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(meteorobs) Survey Finds Nearly 800 Debris Impacts On Hubble
http://www.astronomynow.com/breaking/990412debris/index.html
Survey finds nearly 800 debris impacts on Hubble
FROM NASA'S ORBITAL DEBRIS QUATERLY NEWS
Posted: April 12, 1999
During the second servicing mission of the Hubble Space Telescope (HST) by
the STS-82 mission in February, 1997, an extensive imagery survey was
performed covering approximately 97% of the HST surface. The results of a
dedicated study to identify and to characterize apparent micrometoeoroid and
orbital debris (M/OD) impacts have been recently documented in a new NASA
JSC report, "Survey of the Hubble Space Telescope Micrometeoroid and Orbital
Debris Impacts from Service Mission 2 Imagery," by G.J. Byrne, D.R. Bretz,
M.H. Holly, M.T. Gaunce, and C.A. Sapp.
Employing video, photography, and electronic still imagery (a total of 2500
still frames and 17 hours of video), the analysis team was able to identify
788 potential impacts on the HST aft shroud, equipment section, aft
bulkhead, grapple fixtures, aperture door, and solar arrays. The analysis
process involved first screening and categorizing the images, then imagery
review and M/OD impact identification, followed by mapping and measurements
of the impact features.
Over 500 of the impacts were found on the aft shroud and equipment section
where highly reflective surfaces facilitated detection of impact features.
Approximately 80% of the impact zones measured less than 0.8 cm, although
the largest was 4.7 cm in diameter.
A plot of the number of impacts of a given outer diameter size range
illustrates the expected exponential increase down to a size of 0.4 - 0.5
cm, where sensitivity limits of the imagery apparently lead to a reduced
count. The distribution of impacts around the aft shroud suggest a real
difference in the number of particle impacts on the +V3 and the -V3 sides.
An attempt was also made to compare the number of impacts seen on the first
servicing mission in December 1993 (after 44 months exposure in LEO) and the
second servicing mission (after an additional 38 months exposure in LEO). A
limited comparison of the +V3 quadrant showed an increase in the density of
observed strikes from approximately 5 impacts per square meter to
approximately 20 impacts per square meter. While some of this increase is
undoubtedly due to the superior quality of the imagery obtained during the
second servicing mission, a change in the environment may also be indicated.
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