Aren't we talking about the Whipple shield on the front of an interstellar craft? So wouldn't we know that most impactors will be coming from the front? I guess a big unknown is the distribution of velocities in the interstellar medium--will most of the particles be sitting there (relativistically-speaking) waiting for the ship to hit them, or will they be moving and coming from all directions?

Sorry my misunderstanding...I thought you were talking about shielding for satellites, space stations etc.

Understood. What are the implications for the amount of energy released by the collision? I'm groping in the dark here, admittedly...are you saying that relativity's cap on delta V would cap the energy released? Relativity's so weirdly cool...I guess I'm stuck on conservation of energy, and thinking that the kinetic energy of the two particles would have to add, somehow, even if their relative velocity has to be capped at c. Where does the excess energy go? It's OK, you can say it: I'm soooooo confused.

Relativity is pretty cool alright. energy is conserved. If you apply a force 'F' to an object with mass 'm' at rest it will accelerate (at first) according to Newtonian physics, ie. F=ma. However, as you get close to c this is no longer true, the change in velocity as a function of time decreases. the object's kinetic energy will continue to increase. "If" it were to be going at c it would have infinite kinetic energy.The kinetic energy in the Newtonian regime is E=.5mv^2. In the relativistic regime you must use E=mc^2(gamma-1) where gamma=1/(1-v^2/c^2)^.5.

in short the KE keeps increasing, while v increases less and less. Relativistic collisions will release a lot of energy. I wrote a short story a few months ago here about the Earth getting hit by 1kg projectiles going .9999c. (going from memory the energy of 1kg going .9999c was like a 10Gigaton nuclear bomb, with a LOT of radiation)