re: Windshield damage

Jim Varney (
Mon, 07 Oct 1996 22:38:41 -0700

Philip Chien wrote:

>However several factors (more 'space friendly launch vehicles', lower
>launch rates for both Russia and the U.S., and no tests of 'killer
>satellite' systems in the past several years) have combined to reduce the
>chances of damage by almost an order of magnitude at shuttle, space
>station, Mir altitudes.  At higher altitudes it's a different story though.

I would agree that the population of large junk at low LEO is down,
as this height is self-cleaning.  I'm not sure though that "microdebris,"
if I can coin this word, has declined.  The small stuff comes from
solid propellant combustion byproducts, paint chips, etc.  These come
from normal operations and won't be reduced by the end of weapons
testing or by venting excess propellant.

Its the small stuff that pits the shuttle windows.  And since NASA
estimates that small debris outnumbers micrometeors in LEO, I'd guess
that the majority of the scratches and pits come from small debris.

Debris will increase in number and decrease in size.  Debris begats more
debris -- accretion disk principle.  (Junk collides with junk, spawning
more pieces of smaller size).

Jim Varney       | 121^ 23' 54" W,  38^ 27' 28" N   |           Sacramento, CA
Member, SeeSat-L |           Elev. 31 ft.           |                         
Member, Sacramento Valley Astronomical Society      |