Other meanings of LAGEOS
Space Geodesy
LAGEOS (Laser Geodynamics Satellites) is a pair of passive, spherical satellites launched by NASA for high-precision laser ranging measurements of Earth's shape, rotation, and tectonic motion. The first, LAGEOS-1, was launched in 1976, followed by LAGEOS-2 in 1992. Each satellite is a solid brass core covered with 426 corner-cube retroreflectors, designed to reflect laser pulses from ground stations back to their source. These measurements enable scientists to track continental drift, measure Earth's gravitational field, and study variations in the planet's rotation with millimeter-level accuracy. The satellites have no onboard electronics or moving parts, making them among the most stable and durable objects in orbit, with expected lifetimes of millions of years.
LAGEOS satellites are simple yet highly engineered spheres. Each is a 60-centimeter-diameter brass core weighing about 400 kilograms, covered by a thin aluminum shell. The core is solid, with no internal components, ensuring that the satellite's orbit is affected only by gravity and non-gravitational forces like solar radiation pressure. The 426 corner-cube retroreflectors are made of fused silica (for LAGEOS-1) and germanium (for LAGEOS-2, to allow infrared ranging). These reflectors are arranged to return laser pulses directly to their source, regardless of the satellite's orientation. The satellites are in nearly circular, high-inclination orbits at an altitude of about 5,900 kilometers, which provides long-term orbital stability and global coverage for ground stations.
LAGEOS data have been fundamental to geodesy and geophysics. By measuring the round-trip time of laser pulses to the satellites, scientists can determine the distance between ground stations with millimeter precision. This has enabled the measurement of tectonic plate motion, with rates of a few centimeters per year, confirming the theory of plate tectonics. The satellites also allow precise tracking of Earth's rotation variations, including length-of-day changes and polar motion, which are influenced by atmospheric and oceanic angular momentum. Additionally, LAGEOS orbits are used to map Earth's gravitational field and to test general relativity, particularly the Lense-Thirring effect, where a rotating mass drags spacetime around it. The LAGEOS missions have been instrumental in establishing the International Terrestrial Reference Frame, the standard for global positioning and Earth observation.
LAGEOS-1 was launched on May 4, 1976, aboard a Delta rocket from Vandenberg Air Force Base, as a joint NASA and Smithsonian Astrophysical Observatory project. It was designed to provide a stable reference point for laser ranging, following earlier experiments with the Moon and the Explorer satellites. LAGEOS-2 was launched on October 22, 1992, aboard the Space Shuttle Columbia (STS-52) and deployed from the shuttle's payload bay, with the Italian Space Agency contributing to its construction. The two satellites are often used together to improve the accuracy of measurements. The LAGEOS program has been complemented by other missions, such as the French Starlette and Stella satellites, and the Etalon satellites of the former Soviet Union, which serve similar purposes. The International Laser Ranging Service (ILRS) coordinates the global network of stations that track LAGEOS and other satellites.
Beyond their primary role, LAGEOS satellites carry a unique time capsule. LAGEOS-1 contains a small plaque designed by Carl Sagan and Frank Drake, depicting the Earth's continents and a message intended for future humans or other beings, showing the positions of the continents over millions of years. The satellite is expected to re-enter Earth's atmosphere in about 8.4 million years, making it one of the longest-lived human-made objects. LAGEOS-2 also has a plaque, but with a different design. Another lesser-known fact is that the satellites are used to measure the Earth's gravity field's temporal variations, which can indicate changes in water storage and ice mass. Additionally, the LAGEOS orbits are affected by the Yarkovsky effect, a subtle thermal force that causes a tiny orbital decay, which must be accounted for in precise analyses. The satellites have also been used to test the equivalence principle and to search for possible variations in the gravitational constant.
LAGEOS satellites are expected to remain in orbit for millions of years, serving as a lasting testament to human engineering and scientific curiosity.
Help improve the encyclopedia. Reports go straight to the site manager.