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Ultraviolet Degradation



Cliff Buttschardt, K7RR, asked:

 >We need a material that can wrap around this small cube similar
 >to a rubber band around a newspaper and restrain the antenna 
 >elements that are to "pop" out at {after?} launch.  We need a 
 >material that is VERY susceptible to UV radiation rather than UV 
 >resistant.  The idea here is to allow the antennas to deploy when 
 >enough UV from the sun degrades the antenna restraint in orbit.  
 >Got any ideas what material to use?      

This is an interesting approach and one that shows great 
ingenuity.  A big question, however, is how fast do the antennas 
need to be deployed?  Ultraviolet (and radiation) degradation is 
not a very quick process and you may have to wait quite a while.  
You will have to weigh the strength needed to restrain the antenna 
against the time needed for breaking the band.

Most of my experience as an engineer is with commercial polymers 
and not too many custom plastics.  I am sure a polymer chemist 
could come up with a plastic that is quite sensitive to 
ultraviolet light.  I suggest you post an inquiry on the 
"sci.polymers" Usenet newsgroup.  I am sure someone there could be 
far more help than I.

Of the commercial materials I am familiar with, uninhibited 
polyethylene might be a good choice.  With no ultraviolet 
inhibitor, polyethylene is attacked fairly rapidly by 
ultraviolet.  Radiation and short-wave ultraviolet can cleave the 
polymer backbone.  The same thing is true of PTFE also, but at a 
much slower rate.  The polyethylene used to insulate "ladder-line" 
and TV twin-lead is generally loaded with inhibitors and pigments 
to help it resist the effects of UV.  Some cellulosic polymers 
might also be suitable.

One other possibility I thought of would be to use a heavily 
plasticized material like polyvinyl chloride with a very high 
percentage of a volatile plasticizer.  In the vacuum of space, the 
plasticizer would slowly evaporate leaving the original material 
in a brittle and stretched state which could snap over time.  
Again, this would be a slow process.

     73, Barry L. Ornitz     WA4VZQ     ornitz@tricon.net




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