4 ms·

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 someth

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.
TheLoneWolfling 12y ago
You'd see the "bow wave" regardless - the energy imparted as the impactor hits interstellar medium. To a first approximation, that's on the order of 67kw / m^2 at 0.9c ([1]), which is... non-negligible. And in practice, you'd notice the occasional flashes when you hit a grain of dust. This cannot be solved by a shroud, as you'd then see the interstellar medium hitting the shroud instead. The best response to something like this would be a whipple shield. Except you don't need an actual shield. Just drop a couple stages of a bunch of chaff in its trajectory, or a bunch of spin-stabilized mylar disks. Even ball bearings would be too much. You don't need to stop it, "just" diffuse it enough so that the atmosphere can handle it. [1]: http://www.wolframalpha.com/input/?i=%28%281+-+0.9^2%29^-0.5+-+1%29+*+c^2+*++0.9+*+c+*++%281*0.9+%2B+4*0.1%29+amu%2Fcm^3 http://www.wolframalpha.com/input/?i=%28%281+-+0.9^2%29^-0.5..., Assuming ~1 atom/cc, 90% hydrogen 10% helium
- deeviant 12y ago
  True, but I think a lot of people here are assuming something like .9C or the like when the reality is you nothing nearly that high. 1000 tons at .1c is 9818 megatons, which would be roughly the size of a US air craft carrier. The bow shock would be much less and the I'm assuming it would be using some sort of magnetic scoop ramjet would would channel interstellar medium to the propulsion system rather than striking the bow. With a stealthy design, the thing would be very difficult if not impossible to detect, barring some sort of entirely need detection method.
  - TheLoneWolfling 12y ago
    You use a magnetic scoop ramjet, great. Now you have cyclotron radiation. Congratulations, now you're even more detectable! And even at 0.1c, you encounter a grain of sand, that's, what, ~23MJ of energy released.
    - deeviant 12y ago
      You got me there, good comments. Thanks.

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.

TheLoneWolfling 12y ago

You'd see the "bow wave" regardless - the energy imparted as the impactor hits interstellar medium. To a first approximation, that's on the order of 67kw / m^2 at 0.9c ([1]), which is... non-negligible. And in practice, you'd notice the occasional flashes when you hit a grain of dust. This cannot be solved by a shroud, as you'd then see the interstellar medium hitting the shroud instead. The best response to something like this would be a whipple shield. Except you don't need an actual shield. Just drop a couple stages of a bunch of chaff in its trajectory, or a bunch of spin-stabilized mylar disks. Even ball bearings would be too much. You don't need to stop it, "just" diffuse it enough so that the atmosphere can handle it. [1]: http://www.wolframalpha.com/input/?i=%28%281+-+0.9^2%29^-0.5+-+1%29+*+c^2+*++0.9+*+c+*++%281*0.9+%2B+4*0.1%29+amu%2Fcm^3 http://www.wolframalpha.com/input/?i=%28%281+-+0.9^2%29^-0.5..., Assuming ~1 atom/cc, 90% hydrogen 10% helium

deeviant 12y ago
True, but I think a lot of people here are assuming something like .9C or the like when the reality is you nothing nearly that high. 1000 tons at .1c is 9818 megatons, which would be roughly the size of a US air craft carrier. The bow shock would be much less and the I'm assuming it would be using some sort of magnetic scoop ramjet would would channel interstellar medium to the propulsion system rather than striking the bow. With a stealthy design, the thing would be very difficult if not impossible to detect, barring some sort of entirely need detection method.
- TheLoneWolfling 12y ago
  You use a magnetic scoop ramjet, great. Now you have cyclotron radiation. Congratulations, now you're even more detectable! And even at 0.1c, you encounter a grain of sand, that's, what, ~23MJ of energy released.
  - deeviant 12y ago
    You got me there, good comments. Thanks.