Owen Zurhellen wrote in
:

Dear all: As you may have heard, one of the
difficulties in using the
Space Shuttle's External Tank as an orbiting space station
or factory (rather than allowing it simply to reenter to
destruction) has been thought to be the orange outer
coating that insulates the cryogenic propellants, which
would slowly disintegrate (from micrometeors and the
exosphere's monatomic oxygen) and choke the vicinity with
fine debris. The outer coating of the ET has now been
modified (I'm not sure exactly how) to avoid the problem
that doomed COLUMBIA - relatively large chunks of the
coating falling off during ascent and striking the
orbiter's vulnerable tiles. Would this recent modification
help the on-orbit disintegration problem in any way?

I'm not aware of anything that alters the bulk properties
of the insulation, just the manner in which is it applied
in certain areas.

It's otherwise irrelevant because the tank will never, ever
be used on-orbit for anything.

--Damon