Star Destroyer maneuverability

Howedar · Post by **Howedar** » 2004-08-02 02:38am

Prompted by the ISD-HHverse trainwreck in OSF, I decided to see what (if any) canon ISD maneuverability figures could be derived. Thinking about the ISD in TESB that turns something like 60deg in 3-4sec on intermittant engine firing, I hypothesized that on full burn the main engines could induce a much more radical angular acceleration. However, I was truly astonished at what I came up with.
Calcs page 1 (~850k)
Calcs page 2 (~810k)

Yes, you read that right. Fucking 13 rad/s², or 745 deg/s². Basically this means that after a second of turning (with only one primary engine, mind) an ISD would be turning at about 125 rpm. Holy fuck.

Still though, there is precident for this. As I said above, with only very sporadic firing, Tyrant turned about 60deg in 3-4s in TESB. These crazy-ass numbers are a direct result of the insane linear acceleration that an ISD can achieve.

No doubt many of you are wondering why this crazy turning was not used in, among other situations, the collision later in TESB. There are many possible answers. The bridge crew was obviously not paying attention, they may just not have thought of it. Causing the ship to spin might have put the ISDs in a worse situation than they were already in in terms of damage from a collision. Firing that engine might well impart too much foreward velocity and actually make the collision worse (see
here, the light blue component of the thrust will spin the ISD but the green component will speed it up). Whatever the reason, it can definately be rationalized.

I strongly encourage all of you to go through this work and see if it checks out, I ran the numbers twice but my methodology may be wrong. I really don't like my results here, but the numbers are what they are.

If not, fear the crazy-ass former beached whale ISD spinning like a fucking dervish.

Kazuaki Shimazaki · Post by **Kazuaki Shimazaki** » 2004-08-02 03:16am

Howedar wrote:Causing the ship to spin might have put the ISDs in a worse situation than they were already in in terms of damage from a collision. Firing that engine might well impart too much foreward velocity and actually make the collision worse (see
here, the light blue component of the thrust will spin the ISD but the green component will speed it up). Whatever the reason, it can definately be rationalized.

Only Problem with that theory I can see at a glance is that SW engines can also Reverse (presumably by electromagnetic thrust vectoring or the like), as in cases like Bacta War, when Drysso orders his engines to reverse.

Howedar · Post by **Howedar** » 2004-08-02 03:19am

Which they may well have done, that would not necessarily have any bearing on their maneuverability. It would simply be straight deceleration, not trying to turn.

As I said, just another way to rationalize the incident. Slowing down may have been their best alternative.

nightmare · Post by **nightmare** » 2004-08-02 09:47am

Howedar wrote:Which they may well have done, that would not necessarily have any bearing on their maneuverability. It would simply be straight deceleration, not trying to turn.

As I said, just another way to rationalize the incident. Slowing down may have been their best alternative.

You still have forward thrust when vectoring, so if they didn't slow down, it would have been a severe impact.

Ender · Post by **Ender** » 2004-08-02 11:44am

During the collision sequence, not all the engines were lit. So it couldn't have done as much. Saxton mentions something like that on his page.

Ender · Post by **Ender** » 2004-08-02 11:57am

Ok, errors:
1) Linear acceleration is 4,000 Gs. Mike was beign extra conservative with his 3,000 that you used
2) It will be hard to justify no thrust vectoring from the other engine. On a carrier when we make sharp turns we put 2 engines in reverse and 2 or forward to make the turn sharped. But that might just increase the turn rate here
3) Assumption of constant density: The ship has to carry large amounts of ejecta fuel, and judging from what we see in the OT ICS, they have to be in the aft somewhere obsecured by the engines. So density is not constant, though how that affects these calcs I'm not sure.

Other then that I don't see anything wrong, though you lost me a couple of times in there.

Howedar · Post by **Howedar** » 2004-08-02 02:48pm

Ender wrote:Ok, errors:
1) Linear acceleration is 4,000 Gs. Mike was beign extra conservative with his 3,000 that you used
2) It will be hard to justify no thrust vectoring from the other engine. On a carrier when we make sharp turns we put 2 engines in reverse and 2 or forward to make the turn sharped. But that might just increase the turn rate here

Yes, I was trying to be as conservative as possible. For that matter I'm not entirely sure how we'd account for thrust vectoring and the like (I know it'd increase maneuverability, but not by how much). We're just running one of the outboard engines, not worrying about thrust vectoring. Think of it as turning one of your outboard screws at full and nothing else.

3) Assumption of constant density: The ship has to carry large amounts of ejecta fuel, and judging from what we see in the OT ICS, they have to be in the aft somewhere obsecured by the engines. So density is not constant, though how that affects these calcs I'm not sure.

Yes, you're right. I hadn't thought of that. We're still going to be within a factor of 2 or so, though. If anything, that should increase the turn speed since it will shift the center of mass back and should reduce the moment of inertia.

Phil Skayhan · Post by **Phil Skayhan** » 2004-08-02 07:15pm

Just a quick question, wouldn't it be better to use I for a pyramid, 1/10 M L^2? I think that's right....

Also, perhaps you could apply this to this scene involving the SSD? Try not to laugh too hard. I did that page a few years ago and I haven't had the time to go over it again.

Howedar · Post by **Howedar** » 2004-08-02 07:20pm

I didn't remember the moment of inertia for a pyramid, but yes I could use that instead. I don't think it will change things an awful lot though.

And how amusing, those were the calcs that I couldn't find that resulted in my having to do my own...

Phil Skayhan · Post by **Phil Skayhan** » 2004-08-03 12:07am

Howedar wrote:And how amusing, those were the calcs that I couldn't find that resulted in my having to do my own...

It's probably for the best that you didn't

There's also something from the collision scene that you could look at. Just after the MF does the dive and we view the bottom of all three Star Destroyers, watch the shadow move across the center SD as it rotates downward. That might also give some info on their capabilities.

For linear acceleration, in RotJ, as the SSD begins its dive into the DS, watch the SD just above it begin to accelerate.

The reason I don't do these myself is that my capture device crapped out last year and I have yet to replace it. But as long as your quantifying the capabilities of a SD......

Howedar · Post by **Howedar** » 2004-08-04 04:48am

What, nobody else?

vakundok · Post by **vakundok** » 2004-08-04 05:57am

What do you expect?
The canon and official novelisations mention the ISDs as clumsy. Being able to turn back in approximately 1 or 1.5 second doesn't sound as clumsy ...

0.37 second of such acceleration (ideal for approximately a 100 (2x50) degree turn) would result 30,000 m/s2 stress to the nose. (One whole second would result 186,449 m/s2 stress.) So, the tolerance of the hull limits such acceleration.

Edited due to miscalculations and bad typing.

Post by **NecronLord** » 2004-08-04 06:56am

vakundok wrote:What do you expect?
The canon and official novelisations

The problem is, this is data derived from the films, which outranks them.

vakundok · Post by **vakundok** » 2004-08-04 07:41am

NecronLord wrote:
vakundok wrote:What do you expect?
The canon and official novelisations
The problem is, this is data derived from the films, which outranks them.

As I know, it was based mainly on the monitor in the bunker. It wasn't explicitly stated that:
a, it showed the imperial fleet,
b, the scaling of the monitor was linear,
c, the movement vector was in the plane of the monitor.
d, what the reddish circle was: the DS2, Endor, the shield, or a gravity border?
Oh, and if it was the imperial fleet, closing the trap, where was the rebell fleet on that screen?

Ender · Post by **Ender** » 2004-08-04 04:54pm

vakundok wrote:
NecronLord wrote:
vakundok wrote:What do you expect?
The canon and official novelisations
The problem is, this is data derived from the films, which outranks them.
As I know, it was based mainly on the monitor in the bunker. It wasn't explicitly stated that:
a, it showed the imperial fleet,
b, the scaling of the monitor was linear,
c, the movement vector was in the plane of the monitor.
d, what the reddish circle was: the DS2, Endor, the shield, or a gravity border?
Oh, and if it was the imperial fleet, closing the trap, where was the rebell fleet on that screen?

2) The fact that it is the imperial fleet is confirmed do to vector, princess Leia's expression, and the fact that the rebel fleet came out much much faster then those ships are shown
2) Having it be non linear increases the linear acceleration
3) both forces came out on the smae plane, making this irrelevent.
4) Irrelevent nitpick

Tribun · Post by **Tribun** » 2004-08-04 05:09pm

Maybe we can finally see more on the bunker monitor when the DVD of ROTJ is out. If there is only one ship, that is bigger than all other which are by the way all the same size, then we know it is the imperial fleet.

Howedar · Post by **Howedar** » 2004-08-04 06:34pm

Even if that is not the Imperial fleet, it would be silly to suggest that Mon Cals have an order of magnitude better acceleration than ISDs (particularly given the similar volume apparently devoted to engines in both designs).

vakundok · Post by **vakundok** » 2004-08-04 09:16pm

Ender, it would be easier if you had adressed the points (a, b, c, d). It is quite hard to figure out what is "irrelevant nitpick" to you.

Ender wrote:2) The fact that it is the imperial fleet is confirmed do to vector, princess Leia's expression, and the fact that the rebel fleet came out much much faster then those ships are shown

Her expression? It is even more vague than that she did not comment the presence of an imperial fleet.

Ender wrote:2) Having it be non linear increases the linear acceleration
3) both forces came out on the smae plane, making this irrelevent.

If the plane of the monitor is angled relative to the plane of the fleets or the monitor is non- linear, or the base (the reddish circle) is actually larger than the DS2, the shown speeds and accelerations will only be bigger. It is true, I did not and do not argue that. However there are at least two movements which cannot be used to derive realspace capabilities: Decceleration from hyperspace and travelling in hyperspace.
Does any source (at least on the level of the movie novelisations)explicitly state that the monitor did not show either of these?

My point:
If I say that the monitor showed the hyperspace, and the rebell fleet approaching (still in hyperspace) the gravity bulb of Endor (or the DS2), can you cite evidence to dismiss that? This explanation would fit to Leia's "Han! Hurry! The fleet will be here any moment." line, and that she did not comment the presence of an imperial fleet.

Tribun: Yes, but if there is not a really huge dot, it doesn't mean it is not the imperial fleet.

Howedar: I did not (want to) suggest that. I wanted to show, that we do not know exactly what the monitor showed, and overriding lower level sources (relative to the movies) based solely on one possible interpretation is, well ...
Have you read my previous post about the hull limiting (the time duration of) that acceleration?

Howedar · Post by **Howedar** » 2004-08-04 10:20pm

vakundok wrote:Howedar: I did not (want to) suggest that. I wanted to show, that we do not know exactly what the monitor showed, and overriding lower level sources (relative to the movies) based solely on one possible interpretation is, well ...
Have you read my previous post about the hull limiting (the time duration of) that acceleration?

Multi-thousand G accelerations are well-documented in the movies for many ships, and this is corroberated in the EU (note that there is never any evidence of time-limited acceleration). This rapid turning is a direct consequence of this fantastic acceleration and no matter how much you bitch, you can't change that. I'm sorry if you want to keep your inaccurate EU sources that depict the ISD as a beached whale, but that simply doesn't mesh with the movies.

vakundok · Post by **vakundok** » 2004-08-04 11:36pm

Howedar wrote:Multi-thousand G accelerations are well-documented in the movies for many ships, and this is corroberated in the EU (note that there is never any evidence of time-limited acceleration). This rapid turning is a direct consequence of this fantastic acceleration and no matter how much you bitch, you can't change that. I'm sorry if you want to keep your inaccurate EU sources that depict the ISD as a beached whale, but that simply doesn't mesh with the movies.

The limitation comes from physics. From the centipetal component of the acceleration during the turning. See this
Read B as beta:
a[t]: tangential acceleration
a[t]=B*r=13rad/s2*1100m=14,300m/s2 for the nose (You assumpted the center of mass to 1100 meters from the nose.)
a[cp]: centripetal acceleration.
a[cp]=(B*t)2*r This is where time comes in.
after one whole second of acceleration:
a[cp]=(13rad/s2*1s)square*1100m=185,900m/s2
a: sum acceleration
a2=a[t]2+a[cp]2 a=186,449m/s2
If the hull of the nose section cannot tolerate this, it will suffer damage.

I am currently searching evidence about the monitor scene. I have already found that there was more than I knew about.

Howedar · Post by **Howedar** » 2004-08-05 03:14am

vakundok wrote:The limitation comes from physics. From the centipetal component of the acceleration during the turning. See this
Read B as beta:
a[t]: tangential acceleration
a[t]=B*r=13rad/s2*1100m=14,300m/s2 for the nose (You assumpted the center of mass to 1100 meters from the nose.)
a[cp]: centripetal acceleration.
a[cp]=(B*t)2*r This is where time comes in.
after one whole second of acceleration:
a[cp]=(13rad/s2*1s)square*1100m=185,900m/s2
a: sum acceleration
a2=a[t]2+a[cp]2 a=186,449m/s2
If the hull of the nose section cannot tolerate this, it will suffer damage.

I am currently searching evidence about the monitor scene. I have already found that there was more than I knew about.

I'm not a fucking retard, thank you. I was asking you to justify that nice fat juicy assumption I helpfully bolded for you there.

vakundok · Post by **vakundok** » 2004-08-05 06:37am

Howedar wrote:
vakundok wrote:If the hull of the nose section cannot tolerate this, it will suffer damage.
I'm not a fucking retard, thank you. I was asking you to justify that nice fat juicy assumption I helpfully bolded for you there.

Please? If you overstresses a structure, it will collapse, what to justify on that? The effect is quite similar to a near frontal collision. The nose will try to go back into the ship.
(EDIT: On second thought I am not sure whether the nose will try to go back or try to go forth, since the centripetal acceleration is used to remain on the circle, while its reaction, the centrifugal acceleration is unhandled. I do not know exactly which causes for example the explosion of CDs in faster drives.)

Other:
I examined the monitor scene. The VHS does not show it entirely, so, it was not simply a reddish circle, but the shielded DS2 instead. Likely it is linear, since the DS2 is basicly circle shaped (its width is less than 110% of its height), and it is not in the focus of the monitor. Since it showed the DS2 it likely showed realspace, and because the shape of the DS2 it was likely linear. Since likely both the rebell and the imperial ships (fleets) have the same capabilities, it is really irrelevant, which fleet it was exactly. The acceleration figure for the incoming formation depends (lineary) on the size of the DS2. I derived the followings using 900km shield diameter:
- The minimum acceleration required: 27,886m/s2
- The maximum (used) acceleration it could support: 55,772 m/s2
- (Portrayed) lenght of the formation is between 392.7 and 414.5 kms.
So, you were right and I was wrong. It is possible to derive acceleration figures for the ISDs from that scene. (These results have the same standing on their own as the size of the DS2.) I think this is the situation.

Howedar · Post by **Howedar** » 2004-08-05 03:59pm

vakundok wrote:
Howedar wrote:
vakundok wrote:If the hull of the nose section cannot tolerate this, it will suffer damage.
I'm not a fucking retard, thank you. I was asking you to justify that nice fat juicy assumption I helpfully bolded for you there.
Please? If you overstresses a structure, it will collapse, what to justify on that? The effect is quite similar to a near frontal collision. The nose will try to go back into the ship.
(EDIT: On second thought I am not sure whether the nose will try to go back or try to go forth, since the centripetal acceleration is used to remain on the circle, while its reaction, the centrifugal acceleration is unhandled. I do not know exactly which causes for example the explosion of CDs in faster drives.)

Okay I see we're especially clueless today. Please justify your assumption that the acceleration and consequent maneuverability I've calculated exceed the limits of the structure of the ISD. I know that at some point an arbitrarily high acceleration would overstress the structure. I'm asking you to justify the assumption that this acceleration is beyond that boundary.

nightmare · Post by **nightmare** » 2004-08-05 07:56pm

Erh.. if the ISD can survive 4000 g's of forward acceleration, it's more than likely it can survive an angular acceleration within a magnitude of that, and quite reasonably to assume it can turn at a similar hull stress level. You don't build a ship that would tear itself apart by a hard turn. It's very basic stuff.

Uraniun235 · Post by **Uraniun235** » 2004-08-06 01:31am

Even if that is not the Imperial fleet, it would be silly to suggest that Mon Cals have an order of magnitude better acceleration than ISDs (particularly given the similar volume apparently devoted to engines in both designs).

Wouldn't a good indicator of Mon Cal manueverability be when they took evasive action to avoid colliding with the DS2 shield?

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