Alex Terrell wrote:

(Any thoughts on this? - how effective is 5cm
of steel, followed by 50m of vacuum followed by 4 metres of moon rock
foam, in absorbing a nuclear blast?)

That depends on whether the "blast" delivers any concussive force or
not. Nukes in space can only generate a concussive force with the mass
attached to the nuke (not much) and - if it detonates really close to
the target - what it can ablate off the target.

Otherwise, you only have radiation from the nuke to do damage, and the
radiation from the nuke won't be more penetrating than cosmic rays,
which the shielding can stop.

Mike Miller