|MadSci Network: Physics|
Halfway through his answer, Ben writes on the damage caused by UHECRs here:
His suggestion, that no shielding might be better than some shielding is a good one, as it reduces the risks of spallation - a shower of dangerous secondary and subsequent particles - caused by a UHECR hitting the atoms within a dense shield.
However, it must be said that it is theoretically possible to provide enough shielding to protect a ship from all cosmic rays, providing we don't mind covering our ship with many metres of ray-absorbing materials. Ben suggests ten metres of rock is enough to stop a 200GeV proton.
Let's suppose that that's enough: every square metre of the surface of our ship would therefore need about 25 tonnes of shielding. In real terms this is not practical - an Apollo-type capsule, with a surface area of approximately 40 square metres, would need 1000 tonnes of shielding for its five-tonne mass.
I hope this helps,
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