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This Glittery Gem is in Orbit Helping us Measure the Shape of our Planet

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This ridiculous rhinestone-studded disco-ball is actually a high-precision laser-reflecting satellite still in orbit around the Earth. With only tiny reflectors and no active instruments, it’s provided vital data on the planet’s shape for decades.

The Laser Geodynamics Satellite I (LAGEOS I) launched out of Vandenberg Airforce Base on May 4, 1976. The 407 kilogram (900 pund), 0.6 meter (2 foot) diameter sphere is made from materials that won’t react to the Earth’s magnetic field, and is passive so has no on-board electronics or sensors.


Construction of the LAGEOS I satellite. Image credit: NASA

The aluminum-coated brass sphere is studded with 426 cube corner reflectors. As the first satellite dedicated to high-precision laser ranging, 422 reflectors were made of fused silica glass; the last four were made from germanium for infrared light.


Final launch preparations of LAGEOS I. Image credit: NASA

The satellite also carries a plaque designed by Carl Sagan. The 10 centimeter by 18 centimeter (4 inch by 7 inch) stainless steel plate was a roadmap to Earth akin to the famous Voyager plaques. It contains:

  • Binary digits from 1 to 10;
  • Schematic of Earth in orbit around the Sun, with directional arrows; and
  • 3 maps of the Earths’ surface, marking tectonic changes from 268 million years ago, the present, and an estimate of what the surface will look like 8.4 million years from now.

The plaque mounted on the LAGEOS sphere. Image credit: NASA

Its primary purpose was to measure the Earth’s shape by passively reflecting laser beams from terrestrial ground stations. As an added bonus the satellite also gave NASA their first chance to look into reflectivity and satellite orientation without degradation from satellite orbits or arrays. Distance measurements from bouncing lasers of LAGEOS are used to track changes in the Earth’s surface from continental drift or in its gravitational field from earthquakes and other geophysical phenomena, and to act as a reference point to measure the Earth’s wobble around its axis. It has also been used to confirm frame dragging, the general relativity phenomena where the mass of the Earth warps spacetime.


The geodetic experiment is still in an incredibly stable orbit around the Earth, looping past the poles every 225 minutes. It has no attitude control, so there is no way to adjust its orbit.


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