Laser Ranging Traditional Cache
Quiggle: Archiving listing. If the cache owner decides to replace this cache in the future, it can be unarchived if it meets the current guidelines. Feel free to contact me through my profile if you have any questions.
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Size: 
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A roadside cache in a remote area, on a scenic byway often used by cyclists.
Quiet except at rush hour. Pull off road at intersection, don't cross fences.
Sandwich-sized tupperware, containing mission stickers from several NASA
laser ranging missions. Please replace carefully.
Note the Goddard Geophysical Astronomical Observatory sign. At this site,
NASA has recently ranged to laser altimeters on their way
to Mercury (MESSENGER) at a distance of 24 million km, and in orbit around
Mars (MOLA), at 80 million km. We were able to compute the range to the
Mercury Laser Altimeter (MLA) with a precision of 20 cm, a measurement of a
few parts per trillion. The 1.2-m telescope accomplished this feat with a laser
emitting a mere 15 millijoules of energy per pulse. This is not much more
energy than is output by a pocket laser pointer in one second, although these
pulses are only a few nanoseconds long and fire at several hundred Hertz.
Measurements at the GGAO help establish the precise coordinate system in
which the GPS satellites, and your GPSR, are placed. Ultimately they are used
to determine how fast the sea level is rising due to global warming,
and how much the spinning of the Earth is slowing down due to tidal forces.
In 2008, we will be ranging to a spacecraft in orbit around the Moon to
establish a geodetic coordinate system for future explorers as accurate as
that of the Earth. At night, a short distance down Springfield road, you may
see green flashes of 532-nm laser light used routinely (in clear weather) to
track satellites. The wildlife preserve also keeps light pollution to a minimum.
There is much history in this area. The old Greenbelt airport is nearby,
where the first aircraft-mounted machine guns were tested, as well as
antenna test ranges, the P.G. County baseball recreation fields,
and the Beltsville Agricultural Research Visitor center
that may be reached via Beaver Dam Road. Because of the government
research that takes place, it is likely to remain unspoiled in spite of urban
development around Washington, D.C.
Additional Hints
(Decrypt)
genfu va, pnpur bhg?
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