Instead of having two independent satellites, it had two sets of accelerometers at opposite ends of one, long, tubelike satellite, which each measured gravity at their end of the satellite.īoth experiments were able to generate maps of the Earth’s gravitational field strength from their locations in orbit. NASA/JPL-CaltechĮSA has also had one of these earth-measuring satellites, called GOCE (Gravity field and steady-state Ocean Circulation Explorer) which operated between 20. ![]() Any deviations in their relative distances should be due to something down below, on Earth.Īrtist's rendering of the twin satellites that will compose NASA's Gravity Recovery and Climate. It was a pair of satellites, launched in 2002, which bounced microwaves back and forth between them, very precisely measuring the distance between them, to a sensitivity of about a micron (many times smaller than the width of a human hair.) By additionally communicating with GPS satellites, the GRACE satellites were able to precisely communicate both their absolute positions in orbit around the Earth ( to a precision of about a centimeter), and their motions relative to each other. We can do the exact same thing for pairs of satellites around the Earth, and we have! The Gravity Recovery and Climate Experiment (GRACE) is a NASA mission to do precisely this. ![]() These tiny changes in the distance between the two satellites allow us to map out the density of the ground below, but it's fundamentally a measure of the strength of the gravitational pull of the ground below the satellites. As the satellites go over high density regions, the one of them will feel an increased pull before the other, and the distance between the two satellites will change. Earth’s center of gravity can be located! We talked a few months ago about measuring the force of gravity surrounding the Moon, and that the way we do this measurement is by having twin satellites, and calculating the difference in gravitational pull on each satellite.
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