The Pierre Auger Observatory site mentions the detection of a 3E20 eV (48 J) cosmic ray whose energy, well above the GZK cutoff, was based on an analysis of its atmospheric shower. This was equivalent to the kinetic energy of a baseball with a speed of 79.5 m/s or 177 mph. Of course, cosmic rays with such ulta-high energies are extremely rare. What kind of damage would occur if an astronaut or a space vehicle encountered such a cosmic ray? How would the damage differ from that from the hypothetical 79.5 m/s baseball?
Answer
One must keep in mind also that it is the particle, not the shower that goes through the astronaut in dmckee's estimate above, where he treats the relativistic particle going through matter.
The shower in your question which gave the energy estimate of the parent particle is generated by cascade/sequential collisions of deep angle scattering over a long path. The energy is not released in one go unless the astronaut is very unlucky.
The deep inelastic scattering crossection at those energies is still not up to barn values ( a barn is about the size of a uranium nucleus) so the astronaut would have to be very unlucky even to get one energetic scatter let alone to start a shower.
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