9 ms·

Relativistic kill vehicle

38 points by lelf 12y ago

t0mas88 12y ago
The page mentions accelerating over a longer distance, but wouldn't that defeat the undetectability of the whole thing?
- Arcsech 12y ago
  Under certain circumstances, but since the mass can be (relatively) small due to the extremely high velocity, it can be very hard to spot. Essentially, imagine trying to pick something the size of a telephone pole, angled end-on at you, from 20 miles away out of the entire night sky. By the time it gets close enough to spot easily, it's too late to do much about it. Edit: jjaredsimpson's comment makes a very good point about velocities much closer to 1c. My comment mostly relates to the more immediately practical kinetic bombardment[0], which works on the same idea. [0] https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki/Kinetic_bombardment
- jjaredsimpson 12y ago
  If I accelerate 1000 1kg masses to .99c 1ly away from your planet you can't detect them, and I've just destroyed your entire species (sterilized the planet) with a metric ton of rocks. It doesn't matter how long I take to accelerate them, once they are going fast you are destroyed in 1 year.
  - deeviant 12y ago
    You would need some pretty killer orbital prediction to do this. I would assume you'd start a bit closer.
  - rwallace 12y ago
    With the caveat that at the tech level required to launch such an attack, destruction of one's home planet would constitute something closer to vandalism of a historic site than destruction of one's species. Of course, if you're thinking of a scenario where aliens at that tech level launch such an attack against us 21st-century humans, yes, we'd be toast.
  - TheLoneWolfling 12y ago
    Why are you saying we couldn't detect them? There's enough interstellar medium to make any such impactor detectable. (Rough calculation: 67kw/m^2. And that's not even talking about dust grains (which ends up with much brighter instantaneous flashes))
    - letstryagain 12y ago
      By the time you see it, it will be too late to respond.
      - TheLoneWolfling 12y ago
        Why? Sure, there's time dilation effects, but they are largely cancelled out. We have less notice for a given distance, but we also can see it coming from farther away.
        InclinedPlane 12y ago
        .99c means that you have 1/100th as much time to respond relative to the detection distance. Let's say you spot the impactors an entire light-year away. The light will only reach you less than 4 days before impact. Can you put together an effective response plan in 4 days? If instead you spotted them out in the oort cloud (say, 1000 AU away) you would have less than 2 hours to respond.
        TheLoneWolfling 12y ago
        Right, but that is compensated by the fact that that same time compression also applies to any energy released by the impactor. It'd be putting out >3.5*10^7 watts / m^2 at 0.99c, from our perspective. And a single sand grain hitting it would release 27GJ. Not to mention... How on earth are you managing to keep something together when its being bombarded by hydrogen / helium at 0.99c?
- deeviant 12y ago
  Not necessity. Imagine a spacecraft using a standard inertial propulsion system. It shoots mass one way and it goes in the opposite direction. If it had something like a thrust signature, it would be in exactly the wrong direction for the intended target to see, add in a shroud and it would impossible to detect unless the target had sensors in other systems perpendicular and in between the launch site and target site. Even if detected, what could be done? A planet is not going to change it's trajectory, and even if they fry it with some sort of energy weapon, it would still maintain it's velocity and the associated energy. Truly, in a universe with advanced and aggressive space faring species, a planet would be about the most unsafe place you could be, it would be ridiculous easy for said advanced space faring species to destroy/make uninhabitable a planet. And you would hardly even need a RKV to do it.
  - Terr_ 12y ago
    > Even if detected, what could be done? A large-scale Whipple Shield, maybe? (http://en.wikipedia.org/wiki/Whipple_shield http://en.wikipedia.org/wiki/Whipple_shield) Throw a small moon into its path and engage it from as far away as possible. You'll end up with a lot of smaller slower pieces over a wider area.
    - deeviant 12y ago
      That might work, it would have to be detected soon enough to allow for the time to build it, though.
      - TheLoneWolfling 12y ago
        You don't need to build any sort of permanent structure. Orbits exist. Just coordinate trajectories. Throw a bunch of chaff at it from different trajectories, so that it passes through them in stages.
    - TheLoneWolfling 12y ago
      The biggest problem with Whipple shields with relativistic projectiles is that the projectiles literally don't have time to react. Partly because of the speed itself, partly because of time dilation. You need to throw enough at it that a large chunk of the nuclei in the impactor are hit by nuclei of the atoms you are throwing at it - not an insignificant feat. Small moon may work. Anything less and yes, it's rapidly expanding into a cloud of gas, but nowhere near fast enough. It'll hit the target well before it dissipates significantly if you're not careful.
compsciphd 12y ago
federation couldn't have used these against the Borg? might have saved picard a lot of trouble :)
- delecti 12y ago
  The Borg don't really stay stationed on planets, the Star Trek universe has FTL scanning technology, and as a general rule, physical projectiles are handwaved to be unable to penetrate shields on ships, and even if they didn't, that's exactly what the deflector is for. Sorry you got downvoted though.
lotsofmangos 12y ago
It is also referred to in 'The Algebraist' by Ian M. Banks. It is mentioned that the Dweller species have a habit of taking a very long revenge against any other species stupid enough to wipe a community of them out. So a few generations after a species has completely forgotten about the load of strange jellyfish they killed off in their local gas giant, a shit-ton of sand and gravel comes through their system at a significant fraction of the speed of light.
- theoh 12y ago
  I suspect the initial post was a response to Charlie Stross's remarks about existential risks: http://www.antipope.org/charlie/blog-static/2015/04/on-the-great-filter-existentia.html http://www.antipope.org/charlie/blog-static/2015/04/on-the-g... Since we live in the twitteresque dark ages there's no way to know. Vannevar Bush would be turning in his grave.
quanticle 12y ago
Gwern has a a good write-up about various "realistic" scenarios for interstellar war: http://www.gwern.net/Colder%20Wars http://www.gwern.net/Colder%20Wars
dougk16 12y ago
Question: The article mentions that a 1kg projectile travelling at 99% of the speed of light would have such and such more explosive energy than the most powerful nuclear bob ever detonated. I don't doubt the math, but would the destructive effects (e.g. to a city) of such a projectile weapon actually equal those of a nuclear bomb? I'm not talking about the radiation and such in the aftermath, just the explosion itself. Wouldn't the projectile basically go straight through a planet? Edit: I suppose the shockwave from entering the atmosphere would cause a bit of a rucus too...still interested in any responses.
- blackstache 12y ago
  This might give the beginnings of an idea of what would happen: https://what-if.xkcd.com/1/ https://what-if.xkcd.com/1/
  - dougk16 12y ago
    Interesting, thanks for the link. Intuitively it still seems like much of the energy from the projectile would be absorbed deep in the Earth as it traveled through. For sure it would cause some damage, but it still seems like a nuclear bomb would have a higher effective energy, as far as the tactical goal of taking out a city or something.
    - TheLoneWolfling 12y ago
      You can adjust effective penetration depth by the "density" (read, mass per unit cross-sectional area) of the projectile. You could go anywhere from an osmium needle through to a Mylar disk. Another relevant XKCD: https://what-if.xkcd.com/20/ https://what-if.xkcd.com/20/
- mikeash 12y ago
  From the perspective of the RKV, the Earth will look like a cloud of fast-moving subatomic particles irradiating it with a power that substantially outshines the sun. The particles that make up the RKV will collide with and impart their energy to bits of the Earth (or its atmosphere) in pretty short order. Those will impart their energy to other bits of the Earth, and so forth, forming a normal (aside from scale) shockwave made up of bits of Earth (or its atmosphere) and bits of the vaporized RKV.
deleted 12y ago
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svachalek 12y ago
The recent articles on Artificial Superintelligence have got me thinking about interstellar MAD. It seems that once you have ASI you really have the capability to do anything within the laws of physics because if there's anything you don't know how to do, you just add intelligence until you do. If so, it seems that primitive civilizations can become enormous, exponentially expanding threats to established civilizations in relatively no time at all, and in fact they are extremely vulnerable if they choose not to, not only to established players but to any new ones that come along.
- api 12y ago
  A little off topic but... "you just add intelligence until you do" So many assumptions. I'd challenge everyone to look deeply into learning theory and combinatorics. We have no reason to believe that intelligence is something you can just scale up without bound, and many reasons to believe otherwise. For starters: nature "invented" intelligence hundreds of millions of years ago with the evolution of neural nets, and it's a powerful adaptation that confers significant advantage. Why are we the only intelligence with our level of analytical capability on Earth? If it were so easy to "just add intelligence," almost every large animal in nature should be capable of language, mathematics, and logic by now. As someone who spent many years studying AI, machine learning, combinatorics, evolutionary theory, and related topics, some of the stuff that's been flying around about AI recently is making me itch.
  - 6d0debc071 12y ago
    > For starters: nature "invented" intelligence hundreds of millions of years ago with the evolution of neural nets, and it's a powerful adaptation that confers significant advantage. Why are we the only intelligence with our level of analytical capability on Earth? Lots of animals seem to lack the ability to use fine tools and have limited vocal ranges that would make communication far more difficult. I'm inclined to question the 'significant advantage' part in its unqualified form.
    - api 12y ago
      Strategic thinking, categorization, and the recognition of complex environmental patterns are among the abilities that would be very valuable even for mutes without opposable thumbs.
kmm 12y ago
Interestingly, RKV's travel at speeds that are apparently faster than light, because they immediately follow the light they emit. If an RKV was launched towards us from Sirius at 99% of the speed of light, the news of that launch would reach us 10 years later, with the missile following merely a month later. Thus, if we could track the missile, it would appear to cross 10 light years of distance in that month, at an apparent speed of almost 100c. We can see a related effect in real life with jets coming from black holes and other sources ejecting material at high speeds[1]. This is of course not true superluminal motion, but an optical illusion. 1: http://en.wikipedia.org/wiki/Superluminal_motion http://en.wikipedia.org/wiki/Superluminal_motion
- darkmighty 12y ago
  Also interestingly, this accumulation of energy in front of the vehicle is the cause of Sonic booms. Acoustic waves, and pressure dispersion in general, get accumulated in front of the craft, momentarily creating enormous resistance and temperatures as it passes the speed of sound. Of course the accumulation of light is different in that it can't affect the vehicles themselves due to the principle of relativity (constant speed of light for all inertial observers).
jakeogh 12y ago
(Caution; dont click unless you have atleast an hour to kill) http://www.projectrho.com/public_html/rocket/spacegunexotic.php#id--Relativistic_Weapons http://www.projectrho.com/public_html/rocket/spacegunexotic....
- deeviant 12y ago
  Sigh, I should have heeded your warning. My productivity is not looking too good today.
- henrikschroder 12y ago
  And it links to TV-tropes, oh noooooo.....
EarthLaunch 12y ago
A more interesting idea would be accelerating someone to the point where they meet the end of the universe.
- ringshall 12y ago
  Carl Sagan discussed this in episode 8 of Cosmos. This segment of video[1] progresses from Leonardo DaVinci's flying machines to a relativistic space craft in about 7 minutes. A spacecraft accelerating at 1 g, closer and closer to c, accelerating halfway and decelerating halfway, could travel to Barnard's Star in 8 years ship time; center of the Milky Way Galaxy in 21 years ship time, the Andromeda galaxy in 28 years ship time. "In principle such a journey, mounting the decimal points closer and closer to the speed of light, would even permit us to circumnavigate the known universe in 56 years ship time. We would return tens of billions of years in the far future, with the Earth a charred cinder, and the Sun, dead. Relativistic space flight makes the universe accessible to advanced civilizations, but only to those who go on the journey, not to those who stay home." https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be&t=1600 https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be...

38 points by lelf 12y ago

t0mas88 12y ago

The page mentions accelerating over a longer distance, but wouldn't that defeat the undetectability of the whole thing?

Arcsech 12y ago
Under certain circumstances, but since the mass can be (relatively) small due to the extremely high velocity, it can be very hard to spot. Essentially, imagine trying to pick something the size of a telephone pole, angled end-on at you, from 20 miles away out of the entire night sky. By the time it gets close enough to spot easily, it's too late to do much about it. Edit: jjaredsimpson's comment makes a very good point about velocities much closer to 1c. My comment mostly relates to the more immediately practical kinetic bombardment[0], which works on the same idea. [0] https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki/Kinetic_bombardment
jjaredsimpson 12y ago
If I accelerate 1000 1kg masses to .99c 1ly away from your planet you can't detect them, and I've just destroyed your entire species (sterilized the planet) with a metric ton of rocks. It doesn't matter how long I take to accelerate them, once they are going fast you are destroyed in 1 year.
- deeviant 12y ago
  You would need some pretty killer orbital prediction to do this. I would assume you'd start a bit closer.
- rwallace 12y ago
  With the caveat that at the tech level required to launch such an attack, destruction of one's home planet would constitute something closer to vandalism of a historic site than destruction of one's species. Of course, if you're thinking of a scenario where aliens at that tech level launch such an attack against us 21st-century humans, yes, we'd be toast.
- TheLoneWolfling 12y ago
  Why are you saying we couldn't detect them? There's enough interstellar medium to make any such impactor detectable. (Rough calculation: 67kw/m^2. And that's not even talking about dust grains (which ends up with much brighter instantaneous flashes))
  - letstryagain 12y ago
    By the time you see it, it will be too late to respond.
    - TheLoneWolfling 12y ago
      Why? Sure, there's time dilation effects, but they are largely cancelled out. We have less notice for a given distance, but we also can see it coming from farther away.
      - InclinedPlane 12y ago
        .99c means that you have 1/100th as much time to respond relative to the detection distance. Let's say you spot the impactors an entire light-year away. The light will only reach you less than 4 days before impact. Can you put together an effective response plan in 4 days? If instead you spotted them out in the oort cloud (say, 1000 AU away) you would have less than 2 hours to respond.
        TheLoneWolfling 12y ago
        Right, but that is compensated by the fact that that same time compression also applies to any energy released by the impactor. It'd be putting out >3.5*10^7 watts / m^2 at 0.99c, from our perspective. And a single sand grain hitting it would release 27GJ. Not to mention... How on earth are you managing to keep something together when its being bombarded by hydrogen / helium at 0.99c?
deeviant 12y ago
Not necessity. Imagine a spacecraft using a standard inertial propulsion system. It shoots mass one way and it goes in the opposite direction. If it had something like a thrust signature, it would be in exactly the wrong direction for the intended target to see, add in a shroud and it would impossible to detect unless the target had sensors in other systems perpendicular and in between the launch site and target site. Even if detected, what could be done? A planet is not going to change it's trajectory, and even if they fry it with some sort of energy weapon, it would still maintain it's velocity and the associated energy. Truly, in a universe with advanced and aggressive space faring species, a planet would be about the most unsafe place you could be, it would be ridiculous easy for said advanced space faring species to destroy/make uninhabitable a planet. And you would hardly even need a RKV to do it.
- Terr_ 12y ago
  > Even if detected, what could be done? A large-scale Whipple Shield, maybe? (http://en.wikipedia.org/wiki/Whipple_shield http://en.wikipedia.org/wiki/Whipple_shield) Throw a small moon into its path and engage it from as far away as possible. You'll end up with a lot of smaller slower pieces over a wider area.
  - deeviant 12y ago
    That might work, it would have to be detected soon enough to allow for the time to build it, though.
    - TheLoneWolfling 12y ago
      You don't need to build any sort of permanent structure. Orbits exist. Just coordinate trajectories. Throw a bunch of chaff at it from different trajectories, so that it passes through them in stages.
  - TheLoneWolfling 12y ago
    The biggest problem with Whipple shields with relativistic projectiles is that the projectiles literally don't have time to react. Partly because of the speed itself, partly because of time dilation. You need to throw enough at it that a large chunk of the nuclei in the impactor are hit by nuclei of the atoms you are throwing at it - not an insignificant feat. Small moon may work. Anything less and yes, it's rapidly expanding into a cloud of gas, but nowhere near fast enough. It'll hit the target well before it dissipates significantly if you're not careful.

compsciphd 12y ago

federation couldn't have used these against the Borg? might have saved picard a lot of trouble :)

delecti 12y ago
The Borg don't really stay stationed on planets, the Star Trek universe has FTL scanning technology, and as a general rule, physical projectiles are handwaved to be unable to penetrate shields on ships, and even if they didn't, that's exactly what the deflector is for. Sorry you got downvoted though.

lotsofmangos 12y ago

It is also referred to in 'The Algebraist' by Ian M. Banks. It is mentioned that the Dweller species have a habit of taking a very long revenge against any other species stupid enough to wipe a community of them out. So a few generations after a species has completely forgotten about the load of strange jellyfish they killed off in their local gas giant, a shit-ton of sand and gravel comes through their system at a significant fraction of the speed of light.

theoh 12y ago
I suspect the initial post was a response to Charlie Stross's remarks about existential risks: http://www.antipope.org/charlie/blog-static/2015/04/on-the-great-filter-existentia.html http://www.antipope.org/charlie/blog-static/2015/04/on-the-g... Since we live in the twitteresque dark ages there's no way to know. Vannevar Bush would be turning in his grave.

quanticle 12y ago

Gwern has a a good write-up about various "realistic" scenarios for interstellar war: http://www.gwern.net/Colder%20Wars http://www.gwern.net/Colder%20Wars

dougk16 12y ago

Question: The article mentions that a 1kg projectile travelling at 99% of the speed of light would have such and such more explosive energy than the most powerful nuclear bob ever detonated. I don't doubt the math, but would the destructive effects (e.g. to a city) of such a projectile weapon actually equal those of a nuclear bomb? I'm not talking about the radiation and such in the aftermath, just the explosion itself. Wouldn't the projectile basically go straight through a planet? Edit: I suppose the shockwave from entering the atmosphere would cause a bit of a rucus too...still interested in any responses.

blackstache 12y ago
This might give the beginnings of an idea of what would happen: https://what-if.xkcd.com/1/ https://what-if.xkcd.com/1/
- dougk16 12y ago
  Interesting, thanks for the link. Intuitively it still seems like much of the energy from the projectile would be absorbed deep in the Earth as it traveled through. For sure it would cause some damage, but it still seems like a nuclear bomb would have a higher effective energy, as far as the tactical goal of taking out a city or something.
  - TheLoneWolfling 12y ago
    You can adjust effective penetration depth by the "density" (read, mass per unit cross-sectional area) of the projectile. You could go anywhere from an osmium needle through to a Mylar disk. Another relevant XKCD: https://what-if.xkcd.com/20/ https://what-if.xkcd.com/20/
mikeash 12y ago
From the perspective of the RKV, the Earth will look like a cloud of fast-moving subatomic particles irradiating it with a power that substantially outshines the sun. The particles that make up the RKV will collide with and impart their energy to bits of the Earth (or its atmosphere) in pretty short order. Those will impart their energy to other bits of the Earth, and so forth, forming a normal (aside from scale) shockwave made up of bits of Earth (or its atmosphere) and bits of the vaporized RKV.

deleted 12y ago

[deleted]

deleted 12y ago

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svachalek 12y ago

The recent articles on Artificial Superintelligence have got me thinking about interstellar MAD. It seems that once you have ASI you really have the capability to do anything within the laws of physics because if there's anything you don't know how to do, you just add intelligence until you do. If so, it seems that primitive civilizations can become enormous, exponentially expanding threats to established civilizations in relatively no time at all, and in fact they are extremely vulnerable if they choose not to, not only to established players but to any new ones that come along.

api 12y ago
A little off topic but... "you just add intelligence until you do" So many assumptions. I'd challenge everyone to look deeply into learning theory and combinatorics. We have no reason to believe that intelligence is something you can just scale up without bound, and many reasons to believe otherwise. For starters: nature "invented" intelligence hundreds of millions of years ago with the evolution of neural nets, and it's a powerful adaptation that confers significant advantage. Why are we the only intelligence with our level of analytical capability on Earth? If it were so easy to "just add intelligence," almost every large animal in nature should be capable of language, mathematics, and logic by now. As someone who spent many years studying AI, machine learning, combinatorics, evolutionary theory, and related topics, some of the stuff that's been flying around about AI recently is making me itch.
- 6d0debc071 12y ago
  > For starters: nature "invented" intelligence hundreds of millions of years ago with the evolution of neural nets, and it's a powerful adaptation that confers significant advantage. Why are we the only intelligence with our level of analytical capability on Earth? Lots of animals seem to lack the ability to use fine tools and have limited vocal ranges that would make communication far more difficult. I'm inclined to question the 'significant advantage' part in its unqualified form.
  - api 12y ago
    Strategic thinking, categorization, and the recognition of complex environmental patterns are among the abilities that would be very valuable even for mutes without opposable thumbs.

kmm 12y ago

Interestingly, RKV's travel at speeds that are apparently faster than light, because they immediately follow the light they emit. If an RKV was launched towards us from Sirius at 99% of the speed of light, the news of that launch would reach us 10 years later, with the missile following merely a month later. Thus, if we could track the missile, it would appear to cross 10 light years of distance in that month, at an apparent speed of almost 100c. We can see a related effect in real life with jets coming from black holes and other sources ejecting material at high speeds[1]. This is of course not true superluminal motion, but an optical illusion. 1: http://en.wikipedia.org/wiki/Superluminal_motion http://en.wikipedia.org/wiki/Superluminal_motion

darkmighty 12y ago
Also interestingly, this accumulation of energy in front of the vehicle is the cause of Sonic booms. Acoustic waves, and pressure dispersion in general, get accumulated in front of the craft, momentarily creating enormous resistance and temperatures as it passes the speed of sound. Of course the accumulation of light is different in that it can't affect the vehicles themselves due to the principle of relativity (constant speed of light for all inertial observers).

jakeogh 12y ago

(Caution; dont click unless you have atleast an hour to kill) http://www.projectrho.com/public_html/rocket/spacegunexotic.php#id--Relativistic_Weapons http://www.projectrho.com/public_html/rocket/spacegunexotic....

deeviant 12y ago
Sigh, I should have heeded your warning. My productivity is not looking too good today.
henrikschroder 12y ago
And it links to TV-tropes, oh noooooo.....

EarthLaunch 12y ago

A more interesting idea would be accelerating someone to the point where they meet the end of the universe.

ringshall 12y ago
Carl Sagan discussed this in episode 8 of Cosmos. This segment of video[1] progresses from Leonardo DaVinci's flying machines to a relativistic space craft in about 7 minutes. A spacecraft accelerating at 1 g, closer and closer to c, accelerating halfway and decelerating halfway, could travel to Barnard's Star in 8 years ship time; center of the Milky Way Galaxy in 21 years ship time, the Andromeda galaxy in 28 years ship time. "In principle such a journey, mounting the decimal points closer and closer to the speed of light, would even permit us to circumnavigate the known universe in 56 years ship time. We would return tens of billions of years in the far future, with the Earth a charred cinder, and the Sun, dead. Relativistic space flight makes the universe accessible to advanced civilizations, but only to those who go on the journey, not to those who stay home." https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be&t=1600 https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be...