The LAGEOS satellites are passive vehicles covered with retroreflectors designed to reflect laser beams transmitted from ground stations. By measuring the time between transmission of the beam and reception of the reflected signal from the satellite, stations can precisely measure the distance between themselves and the satellite. These distances can be used to calculate station positions to within 1-3 cm. Long term data sets can be used to monitor the motion of the Earth's tectonic plates, measure the Earth's gravitational field, measure the "wobble" in the Earth's axis of rotation, and better determine the length of an Earth day. LAGEOS 1 was developed by NASA and was placed into a high inclination orbit to permit viewing by ground stations located around the world. LAGEOS 2 was a joint program between NASA and the Italian space agency (ASI), which built the satellite using LAGEOS 1 drawings and specifications, handling fixtures, and other materials provided by NASA.
LAGEOS 2's orbit was selected to provide more coverage of seismically active areas, such as the Mediterranean Basin and California, and may help scientists understand irregularities noted in the motion of LAGEOS 1. 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 world-wide to investigators studying crustal dynamics. LAGEOS 1 also contains a message plaque addressed to human and other beings of the far distant future with maps of the Earth from 3 different eras - 268 million years in the past, present day, and 8 million years in the future (the satellite's estimated decay date). Spacecraft: Both satellites are spherical bodies with an aluminum shell wrapped around a brass core. The design was a compromise between numerous factors including the need to be as heavy as possible to minimise the effects of non-gravitational forces vs. being light enough to be placed in a high orbit and the need to accommodate as many retroreflectors as possible vs. the need to minimise surface area to minimise the effects of solar pressure. The materials were chosen to reduce the effects of the Earth's magnetic field on the satellite's orbit.426 cube-corner retroreflectors are imbedded in the satellites' surface.422 of these are made of fused silica glass while the other 4 are made of germanium. The vehicles have no onboard sensors or electronics, and are not attitude controlled. Payload: Science is performed by reflecting laser light from the vehicle's 426 retroreflectors.
Design Life: 50 years. Total Length: 0.6 m. Maximum Diameter: 0.6 m. Total Mass: 405 kg.
LAGEOS (Laser Geodetic Satellite) was a very dense (high mass-to-area ratio) laser retroreflector satellite which provided a permanent reference point in a very stable orbit for such precision earth-dynamics measurements as crustal motions, regional strains, fault motions, polar motion and earth-rotation variations, solid earth tides, and other kinematic and dynamic parameters associated with earthquake assessment and alleviation. The performance in orbit of LAGEOS was limited only by degradation of the retroreflectors, so many decades of useful life can be expected. The high mass-to-area ratio and the precise, stable (attitude-independent) geometry of the spacecraft, together with the orbit, made this satellite the most precise position reference available. Because it is visible in all parts of the world and has an extended operation life in orbit, LAGEOS can serve as a fundamental standard for decades. Additional Details: Lageos.
60 cm diameter sphere with laser reflectors; deployed from STS-52 10/23/92.