reason in a SPACECRAFT to use two different engines is if one engine is not capable of operating on a lower throttle setting (as on Soyuz) or if the larger engine is designed to use a different type of propellant (as on the space shuttle). Warp drives and impulse engines supposedly use the same high energy plasma produced two different ways, the impulse engines can even produce electroplasma somehow, so the second possibility is out. And warp drives are capable of throttling up to insanely high power levels, and are capable of FRACTIONAL power levels (warp 9.3 and so on) so that, also, is out.

A spaceplane wouldn't need a second type of engine unless it intends powered flight in an atmosphere, in which case it switches from rockets to jets. If you translate this analogy to starships, then it becomes "warp drive and impulse thrust." If you have a rocket engine that can throttle from .1% through 100% and hit every percentage point and fraction in between, then you don't need a jet engine, you can just run your rocket at whatever thrust level is needed to maintain flight speed.

Such as it is with warp drive. If you can travel at warp 1.1, you can travel at warp .1 with the same engine. Impulse engines would only be useful for VERY small velocity changes, close to a few dozen km/s used in orbital maneuvers, and I find it incredibly hard to believe that any field drive would be more efficient in that regard than a reaction system.

 

[Ronald Held]

How much thrust could come out of those exhausts? Maybe a small percentage of the sublight t"thrust"?

 

[Mytran]

Perhaps (on the TOS-E) the centreline positioning of the impulse vents is also where the emergency (newtonian only) thrusters are located

 

[Timo]

And only comes into play at warp speeds. Under impulse power it isn't all that useful; ordinary shields more than suffice.

I'd argue the exact opposite: at warp speeds, the discontinuity at the warp field edge will already help in protecting the ship from the "real world", while at high relativistic speeds the ship is in real danger of being pelleted by deadly dust and heavy nuclei.

Certainly the deflector is up and running at sublight flight modes, and is specifically lit up for that in ST:TMP.

The simple "good reason" is that the impulse engines don't need to be anywhere

That's not a good reason. There would have to be a definite reason for not mounting the glowy bits on the thrust axis, the default position. There never is.

If thrust vectoring is the primary mode of operations, then the glowy bits could be at dorsal bow; the rear mount makes no particular sense in that case.

under impulse power there is again no special reason for a preferred orientation

The Trek fact of the matter is that the ship always moves bow first, with bow defined as "opposite the glowy bits of the impulse drive", but with the glowy bits oriented whichever way (often tilted upwards).

There's no point in exploring the nature of the impulse engines from the point of view of hypothetical starships that behave in a manner not observed on screen. The observed behavior leaves two options: it's not a rocket at all, and thus goes a long way in explaining why starships don't behave like rockets at all, or then it's a thrust-vectoring rocket (perhaps among other things), only engineered in a truly perverse manner that makes one think it's a system of tertiary importance at most.

If you can travel at warp 1.1, you can travel at warp .1 with the same engine.

There's no basis for such a claim, just like there's no basis for the claim that a rocket engine can throttle through all imaginable settings. Some special rocket engine might do that under certain circumstances, but in reality, none do; the reality of warp drive probably reflects that as well.

The division to warp and impulse engines is a step towards realism; integration of the two distinct drives would realistically result in compromises that diminish performance in both warp and sublight regimes, and may thus be done only as an emergency measure (that is, a frigate today can maneuver at port with her turbines, even though the diesels are the reasonable choice) or as a cost-saving measure in a compact vessel.

Perhaps (on the TOS-E) the centreline positioning of the impulse vents is also where the emergency (newtonian only) thrusters are located

For all we know, the things we mistook for impulse engines are the emergency thrusters, and the real impulse engines are the glowy spheres in front of the nacelles, or the subtle grey squares on the pylon surfaces. The TOS ship is ill defined in that regard. Indeed, no Trek ship has had dialogue that would specifically establish where the impulse engines are, or VFX/dialogue synergy that would indicate their exact location through some "hey, now the impulse engines activated and lo, these red things here started glowing at the same time - perhaps there's a connection?" manner.

Timo Saloniemi

 

[Ronald Held]

There is no reason that a warp engine cannot operate at sublight speeds, if the Alcubierre type field is roughly how things work in the Star Trek.

 

[Santaman]

^^ they might be able to but you'd probably could compare it with a Saturn V trying to power a moped to 45Km/u ..the smallest mistake would send it into a wall and crash through half a city at Mach5..

As for the so called impulse exhaust, no.. its the exhaust of the fusion reactors, doesn't do anything thrust wise but gets rid of waste material and heat...

 

[Crazy Eddie]

And only comes into play at warp speeds. Under impulse power it isn't all that useful; ordinary shields more than suffice.

I'd argue the exact opposite: at warp speeds, the discontinuity at the warp field edge will already help in protecting the ship from the "real world", while at high relativistic speeds the ship is in real danger of being pelleted by deadly dust and heavy nuclei.

Certainly the deflector is up and running at sublight flight modes, and is specifically lit up for that in ST:TMP.

But in TMP it undergoes that characteristic color change from orange to blue at warp speeds. Probert and others have stated that the difference in color is a result of power output differences: the deflector is a lot more active at warp than it is at impulse, where it is in a low-power standby mode.

That's not a good reason. There would have to be a definite reason for not mounting the glowy bits on the thrust axis, the default position. There never is.

Tell that to the designers of the space shuttle.

The Trek fact of the matter is that the ship always moves bow first

Yes, even when the ship is in orbit and has no actual reason to do so.

If you can travel at warp 1.1, you can travel at warp .1 with the same engine.

There's no basis for such a claim, just like there's no basis for the claim that a rocket engine can throttle through all imaginable settings.

It's simple logic, actually. An engine that can be configured to operate at 1000 throttle settings can be configured to operate at 1001 settings. If you have enough control of the warp field to produce fractional warp factors, then you can produce fractional sub-warp factors. It would be another thing if warp engines could only be dialed to integer warp factors (it's either warp one or two, nothing in between) but it doesn't work that way.

The division to warp and impulse engines is a step towards realism

Indeed, especially when you consider that a warp drive system cannot be used for orbital maneuvers. And no one is talking about integrating two drives, only that it makes no sense to have two different drives that do the exact same thing when one drive is capable of doing both.

 

[Crazy Eddie]

As for the so called impulse exhaust, no.. its the exhaust of the fusion reactors, doesn't do anything thrust wise but gets rid of waste material and heat...

Why the hell would you want to vent the exhaust from a fusion reactor? 99% of the exhaust is un-fused deuterium, the rest is ionized helium. There is literally NO reason to dump the "exhaust" from a fusion reactor that hasn't been completely fused into helium, UNLESS you're using it as a propulsive reactant mass. If the exhaust itself produces no thrust then there's no reason to get rid of it, just run it through the driver coil and cycle it back into the fusion reactor.

 

[Saquist]

There are very few ships in the Trekiverse for which the impulse engine has been canonically identified in dialog. This usually isn't a problem because "large red glowing thing on the back" is usually sufficient for a visual identification, model makers being as consistent as they are. The designers of the Defiant model obviously included features that were meant to be interpreted as impulse engines and I have no reason to question that choice.

And yet the Techmanual identifies the Impulse engine not by the location of the symmetrical glows but the last 1/4 of the ship.

As for the attack ship, the entire rear pod is lined with large exhaust grilles that are clearly not part of the warp drive and just as obviously meant to be interpreted as an impulse engine of sorts. Considering the attack ship is already meant to be something of a diving/swooping speed demon at impulse, what is the reason not to interpret this as a very high-capacity impulse engine?

Well didn't we set that standard before?
Large Glowy things and what-not?
If you're interpreting the bottom belling of the ship to be an impulse engine exhaust, may I remind you that this orientation has absolutely no design benefit for the ships identified forward moment?

I'm not sure what you mean by "standard" but we have direct dialog references to "maneuvering thrusters" and "emergency thrusters." LaForge's line in "Disaster" implies that the latter uses a kind of exotic chemical propellant that destabilizes when irradiated.

The question is: Is it separate from the RCS thrusters?
Are you talking about Nemesis or STXI? Either way it's the same question: when do we ever see a disruptor blast actually hit the warp core?[/QUOTE]

That wasn't the question I recall.