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Keith Cowing, Space Ref
 These
pictures were taken of the Leonardo MPLM (Multi-Purpose Logistics
Module) at NASA KSC after it returned to Earth from its first
mission. Leonardo is one of three MPLM's provided by Italy and
was flown to the International Space Station last month on mission
STS-102/ISS-5A.1.
These photos
show micrometeoroid damage to a micrometeoroid/orbital debris
(MMOD) shield panel from MPLM FM1 (Leonardo). The panel was penetrated
in two spots (the small pinholes in the photos), but did not damage
the multi-layer insulating blanket beneath. This module was in
space for about a week.
The strike
damage to Leonardo's MDPS (micrometeorite protection system) is
characteristic of other impacts that have been seen on spacecraft.
However, the size of particle that penetrated the shield was a
bit larger than average and was estimated to be traveling rather
fast - at least 10 kilometers/second - when it struck Leonardo.
To put this
impact into perspective, had this piece of space debris hit a
Space Shuttle window it would have left a crater approximately
1 inch (2.5 cm) in diameter. If it had hit a someone wearing an
EVA spacesuit it would have gone partially through the suit and
left a bruise on the person wearing the suit.
Impacts such
as these two are routine for any spacecraft in Earth orbit. The
Long Duration Exposure Facility (LDEF) which spent 5.7 years in
Earth orbit had been struck more than 20,000 times by the time
its was brought back to Earth. The Hubble Space Telescope had
nearly 800 impacts by the time it was repaired in 1997.
How much debris
a spacecraft can expect to collide with - the orbital debris flux
- is a function of mission duration, the size and orientation
of the spacecraft (how big of a target it is), the orbital inclination,
altitude, and the level of solar activity.
Components
of the International Space Station are provided with shielding
so as to reduce the annual risk that impact with a space debris
could cause a critical failure to less than 0.5% This shielding
is also sized to last through the expected 15 year operational
lifetime of the ISS.
Last year,
it was discovered that the Service Module did not have sufficient
shielding to meet requirements levied upon it by the ISS program.
As such, additional shielding panels will be delivered and installed
on the exterior of the Service Module.
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