In an experiment involving a spacecraft en route to the planet Mercury, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Md., and at MIT in Cambridge, Mass., have exchanged laser pulses with the Messenger probe over a distance of nearly 24 million kilometers. Reported in the Jan. 6 issue of Science, the simulation of two-way data communications over an interplanetary distance further indicates the practicability of such high-bandwidth optical solutions in space exploration missions.
In a series of tests of Messenger’s laser altimeter in May 2005, the researchers directed the craft to fire 6-ns, 18-mJ pulses of 1064-nm radiation from its Nd:YAG laser and to record the detection of 10-ns, 15-mJ pulses from a similar laser fired at it from an observatory on Earth to represent echoes. To interpret the exchanges as transmissions, they tagged the events using the spacecraft’s clock, a quartz oscillator stable to approximately one part per billion, and solved for a common range and clock offset.
A full report by the NASA scientists on this work will appear in a future issue of Photonics Spectra.

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