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I'm writing my first sci-fi novella and I'm looking for a bit of guidance from some scientifically literate people. My main premise is that an alien space ship similar to the death star enters Earth's orbit at a low orbit point. Its gravity causes earthquakes, tsunamis, meteor showers and all that fun stuff. My only problem is that I'm not sure how my characters are going to destroy the ship in a way that is scientifically plausible. I have a few ideas so far;

They somehow launch it into the moon, destroying it.

They somehow use gravitational slingshot method to launch it around the moon, Venus and Mercury and into the sun, destroying it.

They somehow pull the ship towards earth into the Roche limit, causing Earth's gravity to tear the ship apart, destroying it.

The problem is that, from my understanding, these methods would either complete destroy earth as well, or they're just scientifically implausible. I'm a bit of a science nerd, but I won't pretend to understand enough astrophysics to finish this story without some help and further research. Obviously, it doesn't need to be completely scientifically accurate, but I'd like to avoid any embarrassingly obvious errors. Any help would be GREATLY appreciated! (go easy on me, it's my first attempt at writing a book!) Thank you in advance!

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    $\begingroup$ Remember we don't want to replicate the Endor Holocaust..... $\endgroup$ – Thucydides Oct 16 '16 at 20:12
  • $\begingroup$ How is the character attacking the ship? Can he get inside or are we limited to shooting it from the outside? $\endgroup$ – Bellerophon Oct 16 '16 at 20:39
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    $\begingroup$ Does the hero know the location of the thermal exhaust port on the enemy ship you know the small opening around 2 meters wide... don't worry unless the blast literally translated all biomass into pure energy to overwhelm Earth binding energy. $\endgroup$ – user6760 Oct 17 '16 at 0:50
  • $\begingroup$ If you watch 'the fifth element' you will see they stopped a giant death star-esque evil entity and turned it into the moon without destroying the planet. Granted they had giant 'lasers' from an ancient alien race! Note, I don't actually know what shot out but it sure did the job. Something to do with the...five elements. $\endgroup$ – EveryBitHelps Oct 17 '16 at 12:19
  • $\begingroup$ If you're thinking of putting a Death Star in orbit, this question might be of interest to you. $\endgroup$ – Mark Oct 18 '16 at 0:16
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You want to destroy a Death Star sized spaceship in low orbit around the Earth! Hold it right there! This proposition needs rethinking.

OK, firstly, a spaceship of this size must be massive if its gravity is interfering with the Earth. So its gravity will have some effect. However, it seems doubtful if the vessel's gravity could go this far. "My main premise is that an alien space ship similar to the death star enters Earth's orbit at a low orbit point. Its gravity causes earthquakes, tsunamis, meteor showers and all that fun stuff."

The tides would be messed up big time. Possibly, earthquakes will be triggered by a new set of earth tides generated by the vessel as it passes overhead of faults and seismic zones. While, tsunamis will follow deep sea seismic events, it not probable these were be happening too frequently. Additional meteor showers are unlikely.

What you have is a gigantic piece of alien technology, admittedly with a mind-bogglingly large mass, in low orbit. This a fabulous asset! Firstly, it is made of processed and refined materials — metals, plastics, ceramics, materials unknown to technology, chemicals and, possibly, exotic timbers. Forget about asteroid mining! This is a gold mine of materials that can start humanity on the road to becoming a spacefaring species.

The giant spaceship must full of alien technology. If you are able to destroy without its passengers and crew popping out armed to their back teeth with laser-guns, then you are free to rummage through its technological golden goodies and kick start several technological revolutions.

Oh! You still want to stop all the earthquakes and tsunamis. That's understandable, under the circumstances. There's no need to destroy the death star sized spaceship. Just send a mission of scientists, engineers, and astronauts to go on board and locate the vessel's control systems. Go for a gentle restart of its propulsion system and move it into a higher, safer orbit around the Earth. Somewhere it will still be readily accessible to new tech hungry humans. There's no need to destroy it. The spaceship is more valuable intact and whole.

NOTE:

This answer predicated on the assumption that if the objective, as stated by the OP, to destroy the gigantic spaceship, then there are no aliens on board to resist attacking it. On the other hand, if there aliens on board and they are prepared to defend their territory to the last drop of our blood, then the situation becomes much more fraught. Time for some two-fisted action to save the day!

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  • $\begingroup$ "crew popping out armed to their BACK TEETH with laser-guns" This made me laugh! $\endgroup$ – CaptClockobob Oct 17 '16 at 23:22
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An alien spaceship the size of the Death Star is going to be largely empty space, if the movies are any indication, so even an object the size of the Earth's Moon isn't going to be anywhere near as massive. On that scale you should actually think of it more as a balloon than a planet. So if there are earthquakes, tidal events and tsunamis, it is because the Aliens are doing this deliberately, not simply because the spaceship is in orbit.

If the ship is crewed with Aliens with hostile intent, then in any realistic scenario we are totally SOL, since we would be dealing with technologies centuries or millennia in advance of our own. Launching nuclear tipped missiles at the object, or even building a massive ground based laser (and launching swarms of "fighting mirrors" to redirect the beam) is more likely to annoy them than do any significant damage, assuming they simply don't shoot down any incoming rockets or rocket launches first.

enter image description here

Fighting Mirrors

Other current warfare ideas are out as well. Hacking an alien computer system would require detailed knowledge of the hardware and software being used, and our laughable attempts at Malware wold be easily blocked by whatever firewall and antivirus systems they have. Biological attacks are even more unlikely (sorry, H.G. Wells) because disease organisms are highly tailored and specific to the organism being targeted. Trees don't catch colds, for example, and an Alien species would be far stranger than that.

What would really make this question more answerable is to provide some context. Why is this in orbit around Earth in the first place? What are the objectives of the Aliens? For that matter, what sorts of technologies do they use? How many of them are there? (A hollow, moon sized spacecraft could theoretically hold trillions of beings, depending on how tightly you can house them and what their material requirements actually are).

As a wild handwave, you could create a sort of nuclear "shotgun" on Earth to fire on the spaceship as it passes overhead, based on the late 1950 era "Pascal A" test shots. During the tests, one of the huge steel caps covering the shaft was blown off by the nuclear device at the bottom, and it was estimated it was launched into space at 6X escape velocity. Realistically, it was probably destroyed by aerodynamic heating and forces on the cap as it flew through the atmosphere, and vanished in a shower of molten iron droplets.

Imagine a silo filed with water. A small nuclear device is submerged in the bottom, and the silo "cap" is actually made of solid steel, perhaps with an ablative coating on the surface. The nuclear device is detonated, turning the water into plasma and propelling the cap at very high velocity into space. The water plasma provides much more efficient coupling of the energy from the nuclear device to the projectile, and a large field of them would pelt the object with thousands of massive slugs moving at 6X or more escape velocity, plus whatever velocity the object is moving at in orbit.

enter image description here

Surprise!

This has the primary advantage of being relatively quick and cheap, built on the ground so the odds of being detected are much lower than launching fighting platforms or weapons into orbit, and there is really nothing to spoof or jam, these are simply unguided steel slugs moving at incredible velocity (@ Mach 150 if they are moving at 6X escape velocity), and deliver their energy to the target by straight kinetic impact. A Deathstar sized target is going to be hard to miss.

Of course, you will create a radioactive wasteland where the "shotgun" was built, and assuming you have "killed" the death star, it is still in orbit (although sending salvage teams aboard will have incredible benefits, as a4android suggested in their answer.

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  • $\begingroup$ Actually bacteria may well be effective against aliens depending on biochemistry etc. Viruses obviously are completely out. $\endgroup$ – Tim B Oct 19 '16 at 8:41
  • $\begingroup$ Loving the shotgun idea, although not convinced the "shell" would hold together and against a target this side you would need more than one/ $\endgroup$ – Tim B Oct 19 '16 at 8:43
  • $\begingroup$ The "shell" may well become a mass of molten iron or even plasma, but it still has the same mass, momentum and kinetic energy. And the answer suggests a large field of these silos; the "shotgun" is firing them all at once to pelt the object with hundreds or thousands of these projectiles. $\endgroup$ – Thucydides Oct 19 '16 at 14:21
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You don't say why your protagonists need to destroy this vessel, so I'm going to go out on a limb here and suggest that as bad as the tidal effects of this large vessel are, it's actually the Evil Aliens (TM) who own this ship that are the real problem. If so, perhaps you need simply disrupt the ship's power plant to destroy the ship. Let me elaborate:

Dr. Rice of the University of Edignburgh (http://www.roe.ac.uk/~wkmr/Teaching/Astronomy1G/Lecture3_6_slides.pdf, among others) indicates that a black hole could be the most efficient way to produce power. Depending on the kind of black hole, matter-to-energy efficiency may be anywhere from 14% to 40%. For comparison, folks at the Physics StackExchange (https://physics.stackexchange.com/questions/72926/in-nuclear-fusion-reaction-what-is-the-percentage-of-mass-converted-to-energy) estimate that a fusion bomb converts less than 0.4% of its mass to energy. This makes the black hold at least an order of magnitude more efficient, and possibly much more.

All that capability makes a managed black hole really useful as a power supply for interplanetary travel. When it arrives at earth, it's also going to contribute a lot of mass to the orbiting vessel, which is why it generates such strong tides.

It would also put a lot of stress on the alien starship -- except, these aliens also have invented artificial gravity. In addition to keeping everyone happy during the long voyage, their antigravity also helps flatten out spacetime in the ship's hull, keeping things stable. Our progagonist doesn't know this, and, in an effort to escape, s/he turns off the ship's gravity in an effort to make life difficult for her pursuers.

Oops.

There is a big flash as the ship collapses into the black hole and our hero(ine) has sacrificed his/her life to eliminate the alien threat. The Earth is saved.

Now all we have to do is figure out how to get that black hole out of LEO. NASA is not amused...

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A Death Star (140 - 160 km diameter - Wikipedia, 120 km diameter Wookiepedia) is very large, yes. The moon (3474 km diameter) is much larger. The first thing we can do is look at the forces involved. How much force does the moon exert on the earth, and how much force this "Death Star" exerts on earth.

The moon is about 384,400 km from Earth and weighs about 7.34767309 * 10^22 kg. The equation for force due to gravity is $F_g = \frac{Gm_1m_2}{r^2}$ where $G$ is the gravitational constant $6.67408 * 10^{-11} \frac{m^3}{kg*s^2}$. Earth is about $5.972 * 10^{24}$ kg. From this we can calculate the force on the Earth due to the moon. Plug in all the numbers and it spits out a force on Earth of $1.98 * 10^{20}$ Newtons $\frac{kg*m}{s^2}$. However, for a 1km block on the surface of earth (earth has a radius of 6371 km), the force is $3.43 * 10^{-5}$ Newtons.

Now, instead of using the moon, lets use this Death Star. Low Earth Orbit is between 160 km and 2000 km in altitude. So let's take the happy medium and say that it's at 1000 km in altitude. Now the hard part. How massive is this Death Star? If we say this Death Star is like an aircraft carrier, we can say that the density of the aircraft carrier is about the density of the Death Star.

Wikipedia lists the Nimitz-Class aircraft carrier at 100,000 long tons. A long ton is about 1016 kg. So the aircraft carrier has a mass of about 101,600,000 kg, or $1.016 * 10^8$ kg. Lets say the volume of the aircraft carrier can be approximated with a triangular prism. The only problem is that I don't know how tall the aircraft carrier is, so this is likely to be a order of magnitude approximation, because I'm going to approximate it using an equilateral triangle. A triangle is $A = \frac{1}{2}bh$ and a prism is $V = Bh$ (big B because the base in this case is an area). A Nimitz-Class aircraft carrier is 1100 ft long and 252 ft wide. That's around 334 meters by 77 meters. Since the triangle is equilateral, the height is $77 * \sin(\frac{\pi}{3}) = 77 * \frac{\sqrt{3}}{2} \approx 66.7$ meters. The area of the triangle is ~2567 m^2 and the volume of the prism ~857500 $m^3$. Now that we have mass and volume we can find density.

Density is mass divided by volume. So the density of the aircraft carrier is ${1.016*10^8 \, kg \over 857500 \, m^3} = 118.5 \frac{kg}{m^3}$. Now we need to find the volume of the Death Star. The Death Star is a sphere, so the only parameter we need is the radius. We stated at the very beginning that the Death Star is about 140 km in diameter, so its radius is about 70 kilometers. The equation for the volume of a sphere is $V = \frac{4}{3}\pi r^3$, so plug in $r = 70$, and the volume of the Death Star is about $1437000 \, km^3$ or $1.437*10^15 \, m^3$. Since the mass-density of an aircraft carrier is a good approximation for the mass density of the Death Star, then we can use the aircraft carrier density times the volume of the Death Star to get its mass.

The mass of the Death Star is $118.5 \frac{kg}{m^3} * 1.437*10^15 \, m^3 = 1.7*10^17 \, kg$. That's pretty massive. Now let's say this Death Star is orbiting at 1000 km above earth's surface. The total force on the earth is $1.25*10^18$ Newtons. That's about two orders of magnitude away from the force on earth from the moon. However the force on a 1 km block on the surface of the earth is $1.14*10^{-5}$.

Huh. That's less than the moon. But we can move it closer. Let's move it in as close as we can, 160km (LEO lower bound) + 70km (radius of Death Star) = 230km. At that height, the force on a 1 km block on the surface of the earth is $2.15*10^{-4}$. Now that's about an order of magnitude above the moon, which we already know causes tides. But is it enough to cause earthquakes?

There are sites on the internet that link the moon cycle and earthquakes. So I would say that it is indeed plausible that the Death Star could cause an earthquake simply by existing.

tldr: the death star could probably cause earthquakes.

Now, how to get rid of it. The easiest thing to do would be to lift its orbit until it no longer causes earthquakes. The easiest way to do that would be to infiltrate the spaceship and get it to put itself in a higher orbit. If there is intelligent life aboard this spaceship (very likely) then getting rid of it is going to be the least of your problems. The simple fact that they are causing earthquakes with little regard for the life on the planet is the first warning bell. They're not here to make friends. And they're here because they want something. They may want us as slaves (unlikely, robots are cheaper) or our minerals (star miners?). In any case, we need more information about who these people are and why they're here. So the first thing to do would be to try and establish contact. Examine the signals that the Death Star gives off. Then, build a plan appropriate to the information provided. If they request a representative of our race, that's the perfect way in. If their ship gives off no signals at all, that means that there is a vulnerability that we can try to take advantage of.

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  • $\begingroup$ The 2016 short novel, “Dark Energy” by Robison Wells explores some of the functions that slaves can serve which robots cannot. So as not to spoil the book, I'll offer a wikipedia page with an analogy that has a title sufficiently obscure that most readers won't understand unless they choose to click on it and spoil the surprise. en.wikipedia.org/wiki/Ichneumonidae $\endgroup$ – ohwilleke Oct 18 '16 at 1:10
  • $\begingroup$ If their ship gives off no signals at all, that means that there is a vulnerability that we can try to take advantage of. - they are dead, or they do not care about u trying take advantage. I would not care on their place. MathJax basic tutorial and quick reference $\endgroup$ – MolbOrg Oct 19 '16 at 7:42
  • $\begingroup$ @MolbOrg If they are dead, then that means the ship is there for the taking, bar any AI or robot janitors. $\endgroup$ – TheZouave Oct 19 '16 at 13:50
  • $\begingroup$ @ohwilleke I can kind of see your point here, as space-faring technology is different from biological technology. But it still bears making the point that bio-mechanical reusable incubation chambers could be used. The real question is if they would be more expensive in terms of space and resources to maintain. $\endgroup$ – TheZouave Oct 19 '16 at 13:53
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This answer assumes that:

The ship has no force field or any barrier whatsoever. The ship has no life forms inside it. The ship does not have any other weapons except the gravitational pull. The ship features the Death Star of Star Wars. The ships gravity is slightly lower than earth. With these assumptions, we could also say that.

The ship has no bridge, or pilot seat. The ship may be "floating", it wont have any engines that will make it fly, but some floating device. The ship only moves forward.

There is really no way of destroying the ship, because its size would really cause destruction of Earth, but what they could do, is put rockets below the ship, which would "push" the object upward, or in any direction that may not cause Earth harm.Applying Newton's second law, The rockets should have the mass and acceleration needed to push the object upward. The rocket would also consider earths gravity pull while pushing the object upward.

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Detonate two Tsar bomba type bombs simultaneously, on opposite points on its surface.

You'll dump some radiation on the earth, but nowhere near enough to do global harm.

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    $\begingroup$ Why opposite points? Why not both on one side? $\endgroup$ – Bellerophon Oct 16 '16 at 20:38
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    $\begingroup$ Welcome to Worldbuilding.SE! While this answer is okay and gets its main point across, I do feel you could improve it by fleshing it out with more detail as to (perhaps) how and why two big nukes would destroy a moon-sized spacecraft. You can (and are encouraged to!) edit your post to improve it at any time. $\endgroup$ – type_outcast Oct 16 '16 at 21:22
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How did it get there? If it was assembled elsewhere, presumably the same alien means of propulsion that caused it to come to its current location could be reversed, ideally with alien allies who are converted to the cause because life on Earth is so cute.

Alternately, you could land it in the Pacific Ocean where the proto-moon made a lot of room when it crashed there the last time several billion years ago, but unlike the proto-moon, you would do it very, very slowly.

But for the "Its gravity causes earthquakes, tsunamis, meteor showers and all that fun stuff." and an apparently unstable orbit, I would have favored some effort to short out its systems in place leaving it inert as a second moon, such as a huge electromagnetic pulse directed towards our best estimate of the location of the control systems. Still, if you could short out its electronics with an EMP and then nudge the inert death star further from Earth to the points where the tidal effects of its gravity on earth were reduced, that would be good.

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well assuming that these aliens are close enough in biology to humans that human viruses could effect them couldn't you just kill them off with some bubonic plague then somehow figure out how to move the ship after they die, thus allowing you to advance the technological level of humans vastly in a short amount of time and allow access to a larger amount of resources that could be gradually "mined" for years

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