Richard
Keep walking, and try to find a local library
Seek out a book on space that will tell you about various matrials found in vacuum, including ICE
Then, guesstimate what happens to ICE when it hits a hard surface travelling at say 1/3 the speed of light which has been exposed to the constant friction of dust particles which produces a fairly significant outer hull temperature...hey presto, oxygen in vacuum
So sure, MOST of this ice will escape back into vacuum and refreeze, but a portion of the molecules will ADHERE to the surface through simple kinetics of the impact, and will commence the process of corrosion. In fact I recon the ice particles will penetrate quite deeply into simple iron even if they have no significant velocity of their own, but if they do, they will go deep.
I can't recall where, but the best description of a space ship's outer hull on close examination was "pockmarked and scarred" assuming no magical deflection shields.
Greg C