(more catching up)

In article ,
Pat Flannery wrote:
"Evaluation of Ice and Frost Accumulation on the Space Shuttle External Tank"

The "hosing it down with water" scheme as a way of preventing ice
formation is one of the most counter-intuitive approaches I've ever
read...

Odd though it may seem, it's not ridiculous. Water sprays are routinely
used to protect orchards from freezing, in places like Florida that only
occasionally get cold weather. (They can afford to let it go a bit
farther: the trees and fruit can have a layer of ice on them! So long as
there's still liquid water flowing over the outside, they can't go below
0degC, which is all that matters -- the sap and juice don't freeze until
several degrees lower.)

The water may start off at ambient air temperature at the top of
the ET, but exactly how much has it cooled by the time it has run
halfway down the LH2 tank?

Given the foam, not too much, you hope. :-) So long as it's still
above freezing by the time it reaches the bottom, that suffices, and
water's heat capacity is pretty high.
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