The spacecraft are aluminum-covered brass spheres with diameters of and masses of, covered with 426 cube-corner retroreflectors, giving them the appearance of giant golf balls. 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. They have no on-board sensors or electronics, and are not attitude-controlled. They orbit at an altitude of, 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 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 make it possible 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 geometry of the LAGEOS spacecraft, together with their extremely regular orbits, make these satellites the most precise position references available.
Mission goals
The LAGEOS mission consists of the following key goals:
Provide an accurate measurement of the satellite's position with respect to Earth.
Ground tracking stations located in many countries have ranged to the satellites and data from these stations are available worldwide to investigators studying crustal dynamics. There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976, and LAGEOS-2 launched in 1992., both LAGEOS spacecraft are routinely tracked by the ILRS network.
Time capsule
LAGEOS-1 also contains a plaque designed by Carl Sagan to indicate to future humanity when LAGEOS-1 was launched. The plaque includes the numbers 1 to 10 in binary. In the upper right is a diagram of the Earth orbiting the Sun, with a binary number 1 indicating one revolution, equaling one year. It then shows 268435456 years in the past, indicated by a left arrow and the arrangement of the Earth's continents at that time. The present arrangement of the Earth's continents is indicated with a 0 and both forward and backward arrows. Then the estimated arrangement of the continents in 8.4 million years with a right facing arrow and 8388608 in binary. LAGEOS itself is shown at launch on the 0 year, and falling to the Earth in the 8.4 million year diagram.
Launch data
LAGEOS 1, launched 4 May 1976, NSSDC ID 1976-039A, NORAD number 8820
LAGEOS 2, deployed 23 October 1992 from STS-52, NSSDC ID 1992-070B, NORAD number 22195
