The first time anyone has achieved one-way laser communication at planetary distances
Since mid-2009, NASA's Lunar Reconnaissance Orbiter has been, as its name would suggest, circling the moon. As its name would also suggest, the little satellite -- skimming the lunar service at a distance of 31 miles -- is also doing some scouting on our behalf: In its two-and-a-half years of lunar orbit, the satellite has created valuable gravitational maps of the moon, documented the trash humans have left on the lunar surface, and otherwise increased our knowledge about our nearest planetary neighbor.
Now, the lunar satellite has done something else, too: served as a surface for art. Specifically, for the most iconic piece of art we have: the Mona Lisa.
And the spacecraft has done that, unsurprisingly, in the service of science. Researchers at NASA Goddard wanted to test the capabilities of lasers as conduits for interplanetary communication -- and the LRO, as it turned out, was the only satellite orbiting around a body other than Earth that is currently tracked by laser. (For the most part, satellites orbiting non-Earth planets rely on radio waves for tracking and other communications.) And the Mona Lisa, for its part, was both easily recognizable and appropriately epic for some interplanetary artwork.
"Precise timing was the key to transmitting the image," NASA notes. The scientists first divided the Mona Lisa image into an array of 152 pixels by 200 pixels, converting each pixel into a shade of gray -- each shade, in turn, represented by a number between zero and 4,095. Each of those pixels was then transmitted from Earth (specifically, from NASA's Next Generation Satellite Laser Ranging, or NGSLR) by a laser pulse -- and that pulse was fired in one of 4,096 possible time slots during a brief time window allotted for laser tracking. This all meant that the complete image was transmitted at a data rate of about 300 bits per second.
The LRO's LOLA instrument used the pixels' arrival times from Earth as data points, reconstructing them based on those times back into ... the familiar half-frown of the Mona Lisa. The space-based version.
The iconic image traveled nearly 240,000 miles in digital form. Which isn't just an artistic feat. "By transmitting the image piggyback on laser pulses that are routinely sent to track LOLA's position," NASA notes, "the team achieved simultaneous laser communication and tracking." This achievement could mean that, in the not-too-distant future, similar laser communications could serve as valuable backups for the radio communications that satellites typically use. Later on, it might even allow communication at higher data rates than present radio links offer.
For the moment, though, it means this: You guys, we just sent the Mona Lisa to the moon.
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