Editing LAGEOS (section)

== Function and operation ==
The spacecraft are [[aluminum]]-covered [[brass]] spheres with diameters of {{convert|60|cm}} and masses of {{convert|400|and|411|kg|lbs|abbr=off}}, covered with 426 cube-corner [[retroreflector]]s, giving them the appearance of [[disco ball]]s.<ref>{{cite web|url=https://science.nasa.gov/missions/lageos-1-2/ |title=Missions - LAGEOS 1&2 - NASA Science |website=Science.nasa.gov |date=1976-05-04 |accessdate=2016-02-22}}</ref><ref>Kramer, Herbert J. (2013) [https://books.google.com/books?id=U3v1CAAAQBAJ&pg=PA149 ''Observation of the Earth and its Environment: Survey of Missions and Sensors''] Springer {{ISBN|9783662090381}} p149</ref><ref>[https://history.nasa.gov/SP-4012/vol3/table4.166.htm LAGEOS Characteristics] ''NASA Historical Data Book'' Volume III Table 4-166 SP-4012</ref> Of these retroreflectors, 422 are made from fused silica glass while the remaining 4 are made from germanium to obtain measurements in the infrared for experimental studies of reflectivity and satellite orientation.<ref name="ILRSLageos"/> They have no on-board sensors or electronics, and are not [[Spacecraft attitude control|attitude-controlled]].

They orbit at an altitude of {{convert|5900|km}},<ref name="LageosQL">{{cite web|url=http://space.jpl.nasa.gov/msl/QuickLooks/lageosQL.html |accessdate=March 31, 2011 |title=JPL Mission and Spacecraft Library, Lageos |website=space.jpl.nasa.gov|archiveurl=https://web.archive.org/web/20110721062751/http://space.jpl.nasa.gov/msl/QuickLooks/lageosQL.html|url-status=dead |archivedate=2011-07-21 }}</ref> well above [[low Earth orbit]] and well below [[geostationary orbit]], at orbital inclinations of 109.8 and 52.6 degrees.

Measurements are made by transmitting pulsed laser beams from Earth [[ground station]]s 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 make it possible to determine positions of points on the Earth with extremely high [[Accuracy and precision|accuracy]] due to the stability of their orbits.
The high [[volume-to-area ratio|mass-to-area ratio]] and the precise, stable ([[attitude (geometry)|attitude]]-independent) geometry of the LAGEOS spacecraft, together with their extremely regular orbits, make these satellites the most precise position references available.