Is a Death Star physically possible?

[radonek]

36 minutes ago, WedgeAntilles said:

Lol. What do you think "thermal exhaust port" means??

At least in part, the Death Star (the first one, anyway) disposes of waste heat by venting hot gas. But aside from the above exhaust port, we really can't assume anything about Death Star cooling systems, because the movies never showed us much of anything.
 

For all I know, it could be wookie for "Lucas never heard of second law of thermodynamics". Because I dare to assume that applies to every cooling system, imperial or not.  Evaporative cooling have this tiny weeny disadvantage of requiring to top off coolant tanks, which is why no longterm design ever used it. Think about it - rebels just need to intercept few coolant shipments and pride of the empire will melt. Whops.

1 hour ago, WedgeAntilles said:

If you mean the trick where you fly a starship right through a planet at FTL, I'm pretty sure that doesn't work in the Star Wars universe.

I mean that any propulsion method powerful enough to be useful must have energy density making it weapon of mass destruction. There is no "trick" about it. (And Interdictor class would just turn every spaceship around into a  relativistic kill vehicle )

[GeneralVeers]

46 minutes ago, radonek said:

For all I know, it could be wookie for "Lucas never heard of second law of thermodynamics". Because I dare to assume that applies to every cooling system, imperial or not. Evaporative cooling have this tiny weeny disadvantage of requiring to top off coolant tanks, which is why no longterm design ever used it. Think about it - rebels just need to intercept few coolant shipments and pride of the empire will melt. Whops.

Irrelevant. We know the Death Star did use this system, because it had thermal exhaust ports. We don't know what other cooling was used, if any, because the movie never mentioned it. Rule Of Fiction Writing # 87: don't explain techie stuff in too much detail. Gets boring. The writers of the movie just didn't care about the low-level technical hardware.

And......please tell me "Whops" was a typo??? Or do you have something against Italians?

 

46 minutes ago, radonek said:

I mean that any propulsion method powerful enough to be useful must have energy density making it weapon of mass destruction.

And as the real-world Earth has demonstrated more than once, nuclear-scale WMD's barely even dent the planet's surface.

 

46 minutes ago, radonek said:

(And Interdictor class would just turn every spaceship around into a  relativistic kill vehicle )

What we've seen in the Star Wars movies is that, when a ship of any kind drops out of hyperspace, it returns to sublight at normal cruise velocity--which is never relativistic. Relativistic speeds have never been used in the Star Wars movies.

And what we've seen in the real world is that a relativistic kill vehicle would be nowhere near enough to smash an entire planet to bits unless the RKV was the size of a moon. The asteroid that wiped out the dinosaurs was six miles across, delivered far more energy than the combined nuclear arsenals of the entire human race, and still barely even made a dent. (yes, I know how you're going to reply to that, and my reply to your reply is that we don't know how fast that six-mile chunk of rock was travelling--and, knowing how you're going to reply to THAT: yes, I looked up that velocity and got a figure of 20 km/sec--which is theoretical)

[KSK]

16 hours ago, WedgeAntilles said:

Lol. What do you think "thermal exhaust port" means??

At least in part, the Death Star (the first one, anyway) disposes of waste heat by venting hot gas. But aside from the above exhaust port, we really can't assume anything about Death Star cooling systems, because the movies never showed us much of anything.

 

If you mean the trick where you fly a starship right through a planet at FTL, I'm pretty sure that doesn't work in the Star Wars universe. Aside from the fact that it's one of the first things the Galactic Empire would have tried, Star Wars canon includes the Interdictor class Star Destroyer, which prevents hyperdrives from operating in its vicinity--by projecting an artificial gravity field. Within the field, ships can't jump to hyperdrive and any ship entering the field on hyperdrive will drop to sublight speed. So it's a safe assumption hyperdrive simply doesn't work in close proximity to planets. Fire a missile at a planet at supralight speed, and it drops to sublight before it hits.

Of course, the first movie offhandedly contradicts this theory when Han Solo makes his remark about "without precise calculations, we could fly right through a star". Apparently, whoever wrote up the idea for the Interdictor didn't watch the movies enough times.......

 

I see no problem with that, depending on what your sublight speeds are and what sort of gravitational field strength you need to trigger a drop-out from hyperspace. Han botches his calculations, Millennium Falcon drops out of hyperspace near a star, carries straight on into the star at sublight speeds before Han can react and asplodes.

Admittedly, 'flying into a star' would be more accurate than 'flying straight through it' but I'll let Han off with that slip of the tongue, given that he was under a certain amount of stress at the time.

Edit: I agree that blowing up a planet by crashing an FTL travelling starship into it wouldn't work though for the reasons you point out.

 

Edited December 31, 2015 by KSK

[cantab]

Considering that Han Solo also bragged about his ship's speed without remembering parsecs measure distance, he was probably exaggerating about hitting a star too.

(And spare me the "flying by black holes" nonsense. I know, I know, it's now been made Star Wars canon, but as far as I'm concerned that's just something Lucas made up instead of admit that he got it wrong.)

Edited December 31, 2015 by cantab

[GeneralVeers]

Yeah, Han's line about "the ship that made the Kessel run in less than twelve parsecs" bothered me the first time I heard it.

I figure it could be thought of this way: Han figured out a way to fly the Kessel run in the shortest distance possible (say, there's asteroids or some other obstacle in the Kessel region that makes the trade run hazardous)

[problemecium]

It bugged me too, but how else were they supposed to handle it? It's either "Sorry, we're idiots" or "Because 'Science'!". They picked "Science" ;P

[Kerbart]

On 12/31/2015 at 7:53 PM, WedgeAntilles said:

And what we've seen in the real world is that a relativistic kill vehicle would be nowhere near enough to smash an entire planet to bits unless the RKV was the size of a moon. The asteroid that wiped out the dinosaurs was six miles across, delivered far more energy than the combined nuclear arsenals of the entire human race, and still barely even made a dent. (yes, I know how you're going to reply to that, and my reply to your reply is that we don't know how fast that six-mile chunk of rock was travelling--and, knowing how you're going to reply to THAT: yes, I looked up that velocity and got a figure of 20 km/sec--which is theoretical)

Energy goes up with the square of the speed. Flying into a planet at 300,000 km/s will deliver a lot more energy than at a mere 20km/s.

Not to mention that fact that once we get close to light speed, we get the double-whammy of the mass increasing due to relativistic effects as well.

[cantab]

1 hour ago, parameciumkid said:

It bugged me too, but how else were they supposed to handle it? It's either "Sorry, we're idiots" or "Because 'Science'!".

Or "Han was bragging", which would seem entirely plausible.

He shot first too.

[problemecium]

No, Han didn't shoot first.

Han shot.

[GeneralVeers]

45 minutes ago, cantab said:

Or "Han was bragging", which would seem entirely plausible.

He shot first too.

Oh, for Pete's sake......

HAN DID NOT SHOOT FIRST. Geez. "First" implied that somebody else fired second, and Greedo didn't. He never got a shot in. Because he was DEAD. They never should have changed this scene, and whoever did should have been fired. Then deported to Guantanamo Bay. With Justin Bieber as a cellmate.
 

1 hour ago, Kerbart said:

Energy goes up with the square of the speed. Flying into a planet at 300,000 km/s will deliver a lot more energy than at a mere 20km/s.

As the Mythbusters have already demonstrated with high-velocity bullets fired into water: faster equals more damage only up to a point. Beyond that, at higher velocity the bullet smashes to bits and comes to a screeching halt sooner rather than later.

Kinetic penetrator? Those also don't do what you want them to--they pierce the target's outer shell, leaving a very small and neat hole in it, then shatter to bits inside. Works nicely with depleted uranium, which has a nasty habit of spontaneously igniting when shattered into small pieces. Doesn't work so well when the projectile contains a warhead that needs to get deep inside the planet without shattering.....

Not gonna blow up a planet that way. Cause an extinction-level event? Maybe. Explode the whole thing? Nope.

[KSK]

"Greedo didn't get a shot off because Han shot him first."

Makes grammatical and narrative sense to me but what do I know.

As for kinetic impactors getting deep enough into a planet - that's what shields are for.

Going back to the waste heat discussion - who needs radiators when you have hyperspace technology. Open one or more hyperspace portals into deep space, stick a particle shield over the entrance so that only radiation can escape and presto - one efficient radiative cooler.

What you don't do of course is to equip the secondary reactor, used to power your hyperspace portals, with a thermal exhaust port. Because you just know that some smartS wannabe Jedi will drop a rock down it for the lols. 

[cantab]

22 hours ago, WedgeAntilles said:

Not gonna blow up a planet that way. Cause an extinction-level event? Maybe. Explode the whole thing? Nope.

Randall Munroe begs to differ

https://what-if.xkcd.com/20/

The Mythbusters results with bullets are irrelevant, results with kinetic energy penetrators are irrelevant, even light gas gun studies are irrelevant. When you're talking about relativistic and ultrarelativistic impacts, more relevant are results from things like particle accelerators, but even then you have to consider the vastly greater number of atoms involved with a massive relativistic impactor.

[GeneralVeers]

WedgeAntilles just plain differs. (I never beg!)

At relativistic velocity, very few kinds of realistic projectile will stay in one piece. Those that do will drill a relatively neat and orderly hole through whatever they hit. The way real-world projectiles do massive amounts of damage is by either shattering into shrapnel (DPU rounds) or by exploding (missiles, rockets, anything that carries a warhead, which has the unavoidable caveat that the projectile has to stay in ONE piece until the warhead goes kaboom).

Then, when you consider the amount of energy--and the size of engine--that's needed to get a moon-sized RKV up to speed, along with the fact that you're using an entire MOON as a one-shot weapon? It's much easier to simply build a Death Star. Mostly because, as long as some hotshot pilot doesn't drop a photon torpedo in the air conditioning system and blow the whole thing up, you can use it more than once.......

[BlueCanary]

On 30/12/2015 at 8:14 PM, WedgeAntilles said:

 

Of course, the first movie offhandedly contradicts this theory when Han Solo makes his remark about "without precise calculations, we could fly right through a star". Apparently, whoever wrote up the idea for the Interdictor didn't watch the movies

Maybe Han meant that they would fly too near a star and be forced into sublight speeds in a position where they would have been fried by heat and radiation, without any way to escape back to hyperspace in time?

Edited January 2, 2016 by BlueCanary

[cantab]

Munroe discusses how, at these speeds - and even at the relatively modest 0.01c speeds - a "solid object" will expand outwards thanks to interacting with its target.

As far as Star Wars goes though, the key point you made is that there's no evidence regular starships can reach the required speeds in realspace, while a collision in hyperspace can do whatever the writers desire. Combine that with the argument I gave that the Death Star doesn't need to deliver the full binding energy of its target, and that a beam weapon isn't subject to the rocket equation whereas a ramming ship might be, and I think we can get a galaxy where the Death Star and weapons like it work but just ramming a planet with a starship doesn't work.

But in general, I stand by that enough mass moving fast enough will destroy a planet.

[MajorLeaugeRocketScience]

Simple answer:Yes

Complicated answer: One way to do it is to, say, open a wormhole at the center of a star. Since we basically know wormholes are possible, just use one of those. Transport all of that nuclear fusion goodness to a gigantic capacitor about the size of Russia. Now say you had 8 of these, as in one for each of the small beams that meet up, like in this picture.

If you squeezed all of that juice into a laser approximately a mile across, and have each laser meet at a point, followed immediately by an even MORE powerful center laser, disturbing the previous balance from when the lasers met, you would have one of the most energy intensive events ever recorded in the history of the universe.

[fredinno]

2 minutes ago, MajorLeaugeRocketScience said:

Simple answer:Yes

Complicated answer: One way to do it is to, say, open a wormhole at the center of a star. Since we basically know wormholes are possible, just use one of those. Transport all of that nuclear fusion goodness to a gigantic capacitor about the size of Russia. Now say you had 8 of these, as in one for each of the small beams that meet up, like in this picture.

If you squeezed all of that juice into a laser approximately a mile across, and have each laser meet at a point, followed immediately by an even MORE powerful center laser, disturbing the previous balance from when the lasers met, you would have one of the most energy intensive events ever recorded in the history of the universe.

...Wormholes have been proven?

[MajorLeaugeRocketScience]

Essentially, yes. Of course, we can't build one yet. But we know black holes exist. A wormhole is basically 2 quantumly entangled black hole singularities with opposite polarities.

 

Quick thought pitch: say the turbo laser, as it's called in the movie, is actually a rail gun. How much mass would be required to destroy a planet, explosively? I saw a US Navy expirement with a 80 pound projectile going Mach 7 smash into a 10 foot thick block of metal WITH NO EXPLOSIVE and make a giant explosion.

Edited January 3, 2016 by MajorLeaugeRocketScience

[GeneralVeers]

17 hours ago, cantab said:

Combine that with the argument I gave that the Death Star doesn't need to deliver the full binding energy of its target

Bingo. Here's a very efficient way the Death Star's main weapon could make a planet go kaboom: use the first-stage beam to drill a hole through the crust and mantle. Then switch the weapon to its second stage, a laser or heat ray that delivers a massive charge of heat energy through the drilled hole to the planet's core (heating the core instead of burrowing through it is important here). Thermal expansion pulverizes the planet from the inside.

An alternate method (less cool because it requires several ships firing from different locations) which is based on one method that's commonly used to destroy cancerous tumors: target the tumor/planet with several high-frequency penetrating beams firing from several directions. Each other point in the planet/patient receives a low radiation dose, but the targeted point gets the grand total. If you can make that enough to produce an explosive shock wave in the core of the planet, you've completed your Evil Overlord final exam!

[sal_vager]

Nice thread @A35K , stickied for January!

[James Todd]

You can't make something that big levitate without really big engines.  As someone who studies engines, I'll tell you right now that even with really big engines, you would need other engines just to hold up their weight.  Even if you had all the money in the world, you can't make something you're not able to think of how to do.  So no, unless we had someone really smart or had really big engines, you couldn't make a DeathStar.

[KSK]

Uhh, levitation wouldn't be a problem since it's just floating in space. Moving a spacecraft the size of a small moon is another matter of course but we're talking about a fictional setting where faster than light travel is routine, so I presume the Death Star relies on hyperdrive to move about rather than gigantic propellant based engines.

[James Todd]

Okay, but how would you get it into space?  Unless you put it together in space you would still need really big engines to get it all the way up there. 

[Starwhip]

On 1/2/2016 at 10:38 AM, cantab said:

But in general, I stand by that enough mass moving fast enough will destroy a planet.

Well, from what I know, you might be able to destroy more than just a planet.

https://en.wikipedia.org/wiki/Relativistic_kill_vehicle

Forgoing the Tyranny of the Rocket Equation, say we accelerated a one thousand kilogram object to approximately the speed of light. Say, 95%.
Equation The result? 3.12x10²⁰ Joules. That is equivalent to approximately 50 Gigatons of TNT.

What if, in the spirit of xkcd, we tried more power?
The Result
Accelerating the object to nearly the speed of light yields an equally ridiculous amount of energy. 2.84x10⁶⁰ Joules. The sixtieth. Equal to 6.79x10⁴¹ Gigatons of TNT.

For some more perspective, here's a handy table. http://www.projectrho.com/public_html/rocket/usefultables.php
According to it, the Big Bang was estimated to be around 3.0x10⁶⁹ Joules. Which gets our number up to 0.0000001% or so of the Big Bang, with a single metric ton.

Perhaps someone else might refine on this. I have not the slightest idea what all this energy would do, nor what fraction of it would be yielded in detonation, or through impact, or whatever an object going so incredibly fast does.

Now, perhaps some more reasonable numbers.
1,000 metric tons at 0.7c
1,000,000 metric tons at 0.5c

Neither of those come close to touching the massive power previously achieved, but they are a good perspective.

[GeneralVeers]

3 hours ago, Starwhip said:

The result? 3.12x10²⁰ Joules. That is equivalent to approximately 50 Gigatons of TNT.

2.84x10⁶⁰ Joules. The sixtieth. Equal to 6.79x10⁴¹ Gigatons of TNT.

etc etc etc

None of these numbers actually tell you anything. It's not the amount of energy--it's where that energy goes.

If you're like me (i.e. computerish and just generally nerdy) you spend more time indoors than out. So right now you're probably receiving a lot more "joules" of energy from the lights in your house/apartment/cardboard box/other domicile, than from the Sun.

Which will give you cancer first? Light bulb or Sun? Even assuming the SAME amount of "joules" received from each, the answer is "the Sun". Because a significant percentage of the Sun's emission spectrum is in high-energy ultraviolet and gamma radiation. Frequencies that penetrate tissue and cellular membranes, impact DNA molecules, and cook them the same way a pancake left on the stove too long turns from tasty dough and sugar into charcoal. Whereas the emission spectrum of a light bulb is much weaker and stands pretty much zero chance of giving you cancer. Ever. (yes, ordinary light bulbs do emit UV radiation, but not enough to pose a risk of any kind)

The point being that sources producing the same number of joules can do vastly different amounts of damage. A high-velocity armor-piercing bullet will drill a neat and relatively painless hole through a person; hitting them in the face with a one-pound rock delivers far less energy, but will break bones and liberate teeth. The way you get bullets to do real damage is not by going through a person--but by spalling or shattering inside the person. Similar for the Durandal anti-runway bomb; instead of merely cratering the runway, the munitions dropped by a Durandal penetrate a few meters into the earth before exploding, creating an underground pocket crater that's a lot harder to fix. Same explosion, deeper underground, much nastier results.

By way of comparison: earthquakes and atomic bombs. At around 8.6 magnitude, an earthquake releases around ten thousand times more energy than the Hiroshima detonation. The radius of damage from an earthquake is highly variable, but the damage done (and the body count!) is a lot more mild than your average nuclear bomb. Fact is, most of the energy of an earthquake is wasted in shaking flexible things (human bodies and wooden houses--even concrete skyscrapers have a good deal of flex in them, damping a lot of the energy). Also, keep in mind that the Earth is three-dimensional. A lot of an earthquake's energy goes down. Which doesn't do a lot of damage to anything except underground pipes. To double the radius of destruction, you have to much-more-than-double the earthquake's energy. Same rule holds with nuclear bombs; because the explosion is three-dimensional, you have to multiply the megatonnage by EIGHT to get double the radius of destruction. Further: an earthquake whose hypocenter is deep underground will exert much less force on the surface.

 

So where's that leave us with relativistic kill vehicles? Well, take Starwhip's first number: 50 gigatons of TNT. That's about fifty magnitude 8.6 earthquakes. When a single 8.6 earthquake strikes anywhere, most people on Earth can't even feel it. The only influence it has on their lives is when they hear about it on the news. As shown one paragraph up, the energy of an earthquake does not dissipate at a linear rate with distance--it's exponential or quadratic or some such. Twice as far away, the shaking is much less than half as powerful. The energy of an earthquake fifty times stronger will dissipate rapidly and still have a very small area of effect. Though anybody IN that area of effect would have a really bad day. If that earthquake's hypocenter is ten miles underground (and most earthquakes do in fact originate pretty deep down), the effects will be far weaker.

The thing that made the 65-million-years-ago asteroid so deadly wasn't the amount of energy delivered. In fact, most of that energy went straight down and was never heard from again. But some of that energy bounced a big cloud of dust into the atmosphere. That's what did the real damage. If the asteroid had been hard enough (or fast enough) to penetrate deeper before shattering, it would have been identical to a deep-crust earthquake: lots of shaking underground, much less shaking on the surface, much less exploding on the surface, no global dust cloud, and therefore no extinction event.

 

Myth busted.

Edited January 5, 2016 by WedgeAntilles