| LAGEOS
missions place into Earth orbit large, dense satellites, shaped like giant golf
balls and covered by reflectors. These serve as targets for laser ranging and
thereby provide an orbiting benchmark for geodynamical studies of the Earth.
The high density of these satellites makes them resistant to outside forces, so
their orbits are stable enough to constitute the most precise position
references ever created.
Measurements are
made by transmitting pulsed laser beams from Earth ground stations to the
satellites. The laser beams then return to Earth after hitting the reflective
surfaces. The travel times are precisely measured, permitting ground stations
in different parts of the Earth to measure separations between the satellites
to better than one inch in several thousand miles.
The LAGEOS
mission has following key scientific goals:
- Determine our
planet's shape
- Determine
tectonic plate movements associated with continental drift
- Further prove
Einstein's General Theory of Relativity
It is the last
goal that is the fundamental physics goal. With two or more LAGEOS satelllites
in orbit, the prediction of Einstein's General Theory of Relativity that the
spin of the Earth will drag space around with it may be tested by looking for
common motion of satellites in different orbits. This is referred to as the
gravitational magnetic effect.
LAGEOS 1 was
launched in 1976. It was the first spacecraft dedicated exclusively to
high-precision laser ranging and provided the first opportunity to acquire
laser-ranging data that were affected by errors originating in the satellite
orbit or satellite array.
LAGEOS-2, based
on the LAGEOS-1 design, was built by the Italian Space Agency and launched in
1992. Although the orbit of LAGEOS-2 was not ideal for the purpose of testing
General Relativity, the predicted dragging of space has now been
observed.
LAGEOS-3 is a
proposed multinational program to place a LAGEOS satellite in the ideal orbit
for testing General Relativity, allowing refinement in the measurement of the
gravitational magnetic dipole moment of the Earth.
For
additional information:
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