Sublight acceleration speeds

[Tyralak]

A discussion about sublight acceleration speeds came up on another board. The question was; When accelerating from a complete stop, how long does it take for a Federation starship to reach full Impulse? I realize this would depend quite a bit on the class of ship, but I can't seem to find much canon information regarding sublight acceleration rates. Any ideas?

 

[Timo]

You reach full impulse when you finish pressing the appropriate button.

Then you sit back and wait for the ship to accelerate at full impulse until she reaches the desired speed, which may take minutes, hours, or days, depending on the speed you desire. It takes a bit longer to reach the same speed at half impulse, and longer still to reach it at 1/10 impulse, but you will get there eventually.

Unless you figure in "air resistance" from the interstellar medium, which may give you an upper speed limit.

Timo Saloniemi

 

[MacLeod]

Depends on how fast you accelerate.

 

[Timo]

Warp factors in many episodes are indicated to be absolute: both a fleeing and a chasing ship in a chase determine their odds by discussing warp factors as if they were fixed speeds. But no episode suggests that impulse settings would be speeds, let alone absolute and universal ones. They are probably different for every ship type, and even for individual ships (depending on their state of repair - 1/4 impulse barely gets Kirk out of spacedock when his ship is wrecked, but is good enough for evading the Doomsday Machine in battle when she is not). And IMHO they are likely to be "throttle settings" that correspond to an acceleration level (with the above caveat about ship types). At least the Tech Manuals never discuss impulse values in terms of speeds - they merely speak of "impulse operations" being conducted at various speeds.

Timo Saloniemi

 

[MacLeod]

Ahead, plot speed.

 

[Tiberius]

You reach full impulse when you finish pressing the appropriate button.

Then you sit back and wait for the ship to accelerate at full impulse until she reaches the desired speed, which may take minutes, hours, or days, depending on the speed you desire. It takes a bit longer to reach the same speed at half impulse, and longer still to reach it at 1/10 impulse, but you will get there eventually.

Unless you figure in "air resistance" from the interstellar medium, which may give you an upper speed limit.

Timo Saloniemi

THis would work only if impulse speeds are a measure of acceleration, not of velocity, yes?

 

[blssdwlf]

1/4 impulse barely gets Kirk out of spacedock when his ship is wrecked, but is good enough for evading the Doomsday Machine in battle when she is not).

Keep in mind that Kirk on the Constellation was going to get overrun by the Doomsday Machine and it was distance (it didn't happen immediately) and the Enterprise's distracting phaser fire that saved Kirk.

As far as TOS goes, calling out 1/4, 1/3 or full impulse doesn't indicate the rate of acceleration but apparently the engine (or power) setting.

The only times we're treated to full or max acceleration at sublight is from "The Squire of Gothos" and "The Corbomite Maneuver" because we know Kirk explicitly calls out for it.

"The Squire of Gothos"
KIRK: Full power acceleration from orbit, Mister Scott.
SCOTT: Full power, sir.

"Corbomite Maneuver"
KIRK: Maximum acceleration when I give the word.

In "The Squire of Gothos", the impulse acceleration is in excess of 10,000 g from observing the viewscreen departure .

Also other indications that max acceleration is needed could also come from dialogue that includes "emergency power to engines", etc.

 

[Timo]

This would work only if impulse speeds are a measure of acceleration, not of velocity, yes?

Yup - or, as stated above, a throttle setting. In space, "maximum speed" is an absurd concept, as all speeds are available to even the feeblest engine provided it doesn't run out of gas (or indeed that it doesn't run on gas so that the rocket equation doesn't apply). Only with the fictional physics of warp drive can one reintroduce the concept of absolute speed and of maximum speed...

The only times we're treated to full or max acceleration at sublight is from...

Yet what else could "full impulse" plausibly mean? It's just as much a "desperation indicator" as all these "full acceleration" and "emergency power" things.

Timo Saloniemi

 

[Tiberius]

I thought that it was generally accepted that full impulse is 1/4 c.

 

[blssdwlf]

The only times we're treated to full or max acceleration at sublight is from...

Yet what else could "full impulse" plausibly mean? It's just as much a "desperation indicator" as all these "full acceleration" and "emergency power" things.

Well that depends. If treated as a throttle setting (which is what I am doing) then the amount of power the impulse engines are delivering at "full throttle" will vary on how much power the impulse system has available and/or if any main power is supplementing the impulse power for acceleration, IMHO.

"Elaan of Troyius":

SULU: Captain, number four shield just collapsed. Impulse power down to thirty one percent.
​

and also "Return of the Archons"

SCOTT: Our shields are holding, but they're taking all our power.
​

SCOTT: If we try to warp out or move on impulse, we'll lose our shields and burn up like a cinder.
​

BTW, the only other instance where "full power impulse" is called for are in "Who Mourns for Adonais". Variations of "Full speed" are called for in "The Corbomite Maneuver" and "Plato's Stepchildren".

Interestingly, "Full ahead" is used in "The Doomsday Machine", "Balance of Terror" and "Miri". In the first two examples, the context is understood to be a combat or emergency situation and Kirk even says in "Balance of Terror":

KIRK: Let's get them while we are. Before we enter the Neutral Zone. Full ahead, Mister Sulu. Maximum warp.
​

But in "Miri", it's just to Warp 1

KIRK: Full ahead. Warp factor one.
SPOCK: Warp factor one, Captain.​

 

[Timo]

I thought that it was generally accepted that full impulse is 1/4 c.

Nope. There's a passage in the TNG Tech Manual that says that impulse operations are normally conducted at 1/4 c to avoid relativistic complications - but the manual is also very clear on it being possible and somewhat commonplace to operate at much higher speeds. The "general acceptance" is just a silly misconception, akin to "Spock was the first Vulcan in Starfleet".

If treated as a throttle setting (which is what I am doing) then the amount of power the impulse engines are delivering at "full throttle" will vary on how much power the impulse system has available

Yup. But "full impulse" then still equals "full acceleration" for the particular circumstances...

But in "Miri", it's just to Warp 1

KIRK: Full ahead. Warp factor one.
SPOCK: Warp factor one, Captain.​

​

Which might well be taken to indicate that warp factor one is a throttle setting as well. But more probably, Kirk just wants to get to warp one as quickly as possible, and then stop accelerating...

Timo Saloniemi

 

[blssdwlf]

Yup. But "full impulse" then still equals "full acceleration" for the particular circumstances...

Yes, agreed depending on the circumstances. "Full impulse" with shields up or other power hungry systems drawing power will likely result in a slower acceleration than if the ship had dumped all its power into the engines for acceleration.

 

[Crazy Eddie]

You reach full impulse when you finish pressing the appropriate button.

Then you sit back and wait for the ship to accelerate at full impulse until she reaches the desired speed, which may take minutes, hours, or days, depending on the speed you desire. It takes a bit longer to reach the same speed at half impulse, and longer still to reach it at 1/10 impulse, but you will get there eventually.

Unless you figure in "air resistance" from the interstellar medium, which may give you an upper speed limit.

Timo Saloniemi

THis would work only if impulse speeds are a measure of acceleration, not of velocity, yes?

"Speed" is relative in space, and is meaningless in the absence of an external reference point.

More to the point: "impulse power" is a unit of... well, power. There's nothing to suggest it implies a specific velocity relative to anything.

 

[Crazy Eddie]

Interestingly, "Full ahead" is used in "The Doomsday Machine", "Balance of Terror" and "Miri". In the first two examples, the context is understood to be a combat or emergency situation and Kirk even says in "Balance of Terror":

KIRK: Let's get them while we are. Before we enter the Neutral Zone. Full ahead, Mister Sulu. Maximum warp.
​

But in "Miri", it's just to Warp 1

KIRK: Full ahead. Warp factor one.
SPOCK: Warp factor one, Captain.​

There is an old theory -- long since ignored by Fandom -- that warp fields don't do much of anything other than lower the inertial mass of the ship so that the actual engines can accelerate the ship a hell of a lot faster than they ordinarily could. "Full ahead" in this case is a throttle setting for the impulse engines while "maximum warp" is a field distortion that lowers the ship's mass by a specified quantity.

My personal belief is that warp engines in the 22nd and 23rd century worked this way while Excelsior's "transwarp drive" supplanted it by the 24th, such that the warp field ITSELF is a propulsive force independent of the impulse engines.

 

[Timo]

...Yet we have "Obsession" where a high-warp chase takes place until it is revealed that a crucial vent in the impulse engines is open, apparently due to ongoing repairs on said engines. Had the impulse engines actually been necessary for the chase, the vent issue would probably have arisen on its own, and not merely when the gaseous alien pushed itself in through the vent.

Scotty did appear to claim that having the vent open would temporarily limit the ship's propulsive capabilities:

Scotty: "Captain, while we're waiting I've taken the liberty of cleaning the radioactive disposal vent on number two impulse engine, but we'll be ready to leave orbit in under half an hour."

Subsequent events did appear to take that half an hour before Kirk gave the order "prepare to break orbit". But since the vent was left open, one would think the limitation would still be in place - and that leaving orbit under warp power without impulse would be common enough a procedure that Scotty wouldn't even notice the little lapse.

Timo Saloniemi

 

[blssdwlf]

And also from "The Ultimate Computer":

SPOCK: Hit in engineering section. Possible damage to her impulse engines. She's still maneuverable on warp drive.
​

Although from "Obsession" it could be interpreted that Scott's engineering crew would be occupied in the cleaning procedures and the delay is from their activity and not from the open impulse vent. And since they did take off from orbit at Warp 8 pursuit of the creature and left the vent open it would appear that it wasn't a detriment at all to warp operations.

SCOTT: Captain, while we're waiting I've taken the liberty of cleaning the radioactive disposal vent on number two impulse engine, but we'll be ready to leave orbit in under half an hour.
​

And lastly, "The Corbomite Maneuver" where the impulse engines are thrown in after the ship was already applying maximum warp acceleration trying to break away from Balok's small ship.

But, the warp engines do sound like they also produce thrust in addition to whatever magic field it uses to move it since "thrust" and "thrusters" are mentioned along with warp speed operations in "The Ultimate Computer", "Court Martial" and "The Voyage Home". So taking a variation of Newtype's idea, the Warp engines sound to me just more powerful versions of the older Impulse engines, IMHO.

 

[Crazy Eddie]

...Yet we have "Obsession" where a high-warp chase takes place until it is revealed that a crucial vent in the impulse engines is open, apparently due to ongoing repairs on said engines. Had the impulse engines actually been necessary for the chase, the vent issue would probably have arisen on its own, and not merely when the gaseous alien pushed itself in through the vent.

Scotty did appear to claim that having the vent open would temporarily limit the ship's propulsive capabilities:

Scotty: "Captain, while we're waiting I've taken the liberty of cleaning the radioactive disposal vent on number two impulse engine, but we'll be ready to leave orbit in under half an hour."

Subsequent events did appear to take that half an hour before Kirk gave the order "prepare to break orbit". But since the vent was left open, one would think the limitation would still be in place - and that leaving orbit under warp power without impulse would be common enough a procedure that Scotty wouldn't even notice the little lapse.

Timo Saloniemi

That or Scotty simply didn't have time to close the vent before they went to warp. It might not have made a difference otherwise... after all, how often does the ship get attacked by dichironium cloud creatures?

Alternatively, it could be that Scotty tuned the port side impulse engine up to 120% of maximum to compensate for the shut-down engine, which may well be standard procedure in situations where the ship isn't explicitly going into combat.

 

[Timo]

All of these are good explanations, and indeed it would be best plotwise if the work on impulse engines were the reason delaying breaking-orbit-and-warping, but the status of the impulse engines as such had no effect on that.

In terms of direct evidence, we have witnessed impulse travel when warp engines are damaged (but generally still glowing blue for the TNG era); we have also witnessed warp travel without a change in the glow of the impulse engines (no brightening for the TFS and TNG eras, no illumination at all for the TOS-R era). The light show might not tell the full tale, but in more general terms of evidence, it doesn't seem as if we would have an obligation or even a reason to think that impulse thrust is necessary for warp travel.

Now, impulse power may be of some use, as per "Corbomite Maneuver"; the difference in magnitude to warp power need not be all that great as far as onscreen evidence goes. Although that must probably be argued to be because warp doesn't consume much power - after all, rerouting of just about anything else, including not only impulse power or weapons power but even things like life support power, will make a difference in warp propulsion.

Timo Saloniemi

 

[Crazy Eddie]

On the one hand, the impulse engines never glowed at all in the TOS era, even when they were on; for the rest of trek after that they glowed constantly, even when they were off (except in dry dock in TMP when the entire ship was powered down). On the other hand, twice in STXI we see the glow in the impulse engines cease just seconds before the ship powers up for warp drive. On still the other hand, the warp nacelles DO seem to play some integral role in impulse power, and the mass-reducing properties of a sub-warp field are probably so crucial to starship maneuvering that the nacelles are the most important part of that system anyway and a starship with a functioning pair of warp drives would still be able to maneuver by cranking up its subspace field to maximum and puttering around on thrusters alone ("She's sustained damage to her impulse engines, but still maneuverable on warp drive.").

I'm finding lately that I'm a late convert to the "field drive" theory for impulse engines; someone recently pointed out to me that a technology base that can directly control gravity would immediately find ways to use artificial gravity as a propulsive force, and I realized that's probably what Trek impulse engines really are: artificial gravity generators that cause the entire ship to "fall" in a desired direction.

That said, I still think that the TOS/TMP warp drives work in some way drastically different from the Excelsior/TNG warp drives, different enough to justify a whole new warp scale but similar enough that older designs would still be in use a hundred years later. It could merely be a different method of achieving the same effect, or it could the same power generating method applied to an entirely different effect for some reason.

 

[Maurice]

On the one hand, the impulse engines never glowed at all in the TOS era, even when they were on; for the rest of trek after that they glowed constantly, even when they were off (except in dry dock in TMP when the entire ship was powered down).

Wrong. Sorry. The impulse engines in TMP were only ON in the shots breaking Earth orbit and zinging by Jupiter. They are OFF from the first warp jump attempt til the end of the picture.