4 ms·

There's also the risk of hitting small dust particles, etc. A quick back of the envelope calculation reveals that hitting a spec of dust that weighs just 1 ug

There's also the risk of hitting small dust particles, etc. A quick back of the envelope calculation reveals that hitting a spec of dust that weighs just 1 ug (a millions of a gram) at 90% c produces ~36 mega joule. Not a huge amount of energy (about the energy of burning 1kg of coal), but still. Hitting a grain of sand (10mg) at 90% c produces ~360 giga joule (energy of a small lightning)

steve19 14y ago
That's the energy of about 20,000 rounds of 5.56mm NATO. The real problem is that it would be concentrated on such a tiny part of the spaceships hull.
DanBC 14y ago
The NASA orbital debris programme has a few pictures of impacts on returned space craft. Obviously these craft are travelling very much slower than 0.9 c. (http://orbitaldebris.jsc.nasa.gov/protect/impacts.html http://orbitaldebris.jsc.nasa.gov/protect/impacts.html) (http://orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html http://orbitaldebris.jsc.nasa.gov/photogallery/photogallery....) And some of the debris is quite large - (http://orbitaldebris.jsc.nasa.gov/photogallery/gallarypage/slag.jpg http://orbitaldebris.jsc.nasa.gov/photogallery/gallarypage/s...) (Is that tape inches?? So that lump is about 1.5 to 2 inches?) There are existing projects researching near earth impacts from high speed objects (http://ares.jsc.nasa.gov/ares/hvit/problem.cfm http://ares.jsc.nasa.gov/ares/hvit/problem.cfm) so maybe there's some trickle through to research between very fast craft and small objects.
quattrofan 14y ago
So you need a very lage ablation shield
juiceandjuice 14y ago
You are making a fundamental error by assuming classical kinetics. At .9c, your first interactions would be electronic (ionization), then nuclear and radiative. The complete and initial ionization of all the atoms of 10mg of, say carbon, would be a lot less than 360 GJ. Then you'd have different interactions depending on your hull material, magnetic shielding/Bremsstrahlung losses, etc... With some complicated magnetic fields, you could probably do something smart to take advantage the different charge/mass ratio of an ionized atom and positron and minimize interaction with a steady/confined positronic cloud. You might be able to annihilate enough electrons of the dust particle to ionize it enough to subsequently deflect it from the ship. Then you'd still have to worry about gamma ray radiation and back pressure and maybe some other interactions. I don't really know about all of this for sure, just a thought.
- linuxhansl 14y ago
  That's quite possible. The mass would not go away, though, and since energy is preserved it would need to dissipate somehow. If you can avoid the collision (as you suggest) by deflecting the particle and thus not change its momentum there would indeed be no (or less) energy to dissipate.

steve19 14y ago

That's the energy of about 20,000 rounds of 5.56mm NATO. The real problem is that it would be concentrated on such a tiny part of the spaceships hull.

DanBC 14y ago

The NASA orbital debris programme has a few pictures of impacts on returned space craft. Obviously these craft are travelling very much slower than 0.9 c. (http://orbitaldebris.jsc.nasa.gov/protect/impacts.html http://orbitaldebris.jsc.nasa.gov/protect/impacts.html) (http://orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html http://orbitaldebris.jsc.nasa.gov/photogallery/photogallery....) And some of the debris is quite large - (http://orbitaldebris.jsc.nasa.gov/photogallery/gallarypage/slag.jpg http://orbitaldebris.jsc.nasa.gov/photogallery/gallarypage/s...) (Is that tape inches?? So that lump is about 1.5 to 2 inches?) There are existing projects researching near earth impacts from high speed objects (http://ares.jsc.nasa.gov/ares/hvit/problem.cfm http://ares.jsc.nasa.gov/ares/hvit/problem.cfm) so maybe there's some trickle through to research between very fast craft and small objects.

quattrofan 14y ago

So you need a very lage ablation shield

juiceandjuice 14y ago

You are making a fundamental error by assuming classical kinetics. At .9c, your first interactions would be electronic (ionization), then nuclear and radiative. The complete and initial ionization of all the atoms of 10mg of, say carbon, would be a lot less than 360 GJ. Then you'd have different interactions depending on your hull material, magnetic shielding/Bremsstrahlung losses, etc... With some complicated magnetic fields, you could probably do something smart to take advantage the different charge/mass ratio of an ionized atom and positron and minimize interaction with a steady/confined positronic cloud. You might be able to annihilate enough electrons of the dust particle to ionize it enough to subsequently deflect it from the ship. Then you'd still have to worry about gamma ray radiation and back pressure and maybe some other interactions. I don't really know about all of this for sure, just a thought.

linuxhansl 14y ago
That's quite possible. The mass would not go away, though, and since energy is preserved it would need to dissipate somehow. If you can avoid the collision (as you suggest) by deflecting the particle and thus not change its momentum there would indeed be no (or less) energy to dissipate.