Effect on surface thermal properties of calibrated exposure to micrometeoroid environment.

An accurate procedure f o r reproducing t h e exposure of metal surfaces t o impaction by micron-size p a r t i c l e s at hy-pervelocit.ies has been employed t o expose t a r g e t s of several ma5erials.After degradation of surface o p t i c a l properties i n varying amounts due t o such exposure, these t a r g e t s were mounted on a simulated space vehicle t h a t w a s then placed i n a s o l s -s p a c e -e n v i r o n n t chamber.I n t h i s chamber t h e pressure was maintahed below IUD Hg, t h e black r a d i a t i o n sink of space was provided a t 4.2O K, and t h e samples w e r e placed i n a beam-simulating solar radiation.maifitained a t 1 s o l a r constant, while reproducing reasonably w e l l t h e s p e c t r a l d i s t r i b u t i o n of solar r a d i a t i o n i n space.Values of normal solar absorptance, t o t a l hemispheric emittance, and equilibrium temperature f o r various materials w e r e thus obtained as a function of exposure t o simulated micrometeoroid impact i o n .Comparison of these data with a c t u a l s a t e l l i t e s m p l e temperature h i s t o r i e s w i l l allow an a l t e r n a t e method of estimating micrometeoroid f l u x i n space, without t h e l i m i t a t i o n s of nomentum c a l i b r a t e d microphone data, o r t h e The i n t e n s i t y of the beam was need f o r hard-to-interpret penetration f l u x measwements.IlWFtODlfCiTION A s p a r t of a n o v e r a l l effort, t o determine the degradation of material surface p r o p e r t i e s while these s w f a c e s are exposed t o t h e micrometeoroid environment i n Earth orbit., a program is i n progress at t h e Lewis Research Center t o simulate t h i s enviromezt .Sirxe labo=.atoryacceleration of p r o j e c t i l e s t o X-5 2056 Experimentally, t h e equilibrium temperatures w e r e determined by approaching equilibrium conditions from values below and values above t h e equilibrium temperature.This procedure resulted i n two asymptotic approaches t o equilibrium that bracketed t h e a c t u a l equilibrium levels and allowed a ready determination of t h e equilibrium temperatures within 5O F.The calculated and measured data are presented i n table I.