Death Star shields vs Alderaanian debris: to scale

[Vance]

There's been a lot of revived debate about how Alderaan was destroyed as of late, and by extension, the power generation of the Death Star and the other warships of the Empire. The vessels shields must have withstood planetary debris regardless of what blew up Alderaan and we know that the Death Star was still in system when Han arrived. Therefore the implication of near-by planetary destruction independently speaks of the power systems on the Death Star.

The novelization of A New Hope says the Death Star was six planetary diameters from Alderaan when it fired. At this distance the hundred-kilometre wide debris travelling at thousands of times the speed of sound would impact the Death Star within a matter of seconds! The to-scale picture below pictures the explosion somewhere between 3 and 4 seconds after destruction. The Death Star cannot possibly have escaped these debris that were travelling millions of miles per hour, and thus its shields must have withstood the barrage.

Full size http://imageprocessor.websimages.com/fi ... 0scale.png

Each one of these debris would deliver a kinetic energy comparable to that delivered by Theia when she slammed into the Earth:
https://www.youtube.com/watch?v=N0uw0T0JvSI#t=54


I'd also note that 6 planetary diameters are conservitive. It looks like the Death Star was closer to Alderaan in the film.

[Purple]

So basically what you are saying with that huge, format breaking and unspoiled image is that when we wish to express imperial superiority by citing the death star we should be looking not at the weapon which destroys planets but the shields which shrug them off afterward?

Works for me.

[Vance]

Yep. Sorry about the size. I'll upload a smaller image to replace .

[Eternal_Freedom]

It's a pretty good standpoint really. Much harder to shrug off as "chain reaction weapons" or some shit like that. Although...

Let me crunch some numbers here. Let us assume that Alderaan is the same size as Earth to 2 s.f. (6400 km radius) and assume that the DS1 is indeed 6 planetary diameters away that makes it's distance 76,800 km.

Assume that the debris expands in a perfect sphere, by the time it reaches the DS1's distance it will have a surface area of 74 billion square kilometres. The DS 1 has a half-sphere facing the planet, so has a surface area that can be hit of 40,200 square kilometres. That means the Death Star's surface occupies only 0.00005% of the total area the debris might cover.

Now, if posit that the debris is flying out as 100 cubic kilometre chunks, then we get 10.98 billion chunks, of which only 0.00005% will be in the right place to hit the Death Star, which translates to just under 600,000 (597,000 to 3 s.f.) of them impacting the DS1 (on average).

Let us go a bit further. The average density of Earth is ~5440 kg/m^3. So each one of those 597,000 chunks will have a mass of 5.44E12 kg/km^3). If we assume the OP is right and it took 4 seconds to cover the distance of 76,800 km they're doing 19,200 km/s which gives a kinetic energy of 0.5*5.44E12*(19,200,000^2) which is 1.002E27 J. Since one megaton is 4.184E15 Joules that gives us an impact energy of...~240 petatons per chunk. Now not all of the ~600,000 chunks will hit head-on and impart all their energy, most will ricochet off the shield. If we assume that, say, only 1/100 of that total kinetic energy is actually dumped into the shield, that means it can withstand 1.43 million petatons of kinetic energy.

Fuck thats a lot.

EDIT: fuck, missed out a factor of 10^3, should be right now.

[Eternal_Freedom]

Incidentally, if I multiply my figure for the debris chunks kinetic energy by the number of chunks, I get a total kinetic energy of the planet's mass of 1.1E37 J. Which is about 1/9th what Mike estimated as the energy of the superlaser blast (1E38). This makes me happy.

[Batman]

It's also moderately useless for figuring out the power generation capacity of the Death Star, which I think was the OP intent. What's the power draw of a wall? A battleship's armour? A bulletproof vest?
Shields standing up to any given bombardment doesn't tell us beans about their power consumption.

[Eternal_Freedom]

Actually it is fairly useful anyway, since all that kinetic energy had to come from somewhere and the only source is the superlaser, which is powered by the Death Star. So we know they can generate and store at least 1.1E37 J. We know that about one day passed between Alderaan blowing up and the Battle of Yavin, where the superlaser was ready to fire again. So in 24 hours (let's be really conservative and say it's actually 48 hours) they managed to generate that much power in addition to however much they need for normal operations and flying the thing through hyperspace.

So, being conservative, in 48 hours (172,800 seconds) they generate at least 1.1E37 J, which gives a power generation of 6.36E31 W. Or about 160,000 times the Sun's luminosity.

[Batman]

I have to admit I didn't think of that. World's Greatest Detective my ass

[Eternal_Freedom]

Detective /= scientist

My degree comes in handy at last!

[Darth Holbytlan]

Actually it is fairly useful anyway, since all that kinetic energy had to come from somewhere and the only source is the superlaser, which is powered by the Death Star.

Actually, no. If you're arguing against a "chain reaction weapon" advocate, they'll just claim the energy came from the planet somehow. Nothing here makes that theory any less plausible than it already was.

What this does do is provide direct evidence for exactly how good SW shields really are in a way that completely bypasses arguments that try to downgrade their capabilities by downgrading those of turbo/superlasers.

[Borgholio]

they'll just claim the energy came from the planet somehow.

That's what the chain-reaction crowd always claims. Easy enough to debunk if you know anything about actual nuclear chain reactions. Earth is made mostly of Iron and Silicon - two of the most stable elements in the periodic table. Neither can undergo fission, and only in the most massive stars can Silicon undergo fusion. Iron is so resistant to fusion that trying to squeeze it too much results in a fucking supernova.

So while using the shield strength method is actually a clever way of arguing the tech level of the Empire, it's probably still going to be easier to beat them over the head with nuclear physics.

[Lord Revan]

isn't also that trying to fusion iron or Silicon is a net energy loss, aka it takes more energy to counter the electro-magnetic repulsive force of the atoms then it you get from fusing them together, thus being the final nail to the coffin to the "it caused a nuclear fusion that caused the planet to blow itself up" theory (if you want to call it that).

[Borgholio]

isn't also that trying to fusion iron or Silicon is a net energy loss, aka it takes more energy to counter the electro-magnetic repulsive force of the atoms then it you get from fusing them together, thus being the final nail to the coffin to the "it caused a nuclear fusion that caused the planet to blow itself up" theory (if you want to call it that).

Well no, you can still get *some* energy out of fusing silicon. It fuses into iron. But that's basically the "last gasp" of a star which only lasts for a few days. Once it hits iron, THEN it becomes a net energy loss which is what eventually causes the core of the star to implode.

So given how a majority of the mass of a planet is iron (net energy loss) and silicon (just barely a net energy gain), it'll take less energy just to blow the damn thing up than trying to get it to fuse.

[Simon_Jester]

The Death Star superlaser clearly could not have induced a fission or fusion reaction inside Alderaan to make it explode, but in and of itself I have no problem with the idea that it induced some other sort of event that caused the explosion.

The visual we see... well frankly, it looks like a model of a planet floating in void and then getting blown up by a firecracker from the inside. With reason, because that's how they did it back in the '70s.

So the idea that an internal explosion induced by some exotic-physics effect really destroyed the planet is fairly consistent with the visuals, arguably more consistent than "a direct energy transfer beam shines on the planet for a moment, then it suddenly blows up all at once." Because a really photorealistic depiction of such an event would show things like debris/gas clouds shooting up around the point of impact, or the beam overpenetrating, or things like that.

[Thanas]

The problem with the chain reaction idea is a practical one as well. If we accept it as a valid theory then we must believe the empire to be so stupid that it build a weapon of mass destruction that is not usable against all planets but only against all planets which have a similar geographical markup.

[Borgholio]

So the idea that an internal explosion induced by some exotic-physics effect really destroyed the planet is fairly consistent with the visuals, arguably more consistent than "a direct energy transfer beam shines on the planet for a moment, then it suddenly blows up all at once." Because a really photorealistic depiction of such an event would show things like debris/gas clouds shooting up around the point of impact, or the beam overpenetrating, or things like that.

So if we accept the idea of exotic physics, does that invalidate the idea that the DS pumped an ungodly amount of energy into the planet and instead used technological trickery to pull it off?

[bilateralrope]

So the idea that an internal explosion induced by some exotic-physics effect really destroyed the planet is fairly consistent with the visuals, arguably more consistent than "a direct energy transfer beam shines on the planet for a moment, then it suddenly blows up all at once." Because a really photorealistic depiction of such an event would show things like debris/gas clouds shooting up around the point of impact, or the beam overpenetrating, or things like that.

Doesn't that depend on how fast it takes to explode the planet after the shield goes down ?

[Sea Skimmer]

The superlaser beam itself might be made of some kind of particle that undergoes a transformation on impact with a sufficent amount of mass to turn its energy into heat which radiates in all directions, to give the more or less uniform explosive effect. It might not work exactly like turbolasers do, and hell turbolasers and blasters seem to be very good at causing explosions too.

[Simon_Jester]

The problem with the chain reaction idea is a practical one as well. If we accept it as a valid theory then we must believe the empire to be so stupid that it build a weapon of mass destruction that is not usable against all planets but only against all planets which have a similar geographical markup.

I don't know. For all I know, the chain reaction will work against anything made out of atoms, and carries sufficient raw energy transfer to overpower planetary shields by brute force. Or the effect is of such a character that it completely bypasses shields.

I'm not saying that the Death Star superlaser must somehow be weakened or inferior because of this. I'm saying that I honestly think the visuals are more consistent with the Death Star firing a "ray that makes giant things blow up" than with the Death Star firing, say, an extremely intense laser or particle beam.

So if we accept the idea of exotic physics, does that invalidate the idea that the DS pumped an ungodly amount of energy into the planet and instead used technological trickery to pull it off?

For all I know, it did both- pumped massive amounts of energy and zapped the planet with something that inexplicably caused it to explode like a giant firecracker, rather than like a rock being blown apart with a laser cannon.

I'm not trying to minimize yields here, I have no interest in the versus debates. I'm just saying... that thing sure looks like an 'explosion-inducing ray' to me.

The superlaser beam itself might be made of some kind of particle that undergoes a transformation on impact with a sufficent amount of mass to turn its energy into heat which radiates in all directions, to give the more or less uniform explosive effect. It might not work exactly like turbolasers do, and hell turbolasers and blasters seem to be very good at causing explosions too.

That is an interesting possibility- that the beam is in effect 'fuzed' to create an omnidirectional burst of energy upon striking a solid object. Or upon penetrating into the interior of a solid object.

[Havok]

Wait... so people argue that a "chainreaction of events" is what destroyed Alderaan? And that that PLANET WIDE reaction, took, what, a millisecond? Isn't that completely implausible based on physics alone?

[Batman]

Based on real world physics, yes. A lot of Star Wars, however, requires our understanding of physics to be at best incomplete.

[Havok]

Well my understanding is that you have to work what you see on film into real world physics. After that you assume "technology solved it" (i.e. hyperspace being "outside" of regular space). A chain reaction of that magnitude, if it couldn't possibly happen, and there is no technology to explain it, must be dismissed as an explanation.

[Batman]

And I think that's what Simon is getting at. At least as he sees it, the destruction of Alderaan as seen in the movies isn't compatible with real world physics*. I happen to disagree, but I also seriously suck at anything involving math.

*It's incompatible with real world physics anyway because even if it is a DET event there's no 'real world' way in hell to generate that much energy in something the size of the Death Star, but from what I can tell Simon is saying 'even if we dump Mike's calculations (and more) into the planet, the results wouldn't look like that'.

[Vance]

Since there is no possible way that the energy needed can be generated from the planet itself (or any chain reaction involving the planet) it must have come from an external source. It is actually easier to hypothesize ways in which the energy could be generated inside the Death Star than it is to explain any impossibly energetic chain reactions involving the planet itself, which is composed of known materials (mostly silicon and iron).

The asteroid could store matter (to be annihilated with anti-matter) at densities hundreds of thousands of times denser than iron, thus containing enough fuel to generate 1e38 Joules of energy. Or the Death star could have some kind of dimensional tap from which it draws power from another dimension, or another point in space.

The energy required to accelerate mass into motion is impossible to circumvent, so there is no way of getting rid of those 1e38 Joules regardless of where they come from.

[Vance]

External Freedom, the density of those superheated blobs is probably orders of magnitude lower than the planet. I believe the best method would be to divide the total mass of the planet by the total volume of the explosion by this point of expansion, and then work out what fraction of that explosion is represented by the big fiery ball in the bottom left. Then multiply the calculated density minus the huge fiery sphere by the volume of the superheated debris...

If you'd like to do this calculation before I do then you could derive the info you need from this page http://www.galacticempirewars.com/death-star-firepower

Using this image and assuming the explosion is 3 times greater than the measured line would be very conservative, to say the least.
http://imageprocessor.websimages.com/wi ... uction.png

It's also moderately useless for figuring out the power generation capacity of the Death Star, which I think was the OP intent. What's the power draw of a wall? A battleship's armour? A bulletproof vest?
Shields standing up to any given bombardment doesn't tell us beans about their power consumption.

I disagree. Both shields and turbolasers are powered by a ships main reactor. If shields could withstand energy orders of magnitude greater than the power which they consume then the output of turbolasers would be comparatively trivial.