LAGEOS
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LAGEOS, or Laser Geodynamics Satellites, are a series of scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth.
The spacecraft are aluminum-covered brass spheres with a diameter of 60 cm and a mass of 411 kg, covered with retro-reflectors, giving them the appearance of giant golf balls. They have no onboard sensors or electronics, and are not altitude controlled. They orbit at an altitude of 5,900 km[1], well above low earth orbit and well below geosynchronous orbit.
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.
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 satellite (which will re-enter the atmosphere in 8.4 million years) also contains a plaque showing the arrangement of the Earth's continents in the past, present, and future.
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[edit] Launch data
- LAGEOS 1, launched 4 May 1976, COSPAR ID 1976-039A, NORAD number 8820
- LAGEOS 2, deployed 23 October 1992 from STS-52, COSPAR ID 1992-070B, NORAD number 22195
[edit] See also
[edit] References
- Neil Ashby (2004). "General relativity: frame-dragging confirmed". Nature 431 (7011): 918-919. PMID 15496905.
- I. Ciufolini, E. C. Pavlis (2004). "A confirmation of the general relativistic prediction of the Lense–Thirring effect.". Nature 431: 958-960. PMID 15496915.
[edit] External links
This article contains material that originally came from a NASA website. According to their site usage guidelines, "NASA material is not protected by copyright unless noted". For more information, please review NASA's use guidelines.
The first version of this article was adapted from the public domain NASA website at http://www.earth.nasa.gov/history/lageos/lageos.html
