Regarding the mass of Lucrehulk coreships at Geonosis

[Estrecca]

Quite the pretentious thread title, isn't it? It is quite descriptive of an idea that struck me today, upon seeing again the battle of Geonosis, and the essence of that idea is that there is a form of calculating an upper limit for the mass of a TradeFed Core Ship.

After being hit repeteadly by the Republic SPHA-T Walkers, one of these crashes against the ground at speeds that my rough eyeball scaling suggest of ~200 m/s. Considering that we are talking about the impact of something the size of a small mountain, the effects seen in the movie are remarkably tame.

Supposing that the impact caused a magnitude 7 earthquake (and what we actually see does not come even remotely close, considering that not far from the point of impact both the droids and the clones were still in neat formations), it would mean an energy release of roughly 2E17 joules. Meaning that the Lucrehulk coreship has at most a mass of 5E12 kg or 5 billion tons.

This sounds like a lot, but the Coreships are surprisingly large craft (around a hundred times the size of an Intrepid-class UFP ship, to put it in perspective for Trek) and this is the high end (and a generous high end, for it would need the Coreship to be solid and several times the density of uranium).

Comments?

[Mike DiCenso]

Well let's see here... The TF ship's core appears to be around 600 meters wide, so a fall of around 200 meters/sec is probably reasonable there. However, the energy released by the core's impact with the ground does not in any way come near what would be the equivalent of 476 megatons (if I did my coversions correctly) as that would likely devastate hundreds of square kilometers! So "upper limit" here is a very extremely favorable bent-over-backwards one to say the least.
-Mike

[Estrecca]

Well let's see here... The TF ship's core appears to be around 600 meters wide, so a fall of around 200 meters/sec is probably reasonable there. However, the energy released by the core's impact with the ground does not in any way come near what would be the equivalent of 476 megatons (if I did my coversions correctly) as that would likely devastate hundreds of square kilometers! So "upper limit" here is a very extremely favorable bent-over-backwards one to say the least.

First, you erred by an order of magnitude. Its 47.6 megatons, roughly in the ballpark of the Tsar Bomb.

Second, yes it is meant to be an extremely favorable one (it is in fact more favorable than what can be derived from the ICS and Saxton's SWTC, that yields ~3.5E12 kg).

If I have done this is because the utter lack of anything in AOTC that comes close to this is a very powerful argument against hiperdensity fuels and, by extension, the entire ICS conundrum.

[2046]

It's tempting to conclude that the core ships are very lightly constructed.

However, I think it best to acknowledge that repulsorlifts must've been in operation while the vessel was lifting off, and thus the true mass of the vessels could be 'masked', as it were, by there being only a partial failure.

This would presuppose, however, that repulsorlifts operate as a sort of specialized anti-gravitational mass-lightening, or some sort of inertial dampening that could radiate outward.

Hmm, lemme back up a bit on that.

There are various forms of what might be called 'antigravity'. Rockets, flying vehicles, and even maglev trains overcome gravity in conventional ways by appealing to greater forces. But of course such conventional antigravity is not what we're interested in, because in all cases gravity is still operating on the vehicle the entire time. The general idea of sci-fi antigravity is that gravity is nullified via some sort of technobabble.

How this happens depends on how one wishes to view gravity. A Trekkish view of gravitons would give you discrete quanta of gravity to work with, whereas a more straight-relativistic view of gravity as merely the bending of the spacetime due to mass means you have to figure some way for a vessel to 'tack against the wind'.

So far as I can quickly figure, there are two main methods for getting antigravity, and some submethods, from the perspective of sci-fi 'realism'. I've been batting such ideas around in my head and will now splooge them out haphazardly:

1. A technobabble field nullifies gravitation.

a. This could be done via some sort of 'antigraviton' technobabble. In other words, a device creates a sort of antigravity field that pushes back against gravity, like a tractor beam in reverse against the ground. While there's no way to know for sure, this sounds power-intensive.

Such a system would mean you could basically push off against anything, though Star Wars repulsorlifts are said to require a gravity field to push against. Other forms of thrust really wouldn't be needed here, unless it was more efficient to only push to some extent but then use other methods for the rest.

But given the gravity field requirement, I don't think this is necessarily the best conclusion.

b. Alternately, a 'reflector' system could be employed that takes gravity's pull and redirects it via some sort of technobabble ("tacking against the wind"). Given the descriptions of Star Wars antigravs . . . such as only being able to operate within a planet's gravitational field, considered to be within six planetary diameters . . . this has generally sounded to me like the most likely option for Star Wars, though the jury wasn't in.

This option wouldn't provide any thrust . . . it would simply keep you from falling. Given Cloud City, this sounds pretty good. It would also have the advantage of possibly being very light on the power requirements.

2. A technobabble field counteracts gravity by nullifying or reducing mass.

a. If you have very little mass, then while you'd still fall toward the ground at the same rate, you would have to expend far less energy to get moving upward. So the antigrav tanks on Naboo, which produced quite a bit of breeze underneath them, could be thought of as having a simple fan to keep their reduced mass airborne.

But that would, I would think, screw with your inertia. So examples like the antigrav tanks in the Naboo jungle wouldn't work well, 'cause they'd just bounce off of the trees instead of knocking them down.

So maybe the core ships are lightly built . . . unless one concludes that a multitude of repulsorlift systems are in use, or unless one can determine a way for a gravity reflector system to reduce the inertia of the ship smacking the ground at 200m/s.

[GStone]

If it was a reflector system, it should still impede a lot of acceleration to the planet, so it'd be like dropping something really big from just a small distance above the ground. I'm also assuming that they were trying to use back ups and/or had partial power to the damaged reflector.

[Mr. Oragahn]

I believe the shock's been absorbed due to the fact that the core didn't hit the ground, but likely a giant hatch. Notice how it seemsto hit some surface at ground level, while the ship's literally being falling back into the pit where it was from.
Pits are roughly half a core high.

[2046]

A reflector system would affect the acceleration (hmm, might be possible to work out the acceleration of gravity on that example), but the problem is that we need something to mitigate the mass . . . unless core ships are built out of tin foil.

If we call that a 10 kiloton (41.84 TJ) smack to the ground, for instance (a number I've simply picked from my posterior, though it sounds closer than Tsar Bomba), then at the given 200m/s the mass of the core ship would be:

KE = .5mv^2
41,839,999,999,999.9936 = .5m (4000)
41,839,999,999,999.9936 = m (2000)
m = 41,839,999,999,999.9936/2000
m = 20,919,999,999.9999968 kg
m = 20,920,000 tonnes

Given the earlier value of 600m for the spherical core ship, then the volume is simply 4/3 pi r^3, or 113,097,335 m^3, not counting the extra giblets around the bridge. The density would thus be 184.9 kg/m^3.

That would make it only around twice as heavy as air, and the vehicle would float extremely well in water.

The remaining things to consider are:

1. How much energy the impact actually represents . . . this may be difficult to know, since the ship itself 'eats' some of the energy by falling apart most crunchily.

2. Further, the ground of Geonosis doesn't seem to be a perfect surface for such estimates either.

There are some other issues that'll make this more than a back-of-the-envelope thing, but this is an interesting case to work with.

[GStone]

A reflector system would affect the acceleration (hmm, might be possible to work out the acceleration of gravity on that example), but the problem is that we need something to mitigate the mass . . . unless core ships are built out of tin foil.

Given the design of Wars vessels to shave off as much excess weight as possible, and given how completely most of them explode with the rated power of turbolasers, I'd say somewhere along the lines of modern building materials with some leeway for them being a little lighter, while being somewhat stronger. My off the cuff guess would be the same as an average building of a city that's at least 15-20 stories tall. I would guess that there's a lot of open spaces inside the cores. With no obvious expulsion points for waste products for power generation, they must be doing something with it, even if it's just temporary. You've got crew quarters, the mess hall, waste recelamation, storage tanks for air, cargo holds, space to run power conduits and coolant lines, etc. Inside, we also see that there are long halls, meeting rooms, etc.

They may have reinforced the structure of the core in transforming their ships into battleships, but since they crack under their own mass when impacting sand/rock, they aren't designed to survive uncontrolled reentry. Whatever the rating is for the surface, it isn't that high. The damage caused by the canons that punched through before it dropped wasn't that significant to the outer structure, at least in appearance.

1. How much energy the impact actually represents . . . this may be difficult to know, since the ship itself 'eats' some of the energy by falling apart most crunchily.

Since the ship didn't break into tiny tiny chunks, I'd say the best way to get a lower limit would be to work with the level of KE necessary for sandstorms and work upward...only I don't know of any evaluations that have ever been done on sandstorms.

[Mike DiCenso]

Well let's see here... The TF ship's core appears to be around 600 meters wide, so a fall of around 200 meters/sec is probably reasonable there. However, the energy released by the core's impact with the ground does not in any way come near what would be the equivalent of 476 megatons (if I did my coversions correctly) as that would likely devastate hundreds of square kilometers! So "upper limit" here is a very extremely favorable bent-over-backwards one to say the least.

First, you erred by an order of magnitude. Its 47.6 megatons, roughly in the ballpark of the Tsar Bomb.

Second, yes it is meant to be an extremely favorable one (it is in fact more favorable than what can be derived from the ICS and Saxton's SWTC, that yields ~3.5E12 kg).

If I have done this is because the utter lack of anything in AOTC that comes close to this is a very powerful argument against hiperdensity fuels and, by extension, the entire ICS conundrum.

Well, actually I typo-errored. I didn't put the period in-between the seven and six as I had intended to. I also understand that it was ment to be an extreme upper limit, and in consensus with that view, but was qualifying it further as being likely the very upper limit.
-Mike

[Mike DiCenso]

I believe the shock's been absorbed due to the fact that the core didn't hit the ground, but likely a giant hatch. Notice how it seemsto hit some surface at ground level, while the ship's literally being falling back into the pit where it was from.
Pits are roughly half a core high.

I'am not sure that this entirely explains away the lack of damaging effects that we see in the movie. For example, in real life, the impact of the meteor that created the 1.2 km wide Barringer Crater (aka Meteor Crater) in Arizona was rated at the equivalent of 2.5 megatons. A vastly greater amount of material from the area surrounding the core section's crash site should be displaced than what we saw, given the very extreme upper-limit estimate. Additionaly, there should be enourmous atmospheric effects. The Barringer Cater impact is estimated to have released 6.5 megatons of energy to the surrounding atmosphere in the form of a massive shockwave that devastated the surrounding plains out to 40 km. At best, the crashing core ship releases energy on that level.
-Mike

[Mr. Oragahn]

I believe the shock's been absorbed due to the fact that the core didn't hit the ground, but likely a giant hatch. Notice how it seemsto hit some surface at ground level, while the ship's literally being falling back into the pit where it was from.
Pits are roughly half a core high.

I'am not sure that this entirely explains away the lack of damaging effects that we see in the movie. For example, in real life, the impact of the meteor that created the 1.2 km wide Barringer Crater (aka Meteor Crater) in Arizona was rated at the equivalent of 2.5 megatons. A vastly greater amount of material from the area surrounding the core section's crash site should be displaced than what we saw, given the very extreme upper-limit estimate. Additionaly, there should be enourmous atmospheric effects. The Barringer Cater impact is estimated to have released 6.5 megatons of energy to the surrounding atmosphere in the form of a massive shockwave that devastated the surrounding plains out to 40 km. At best, the crashing core ship releases energy on that level.
-Mike

But let's remember that under that hatch - because it can only be that - there was the pit. Once you add the hatch (enough thickness, but I guess looking at AOTC could show how thick the edges of a core pit's hatch could be) and the void beneath, it can largely count for big part of the lack of damage.

Plus a core ship is ought to be hollow inside, and even if it's made of strong materials, it's not dense like an asteroid. It can't pretend impart as much solid KE at the point of impact as would a solid and dense impactor.
Considering that the core cracked on impact, we know why there was a lack of anything more impressive.

[Nonamer]

Maybe we should consider the possibility that the tradefed ship is a lot smaller than we think?

[Nonamer]

A reflector system would affect the acceleration (hmm, might be possible to work out the acceleration of gravity on that example), but the problem is that we need something to mitigate the mass . . . unless core ships are built out of tin foil.

If we call that a 10 kiloton (41.84 TJ) smack to the ground, for instance (a number I've simply picked from my posterior, though it sounds closer than Tsar Bomba), then at the given 200m/s the mass of the core ship would be:

KE = .5mv^2
41,839,999,999,999.9936 = .5m (4000)
41,839,999,999,999.9936 = m (2000)
m = 41,839,999,999,999.9936/2000
m = 20,919,999,999.9999968 kg
m = 20,920,000 tonnes

Given the earlier value of 600m for the spherical core ship, then the volume is simply 4/3 pi r^3, or 113,097,335 m^3, not counting the extra giblets around the bridge. The density would thus be 184.9 kg/m^3.

That would make it only around twice as heavy as air, and the vehicle would float extremely well in water.

Not a surprise. For instance, the World Trade Centers that fell were 450,000 tons each. Doing the math, that makes them:

(450 000 000 kg) / ((208 ft) * (208 ft) * (1 368 ft)) = 268.506534 kg / m^3

Only marginally heavier. That's because the world trade centers were only steel skeletons filled mostly with air. Assuming in the SW ships are made of some sort of lightweight alloy and filled with air as well, the density could reasonably go even lower than what you're giving. (Also, you're about 2 orders of magnitude wrong about the density of air, which is about 1.2 kg / m^3).

The remaining things to consider are:

1. How much energy the impact actually represents . . . this may be difficult to know, since the ship itself 'eats' some of the energy by falling apart most crunchily.

2. Further, the ground of Geonosis doesn't seem to be a perfect surface for such estimates either.

There are some other issues that'll make this more than a back-of-the-envelope thing, but this is an interesting case to work with.

True, but the back-of-the-envelope calculation is not unreasonable.

PS: Yeah, using the WTCs may be a tad tasteless, but they are really easily to find the volumes of.

[Estrecca]

But let's remember that under that hatch - because it can only be that - there was the pit. Once you add the hatch (enough thickness, but I guess looking at AOTC could show how thick the edges of a core pit's hatch could be) and the void beneath, it can largely count for big part of the lack of damage.

Plus a core ship is ought to be hollow inside, and even if it's made of strong materials, it's not dense like an asteroid. It can't pretend impart as much solid KE at the point of impact as would a solid and dense impactor.
Considering that the core cracked on impact, we know why there was a lack of anything more impressive.

Neither the hatch, nor the pit can justify the apparent lack of seismic effects in the neighbourhood (even the battledroids didn't fall after the crash and they have been shown to have poor balance), because neither can prevent momentum transmission and we are talking about a lot of momentum here. Also, whether the core ship actually hit the hatch is debatable, considering that in the moments before the dust hides it, the sphere doesn't seem to sink into the pit.

[Jedi Master Spock]

As a matter of fact, the amount of kinetic energy that is transmitted into seismic effects in an impact tends not very large.

While they're talking about very high velocity impactors, the WTC towers are indeed somewhere around the ballpark we're talking about in terms of energy and velocity, and are largely assumed to have been in near-freefall in terms of how fast they hit the ground. So:

Each tower had around 1e12 joules of gravitational potential (sure, the assumptions are simplified there, but it's good to within +/- 0.5 orders of magnitude with those sorts of assumptions), and the impact of the north tower falling was a 2.3 Richter event - i.e., ~180 megajoules, or on the order of 1.6e-4.

As it turns out, most calculations of the GPE of the WTC are a bit lower, meaning it's quite appropriate to round back down to the figure the impact calculator uses, of 1e-4.

Using that figure, we would have a Richter 3.2 seismic event from a 10 kiloton impact of a coreship - i.e., a shudder of the earth that could easily be overlooked, and one that we can easily imagine failing to knock over droids in formation.