[TML] Astronaut prepares to risk life for spacewalk

[Timothy Little]

On Sun, Nov 04, 2007 at 11:51:56PM -0500, Richard Aiken wrote:
> An umbrella made of smoked glass?  Maybe double-walled, with a
> coolant in between?  You only cool it enough that the radiated heat
> keeps the covered item at a reasonable working temp.  Essentially a
> medieval mantlet sheild, except the beseiged castle is the Sun
> . . . :-)

Actually on further thought, having a hot umbrella shading some more
temperature-sensitive item may be a good thing.  If the hot umbrella
floods one half of the item's "sky" with its thermal radiation and the
other half is colder, then the item should maintain a reasonable
temperature balance in between.


There's another passive thermal trick that may be possible: Design the
surface composition so that it has high emissivity in wavelengths
about half an octave above the spectrum peak for its design
temperature, and very low in longer wavelengths.  The visible spectrum
emissivity would need to be tailored for the expected solar flux, but
probably fairly low.

This would make it appear visually white, meaning that it would not
absorb much sunlight.  If it was hotter than its design temperature it
would radiate rapidly, hopefully cooling it down.  If cooler, it would
radiate much slower and thus be more likely to warm up.  Hence it
would passively maintain a more consistent temperature in varying
amounts of incident radiation.

More advanced surfaces could do even better.  For example, a
thermochromic material that goes dark in visible light and reflective
in IR below a certain temperature, and the reverse when hot.  The
colour-changing T-shirts that were all the rage in the 80s serve as a
primitive example in visible light.


- Tim