Satellites play chase to measure gravity, achieve picometer accuracy


Enlarge (credit: NASA/JPL-Caltech)

The spinoffs from gravitational wave detectors are not just new scientific discoveries. The technology also has other uses. A good example of this is the gravity-measuring mission, GRACE Follow On, which was launched last year. The first reports on its laser rangefinder’s performance have been released, and it makes for impressive reading.

Gravitational wave detectors work by measuring tiny changes in the distance between two mirrors. Ripples in space-time cause a tiny oscillation in that distance, which is then detected by comparing the phase shift between light that has traveled between the two mirrors and light that has traveled along a path that was unaffected by the gravitational wave. To put it in perspective, a gravitational wave detector measures changes that are far smaller than the diameter of an atom and are more like the diameter of a single proton.

The gravity of GRACE

Similar technology found its way into space to increase the sensitivity of Earth-monitoring instruments. On Earth, we have stationary detectors that wait for gravitational waves to pass through them. In orbit, the detector is moving and can measure subtle changes in the Earth’s gravitational field.

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