Science Fair Project Encyclopedia
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 reflecting surfaces; the travel times are precisely measured, permitting ground stations in different parts of the Earth to measure their separations to better than one inch in thousands of miles.
The LAGEOS satellites are able to determine positions of points on the Earth with extremely high accuracy due to the stability of their orbits.
The high mass-to-area ratio and the precise, stable (attitude-independent) geometry of the LAGEOS spacecraft, together with their extremely regular orbits, make these satellites the most precise position references available.
The LAGEOS mission consists of the following key goals:
- Provide an accurate measurement of the satellite's position with respect to Earth,
- Determine the planet's shape (geoid) and,
- Determine tectonic plate movements associated with continental drift.
Ground tracking stations are located in many countries (including the US, Mexico, France, Germany, Poland, Australia, Egypt, China, Peru, Italy, and Japan) and data from these stations is available worldwide to investigators studying crustal dynamics.
There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976, and LAGEOS-2 launched in 1992. As of 2004, both LAGEOS spacecraft are still in service.
An analysis of the laser-ranging data obtained by the two LAGEOS satellites, published in 1997, claimed to have found evidence of the frame-dragging effect predicted by Einstein's theory of general relativity with an accuracy of about 20 percent. See Neil Ashby in Nature, Volume 431, Issue 7011, pp. 918-919 (2004) and I. Ciufolini, E. C. Pavlis. "A confirmation of the general relativistic prediction of the Lense–Thirring effect." Nature 431, 958 - 960 (21 October 2004); doi:10.1038/nature03007
This effect is the same one that the Gravity Probe B satellite mission, unusual for its planned precision and its long time for planning, funding, and launching (from a suggestion by Professor Leonard Schiff in 1959, through formal planning starting in the 1960s, until launch April 20, 2004), seeks to measure.
The first version of this article was adapted from the public domain NASA website at http://www.earth.nasa.gov/history/lageos/lageos.html
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