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.
There are existing projects researching near earth impacts from high speed objects (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.
(http://orbitaldebris.jsc.nasa.gov/protect/impacts.html)
(http://orbitaldebris.jsc.nasa.gov/photogallery/photogallery....)
And some of the debris is quite large - (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) so maybe there's some trickle through to research between very fast craft and small objects.