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[Programme]
Session 9: "Hypervelocity Impact
Effects on Spacecraft"
Date: Thursday
10.30-11.45
Hypervelocity Impact Effects on
Spacecraft
Gerhard Drolshagen (ESA/ESTEC)
Every spacecraft in orbit is exposed to a
certain flux of impacting particulates. These
impacts occur at typical velocities between a few
and some tens of kilometers per second. Submicron
and micron sized particles can lead to a
degradation of sensitive spacecraft surfaces and
equipment, like mirrors, optical sensors and
thermal control surfaces. Somewhat larger particles
with diameters in the range of tens to hundreds of
microns can penetrate outer spacecraft coatings and
foils as well as solar cells. Penetration of solar
cells can lead to short circuits and subsequently
to a degradation of the power supply. Craters
resulting from hypervelocity impacts are typically
3-20 times larger (depending on the material and
impact parameters) then the impactor. That implies
that even submillimeter sized particles can cause
problems for sensors and for the future use of
impacted surfaces (e.g. sealing, Shuttle windows).
In addition to these mechanical effects, every
hypervelocity impact creates an impact plasma. Such
an impact generated plasma can lead to
electromagnetic interference with spacecraft
systems and payloads. More importantly, the impact
plasma can also trigger a discharge of
electrostatically charged dielectric surfaces,
releasing a current which is much larger than what
would be possible by the impact alone. Millimeter
sized particles can penetrate exposed tanks and
seriously damage certain equipment. In addition the
momentum transfer can lead to attitude problems.
Impactors of cm size or larger will typically lead
to complete destruction of the impacted spacecraft
part. The presentation will give an overview of the
hypervelocity impact effects on spacecraft and also
briefly address some common protection measures.
9.1
Cosmic Dust and Micro-debris Measurements on
Space Station MIR
J.C. Mandeville and M. Bariteau
(ONERA/DESP, 2 Av. E. Belin, 31400 Toulouse,
France. E-mail: mandevil@onecert.fr)
Investigation of impact features found on
material retrieved from low earth orbit, after
exposure to space for a long period of time, has
provided us with a great deal of data on the
particulate environment, either natural or
man-made. Between 1987 and 1997, several detection
devices have been deployed outside the Russian MIR
space station. The passive sensors are composed
primarily of stacked thin metal foils (gold and
aluminum). The size of holes or impact craters give
information on the size or shape of the impacting
particles. In addition, solar cells from a solar
array retrieved by a Shuttle-MIR mission have been
searched for impact craters. Samples have been
retrieved for laboratory analysis and flux of
impacting particles has been derived. Comparison
with data from LDEF, and HST provides insight in
the long-term evolution of small particle
population and in the debris environment of a
permanently manned station. Between 1987 and 1997,
no peculiar enhancement in the population of
microdebris in the vicinity of the MIR station was
seen. Several samples show evidence of secondary
impact cratering: an attempt is made to locate the
origin of primary impact sites. For routine
monitoring of space environment the method provides
a low cost and reliable tool, if the retrieval of
material is possible. However, as short term
fluctuations in the flux of particles are not
visible with passive experiments, they should
benefit from data obtained by active experiments.
9.2
Capture of Meteoroids by Aerogel Exposed on
the MIR
G. Ferrini and L. Colangeli (Osservatorio
Astronomico di Capodimonte, Napoli), P. Palumbo
(Istituto Universitario Navale, Napoli), A.J.
Westphal (Space Sciences Laboratory, University of
California at Berkeley) and J. Borg (Institut
d'Astrophysique Spatiale, Université Paris
Sud)
The Earth orbit environment is an ideal place
for the collection of meteoroids of different
origins. The intact capture of these solid
particles in space is of special interest for
cosmic dust research in order to understand their
nature, to assure the complete characterisation of
their chemical composition and to determine their
orbits and relative contribution to the total flux
in the Solar System. Searching for these results,
in the last few years a number of experiments were
carried out in Low Earth Orbit, many of which
onboard the Russian MIR Space Station. The COMET-99
experiment flew on the MIR between November 1998
and April 1999, during Earth encounter with
Leonids. With the aim of in situ collection of
particles from this meteor stream, a package
composed of different dust collectors, belonging to
various capture experiments, was exposed to space.
Among these collectors, two blocks of silica
aerogel provided by the Cosmic Physics Laboratory
of Napoli were included. Laboratory analyses on
these aerogels show a conspicuous presence of
tracks and captured solid particles. Here we
present our results on the extraction and analysis
of collected grains. 9.3
Comparison of Meteoroid and Space Debris
Fluxes to Spacecraft in Earth Orbit
Veronika Ekstrand and Gerard
Drolshagen(ESA/ESTEC)
Spacecraft in earth orbit will be impacted by
natural meteoroids and man-made space debris
particles. The relative ratio depends mainly on the
spacecraft orbit and attitude. Predicted number of
impacts from different flux models will be
presented for particle sizes ranging from microns
to cm. For low Earth orbits meteoroid fluxes
dominate for sizes between some tens of microns and
about 1mm while space debris is more abundant for
smaller and larger sizes. The mode differences for
a given population indicate the present level of
uncertainty. 9.4
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