ACM News 23/01/2013
The U.S. National Aeronautics and Space Administration (NASA) used laser technology to transmit an image of the Mona Lisa to the moon by beaming it to the Lunar Reconnaissance Orbiter (LRO) along with routine tracking data. “Because LRO is already set up to receive laser signals through the [Lunar Orbiter Laser Altimeter (LOLA)] instrument, we had a unique opportunity to demonstrate one-way laser communication with a distant satellite,” says NASA scientist Xiaoli Sun. The Mona Lisa was reduced to 152 by 200 pixels, and each pixel was sent to the LOLA during the brief interval when the laser beam was not occupied by tracking and mission data. The data pulse was delayed to determine how much to darken a pixel, while the amount of shading for each pixel was ascertained by the time differential between when the LRO expected to receive the data and the actual time of the data’s arrival. Assembling the image on the other end without interruption was accomplished through use of the Reed-Solomon error-correcting code. “This is the first time anyone has achieved one-way laser communication at planetary distances,” notes the Massachusetts Institute of Technology’s David Smith.