On Fri, Jan 01, 2016 at 09:06:53PM -0500, Richard Aiken wrote:
> So . . . it seems that the answer to the OP's question lies in comparing
> how much oxygen a sheet of iron is exposed to at sea level, versus the 10
> to the 16th atoms of atomic oxygen per second per square centimeter which
> the relevant bits of a satellite is exposed to in low earth orbit (which is
> - apparently - not quite an actual vacuum).

The situations are not really comparable.  Although iron does react
with oxygen, the chance of a reaction occurring with a (comparatively)
cold and inert oxygen molecule is very low.

The oxygen in low orbit is monoatomic: very greatly more reactive, and
will react with many substances that ordinary molecular oxygen will
not.  What's more, most of it is moving at 6-9 km/s when it hits a
spacecraft surface.  The chemical effect of this is that there's lots
of energy to break bonds in the material and overcome activation
barriers.

Counting numbers of oxygen atoms won't really help at all.

The good news is that almost all of the corrosion occurs on external
surfaces that face the direction of motion in some way.  Those are
easily predicted for the design.  Interior components are mostly
shielded since the satellite is moving very much faster than the
average speed of the atoms in the extremely rarefied gas.

> Of interest is that the article notes that "no satellites have been
> crippled by atomic oxygen."

That's because all satellites after the first few were designed to
take these effects into account.  If they were not, then some
satellites would certainly have been crippled.

I do agree that the actual kilogram amount of corrosion is generally
very, very little though.

- Tim