[FPSPACE] moon laser experiment, that ran 40 years, is to be ended

[Peter Pesavento]

>From the Guardian (UK)

 

http://www.guardian.co.uk/technology/2009/jun/21/mcdonald-observatory-space-
laser-funding

 


After 40 years' reflection, laser moon mirror project is axed


US research that began with the first Apollo landing - and helped to prove
that the moon is moving away from Earth - is to be axed

 <http://www.guardian.co.uk/profile/robinmckie> Robin McKie, science editor

Sunday 21 June 2009

 

An experiment, begun when Apollo 11 astronauts Neil Armstrong and Buzz
Aldrin left a mirror on the lunar surface 40 years ago to allow Earth-based
astronomers to fire lasers at it, has been ended by American science chiefs.

The National Science Foundation (NSF) last week wrote to scientists working
at the McDonald Laser ranging station at Fort Davis in Texas to tell them
the annual $125,000 funding for their research project was going be
terminated following a review of its scientific merits.

The decision means that four decades of continuous lunar laser research at
the McDonald Observatory, run by the University of Texas at Austin, will be
halted by the end of this year. Among the project's unlikely achievements
has been the discovery that the moon is moving away from Earth at a rate of
two-and-a-half inches a year.

The mirror's existence, and the fact that astronomers can bounce lasers off
it and detect the returning beam, has also provided Nasa and other
scientists with compelling evidence to refute the claims of moon-landing
deniers who claim the Apollo lunar mission were hoaxes filmed in an
Earth-based studio. 

"It is a bitter-sweet feeling to know this is going to come to end at
McDonald," said Peter Shelus, head of the laser ranging project. "We have
done a great deal of important work using the moon mirrors but it is clearly
time for it to end. However, we are hopeful that this work will be continued
at other astronomy centres."

The mirror left by Aldrin and Armstrong after they landed on the Sea of
Tranquillity on 21 July 1969, was one of five known as "corner mirrors" or
"retro-reflector arrays" that were taken to the moon in the later Sixties
and early Seventies. Two other corner mirrors were brought to the moon by
astronauts on later manned lunar flights, on the Apollo 14 and the Apollo 15
missions. In addition, a second pair were built by French scientists and
flown to the moon by the Soviet Union on their robot Luna probes.

Corner mirrors are important scientific instruments because, when struck
precisely by a laser beam, they reflect that beam in a parallel path
straight back to the source of the laser.

"Essentially, we measure when that beam goes out and when it comes back,"
said Shelus. "We know the speed of light, of course, so that timing allows
us to calculate the moon's distance with incredible precision."

After these laser measurements were amassed for years, calculations by
astronomers at the McDonald Observatory showed that as the moon orbits
Earth, it creates a bulge of water that travels round the planet behind it.
This bulge - which we experience as tides - exerts a gravitational pull on
the moon, slowing it down as it circles Earth at a distance of 240,000
miles. 

As a consequence of being held back by this pull, the orbit of the moon
becomes altered and it moves slowly away from Earth - at a rate of
two-and-a-half inches a year. These measurements have, in turn, allowed
scientists to carry out valuable tests of theories about relativity and
gravity, added Shelus. 

A spokesman from the NSF told the Observer last week that, after carrying
out two reviews, it had decided there was no longer "a strong science case"
for continuing its 40-year support for the lunar laser ranging project. The
spokesman added that two other astronomy centres - at Apache Point in Texas
and Observatoire de la Côte d'Azure in France - were expected to carry out
lunar-ranging experiments in future.

"These are very good centres," said Shelus. "However, it does mean that the
continuity of our measurements, which we have established since the Apollo
missions, will now have to stop. It is, rather sadly, the end of an era."

 

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