[meteorite-list] Preventing the Sky Falling in on Moon Bases

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed May 3 18:54:45 2006
Message-ID: <200605032025.NAA25850_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn9099-preventing-the-sky-falling-in-on-moon-bases.html

Preventing the sky falling in on Moon bases
Kelly Young
New Scientist
03 May 2006

A meteoroid blasting through a Moon base would be a bad day in space.
So, with NASA now planning to return astronauts to the Moon as early as
2018, scientists are combing through 30-year-old seismic data to see
exactly how big a threat impacts pose to future lunar explorers.

NASA astronauts left four seismometers on the lunar surface during
Apollo missions 12, 14, 15 and 16 missions. They operated from 1969
until 1977, recording 12,000 seismic events. In those eight years, NASA
also measured impacts from nine spacecraft that crashed into the Moon,
to calibrate the seismometers.

So far, 1743 of those events have been linked to meteoroids striking the
lunar surface. Between 3000 and 6000 are thought likely to be Moon
quakes, caused by internal movements.

But that leaves thousands of events without a likely known cause: in
some cases, the events were simply too faint to easily determine the
source. But Bill Cooke and Anne Diekmann, at the Meteoroid Environment
Office at NASA's Marshall Space Flight Center in Huntsville, Alabama,
US, are now using computers and sophisticated algorithms to take another
look at the data.

No shield

In particular, Cooke and Diekmann are looking for events caused by
meteoroids with a mass of 1 kilogram or greater, which are about 10
centimetres across. "I hope to get a good idea of how many of these
bigger meteoroids hit the moon per year," says Cooke.

He also hopes to learn more about the meteor showers on the Moon. These
showers affect both the Earth and the Moon, but the latter "is far
enough away from Earth that there should be some slight difference".

And while small meteoroids burn up in the Earth's atmosphere, the Moon
has no such built-in shield. The Moon has an area equivalent to that of
Africa, and the standard meteoroid model, based largely on Earth data,
suggests between 300 and 400 impacts annually from meteoroids larger
than 1 kilogram.

Heavily armoured

But there will be a much higher number of impacts from particle smaller
than that, which will have been difficult for the seismometers to
detect. "Your biggest threat on the Moon is going to come from the
smaller stuff," Cooke told New Scientist.

A crewed lunar base would have to be well armoured to protect against
even small particles, given that they could be travelling at about 70
kilometres per second.

Astronauts are likely to have to stay indoors and postpone spacewalks
during a known meteor shower. Their spacesuits cannot be fortified
heavily enough as they would then be robbed of flexibility. "There could
be times when you just have to batten down the hatches," Cooke says.

Another assessment of the threat posed by micrometeoroids will be
provided by NASA's Lunar Reconnaissance Orbiter, which is scheduled to
launch in October 2008.

Its high-resolution camera will be able to look at craters formed by
meteoroids smashing into the Moon. By finding out how many craters have
formed since the Apollo mission, scientists should be able to determine
the rate of meteoroid impacts.
Received on Wed 03 May 2006 04:25:48 PM PDT