Flare Sci-Fi Forums: Reverse Impulse?

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Posted by Daniel (Member # 453) on :

Although I know we have seen reverse warp, have we ever seen reverse impulse ordered? If so, may I ask how this actually happens? Do they use a low-level warp field or something?

(The reason I ask is because I'm in the middle of drafting up a starship, modified Olympic-class. I was planning on moving the impulse units to the nacelle pylons and was wondering whether or not it would be beneficial to have impulse exhaust vents facing both directions.)

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Posted by Michael Dracon (Member # 4) on :

"Full reverse" is something that has been yelled in several episodes. I always thought this to be impulse speed.

I know we have had several instances where reverse impulse was indeed used. I believe the explaination to be that impulse is actually a low level warp field.

This is somewhat proven by the 'hyper impulse' drive of the Aeon in "Future's End", which was used to go to warp speed. I say somewhat because it is technology of the future.

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Max: "And?"
Terry: "I forgot."
Max: "Come on, Clinton was the fun one, then came the boring one."
Terry: "They're all boring."

- Batman Beyond (aka: Batman of the Future)

Posted by Eclipse (Member # 472) on :

Reverse warp I can understand - just reverse the firing order for the warp coils. Reverse impulse, though, would need a forward-facing vent. Given that we've never seen a fully forward-facing engine, that probably means there are plates that can slide into place to redirect thrust in a forward-ish direction (like with today's airliner jet engines). Either that or some yukky subspace trick.

Posted by Matrix (Member # 376) on :

I think its a "yukky subspace trick". Maybe the impulse vents can somehow PULL the ship as well as PUSH the ship.

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Posted by TSN (Member # 31) on :

Wasn't it established by the TNGTM that they use forcefields to direct the impulse exhaust in order to go different directions, including backward?

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Posted by Daniel (Member # 453) on :

I seem to recall Kirk ordering reverse impulse in ST:TUC. It might have been reverse thrusters.

In any case, so do you all think it would be pointless to include forward facing impulse vents on this ship?

Posted by Tech Sergeant Chen (Member # 350) on :

If it's the scene you're thinking of, I believe Kirk's exact words were, "Back off! Back off!"

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Never give up. Never surrender.

Posted by Daniel (Member # 453) on :

Hmmm, I took a look at several schematics of Voyager, and hey, what do you know? It *looks* like she's got forward facing impulse vents.

Also, I just checked ST:TUC, and Kirk said, and I quote, "Reverse engines! All astern, one half impulse power! Back off, back off!"

So we have had reverse impulse ordered. TNG:TM says nothing about forcefield manipulation of impulse exhaust as far as I can tell.

Posted by Mark Nguyen (Member # 469) on :

Add to that, Captain Harriman: "All engines FULL REVERSE!!!"

Mark

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Posted by Shik (Member # 343) on :

And even before that, from ST3...

Kirk to Sulu: [as he sits down in chair & stares at viewscreen] "Back one-quarter impulse..." [insert rocking Hornerian fanfare here]

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"For people with resources, the right events happen. They may look like coincidences, but they arise out of necessity." --T�rk Hviid

Posted by Mikey T (Member # 144) on :

I thought that full reverse had something to do with the RCS thrusters. But I doubt that with even all the Galaxy Class RCS packs would be able to do that.

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Posted by Michael Dracon (Member # 4) on :

I still like to know how the Enterprise-D did that weird turn near the end of 'Yesterday's Enterprise'.

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Terry: "Carter, Reagan, Bush, Clinton, ...."
Max: "And?"
Terry: "I forgot."
Max: "Come on, Clinton was the fun one, then came the boring one."
Terry: "They're all boring."

- Batman Beyond (aka: Batman of the Future)

Posted by Timo (Member # 245) on :

The idea of "thrust reverser plates" made out of forcefields makes the most sense to me. It seems perfectly plausible for those ships with their engines on the aft end of a narrow saucer (so that the reverse jets can go above and below the saucer), or on a narrow vertical neck (so that the jets can go port & stbd of the neck). Also, in "Relics" LaForge and Scotty realize the E-D has been sucked into the Dyson sphere because they spot the marks of her fighting back the tractor beam - marks that could well be where her reversed jets hit the sphere surface. (The location of the impulse engines of the Olympic class does raise questions, though. How can you reverse the jets past that bulky spherical hull?)

Reversed thrust would probably not be as efficient as nonreversed thrust. Thus, going "1/4 impulse" aft would result in a noticeably lower acceleration than going 1/4 impulse forward - and the scene in ST3 would be easily explained. We wouldn't have to attribute ALL of the ship's sluggishness in that scene to the battle damage she had received...

Of course, the ships would have to have another method of braking in addition to this weak reverse-thrust impulse. After all, starships can stop *very* rapidly when they want to, performing *far* more radical decelerations than accelerations. This is where the "yukky subspace tricks" come to play, most probably. But these tricks cannot be used for acceleration, only for deceleration...

Timo Saloniemi

Posted by PsyLiam (Member # 73) on :

I think reverse Impulse speed would be limited somehow. It might screw up the SIF (like I imagine reverse warp does. Which I can't actually ever remember taking place. Anyone remember an instance?)

The best graphical representation of reverse Impulse is possible The Nth Degree (season 4 TNG). As the probe approaches the Enterprise, Picard orders reverse Impulse (1/4 I believe), and we see the ship reversing away. Picard then orders full Impulse, and then we see the Enterprise swing around, and race off at full impulse.

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Posted by The359 (Member # 37) on :

THe way I imagine reverse impulse would work is that forcefields can be made to form whatever shape you want. Because of this, you merely take a "scoop" shaped forcefield projected just aft of the impulse engines. The material that pushes the ship hits the forcefueld, and curves around until it is moving in the other direction, which causes the ship to move. This bending of forcefields could also allow the ship to make rather fast turns using impulse engines instead of RCS thrusters.

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Posted by Daniel (Member # 453) on :

Although I agree reverse impulse would be less effective than forward impulse, the acceleration values do not change. Full impulse will always be 1/4 the speed of light. 1/2 impulse will always be 1/8 the speed of light, and so on.

IIRC, we've seem reverse warp in many instances. When Kirk is trying to escape Balok's ship, didn't they go into reverse warp? and didn't the Ent-D go into reverse warp in "Farpoint?" Then again, maybe they didn't.

Also, I would just like to point out, a forcefield to manipulate thrust created by the engines would have to be pretty darn big and very strong. Don't you think it would be a waste of energy?

Posted by Timo (Member # 245) on :

But we already know that 1/4 impulse is NOT 1/16 of the speed of light. We have seen the movie Enterprise ordered to 1/4 impulse, and CRAWLING at something like 5 m/s.

In fact, there is no on-screen evidence at all that full impulse should equate 0.25c, either. This is just background information from the Tech Manual. Unlike the warp speed charts, which are semi-supported by some episodes because Okuda or Sternbach took the time to work out some travel time references for warp travel and insert them into episode dialogue, the impulse definition from the Tech Manual has never been worked into dialogue.

We do not know how fast the ships travel when at impulse, because the visual effects obviously lie to us - the distances are falsified, so that an engagement at 5,000 km shows the ships actually 500m apart or less, and we can't even tell for sure if some sequences aren't "filmed in slow motion" for aesthetic reasons. All we know is that it is possible to get from Earth out to Jupiter in a couple of hours at impulse speeds (as in TMP), requiring a rather high percentage of c.

However, we can deduce from things like ST3 that the command of "X impulse" does not immediately take the ship to a speed. There is definitely an acceleration time involved, and initially the ship seems to be barely moving.

Timo Saloniemi

Posted by Nim (Member # 205) on :

In that coffee nebula ep, Tom Paris set Voyager at full thrusters, "at all of 300 kph." That sounds faster than 1/4 impulse...

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Posted by Nim (Member # 205) on :

Ok, lame as I am, I calculated, and 300 kph is 83 m/s, so Voyager's thrusters are faster than the refit E's impulse, if we judge visually.

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Posted by Timo (Member # 245) on :

But we can't judge visually very easily, since a ship seemingly of the refit E's design (namely, the E-A) shot out of Earth's Spacedock at something like 500 m/s (or more than a ship's length per second) in ST6, again when commanded to "1/4 impulse".

All the problems of establishing the speed of an impulse-propelled ship would be removed if one simply accepted the command "X% impulse" as meaning "crank the impulse engines up to X% of their maximum power, helmsman, pretty please". Then the ship could be traveling at any speed between zero and lightspeed when at "X impulse". Zero speed a couple of seconds after the command was given; (near) lightspeed a couple of days, months or years after the command was given, depending on the value of X.

Is there any episode or movie scene where we would see a ship go to a significant fraction of lightspeed under impulse power within just a few seconds? IIRC, all the canonical sources give plenty of time for the ships to accelerate, allowing for accelerations below a thousand gee, just like the TNG TM suggests.

Timo Saloniemi

Posted by Daniel (Member # 453) on :

But if we were to accept that, then one ship at full impulse could very well be traveling at .99 c, while another, older ship could be at full impulse and only going .75 c. There is no standard for comparison if we base impulse speed on percent possible output by the impulse engines.

You can't say, "the unknown vessel has just dropped to one-quarter impulse speed." Or, "the Ticonderoga just left the system at full impulse."

Posted by TSN (Member # 31) on :

But have they ever said that? Or, if they have, has it been about a ship they wouldn't have specs on?

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Posted by Timo (Member # 245) on :

And did they really want to hear precise estimates of the ship's speed in these cases? Or just the confirmation that the ship is going in direction X at

a) the maximum speed it can muster, signifying aggression/fear, or

b) a leisurely pace signifying innocence/arrogance?

Actually, it would only be a positive thing if the references to impulse-speed maneuvers never gave valid and precise information about speeds. Speeds are purely relative in space, after all (even in the Newtonian sense), and specifying the speed AND the frame of reference might be too slow and tedious for tactical use. Better just ignore the speeds, which don't matter all that much in the end, and let the targeting or navigation computers work them out.

Most times when speed would matter, it would better be expressed as ETA anyway.

Timo Saloniemi

Posted by Treknophyle (Member # 509) on :

I am of the opinion that "full impulse" refers to the full output of the fusion reactors through the rocket nozzle - and has little to do with the speed - they simply shut down the impulse frive when they have achieved the speed required.

Thus, since every class of ship has a different mass, and every class of ship has a different impulse drive configuration, it stands to reason that "full impulse" refers to a different acceleration for each class - and they shut down at the same speed (1/4 c?).

And I concur with Timo - force-field "vectoring plates" (operating much as the vectoring plates on a present-day jet airliner) sounds about right for "reverse impulse" modality.

Cudos Timo and Daniel. I will include force-field generators for this purpose in my deck plans.

Whoever is in charge of the Plans database - please make a note of this.

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Posted by The359 (Member # 37) on :

*raises hand*

I believe I pointed out that forcefields can be used to vector thrust when needed for different directions.

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"No, 3 & 6 are mandatory, so you only have to do them if you want"

Alex, fellow classmate, trying to explain an assignment (2/2/01)

Posted by Shik (Member # 343) on :

No need, Dave. Look at the Intrepid impulse housings. There's a very clear point at which you see 4 small circles in the front of them. Reverse vents? Probably.

I have the Foundation Imaging 5-views. Big files, but I can always send them. Assuming them made it through the Eating intact.

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"For people with resources, the right events happen. They may look like coincidences, but they arise out of necessity." --T�rk Hviid

Posted by Michael Dracon (Member # 4) on :

I believe the Sovereign class also has some type of reverse vents under the standard impulse engines. But what about other ships, like the Galaxy class?

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Terry: "Carter, Reagan, Bush, Clinton, ...."
Max: "And?"
Terry: "I forgot."
Max: "Come on, Clinton was the fun one, then came the boring one."
Terry: "They're all boring."

- Batman Beyond (aka: Batman of the Future)

Posted by Timo (Member # 245) on :

Given how treknology in general seems to be sliding downhill as time goes by, I wouldn't wonder if forcefield reversers were a technology recently forgotten... The way Starfleet forgot how to manufacture those smaller-than-Nokia-phone phasers that vaporize the victim with one shot, or those automatically raising shields, or FTL phasers.

Or then Starfleet might have opted for lower technology for reasons of robustness and reliability. The E-E does away with many luxuries and high-tech devices already, with flashing video screens instead of the more civilized Okudagrams, and with superclumsy rifles doing a worse job than those early palm-sized type 1 phasers. Perhaps forcefield reversing is another luxury the ship cannot afford?

Or then the ship has forcefield reversers, and these ventral "exhausts" are for some other purpose completely. Or then Starfleet simply found out that a combination of mechanical and forcefield vectoring is actually the best way to go after all.

Timo Saloniemi