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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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