astronauts coolant problem

Taken from section 24 as it stands in the faq now. I may give
this problem it's own section in the futu

Another anomaly, how did the astronauts keep cool on the Moon?
They had backpacks which dissipated heat via the sublimation of
ice from a porous plate located inside their backpack which,
presumably, because it would have been in the shade and out of
the sunlight would have been very cold. The trouble with this is
that we now know that ice deposits have been found on the Moon's
surface on the permanently shady side of some polar craters.
So, water ice either "evaporates" away or it doesn't. Which is it?
Actually if we study the phase diagram for water we discover that
water does actually exist as both solid and vapour below it's
freezing point. Not only that but that it (water ice) exerts a
vapour pressure from its solid form (of which there are several)
and it is this which carries away the heat load produced by the
astronaut as he toils on the Lunar surface. Just like we lose
heat by water evaporation from our bodies when we are hot the
porous plate in the backpack dissipates heat generated by the
astronaut which would make it unbearable inside the space suit
otherwise. The trouble with this is that the vapour pressure of
solid ice decreases rapidly with temperature and below zero degrees
Celsius it is a small fraction of what it is at room temperature.
And at very low temperatures like -200F it is quite negligible.
In basic terms what this means is that there is not enough water
vapour emitted (sublimated) by the solid ice on the plate to cool
the astronaut fast enough. Not unless he has a porous plate with
maybe 4 times or more the surface area of the human body. And that
is at the melting point not -200F where something the size of a
football field will be required. So, the temperature of the plate
if it is a small one will have to rise significantly in order to
increase vapour pressure as it inadequately tries to dissipate the
heat generated by the astronauts metabolism and in a short time it
will have melted all the ice on the plate. Thereafter huge coolant
water losses ensue as the liquid water practically explodes out
of the plate and into the vaccuum but the plate cannot cool down
with this expansion because the astronaut is heating it to this point.
Liquid coolant water loss ensues. How much and at what rate depends
on the size and properties of the porous plate of course. Is this
really how it was meant to work? What happened to the "sublimation"
mechanism as the main heat transfer process?