May 05, 2016

On May 4, 1976, NASA launched a cannonball-shaped satellite that transformed studies of Earth’s shape, rotation and gravity field.
LAGEOS – short for Laser Geodynamic Satellite – was the first NASA orbiter dedicated to the precision measurement technique called laser ranging. With it, scientists have measured the movement of Earth’s tectonic plates, detected irregularities in the rotation of the planet, weighed it, and tracked small shifts in its center of mass.

Small deviations in the satellite’s orbit were used to develop early models of Earth’s gravitational field. Further perturbations in the orbit helped explain how sunlight heating small objects can affect their orbits, including near-Earth asteroids.
Built to last, the 900-pound (about 400 kilograms) satellite is passive, with no on-board sensors or electronics and no moving parts. Its brass core is covered by an aluminum shell that is dotted with 426 retroreflectors, making the satellite look like a giant golf ball.

“LAGEOS is elegantly simple – a ball covered with reflecting prisms,” said Stephen Merkowitz, manager of NASA’s Space Geodesy Project at the agency’s Goddard Space Flight Center in Greenbelt, Maryland. “But it set a new standard for laser ranging and has provided 40 years of continuity for these measurements.”
The satellite was launched from the Vandenberg Air Force Base in California. The design, development and construction of the orbiter was managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.

Image:
(A) Half-scale model of LAGEOS satellite.
(B) The surface of LAGEOS is dotted with 426 cube-corner prisms to reflect laser pulses transmitted from ground stations on Earth. One sector of a model is shown here. With LAGEOS, the accuracy of laser ranging measurements improved from about 3 feet (1 meter) to less than half an inch (1 centimeter).

(C) LAGEOS carries a plaque designed by Carl Sagan to be a message to future civilizations. At the top, the numbers one through 10 are written in binary notation, and Earth is shown orbiting the sun. The three lower panels depict maps of Earth at different epochs. One shows Earth 268 million years ago, when the continents were joined as the land mass Pangaea. The middle map shows the continents when LAGEOS launched. The last panel projects the configuration 8.4 million years in the future – when the satellite was predicted to fall to Earth.