Imperial Star Destroyer power generation

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Picard578
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Imperial Star Destroyer power generation

Post by Picard578 » Mon Jul 23, 2018 2:18 pm

https://starwars.wikia.com/wiki/Imperia ... _Destroyer
The ship however was not suited towards planetary atmospheres, in which full power was required to stay aloft. Any interruption in the power supply in atmosphere could be catastrophic to the vessel, despite all vital equipment being shielded.[17] The primary power generator on board the ship was large enough relative to the rest of the craft to protrude with a ventral bulb.[5]
What does this say about ISD's power generation capability?

So, by using Darkstar's figures of 34,767,000 / 69,534,000 t, and assuming basically zero altitude (we see assault ships hovering very low in AotC). Now, I had to find formula on 'net, but:

Ship mass: 69.534.000.000 kg
F = ma = 69.534.000.000 kg * 10 m/s^2 = 695.340.000.000 N = 695,34 MW.

So basically minimum power generation is 348 MW (using lower mass figure). Of course, this means that it would be unable to accelerate away from the planet.

Does this look right?

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Re: Imperial Star Destroyer power generation

Post by Mike DiCenso » Thu Jul 26, 2018 2:37 pm

I assume you went intentionally with the low-end estimate for an ISD rather than the upper end number, but then? However, since you went with the upper estimate mass in newtons. At 10 m/s, assuming the low-end mass of 37,767 million tons, F = 347,670,000,000 N or 3.4767e+11 J or 347.6 terajoules/s as the low-end is what I get.
-Mike

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Re: Imperial Star Destroyer power generation

Post by Sothis » Thu Jul 26, 2018 4:48 pm

I was wondering (this Thread made me ponder it) what other ships in the SWverse can truly challenge an ISD?

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Re: Imperial Star Destroyer power generation

Post by 2046 » Sun Jul 29, 2018 5:20 am

The idea an ISD would need to be running at full power just to "stay aloft" seems… quite odd. For instance, how does it then escape the atmosphere?

Then again, my ISD power generation page does feature a conclusion of 400-500TW max, which is awfully close to Mike's result. That said, however, anti-gravs aren't treated like super-efficient rockets in Star Wars, which is what's suggested by such calculations. If anything, the fact that things are left floating all the time suggests a technology much more kind to the batteries.

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Re: Imperial Star Destroyer power generation

Post by Iscander » Sat Aug 11, 2018 3:13 pm

Unfortunately thrust(force) and power are not so easy to interchange.

I don’t disagree with 2049’s assessment that treating Star Wars repulser lift as rocket is incorrect, but lacking more information on the efficiency of their anti-gravity engines or baring someone actual inventing anti-gravity this is probably the best method we have of approximating it with tech we understand. And we can at least draw and equivalence.

Even give that though it does come with its own problems, like introducing more unknowns into the equation. Notably Specific Impulse, or effective Specific Impulse, since the actual lifting mechanism is in question.

Knowns and assumptions:
Mass = 40 Million tons, treating as metric tonnes (Disney Star Wars comics)
Local gravity = 1 gee = 9.81 m/s^2

For **** Thrust = F = m * a = ṁ_dot * v_exhaust ****
m_dot is the mass flow rate and v_exhaust is the leaving velocity of the thruster exhaust
Isp is related to exhaust velocity by **** I_sp = v_exhaust / g_0 **** so once we select an Isp value, we can solve for m_dot from the previous equation. Then solve for Energy with **** KE = 1/2 m_dot * v_exhaust^2****

For a range of Isp (Specific Impulse) values
Isp1 = 1 sec (effectively moving full own mass each second with engines) 1.92E+12 watts or 460 Tonnes/sec
Isp2 = 21,400 sec (Dual stage ion thruster) 4.11E+16 watts or 9.8 MT/sec *
Isp3 = 30,570,000 sec (Photon rocket) 5.88E+19 watts or 14 GT/sec
I will rule out number 3 out of hand baring incredibly poor efficiency, since the energy to launch from surface to LEO is only 60MJ/kg (573.6 MT) for a 40 Million-ton ISD.

For a rough confirmation of these values, I’ll look at potential energy
PE=mg∆h
Where ∆h is from the time dependent **** d = V_0 * t + 1/2 a * t^2****. For a single second, the ISP would fall 4.095m without its engines firing in a 1gee field.
Per second the ISD will need to overcome 1.92E+12 watts or 460 Tonnes/sec of ∆PE/sec.

Assuming a 100% efficient engine and no transfer losses, you need at least 460 tonnes/sec and an effective Isp of 1.

Let’s look at inefficiency real quick.
A quick web search gives me about 6% losses for transmission and distribution of electrical power in the USA. So, 94% efficient. And a NEMA premium efficiency electric motor runs from 85.5-96.2% so let’s say 90% for arguments sake.

That knocks up total power to around 544 tonnes/sec for staying aloft.

Starting to feel like Disney may have gone overboard on the Nerf bat since they took over, because GJ turbolasers are starting to look more reasonable than kT. Between this, Rebels, and the underwhelming power of the Dreadnought assault cannon in TLJ.


* Had to correct the typo 4.11E+11 watts to the correct value 4.11E+16 watts
Last edited by Iscander on Wed Aug 15, 2018 2:04 am, edited 1 time in total.

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Re: Imperial Star Destroyer power generation

Post by Iscander » Sun Aug 12, 2018 2:58 pm

Now that is predicated pretty heavily on a very high energy efficiency since everything from ISDs to droid remotes have a repulsor lift and running out of fuel never seems to be a concern for any of them. At least while hovering.

Now it could also be true that it is a tech that doesn't scale up as efficiently and the power requirements for the ISD would be much higher.

But the above hits a lower limit, and also lays out a range of other options dependent on the engine operation.

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Re: Imperial Star Destroyer power generation

Post by Picard578 » Fri Aug 17, 2018 11:48 am

Mike DiCenso wrote:
Thu Jul 26, 2018 2:37 pm
I assume you went intentionally with the low-end estimate for an ISD rather than the upper end number, but then? However, since you went with the upper estimate mass in newtons. At 10 m/s, assuming the low-end mass of 37,767 million tons, F = 347,670,000,000 N or 3.4767e+11 J or 347.6 terajoules/s as the low-end is what I get.
-Mike
I calculated both low (348 MW) and high (695 MW) ends.
2046 wrote:
Sun Jul 29, 2018 5:20 am
The idea an ISD would need to be running at full power just to "stay aloft" seems… quite odd. For instance, how does it then escape the atmosphere?

Then again, my ISD power generation page does feature a conclusion of 400-500TW max, which is awfully close to Mike's result. That said, however, anti-gravs aren't treated like super-efficient rockets in Star Wars, which is what's suggested by such calculations. If anything, the fact that things are left floating all the time suggests a technology much more kind to the batteries.
I screwed up a bit there. I calculated maximum power requirement of 695 MW, which compared to 400 TW (or 400.000.000 MW) is 0,0002%. If anything, power requirement I calculated might be too low.

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Re: Imperial Star Destroyer power generation

Post by 359 » Sun Aug 19, 2018 7:33 pm

It's an interesting note on power, however you cannot directly calculate power from thrust like that.
The units for Watts = Newtons * Meters / Seconds. There needs to be some form of displacement over time to use kinematics, not just would-be displacement, but the thing must actually move. In conventional thrusters we'd measure the displacement of the engine exhaust and use it's mass, acceleration, and displacement to calculate power for a hovering object.

A while back I did a similar analysis for acclamator-class transports here. But there I measured the motion of the ship to get engine output power on the order of 6.7 to 8.4 TW for the transport.


EDIT: Somehow missed Iscandar's excellent thrust analysis when writing this...

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Re: Imperial Star Destroyer power generation

Post by 359 » Sun Aug 19, 2018 7:41 pm

Iscandar wrote:For a rough confirmation of these values, I’ll look at potential energy
PE=mg∆h
Where ∆h is from the time dependent **** d = V_0 * t + 1/2 a * t^2****. For a single second, the ISP would fall 4.095m without its engines firing in a 1gee field.
Per second the ISD will need to overcome 1.92E+12 watts or 460 Tonnes/sec of ∆PE/sec.
You'd probably want to take the limit: lim(∆t->0)∆h to get an accurate value, using a whole second for the interval is going to massively inflate the result.

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Re: Imperial Star Destroyer power generation

Post by Darth Spock » Sun Oct 21, 2018 7:34 pm

2046 wrote:
Sun Jul 29, 2018 5:20 am
The idea an ISD would need to be running at full power just to "stay aloft" seems… quite odd. For instance, how does it then escape the atmosphere?

Then again, my ISD power generation page does feature a conclusion of 400-500TW max, which is awfully close to Mike's result. That said, however, anti-gravs aren't treated like super-efficient rockets in Star Wars, which is what's suggested by such calculations. If anything, the fact that things are left floating all the time suggests a technology much more kind to the batteries.
This pretty much reflects my thought on this, along with the obvious lack of serious downward thrusters compared to the rear. It's especially odd considering just how common seeing ISD's in atmosphere has become in Disney canon, hanging above cities like zephyrs in Rogue One and the Rebels series. If we're dedicated to connecting every bit of side info spread here and there under the new system, that reference could pertain to whatever anti-gravity system these ships use being barely adequate for maintaining hover within a common Earth-like atmosphere and needing to be fully powered to retain buoyancy.

That's actually one other factor that might be worth considering. I've noticed that some hover craft seem to be definitely limited to a limited distance above a surface, like the name repulsor lift would imply, but if some of the more high flying examples are able to negate gravitational effects, even if only to a partial degree, some of the most voluminous vessels might actually gain enough lift within an atmosphere to dedicate it's thrusters to maneuvering rather than just staying aloft.

This in turn could correlate with evidence that Star Wars vessels seem to use orbital mechanics more than I would have expected when outside an atmosphere when they might otherwise just use antigravity. Examples including the hot reentry at the beginning of ROTS, as well my suspicion that the gate on Scarif in R.O. is moving a in high speed low orbit, and the DS II in ROTJ possibly being in a high geosynchronous orbit. Sorry for the lack of references on those last two, they're still in my research folders, but I'm quite confident in them. Then again, the opening battle in TLJ seems to contradict the idea.

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Re: Imperial Star Destroyer power generation

Post by 2046 » Sun Oct 21, 2018 8:15 pm

The reference to buoyancy makes me ponder whether an ISD floating over a city would aim for any Cloud Nine effect. I'll want to modify these calcs later:

https://worldbuilding.stackexchange.com ... e-be-built

(I'm not suggesting that one could easily float with that alone, mind you, merely wondering if it would be worthwhile to shave some lift requirements off.)

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Re: Imperial Star Destroyer power generation

Post by 2046 » Sun Oct 21, 2018 8:24 pm

Darth Spock wrote:
Sun Oct 21, 2018 7:34 pm
the DS II in ROTJ possibly being in a high geosynchronous orbit.
I do not think that works, just FYI.

http://st-v-sw.net/STSWdeathstarsizes-2.html

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Re: Imperial Star Destroyer power generation

Post by Darth Spock » Tue Oct 23, 2018 4:50 am

2046 wrote:
Sun Oct 21, 2018 8:15 pm
The reference to buoyancy makes me ponder whether an ISD floating over a city would aim for any Cloud Nine effect. I'll want to modify these calcs later:

https://worldbuilding.stackexchange.com ... e-be-built

(I'm not suggesting that one could easily float with that alone, mind you, merely wondering if it would be worthwhile to shave some lift requirements off.)
That's about all I expected, the point at which those beasts actually would "float" in standard atmosphere represents a ridiculously effective gravity negation technology, but that appears to be the case anyway, and the possibility seemed noteworthy.

2046 wrote:
Sun Oct 21, 2018 8:24 pm
Darth Spock wrote:
Sun Oct 21, 2018 7:34 pm
the DS II in ROTJ possibly being in a high geosynchronous orbit.
I do not think that works, just FYI.

http://st-v-sw.net/STSWdeathstarsizes-2.html
Perhaps not, I was always inclined to agree with your scaling on that too, but it was the insane size of Starkiller base and a number of other oddities that got me wondering about the DSII again. The odd lighting, viewing angles, the odd direction of the shield projector dish (if that's even what it is), the rebel fleet flying right toward Endor after the battle etc. started bothering me. An old reference to an Ewok apocalypse combined with new ideas about the use of standard orbits in Star Wars started me reevaluating the station.

A while back I started questioning the scaling reliability of a lot of scenes in outer space, taking perspective distortion into account. The "dolly zoom" effect is a great visual example of the potential distortion, and even turned up in the CGI Clone Wars cartoon for crying out loud. Ideally I'd assume any visuals represent a 1:1 example of what is shown rather than being subject to dramatic camera work, but that obviously isn't what we're dealing with. Of course, this could be useful too, for instance possibly eliminating some superfluous BoP classes.

Taking something like this into account could make some of your scaling observations, while sound, a bit more flexible than previously thought. The other view of Endor and the DSII being distorted by hyperspace emergence isn't unreasonable, but wouldn't convince me by itself considering how long this view lasts after the ships were in real space, and since similar effects aren't noticeable in other hyperspace emergences. These views are from within ships cockpits however, greatly limiting the potential for perspective distortion, and quite possibly representing a more true eye view of the system.
I'm also not convinced personally that the docking bays used on screen are even in the equatorial trench. If the station is significantly larger, there would be reason to have additional docking facilities near the poles, and such a trench could be fairly difficult to pick out from a distance on a sufficiently larger sphere.
The biggest drawback is the distinct lack of curvature visible on the DSII surface during the Executer crash, which is probably the single most problematic consideration against the DSII having too small a diameter.
Having built up to this point, I casually flew into this mess: LINK. The views are inconsistent, but with the ship moving and the camera angle changing within the cockpit, its not an obvious F/X glitch either. This is where I dumped the thing in my arrg-sort-it-all-out-later pile. This is probably also a good time to mention that a jumbo DSII isn't exactly high on my SW canon wish list, but rather that I suspect some flexibility in the scale of the station, as well as the exact size, gravity and length of day on Endor might help tidy up some oddities in those scenes.

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Re: Imperial Star Destroyer power generation

Post by 2046 » Tue Oct 23, 2018 11:05 am

Camera effects are a thing, but need to be demonstrable.

I rather doubt any evidence of a non-equatorial trench can be found. At different latitudes the angle of it would be different, as well as the hull we see above and below it.

The Tyderium approach would seemingly also constrain the station size to something in the smaller category. A proper relative scaling could be done that attempts to estimate speed and distance based on relative sizes of the Executor and DS2. By eyeball, though, it doesn't look like anything Saxtonian would work.

Keep at it, though. I've been wrong before.

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Re: Imperial Star Destroyer power generation

Post by Darth Spock » Sat Nov 03, 2018 7:02 pm

2046 wrote:
Tue Oct 23, 2018 11:05 am
I rather doubt any evidence of a non-equatorial trench can be found. At different latitudes the angle of it would be different, as well as the hull we see above and below it.
It's funny you mention the different angles at latitude, as that was one of the things that bothered initially. Looking at the angle of shadow being cast into the docking trench here, it doesn't match with the angle of the sun relative to the equatorial trench here, which also looks to be completely in shadow here, (although the ISD indicates the light source is at a lower angle, I'unno). Having the docking bay be in radial alignment away from the equator makes no sense, but having concentric outer decks actually works with canon. Having the docking bay aligning perpendicular to the radius and matching up the angles of the shadows and the light source would put it north and west of the SL dish, somewhere around the DSII's equivalent of the 60th parallel, facing in the general direction of the northern pole and the sun. This would come with the added bonus of explaining Endor's absence when looking out from inside the docking bays as well, since I'd normally expect it to be visible from an equatorial bay judging by the apparent light source and the downward facing camera angle (instead trading it for a lack of DS hull being visible, bleh). Of course, the curvature visible from inside the trench would require that it be protruding from the surface like a kind of docking silo. Additionally, your super-trench rebuttal shows that this thing would need to be sticking out a good 3 km or so from the surface, like a giant wart. I never got around to checking how big the implied curvature should be when viewed from inside the trench.

As I mentioned earlier, this scaling re-evaluation was actually something of a side effect from looking for examples of stationary orbits in SW. Of course this all hinges heavily on the angle of the sun too, something I've grown hesitant to put much stock into ever since I saw the F/X crews using their dark CGI magic to arbitrarily move the sun to change the lighting for scenes in both TPM and RO. All in all, I suppose this stuff is possible, but I'm inclined to agree that the jumbo DSII creates more problems than it solves, and pushes realm of plausibility to its limit. I guess it just goes to show that sometimes in this kind of analysis a few pieces just refuse to get in line and something somewhere has to be discarded/ignored.
On top of that, I only just thought to check wookieepedia for the most recent "official" information, and Endor has apparently been scaled at ~ 4900 km in diameter, which fits really well with the ~160 km diameter. The same entry said the DSII was stabilized by ground based repulsors. Ultimately the smaller figure is just cleaner to go with, I guess it's probably just a well to scrap the idea for a stationary orbit on this one, which was all I meant to touch on before going off on this tangent. I'm afraid I got a little ahead of myself on this one, I usually vet my ideas more thoroughly before releasing them into the wild -- which is why I never contribute any new material!!!

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