The most well-known portrait of a woman in the world is over the moon — literally — after NASA managed to beam an image of the Mona Lisa directly to a satellite orbiting the lunar body.
How far did she have to travel? Nearly 240,000 miles, says NASA, shot by laser from the agency’s Goddard Space Flight Center in Greenbelt, Maryland to an instrument on NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft called the Lunar Orbiter Laser Altimeter, or LOLA.
NASA routinely uses lasers to track the LRO’s altimeter as it orbits the moon, and back in 2006 we were sending laser pulses between NASA spacecraft and Earth-based observatories separated by millions of miles. The wrinkle here: This was apparently the first time we’ve managed one-way laser communication at planetary distances, says LOLA principal investigator David Smith with MIT.
To send the Mona Lisa into space required flawless digital timing. First, a black and white version of the famous Italian painting was broken into a 152 x 200 pixel grid, with each pixel represented by a number between zero and 4,095 that corresponded to a shade of gray. Those values were then transmitted, one at a time, in 4,096 discrete bursts at a rate of about 300 bits per second.
On the receiving end, LOLA was able to reassemble the precise grayscale values based on the arrival times of each pulse, and NASA says it managed to do so without interrupting the LRO’s primary job of mapping the moon’s elevation and terrain. Where the earth’s atmosphere interfered, causing pixel errors, NASA employed the same error-correction code algorithm used with CDs and DVDs to smooth things over.
“In the near future, this type of simple laser communication might serve as a backup for the radio communication that satellites use,” said Smith. “In the more distant future, it may allow communication at higher data rates than present radio links can provide.”