By J. Hyde, E. Christiansen, & R. Bernhard

Three hypervelocity impacts were observed on the cylinder region of the
MPLM 1 after STS-102/5A.1. The impacts caused only superficial damage
to the outer bumper. The most significant of the three was a 1.44 mm
diameter hole in the 0.8 mm thick aluminum bumper of the Meteoroid Debris
Protection System (MDPS). It was determined from Scanning Electron
Microscope (SEM) analysis that the hole was caused by orbital debris, a
fragment of spacecraft paint approximately 0.5 mm in diameter. The other
two impacts produced craters in the MDPS bumper. There was no observed
damage to the MLI thermal blanket underneath or to the MPLM1 pressure wall.

A BUMPER code analysis was performed with post-flight attitude data to
determine the regions of the MPLM1 cylinder that were most likely to be
hit by meteoroid and orbital debris particles in the general size ranges
of the observed impacts. All three impacts were near the region with the
highest risk. The analysis indicated that the bumper had a 1 in 5 chance
of being perforated during the 6 days of exposure and that orbital debris
was most likely to cause the penetration.

Five hypervelocity impacts were detected on the aluminum housing of an EVA
Safety Tether returned on STS-97/4A after nearly two years on orbit. The
largest impact, a 0.83 mm diameter by 0.45 mm deep crater, was caused by
an estimated 0.3 mm diameter orbital debris particle. SEM analysis of
crater residue revealed an abundance of silicon, indicating that the
impactor may have originated from a glass window or a solar panel. The
craters did not effect the on-orbit operation of the tether or prevent its

Probability calculations using post-flight data indicated a 1 in 114 chance
that the tether housing would be impacted by a 0.3 mm diameter projectile
during the two-year exposure period, an impact risk of less than 1%.


[Figure 1:
MPLM bumper perforation risk plot, with impact locations noted.

[Figure 2:
Inspection of 21.2 cm (8.4 inch) long tether housing.