NASA's satellites study earth, powered by Aluminium

Aluminium is called the ‘Metal of the Future’, and rightly so. It forms the basis of futuristic technologies and objects such as rockets and satellites which take human endeavours further. NASA’s LAGEOS satellites launched 41 years ago into space speak volumes about innovation and the passion of our species to go beyond in search of knowledge.

LAGEOS - LAser GEOdynamics Satellite or LAser Geometric Environmental Observation Survey, are a series of two scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth. The cannonball shaped satellites have transformed the area of precision measurement technique called laser ranging to measure the movement of Earth’s tectonic plates, detected irregularities in the rotation of the planet. Scientists have able to track small shifts in the earth’s centre of mass.

The LAGEOS mission was created with these goals in mind:

Provide an accurate measurement of the satellite's position with respect to Earth.
Determine the planet's shape (geoid).
Determine tectonic plate movements associated with continental drift.

There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976, and LAGEOS-2 launched in 1992. These satellites have been constructed in such a way that they have a high mass-to-area ratio which is crucial for precise measurements to determine positions of points on the Earth and simultaneously provide much stability (attitude-independent geometry).

The main components of the satellites are a large number of retroreflectors, 426 to be precise. 422 of the retroreflectors 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 onboard sensors or electronics.

The satellite was designed to accommodate these retroreflectors in a way that would not be affected by solar radiation drag. Aluminium would have been too light for the entire body of the sphere, while brass would have weighed too much. Design engineers finally decided on combining two aluminium hemispheres bolted together around a brass core to provide a large mass/surface ratio. Materials were selected to reduce magnetic effects between the satellite and the Earth's magnetic field. They took the shape of a gigantic golf ball!

They orbit at an altitude of 5,900 kilometres (3,700 mi), 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.

REF:

https://youtu.be/zWphd6HAaHA
https://lageos.cddis.eosdis.nasa.gov/Design/index.html
https://en.wikipedia.org/wiki/LAGEOS
https://www.nasa.gov/feature/goddard/2016/now-40-nasas-lageos-set-the-bar-for-studies-of-earth

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