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Thread: Relativistic Kill Vehicles and the Fermi Paradox

  1. #76
    Senior Contributor Monash's Avatar
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    Quote Originally Posted by WABs_OOE View Post
    It's getting to the solar system that is the problem. Not hitting the planet itself. If the solar system travels a predictable path, ie didn't run into some major black holes that would alter it's course, then you can reasonably get your asterioid into the general area. After that, you can use onboard intelligence to deploy reflective surfaces to use solar winds to guide you onto target.
    Possibly but you also have to allow for the vagaries of random chance. You can compute a course that will avoid significant gravitational deflections (you might even be able to use them to your advantage). The question is how do you cope with random influences like micrometeorite impacts, galactic gas/dust effects and radiation pressure - which as you noted generates force.
    Last edited by Monash; 14 Apr 18, at 08:08.
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    Quote Originally Posted by Monash View Post
    Possibly but you also have to allow for the vagaries of random chance. You can compute a course that will avoid significant gravitational deflections (you might even be able to use them to your advantage). The question is how do you cope with random influences like micrometeorite impacts, galactic gas/dust effects and radiation pressure - which as you noted generates force.
    Well, yes and no. For the centre of the galaxy, you're absolutely right but life as we know it could not exist there but out in the arms, it's mostly space. They would know the source of such particles, ie stars and predict the likelyhood of such impacts. It's the same reason why we can go through the Asteroid Belt to get to Mars. It's mostly space.

    It's the unseen black holes you have to worry about.

    Edit: This got to be the nerdiest thread on WAB.
    Last edited by WABs_OOE; 14 Apr 18, at 17:14.

  3. #78
    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by WABs_OOE View Post
    Edit: This got to be the nerdiest thread on WAB.
    Mea culpa. :-)

    Nerdy can still be interesting though.

    BTW, this video is a must-watch:

    https://www.youtube.com/watch?v=NFTaiWInZ44
    Last edited by Ironduke; 14 Apr 18, at 23:10.
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  4. #79
    Senior Contributor Monash's Avatar
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    Quote Originally Posted by WABs_OOE View Post
    Well, yes and no. For the centre of the galaxy, you're absolutely right but life as we know it could not exist there but out in the arms, it's mostly space. They would know the source of such particles, ie stars and predict the likelyhood of such impacts. It's the same reason why we can go through the Asteroid Belt to get to Mars. It's mostly space.
    The big stuff yes, it's the little stuff that's the killer in terms of accuracy over long ranges (think hundreds/thousands of light years). You could infer or even detect asteroids belts and other major obstacles but random micrometeorite impacts or solar flares? The cumulative effect of these kind of events would be critical to any mission based on a 'simple' ballistic calculation. IMO you would have no chance without a onboard navigation system and some kind of drive to make course corrections. ... and yes, this is as 'nerdy' a thread as I have ever seen on WAB. What can I say except 'nerds rule'.
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    Quote Originally Posted by Monash View Post
    The big stuff yes, it's the little stuff that's the killer in terms of accuracy over long ranges (think hundreds/thousands of light years). You could infer or even detect asteroids belts and other major obstacles but random micrometeorite impacts or solar flares? The cumulative effect of these kind of events would be critical to any mission based on a 'simple' ballistic calculation. IMO you would have no chance without a onboard navigation system and some kind of drive to make course corrections. ... and yes, this is as 'nerdy' a thread as I have ever seen on WAB. What can I say except 'nerds rule'.
    Something what you said. There is no way for that asteroid to make it one straight line trip from home to target. Sooner or later, they have to pass through other star systems. Why wouldn't the aliens do what we do? Use large gravitational source as sling shots? We use planets to hurl VOYAGEUR and PIONEER out. Why would not aliens do the same with star systems? Aim the asteroid at the nearest star. Find suitable planets. If found, crash. If not, sling shot around the star to the next star system and so on and so on.

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    Senior Contributor Monash's Avatar
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    Yes, they would have to sling shot, if only across the outer 'edge' of various stellar gravity wells. Trouble is the more systems they pass by/through the greater the effect those systems will have on the asteroid. It will get hit by random debris and solar radiation so course corrections seem inevitable.

    Hollowed out asteroids would be good candidates for survey missions though.
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    Quote Originally Posted by Monash View Post
    Yes, they would have to sling shot, if only across the outer 'edge' of various stellar gravity wells. Trouble is the more systems they pass by/through the greater the effect those systems will have on the asteroid. It will get hit by random debris and solar radiation so course corrections seem inevitable.
    But wouldn't course correction be the case when slingshotting out of the system? The AI to decide to crash would have to course correct to hit a planet. It could just as easily use its reflective surfaces to plot a course to slingshot to the next star system.

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    Senior Contributor Monash's Avatar
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    Yep, but as I originally interpreted the proposal it was that aliens could launch a 'dumb' asteroid and rely on extremely sophisticated math calc and ultra-precise astronomical measurements to calculate a purely ballistic path from A to B. Across thousands of light years!

    My point was that you might (at least over the first few systems) be able to calculate the approach to a target star so that the you use its gravity field to curve it round towards the next target. It would mean you have to make accurate measurements of the rate of solar rotation and the strength of a target stars the gravity fields etc in advance of launch but in theory it is doable.

    But what you couldn't do is calculate the effect of any specific meteorite impacts etc during the trip because they would be impossible to predict in advance. You might be able to calculate a probability curve for impacts over the course of centuries but what you couldn't do is predict the effect any single hit would have. This is because each individual impact is a random event in terms of it's mass and direction.
    Last edited by Monash; 17 Apr 18, at 12:55.
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    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by citanon View Post
    Now you take that probability, and put the following conditions onto the 100 billion to 500 billion starts in our galaxy:

    1: not in the galactic core
    2: Sun like
    3: has planets orbiting in the habitable zone
    4: is sufficiently stable to not fry habitable planets with solar flares
    5: does not have other unfavorable astronomical calamities going on in its neighborhood

    Finally, out of all of the above, if intelligent life emerges, is it technological life? What if you had an ocean world with very smart alien dolphins who have no use for technology what so ever? Seems like the chances of intelligent technological life existing at the same time within a million year time span might be quite small.
    I'm not an astrophysicist, but from my layman's understanding, a red dwarf seems like it would be an ideal place for life to evolve, with a lifespan measured in the trillions of years, and a constant temperature and stability. From what little I know, a planet would need to orbit much closer to a red dwarf than a yellow dwarf like our Sun. Potential downsides I see for life evolving on a planet orbiting a red dwarf would be the potential for the planet to be tidally locked to the star, and also that a red dwarf may be perhaps too stable and consistent, and not give impetus toward accelerating the evolutionary process that a more variable yellow dwarf would.
    Last edited by Ironduke; 01 Jul 18, at 16:25.
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    Red drawfs tend to have fluctuations in their output that cause issues for a potentially habitable planet. Intense radiation from a star can basically blast the atmosphere off a planet. It is suspected that this is what happened to mars, and that the earths magnetic field (gifted to us by the metallic core) is what has allowed the earth to retain atmosphere for this long. It's likely that a magnetic field is a precursor to an environment stable enough to develop life.

    Getting back to the original topic, it seems to me most any ship capable of a trip duration that we would consider survivable time frame would basically be a weapon. Even accelerating a modest mass, say 1000-3000 tons, at 0.01g consistently would add about 1%c per year and give you impact measured in gigatons at the arrival point in only a half dozen light years. A probe specifically designed to gravity assist rather than slow down so as to investigate multiple star systems would be indistinguishable from a weapon designed to devastate a biosphere.

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