The LAGEOS-1 satellite.

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. Image File history File links LAGEOS-NASA.jpg Image of LAGEOS satellite, courtesy of NASA (therefore PD); http://library01. ... Image File history File links LAGEOS-NASA.jpg Image of LAGEOS satellite, courtesy of NASA (therefore PD); http://library01. ... A satellite is an object that orbits another object (known as its primary). ... In satellite laser ranging (SLR) a global network of observation stations measure the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. ...

The spacecraft are aluminum covered brass spheres covered with retro-reflectors, giving them the appearance of giant golf balls. They have no onboard sensors or electronics, and are not attitude controlled. Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Brass is an alloy of copper and zinc. ... A retroreflector is a device that sends light or other radiation back where it came from regardless of the angle of incidence, unlike a mirror, which does that only if the mirror is exactly perpendicular to the light beam. ...

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. The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Portrayal of shifting continents The concept of continental drift was first proposed by Alfred Wegener. ...

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. According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ... Two-dimensional visualization of space-time distortion. ...

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. Gravity Probe B (GP-B) is a satellite-based mission to measure the stress-energy tensor (the distribution, and especially the motion, of matter) in and near Earth, and thus to test related models; in application of Einsteins general theory of relativity. ... 1960 was a leap year starting on Friday (link will take you to calendar). ...

See also

• geodesy
• general relativity

It has been suggested that Geodetic datum be merged into this article or section. ... Two-dimensional visualization of space-time distortion. ...

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

Nature is one of the oldest and most reputable general-purpose scientific journals, first published on November 4, 1869. ... Nature is one of the oldest and most reputable general-purpose scientific journals, first published on November 4, 1869. ...

External links

• http://www.earth.nasa.gov/history/lageos/lageos.html

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The first version of this article was adapted from the public domain NASA website at http://www.earth.nasa.gov/history/lageos/lageos.html NASA Logo Listen to this article · (info) This audio file was created from the revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... For copyright issues in relation to Wikipedia itself, see Wikipedia:Copyrights. ...