Results 1 to 14 of 14

Thread: Relativistic Kill Vehicles and the Fermi Paradox

  1. #1
    Former Staff Senior Contributor Ironduke's Avatar
    Join Date
    02 Aug 03
    Location
    Minneapolis
    Posts
    10,302

    Relativistic Kill Vehicles and the Fermi Paradox

    A Wikipedia primer:
    https://en.wikipedia.org/wiki/Relativistic_kill_vehicle

    As a guy whose favorite genre of fiction is science fiction, and I've read a large number of books and have seen most of the sci-fi TV shows and films ever made, I got to thinking one day - what would occur if we were actually able to accomplish space travel at relativistic speeds? Meaning, space travel at significant fractions of the speed of light.

    In the books I've read, I eventually came across one in which relativistic kill vehicles are used as weapons in warfare. Quite interesting stuff.

    It sparked curiosity in me - if we were able to accelerate a space vehicle to relativistic speeds, and it were to impact an object, say, the Earth, what kind of destruction would it do?

    I took two figures - the first being a mass equal to that of the space shuttle (~2 million kg), and picked a speed, in this case, 50% of the speed of light (~150,000,000 meters per second), and plugged it into a kinetic energy calculator (http://www.1728.org/energy.htm).

    The result I came up with was 5.3776e+6 megatons (TNT equivalent).

    Or, converted from scientific notation to regular decimal, 5,377,600 megatons.

    By comparison, the Chicxulub Impact Event that occurred 65 million years ago is estimated to have had an impact equivalent to 130 million megatons. A 48.5 million kg mass traveling at 50% C, if the calculations are to hold true, would impact with the same energy. Obviously, greater masses traveling at these speeds, the magnitude of the impact would scale with mass.

    If we were to develop this technology that enabled us to travel at relativistic speeds - it seems likely it would result in our own extinction. A world-ender - all that may be left of the Earth is an asteroid belt circling the Sun at 93 million miles. Perhaps within months, or years/decades at the most. An impact might come about via pilot error, malfunction, or even a hijacking and intentional targeting of the planet - the end result would be just the same.

    Perhaps the final and ultimate occurrence of Murphy's Law - anything that can go wrong, will go wrong. I can't imagine something not going wrong if we were to have this technology at our disposal.

    Which leaves me wondering - have these factors at all been taken into consideration by scientists and engineers who theorize about these technologies, and wish to develop space travel at these sorts of speeds?

    It also left me wondering - maybe this is the answer to the Fermi Paradox? That the reason we've never been contacted is that every civilization that may have ever developed this technology, soon went extinct by their own hand shortly thereafter?
    Last edited by Ironduke; 04 Jun 17, at 16:36.

  2. #2
    Senior Contributor
    Join Date
    12 Aug 08
    Location
    UK/Europe
    Posts
    4,065
    Not sure about this theorising... of course if one managed to speed up a vehicle - or only a lump of rock - to beyond light speed and direct it at a planet the result would be catastrophic for any life on that planet, and most likely any small to medium sized planet depending on the size of vehicle/rock. However the closer ones get's - theoretically - to the speed of light the smaller one becomes as it were. In 'special relativity' the innert mass of the object - as of say my wine glass on the table - does not become added to by it's momentum. Only it's 'relativistic mass' (that seen by outside 'stationary' observer) changes but they are not in the same 'time frame' so to speak but by special relativity mass and energy are the same. The energy preservation rule also applies I imagine - even in space; how hard one can hurl an object subject to 'solar winds' and gravitational forces - towards it's desired destination will effect both it's aim and impact. Of course one can also use gravitational forces to accelerate objects as we have been doing for some time.

    I used to read my Brother's sci fi books after he left home and gleaned some theoretical physics at Uni as well as my own reading (mostly learning how to do the quantum equations) and I do not think myself that the "relativistic speeds" (which I assume to mean near light speed) can be reached. As you probably know it would (theoretically) require the entire energy of the Universe to achieve light speed. This though does not mean we cannot travel far outside our own galaxy; time and space bend with gravitational and electro magnetic forces. If the universe can be bent - or even folded as it were - then distances between two points which are two dimensionally far away become far closer.

  3. #3
    Senior Contributor Monash's Avatar
    Join Date
    01 Mar 10
    Location
    Sydney
    Posts
    1,466
    I've read speculative articles and SF on this issue myself. I think the key issue would be the distance between any two technically advanced civilizations. As far as we can tell there is there are no technically advanced (superior) civilizations within at least 100 LY of our solar system. This is based on the principal that we have the capacity to detect the emissions of such a superior, space based civilization out to around that distance and so far - Nada.

    That said humans have only been transmitting radio signals for about 100 years or so and the vast majority of those signals don't actually escape into outer space, at least I have read scientific articles to this effect. Apparently certain long wave radar emissions and spaced based telemetry broadcasts do escape the solar system but most TV and radio broadcasts don't so anyone listening with hostile intent won't 'hear' anything for decades yet if not centuries.

    So using your scenario and assuming we emitted a signal 20 years ago that is detected by a hostile civilization 120 LY away we still have 100 years to go before they even detect it. Then assuming they immediately launch your relativistic 'space shuttle' at .5C we have another 250 years or so before it arrives (allowing for acceleration time). In total then we would have something like 350 years before the attack arrives. And of course pushing the distance between us out even farther to the thousands of light years that some scientists believe must separate any two advanced civilizations in this galaxy makes the problem even worse for an attacker.

    I'm certainly in no position to predict human technical development out that far into the future but assuming we don't blow ourselves up first (thereby saving E.T the trouble) I would think by that time (350 years plus) humanity would at least in part be a spaced based culture having spread out across the solar system. We might even be contemplating if not yet attempting our own interstellar missions. This means two things, firstly we are no longer confined to one planet and secondly we have at least some capacity to interdict any attack with high velocity projectiles of our own. This should mean single shot attacks are unlikely to work.

    On the plus side for the defenders the important thing is not so much having drives capable of matching the speed of the incoming projectile as is having very good sensors that can detect the approaching missile while it is still several light weeks or months away - at least. You then have a chance to launch a swarm of low V interceptors, preferably from somewhere out past Jupiter with the intention of killing the vessel in the outer solar system - if not further out. You don't need speed to do this so much as accuracy because the incoming projectile will presumably have limited maneuverability itself - dodging incoming attacks at .5C will almost certainly throw it off its track. For that matter you could have a multi layered defense with a final line of defense around the earth/lunar gravity well.

    (I'm assuming for my argument that high C vessels have a distinct 'signature' in the form of EM emissions given off via interactions with the interstellar medium i.e. a 2 mil kg vessel striking hydrogen atoms in space at .5C is going to displace and accelerate those atoms and other particles out of the way - I think that process would generate 'noise' that could be detected by sophisticated, space based sensors.)

    So in summary I would guess that by this time this issue becomes a potential problem we will have the means of dealing with it. And any attacker is only going to get one chance before we return the favor - with interest.

    Cheers
    Last edited by Monash; 05 Jun 17, at 04:01.

  4. #4
    Senior Contributor antimony's Avatar
    Join Date
    22 Feb 08
    Location
    Seattle, WA
    Posts
    3,910
    Quote Originally Posted by Ironduke View Post
    A Wikipedia primer:
    https://en.wikipedia.org/wiki/Relativistic_kill_vehicle

    As a guy whose favorite genre of fiction is science fiction, and I've read a large number of books and have seen most of the sci-fi TV shows and films ever made, I got to thinking one day - what would occur if we were actually able to accomplish space travel at relativistic speeds? Meaning, space travel at significant fractions of the speed of light.

    In the books I've read, I eventually came across one in which relativistic kill vehicles are used as weapons in warfare. Quite interesting stuff.

    It sparked curiosity in me - if we were able to accelerate a space vehicle to relativistic speeds, and it were to impact an object, say, the Earth, what kind of destruction would it do?

    I took two figures - the first being a mass equal to that of the space shuttle (~2 million kg), and picked a speed, in this case, 50% of the speed of light (~150,000,000 meters per second), and plugged it into a kinetic energy calculator (http://www.1728.org/energy.htm).

    The result I came up with was 5.3776e+6 megatons (TNT equivalent).

    Or, converted from scientific notation to regular decimal, 5,377,600 megatons.

    By comparison, the Chicxulub Impact Event that occurred 65 million years ago is estimated to have had an impact equivalent to 130 million megatons. A 48.5 million kg mass traveling at 50% C, if the calculations are to hold true, would impact with the same energy. Obviously, greater masses traveling at these speeds, the magnitude of the impact would scale with mass.

    If we were to develop this technology that enabled us to travel at relativistic speeds - it seems likely it would result in our own extinction. A world-ender - all that may be left of the Earth is an asteroid belt circling the Sun at 93 million miles. Perhaps within months, or years/decades at the most. An impact might come about via pilot error, malfunction, or even a hijacking and intentional targeting of the planet - the end result would be just the same.

    Perhaps the final and ultimate occurrence of Murphy's Law - anything that can go wrong, will go wrong. I can't imagine something not going wrong if we were to have this technology at our disposal.

    Which leaves me wondering - have these factors at all been taken into consideration by scientists and engineers who theorize about these technologies, and wish to develop space travel at these sorts of speeds?

    It also left me wondering - maybe this is the answer to the Fermi Paradox? That the reason we've never been contacted is that every civilization that may have ever developed this technology, soon went extinct by their own hand shortly thereafter?
    To me, aiming to travel at relativistic speeds do not make any sense at all. First, it would not help with any kind of interstellar travel. Second, the time dilation effect.

    I would pin my hope on actually getting something like the Alcubierre Drive (https://en.wikipedia.org/wiki/Alcubierre_drive) working. Nasa's Eagleworks was working to test out the theory since 2011, have not heard from them for a while.

    https://ntrs.nasa.gov/archive/nasa/c...0130011213.pdf
    "Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?" ~ Epicurus

  5. #5
    Former Staff Senior Contributor Ironduke's Avatar
    Join Date
    02 Aug 03
    Location
    Minneapolis
    Posts
    10,302
    Quote Originally Posted by Monash View Post
    So using your scenario and assuming we emitted a signal 20 years ago that is detected by a hostile civilization 120 LY away we still have 100 years to go before they even detect it. Then assuming they immediately launch your relativistic 'space shuttle' at .5C we have another 250 years or so before it arrives (allowing for acceleration time). In total then we would have something like 350 years before the attack arrives. And of course pushing the distance between us out even farther to the thousands of light years that some scientists believe must separate any two advanced civilizations in this galaxy makes the problem even worse for an attacker.
    I'd love to address your post at greater length - about to head to bed here - but what I'm referring to is an "own goal" event.

  6. #6
    Senior Contributor Monash's Avatar
    Join Date
    01 Mar 10
    Location
    Sydney
    Posts
    1,466
    Quote Originally Posted by Ironduke View Post
    I'd love to address your post at greater length - about to head to bed here - but what I'm referring to is an "own goal" event.
    I suppose an 'own goal' is possible but I also think it unlikely. Firstly as I observed before Earth wouldn't be in position to create extra solar colonies until long after it had expanded out into the solar system and become a space based culture - or at least it's machines had. So again a single relatavistic strike isn't going to do it.

    Secondly if/when we do start founding extra solar colonies there isn't any chance of a 'Terran Empire' springing up to control everything. The distances and time delays are simply too large to be manageable. You can't run an empire where the decision loop between HQ and the 'colonies' is measured in human lifetimes. So more than likely every colony you found is on its own from day one, master of its own fate. Assuming ideological or religious differences arose for instance between one colony and 'home' you are most likely too far apart to be a threat to each others ideas or beliefs. Hell you'd be too far apart to even exchange insults via radio effectively!

    There' also two ways the colonization program can go (I think). Plan (A) is you colonize most stars along a given 'string' via a chain of space habitats build orbiting each (or most) of the stars in that chain. This creates lots of mini colonies' but also makes it hard if not impossible for any one colony to take out or damage all the others. There could be hundreds of them busily mining the resources of the their respective systems to expand their habitats.

    Plan (B) involves you pushing on outwards until you find stars with habitable planets or more likely those with worlds that can be terraformed. Best we can tell at the moment truly earth type worlds are uber rare. There might not be more than a handful across the entire galaxy. Terraformable worlds would be much more common but would still widely spaced - they still have to be Goldilocks planets after all. This plan ends up with the same problem that an alien attacker would have. Your colonies are so far apart that 'attacks' would take centuries if not thousands of years to strike home. Maybe you do both (A) and (B). In that case you still end up with multiple targets that can strike back if you 'miss' plus a number of home worlds that are so far apart strikes are impracticable.

    Finally IMO Earth, located as it would be at the at the center of of a 'sphere of influence' would still be an important source of news and scientific and technical advances for all the colonies simply because it would be the oldest world in the 'human zone'. It would also possibly lie at the center of a network of high C space craft that act as messengers and/or transports taking high value payloads to the other worlds. As such Earth would have more value intact than destroyed. I suspect most colonies would probably not want to see it knocked out and would take retaliatory action against any colony that tried - assuming any attack was successful (and again given the fact that Earth is the oldest world in the network it would have or should have the most advanced and best developed defensive networks on the block.
    Last edited by Monash; 05 Jun 17, at 10:43.

  7. #7
    Staff Emeritus
    Military Professional
    Contrary by Nature.
    zraver's Avatar
    Join Date
    22 Oct 06
    Location
    Arkansas
    Posts
    14,504
    Quote Originally Posted by Monash View Post
    I suppose an 'own goal' is possible but I also think it unlikely. Firstly as I observed before Earth wouldn't be in position to create extra solar colonies until long after it had expanded out into the solar system and become a space based culture - or at least it's machines had. So again a single relatavistic strike isn't going to do it.
    Not so sure, the Battle Tech universe uses fusion powered drop ships that accelerate inward from the nadir or zenith points of a star system. At a half way point they flip over and decelerate. A 10,000 ton ship accelerating at 1g for say 20 days they are travelling at near 38 million mph. If a stars gravitational zenith is say 30au away the drop ship would cross the distance in about 55 days. If they don't flip over and just keep accelerating by day 40 they are travelling more than 75 million mph... That is only about 25% of light speed but it is relativistic. I freely admit i don't know at what point moving 1 kilogram 1 meter goes from costing Y (non-relativistic) energy to an ever increasing X (relativistic) energy.

  8. #8
    Senior Contributor
    Join Date
    13 Nov 07
    Posts
    3,531
    I think by "own goal" Iron Duke probably means accidents might happen with a lot of relativistic travel.

    But, there are ways to mitigate this. Travel in between established outposts, are likely to occur via laser powered lightsail. In that case you'd set the receiving station in a system well outside the core planets.

    Also you can set a speed limit of say .5c.

    Going heavily relativistic only makes sense for shortening the passenger's journey. You can try to do that for going to new worlds, but you'd still need to slow down well outside of solar systems as any dust strike would become increasingly catastrophic. To an incoming relativistic ship the space dust around a star system might look very dense.

  9. #9
    Senior Contributor Monash's Avatar
    Join Date
    01 Mar 10
    Location
    Sydney
    Posts
    1,466
    Yep all good points. I had been meaning to comment on the idea of using 'sand' as an interdiction weapon for incoming high C strikes. Instead of trying to take out the kill vehicle with convention warheads you put a 'cloud' of low signature gram size particles in its path. Harder to see and avoid and the shock of even one impact is likely to damage guidance and control systems. Also true about more conventional in-system strikes. You certainly don't need speeds anywhere near even a fraction of C to do significant damage. In fact recent announcements about proposals to shift asteroids into near Earth orbit for mining purposes leaves the door open to all sorts of 'oops' moments followed shortly thereafter by a loud bang.

    In the future I assume there will be strict traffic control procedures the closer you get to Earth and certainly once you transit into the Earth/Moon gravity well since this will undoubtedly be the busiest flight space in the solar system for many generations to come. (It would probably also be wise to back up the the traffics control network with some emergency kill vehicles just to reinforce the rules.) For the rest I don't see speeds within the inner system ever getting anywhere near even .01C because the distances involved don't warrant it. Even a trip to Pluto for that matter could be done in relatively quick time (think weeks or months) without getting anywhere near that speed.

    I think the risk comes instead from the mass/size of the structure and ships we are likely to be building, moving or traveling around in. After all the asteroid that killed off the dinosaurs was deadly not so much because of its speed but because of its mass. Compared to some of the speeds we've been discussing here it was moving at a snails pace when it hit.
    Last edited by Monash; 11 Jun 17, at 08:40.

  10. #10
    Staff Emeritus
    Military Professional
    Contrary by Nature.
    zraver's Avatar
    Join Date
    22 Oct 06
    Location
    Arkansas
    Posts
    14,504
    Quote Originally Posted by citanon View Post
    I

    Going heavily relativistic only makes sense for shortening the passenger's journey.
    You'd likely end up with dedicated passenger routes vs cargo routes. it cost a lot more to move bio mass than any type of dead weight freight. Moving miners and researchers in system, moving colonists, miners, tourists etc out system would put a premium of speed. Assuming that most in system dust is on the same plane as the planets, an arcing flight path would allow greater speed and a way to carve of distance.

  11. #11
    Senior Contributor Monash's Avatar
    Join Date
    01 Mar 10
    Location
    Sydney
    Posts
    1,466
    Can't see there ever being a demand for the wholesale movement of humans through interstellar space (i.e. as a percentage of the total human population). Every gram of matter you send to the stars at high C speeds costs you big time, just like boosting anything into orbit.

    Assuming there's no escaping Einstein's speed limit you only send the minimum number of humans you have to on any mission, just enough specialists to complete the mission or just enough colonists to get a settlement off the ground. Automation is going to multiply human input immensely and you could always boost the gene pool of colonies with sperm and egg deliveries if required.

    Amendment: unless of course we advance to the point of technological transcendence and start building planet or at least moon sized vessels - at which point I'm not sure the term 'human' would be appropriate anymore.
    Last edited by Monash; 15 Jun 17, at 13:59.

  12. #12
    Staff Emeritus
    Military Professional
    Contrary by Nature.
    zraver's Avatar
    Join Date
    22 Oct 06
    Location
    Arkansas
    Posts
    14,504
    Quote Originally Posted by Monash View Post
    Can't see there ever being a demand for the wholesale movement of humans through interstellar space (i.e. as a percentage of the total human population). Every gram of matter you send to the stars at high C speeds costs you big time, just like boosting anything into orbit.

    Assuming there's no escaping Einstein's speed limit you only send the minimum number of humans you have to on any mission, just enough specialists to complete the mission or just enough colonists to get a settlement off the ground. Automation is going to multiply human input immensely and you could always boost the gene pool of colonies with sperm and egg deliveries if required.

    Amendment: unless of course we advance to the point of technological transcendence and start building planet or at least moon sized vessels - at which point I'm not sure the term 'human' would be appropriate anymore.
    Affordable and portable fusion could drastically cut the cost of both boosting to orbit, and moving things through space. The Earth has a carrying capacity of about 12 billion people but we are past the ideal at 7 billion. So even if robots can do most of the work on Earth, there is still going to be a lot of pressure to move people off planet. Both to plant flags in order to claim resources and as a means of social engineering

  13. #13
    Senior Contributor Monash's Avatar
    Join Date
    01 Mar 10
    Location
    Sydney
    Posts
    1,466
    Quote Originally Posted by zraver View Post
    Affordable and portable fusion could drastically cut the cost of both boosting to orbit, and moving things through space. The Earth has a carrying capacity of about 12 billion people but we are past the ideal at 7 billion. So even if robots can do most of the work on Earth, there is still going to be a lot of pressure to move people off planet. Both to plant flags in order to claim resources and as a means of social engineering
    Z, while I agree fusion drives would be a boon to solar transportation they (and any other currently feasible form of propulsion) are not a solution to the problem of human over population. Assuming for the moment that 12 billion is the maximum sustainable carrying capacity of the globe we are currently projected to reach that level somewhere around the end of this century. That's 80 years from now and there's simply no way in hell we are going to develop the technical capacity to lift anywhere near enough people into space to make a difference in that time frame!

    The issue is that there are in fact two problems here. One is the problem of human overpopulation and the other is the problem of protecting humanities long term survival as a species. You need the right tool for each problem and while space travel is the perfect tool for solving the latter problem it's a lousy tool for fixing the former. As stated above we are simply not going to be able to lift 10s of millions of humans (per year) into space in anywhere near the time frame needed. Thousands yes, millions no.

    The problem of overpopulation can only really be tackled by drawing on the same polices that have worked so well in the West i.e investments in the education of women, health care and the raising of living standards etc. Trying to use space travel won't work. Basic biology (and geometry) tell us this is the case. Take any bacteria and put it in a petrie dish. Initially the colony expands rapidly outwards from the point of origin as it exploits the local resources immediately around it. The outer edge of the colony always has access to nutrition and so expands. After a short time however the core of the colony starts to die off because it exhausts local nutrients and cannot access those at the rim. The result is a familiar 'doughnut' pattern seen time and time again with a ring of 'healthy' bacteria surrounding a dead zone in the middle. Humanity would face the same problem, unless population growth is controlled by other means outward expansion would see colonies on the rim growing at the expense of those in the middle which would eventually 'starve' because they will never be able to shift people to the 'rim' faster than those colonies already there.

    What space flight can potentially let us do is set up viable colonies in the solar system that can exploit the resources there for the benefit of everyone while also acting as a protective reservoir against any event that leads to the extinction of humanity on Earth itself. Crossing interstellar space opens up the galaxy to human exploitation but doesn't change the basic equation.
    Last edited by Monash; 17 Jun 17, at 15:17.

  14. #14
    Staff Emeritus
    Military Professional
    Contrary by Nature.
    zraver's Avatar
    Join Date
    22 Oct 06
    Location
    Arkansas
    Posts
    14,504
    Quote Originally Posted by Monash View Post
    Z, while I agree fusion drives would be a boon to solar transportation they (and any other currently feasible form of propulsion) are not a solution to the problem of human over population. Assuming for the moment that 12 billion is the maximum sustainable carrying capacity of the globe we are currently projected to reach that level somewhere around the end of this century. That's 80 years from now and there's simply no way in hell we are going to develop the technical capacity to lift anywhere near enough people into space to make a difference in that time frame!

    The issue is that there are in fact two problems here. One is the problem of human overpopulation and the other is the problem of protecting humanities long term survival as a species. You need the right tool for each problem and while space travel is the perfect tool for solving the latter problem it's a lousy tool for fixing the former. As stated above we are simply not going to be able to lift 10s of millions of humans (per year) into space in anywhere near the time frame needed. Thousands yes, millions no.

    The problem of overpopulation can only really be tackled by drawing on the same polices that have worked so well in the West i.e investments in the education of women, health care and the raising of living standards etc. Trying to use space travel won't work. Basic biology (and geometry) tell us this is the case. Take any bacteria and put it in a petrie dish. Initially the colony expands rapidly outwards from the point of origin as it exploits the local resources immediately around it. The outer edge of the colony always has access to nutrition and so expands. After a short time however the core of the colony starts to die off because it exhausts local nutrients and cannot access those at the rim. The result is a familiar 'doughnut' pattern seen time and time again with a ring of 'healthy' bacteria surrounding a dead zone in the middle. Humanity would face the same problem, unless population growth is controlled by other means outward expansion would see colonies on the rim growing at the expense of those in the middle which would eventually 'starve' because they will never be able to shift people to the 'rim' faster than those colonies already there.

    What space flight can potentially let us do is set up viable colonies in the solar system that can exploit the resources there for the benefit of everyone while also acting as a protective reservoir against any event that leads to the extinction of humanity on Earth itself. Crossing interstellar space opens up the galaxy to human exploitation but doesn't change the basic equation.

    good points.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Resource Course (Paradox of Plenty) development in SW Asia and Africa
    By Ironduke in forum International Defense and Terrorism Topics
    Replies: 8
    Last Post: 05 Feb 11,, 22:58
  2. Replies: 2
    Last Post: 19 Aug 08,, 05:06
  3. The Nuclear Paradox
    By 1947 in forum International Politics
    Replies: 39
    Last Post: 15 Jun 08,, 01:32
  4. BMD Family of Vehicles
    By kNikS in forum Ground Warfare
    Replies: 116
    Last Post: 25 Apr 07,, 21:44
  5. Is this a paradox?
    By jazzelf in forum American Politics & Economy
    Replies: 3
    Last Post: 17 Oct 04,, 15:44

Share this thread with friends:

Share this thread with friends:

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •