SMART-1 impact simulated in a laboratory sand-box (Forwarded)

ESA news
http://www.esa.int

11 September 2006

SMART-1 impact simulated in a laboratory sand-box

Laboratory simulations of the SMART-1 impact performed at the University of
Kent, United Kingdom, suggest that the impact may have caused a clearly
elongated lunar crater, and produced a high-speed rebounding for the
spacecraft.

This may help explain some properties of the dust cloud observed just after
the actual impact of SMART-1 on the Moon.

The simulations were performed by M.J. Burchell and M.J.Cole at the
University of Kent. For the test, they used a high-speed, two-stage light
gas gun to shoot at 2 kilometres per second a 2-millimitre aluminium sphere
that simulated the SMART-1 spacecraft. The target was a tray of sand,
similar to lunar soil.

"We called for such laboratory simulations and numerical modelling of the
SMART-1 impact as a crucial test to understand the processes at work in
space-bound and artificial impacts," said Bernard Foing, ESA SMART-1 Project
Scientist.

Data from a previous project, in which Burchell and Cole made use of coarse
grained sand, had shown that for an impact at a 10-degree incidence the
fastest ejected material travelled forward (within about plus or minus 5
degree angle with respect to the impact direction) at 120 percent of the
impact speed -- a higher value than the impacting projectile had.

However, at that 10-degree incidence angle only one percent of the material
excavated by the impact went forwards and the percentage decreased as the
angle got shallower. Out of that one percent, about 75 percent was at an
angle to the surface greater than 10 degrees.

"To reproduce the SMART-1 scenario we simulated an impact at two degrees
incidence. The result was a nice non-circular crater," said Mark Burchell.
"According to the test's results, the fine grained dust of the lunar surface
was to raise a cloud of ejected material, which would have spread out
sideways, as well as in a forward direction."

Based solely on the results and ignoring scaling issues, Burchell and Cole
predicted the size for the SMART-1 impact crater, expected to be 7 metres
long and 4.5 metres wide. This was compatible with ESA's scaling-law
predictions on the size of the SMART-1 crater.

Burchell and Cole also observed a 'ricochet-projectile' phenomenon,
suggesting a bounce like that of a single object that had undergone some
deformation, with a slight 20 percent loss of speed during the impact.

"Based on the latest topography analysis, SMART-1 touched down with a very
grazing incidence not higher than a few degrees," said Foing. "Therefore it
might have bounced in a similar way to the flying bullet in the sand box,
like a stone skipping on water."

"The result of these simulations may explain some of the properties of the
clouds detected by the Canada-France-Hawaii telescope (CFHT) up to 100
seconds after the flash," added Pascale Ehrenfreund, coordinator of the
SMART-1 impact ground-based observation campaign. "These were spread at some
tens of kilometres downstream from impact," she concluded.

For more information

Bernard Foing, ESA SMART-1 Project Scientist
Email: bernard.foing @ esa.int

Mark Burchell, University of Kent, United Kingdom
Email: M.J.Burchell @ kent.ac.uk

Pascale Ehrenfreund, SMART-1 ground-based impact campaign coordinator,
Leiden University, The Netherlands
Email: pascale @ strw.leidenuniv.nl

[NOTE: Image supporting this release are available at
http://www.esa.int/SPECIALS/SMART-1/SEM8SH7LURE_1.html ]

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* Looking at the Moon
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Related links

* Space-X
http://www.space-x.ch/
* Advanced Moon micro-Imager Experiment (AMIE)
http://www.space-x.ch/Amie.htm
* More about SMART-1 impact ground observations
http://sci.esa.int/science-e/www/obj...objectid=39841
* Virtual Moon Atlas
http://www.astrosurf.com/avl
* Amateur astronomy at Sternwarte Stuttgart (in German)
http://www.sternwarte.de
* Amateur astronomy by Silvia Kowollik (in German)
http://www.silvia-kowollik.de/astro/