Re: Spaceship collision with 1mg meteorite

Collisions with particles in space certainly become a larger concern as spacecraft velocities increase. At 1/10 the speed of light, a collision with a 1 mg particle releases 447 million joules of energy, about the same as exploding 100 kg of TNT. That's a lot of energy that a spacecraft needs to protect itself from.

Outside the inner Solar System, spacecraft encounter micrometer-sized particles every few days. These have a typical mass on the order of picograms; a collision at 1/10 the speed of light will release only about a joule, which is easily dissipated by a mechanical shield.

Nobody really knows what the particle size distribution looks like in interstellar space, but it is almost certainly far less dense than what we see in the Solar System. So the chance of encountering a particle massive enough to destroy a spacecraft is probably not very large. However, the consequences of a chance collision with a larger particle are so serious that I think the risk will have to be considered seriously when we reach the point of being able to build craft that can reach such high speeds.

It is fun to do kinetic energy calculations and figure out just how dangerous even tiny particles are when encountered at high speeds. Here's a nice resource about kinetic energy, http://en.wikipedia.org/wiki/Kinetic_energy, and this is a good site to convert from joules to all sorts of other interesting units of energy, http://www.onlineconversion.com/energy.htm.