Thorfinn.au (1140205) writes "A group of JPL scientists, working on improving space-scale laser ranging, believe they could one day measure the distance from Earth to Mars with millimetre accuracy.
If their scheme were adopted, it would have to wait until a new Mars mission takes place to put a laser on the red planet. That's because, unlike Earth-Moon laser ranging, which uses reflectors on the Moon, the new design calls for lasers at both ends of the measurement.
The problem with reaching beyond Earth-Moon distances, the researchers explain, is that the signal falls off by the radius to the power of four – which puts Mars out of reach. An active scheme only deteriorates by R squared, which extends distances “thousands of times”."
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