Impulse Drive, Therories on how it works?

[Mytran]

True. To expand on Spock's statement: Simple nuclear-powered gravity engines. Maybe very low acceleration affairs with high top speeds. Within system, they would be slow due to always accelerating then de-accelerating between planets, hence sleeper ships are needed. The BB just kept accelerating until something failed or ran out of nuclear fuel. Knowing the distance from Earth would narrow down on the top speed the BB attained before it powered down thrust.

A key statement to bear in mind when analysing the speed of the SS Botany Bay is from Lt McGyvers: "It took years just to travel from one planet to another".
Which planets and how many years she does not specify, so let's try the Earth to Saturn run (such as the mission undertaken by Shawn Geoffrey Christopher) and reduce the travel time to just 2 years:

• The distance from Earth to Saturn (max) is 1.593 billion KM
• A sleeper ship could cover it in 2 years, averaging 25km/s (0.0083% of lightspeed or 0.000083c)
• If they implement this mission by constantly accelerating for the first half of the journey (peaking at 50 km/s) and then constantly decelerate for the second half, what's the rate of acceleration used?
• Acceleration is 0.0015844 m/s^2 (https://www.omnicalculator.com/physics/acceleration)
• At this constant rate of acceleration, after 270 years they would have achieved 13,500 km/s which is 4.5% of lightspeed or 0.045c
• The distance travelled would be approx 57.5 trillion KM or 6 light years

While 6 light years isn't very far from Earth, it is far enough for the Botany Bay to be swept up in a passing ion storm or other interstellar phenomena (worm hole!) without such an event having to take place on Earth's doorstep.

Of course, this all assumes that the engines are capable of running continuously for 270 years and that enough nuclear fuel is carried on board!

 

[Henoch]

• If they implement this mission by constantly accelerating for the first half of the journey (peaking at 50 km/s) and then constantly decelerate for the second half, what's the rate of acceleration used?

• Acceleration is 0.0015844 m/s^2 (https://www.omnicalculator.com/physics/acceleration)

Pictures of the Botany Bay show a vertical launch on rockets. If similar to the Space Shuttle, then during launch it may have seen 3 G's. Airline passengers aboard a commercial airline reach about 1.5 G’s. The ship structure can surely withstand much higher G's, so, it is not a structural integrity issue. It must be an engine performance issue, i.e. early gravity drives must suck.

 

[Mytran]

Pictures of the Botany Bay show a vertical launch on rockets. If similar to the Space Shuttle, then during launch it may have seen 3 G's. Airline passengers aboard a commercial airline reach about 1.5 G’s. The ship structure can surely withstand much higher G's, so, it is not a structural integrity issue. It must be an engine performance issue, i.e. early gravity drives must suck.

The thing is, acceleration at even 1G is 9.8 m/s^2 is just phenomenally faster than the acceleration in my 2 year jaunt to Saturn example.
If the Botany Bay could continuously accelerate and decelerate at 1G then she'd be at Saturn in just over 9 days!

 

[Timo]

A gravity engine that does marginally better than a solar sail would still be a massive hit in early planetary exploration and exploitation. It might not yet make the related organizations abandon chemical or nuclear rockets in disgust, especially since those can take people to Mars in "months" instead of "years" even if cargo travels by the more efficient gravity engines. But if cryogenic sleep is also an established technology, then combining it with gravity engines might indeed result in total lack of interest in chemical or nuclear rocketry, and omission of spacecraft types that could travel to Mars or even Jupiter or Saturn in "months".

However, we might be better off giving the pre-2018 ships a performance an order of magnitude better than above, and accepting that "years" would be involved in two-way missions that included mission time at destination - there not yet being enough infrastructure at the far end to warrant calling a single leg of a space journey "travel from one planet to another". Plus, "planets" would be the gas giants, Mars being singularly uninteresting for some reason (basic exploration still happens in the 2030s, nobody bothers to set up a colony until 2103).

This would still best be combined with a drive that gains in performance once it clears the vicinity of Sol. And doesn't require propellant, even if it consumes a bit of fuel.

Timo Saloniemi

 

[BK613]

OFFS, evaluating based on engine performance alone is flawed. As long as you are no dealing with magic-tech, then:
1) you cannot ignore the Sun, meaning that you just don't point the nose of your ship at Saturn and fly. Paths between origin and destination will be elliptical arcs as they are really parts of orbits around the Sun.
2) you cannot ignore the positions of the planets. The reason NASA needs two years or so to go to Mars is that Earth and Mars have to be just so, both going and returning.

 

[Go-Captain]

Since Bottany Bay and the 21st century sleeper satellite in "The Neutral Zone" both have deck gravity, it's possible other things existed fairly early as well. Though it's a big leap. It's not out of the question that warp drive actually started with low level impulse engines as augmented chemical or nuclear rockets. That makes Chochran's work less revolutionary than evolution but no less important since he is still first to run a ship purely by way of space warp.

 

[Timo]

OFFS, evaluating based on engine performance alone is flawed. As long as you are no dealing with magic-tech, then:
1) you cannot ignore the Sun, meaning that you just don't point the nose of your ship at Saturn and fly. Paths between origin and destination will be elliptical arcs as they are really parts of orbits around the Sun.
2) you cannot ignore the positions of the planets. The reason NASA needs two years or so to go to Mars is that Earth and Mars have to be just so, both going and returning.

To nitpick, neither a solar sail nor a putative gravity engine would use elliptical transit orbits, but spirals, with the going getting better with time and distance, and actually offering more course options later on in the mission. And there probably would be no braking with the drive involved, but rather an aerocapture maneuver of some sort at the destination; symmetry would not be a feature of travel of this type.

Since Bottany Bay and the 21st century sleeper satellite in "The Neutral Zone" both have deck gravity, it's possible other things existed fairly early as well. Though it's a big leap. It's not out of the question that warp drive actually started with low level impulse engines as augmented chemical or nuclear rockets. That makes Chochran's work less revolutionary than evolution but no less important since he is still first to run a ship purely by way of space warp.

It is sort of intuitive that impulse as described would involve reducing the mass to be accelerated, up to the theoretical limit - which really equates lightspeed with zero rest mass. And then warp would turn the mass negative and the velocities would go FTL...

We have to balance this introduction of magic tech against the lack of magic in the everyday life we witness in the Trek 1990s and 2010s. It's not an easy act, either. Sure, we could say gravity tech is so hugely expensive that only spacecraft get it, and flying cars thus won't exist until after WWIII. But then we see it "wasted" on the corpsesat... I guess our best bet is that "it's complicated", and gravity engines do exist but aren't an instant solution to all STL travel from walking to the drug store to visiting Neptune. But that eventually they will be!

Timo Saloniemi

 

[BK613]

To nitpick, neither a solar sail nor a putative gravity engine would use elliptical transit orbits, but spirals, with the going getting better with time and distance, and actually offering more course options later on in the mission. And there probably would be no braking with the drive involved, but rather an aerocapture maneuver of some sort at the destination; symmetry would not be a feature of travel of this type

I agree that I was way too specific, but whether spiral, ellipse, circle, parabola or hyperbola, or some combination of those, you are still in the Sun's gravity well and absent magic-tech your path is going to be some curve. Failure to account for that fact will lead to spurious conclusions.

 

[Henoch]

Getting back on topic, the general move for the Impulse Drive seems toward a gravity drive. This is my long held preference by the way. To resolve the fusion explosion dialog in The Doomsday Machine, I see the Impulse Drive powered by backup fusion power (which burns fuel) when not powered by the primary warp drive power system.

 

[Imaus]

My guess at Impulse Drive types:

Early impulse drives/cheap drives are fusion rockets, this is what the Ares IV and so might had toted around and about, allowing for easier (but not casual) interplanetary travel.

Middle impulse drives/standard drives are conversion or compact antimatter beam drives, turning the remass to 90+% energy and 10% 'waste' or less, these are true interplanetary beasts and might be enough to jump system to system if you have enough fuel/remass for it and a dozen years to spare (if the drive = .33 c)

High-end Impulse drives are small warp rings for sublight travel, allowing anything from 0.000001 to 0.99c travel.

Which one is the most common? Probably sublight warp-drive rings at this point. Fusion drives are still 'dirty' and maybe inefficient. Total conversion might be too complex. Just use the devil you know, and have a sublight-warp field/drive; the other two rely on the drive being far away from anything else; and the small warp rings allow for what is seen on screen, such as 0.5c claims or more. Why not just use the normal warp drive? Eh, why strain the main wheels when the smaller wheels are good enough for the odd job, right? This way you can keep the main drive cooking/on standby to warp out without degrading it while the smaller drive does the hard work for the local affairs.

(0.5c+ is -) ...a ridiculous amount of speed, even our best antimatter beam core theoretical designs with 12 tesla magnetic thrusters give you .333~c, and not at the flick of a button either but over hours, days of acceleration.

 

[Timo]

...How fast an impulse drive achieves any given speed in Trek is unknown, by and large. Impulse travel is seldom if ever directly associated with speeds: "Full impulse!" may be commanded, but what is achieved with it and when is not explicated.

This in contrast with warp where the skipper says "Warp five!" and the helm not only says "Understood, striving to achieve warp five as soon as possible, Sir!" but the plot actually involves the ship immediately attaining warp five and thus matching the speed of the hunter or prey involved.

Impulse commands may be speed settings or then throttle settings. Given how it is possible for us to estimate impulse speeds even when they are not explicated, and given how the same command may yield extremely different speeds (cf. the crawling achieved with "One quarter impulse!" in the TOS movies), the evidence would seem to point towards throttle settings, with different engines then giving different accelerations which translate to different speeds depending on the duration of acceleration (and, thankfully, making "contradiction" an inapplicable concept here!).

Warp commands apparently aren't throttle settings that would result in acceleration that indirectly results in speed - otherwise the chase scenes where the enemy performance is likewise established in warp factors would not make sense. This does not mean warp and impulse would absolutely have to be fundamentally separate and dissimilar drive types. It's just what is dictated by practice: the "weaker warp" of impulse would involve acceleration times, while the "stronger warp" of warp would not.

Timo Saloniemi

 

[Mytran]

I agree that I was way too specific, but whether spiral, ellipse, circle, parabola or hyperbola, or some combination of those, you are still in the Sun's gravity well and absent magic-tech your path is going to be some curve. Failure to account for that fact will lead to spurious conclusions.

Fair point, I had previously just drawn a straight line between average orbital distances of Earth and Saturn, assuming they were on exact opposite sides of Earth at the same time (approx 1.6 billion KM).
Calculating an expanding orbital path between the two points increases that to (I think) approx 2 billion KM, which could achieved by an average speed of 32 KM/S over a 2 year period.
However, the Earth itself is already travelling at 30 KM/S so any craft leaving our planet would only need to increase its speed by an average of 2KM/S over that 2 year period in order to reach its target - an even more feeble amount of acceleration that would be next to useless when the Botany Bay is taken interstellar!
Or am I missing something?

 

[Ronald Held]

I assume all impulse drive ships imply fusion rockets with some form of inertia lowering. I did not think The DY class of the 1990's has anything but the grav playing.

 

[Mytran]

I assume all impulse drive ships imply fusion rockets with some form of inertia lowering. I did not think The DY class of the 1990's has anything but the grav playing.

That was my thought too - if the Botany Bay used gravimetrics to artificially lower its mass (thus travelling faster) then that tech needs to remain fully powered for 270 years, otherwise it was drop back to "normal" speed as soon as its true mass returned.

 

[BK613]

Fair point, I had previously just drawn a straight line between average orbital distances of Earth and Saturn, assuming they were on exact opposite sides of Earth at the same time (approx 1.6 billion KM).
Calculating an expanding orbital path between the two points increases that to (I think) approx 2 billion KM, which could achieved by an average speed of 32 KM/S over a 2 year period.
However, the Earth itself is already travelling at 30 KM/S so any craft leaving our planet would only need to increase its speed by an average of 2KM/S over that 2 year period in order to reach its target - an even more feeble amount of acceleration that would be next to useless when the Botany Bay is taken interstellar!
Or am I missing something?

It seems to me (and I will preamble an apology if I'm misunderstanding this) but you are calculating from a point-to-point-in-a-flat-plane perspective. We are in a gravity well (the Sun's) which means thrust changes the orbit of the spacecraft and not just linearly adds velocity. So the prospective should be climbing up from from Earth's orbit to Saturn's orbit, recognizing that some of the work your engine is doing ends up being represented by that change in orbital distance. Some of this can seem counter-intuitive: for example, it requires a more powerful rocket to launch to geosynchronous orbit than it does to reach the ISS*, yet the orbital velocity at the altitude of the ISS is much higher than the velocity of a geosync satellite. (This website is both a good tutorial and also has the math.)

My point in bringing up orbital mechanics in the first place though, is to add real world delays into the BB moving around the solar system, delays that aren't based on engine performance but would be included in a general statement that it took "years" between planets. Delays such as waiting for the correct planetary positions, etc.

*(carrying the same payload mass)

 

[Mytran]

It seems to me (and I will preamble an apology if I'm misunderstanding this) but you are calculating from a point-to-point-in-a-flat-plane perspective. We are in a gravity well (the Sun's) which means thrust changes the orbit of the spacecraft and not just linearly adds velocity. So the prospective should be climbing up from from Earth's orbit to Saturn's orbit, recognizing that some of the work your engine is doing ends up being represented by that change in orbital distance. Some of this can seem counter-intuitive: for example, it requires a more powerful rocket to launch to geosynchronous orbit than it does to reach the ISS*, yet the orbital velocity at the altitude of the ISS is much higher than the velocity of a geosync satellite. (This website is both a good tutorial and also has the math.)

My point in bringing up orbital mechanics in the first place though, is to add real world delays into the BB moving around the solar system, delays that aren't based on engine performance but would be included in a general statement that it took "years" between planets. Delays such as waiting for the correct planetary positions, etc.

*(carrying the same payload mass)

This is getting way out my mathematical comfort zone!
It does make for interesting reading though.

As regards the overall journey time being inclusive of all the waiting around for planetary alignment I suppose it's possible, but McGivers' statement was specifically in response to dialogue about why Botany Bay had stasis pods on board.

MARLA: Captain, it's a sleeper ship.
KIRK: Suspended animation.
MARLA: I've seen old photographs of this. Necessary because of the time involved in space travel until about the year 2018. It took years just to travel from one planet to another.

 

[Timo]

OTOH, we should note above that the fact that a DY-100 has sleeper ship innards comes as a surprise to McGivers.

We thus learn that not all the ships equipped with DY-100 level propulsion had suspended animation facilities aboard. Not even all crewed ones, since McGivers did know she was boarding a ship of that sort.

Perhaps DY-100 was capable of going to Mars and back in a few weeks, and it was the sorties to the more interesting gas giant moons that required cryosleep - plus, and hence, were flown at different acceleration profiles, to save on fuel. Only, Khan chose an aggressive acceleration profile for his mission, with cryosleep.

Timo Saloniemi

 

[Ronald Held]

Khan needed the cryosleep Chambers to survive long enough to get to another star system.

 

[Timo]

Assuming he intended to. We never learn of any destination he would have been interested in - and the whole idea of creating a settlement away from Earth seems to come as a surprise and a revelation to him when Kirk suggests the thing. If Khan wasn't going to settle, why would he be flying to another star system?

When Khan wakes up, his one question is "How long?". This would indeed be the only relevant question if his plan was

1) Sail out quietly, leaving Earth and its disgruntled villagers behind
2) Wait till the villagers forget you
3) Wait further till they develop true interstellar travel
4) Wait even further till they find you
5) If it has been long enough, exploit the fact that they no longer remember you, and hijack their spacecraft
6) Return to Earth and be prince of billions rather than mere millions.

However, his plan might also have been

1) Escape to Mars or Ganymede or Titan
2) Take over the colony there
3) Return one day to reconquer Earth

in which case he simply mis-set his alarm clock and went past his goal.

Or then there was no plan, and a rival (Stavos Keniclius?) just packed him in ice and shot him into space in a ship ah so humorously named Botany Bay.

Timo Saloniemi

 

[BK613]

This is getting way out my mathematical comfort zone!
It does make for interesting reading though.

I thought it (the website) the perfect balance between reading around the math to get the gist of it all and doing the math if you were into that.

As regards the overall journey time being inclusive of all the waiting around for planetary alignment I suppose it's possible, but McGivers' statement was specifically in response to dialogue about why Botany Bay had stasis pods on board.

I dunno, I think she is just being concise, giving her CO a brief summary of what he is seeing without getting into minutiae. So I think "and back" is implied. YMMV.