Using lasers to communicate at planetary distances is something that may sound like sci-fi, but it is a real technology being developed by NASA as a means of communicating with spacecraft faster and more efficiently than can be done now.
The latest test had a distinctly artistic feel to it - an image of the Mona Lisa was beamed from Earth to the Moon, or more specifically the Lunar Reconnaissance Orbiter spacecraft nearly 386,000 kilometres (240,000 miles) away, using the Lunar Orbiter Laser Altimeter (LOLA) instrument.
As LOLA's principal investigator, David Smith, explains, "This is the first time anyone has achieved one-way laser communication at planetary distances. In the near future, this type of simple laser communication might serve as a backup for the radio communication that satellites use. In the more distant future, it may allow communication at higher data rates than present radio links can provide."
The image was sent by piggybacking it on laser pulses used to track the spacecraft's position in lunar orbit. LRO is the only orbiting spacecraft (of any solar system body other than Earth) to be tracked by laser as well as radio waves. The image was then successfully returned to Earth by LRO using radio telemetry.
"Because LRO is already set up to receive laser signals through the LOLA instrument, we had a unique opportunity to demonstrate one-way laser communication with a distant satellite," according to Xiaoli Sun, a LOLA scientist at NASA Goddard. He is also the lead author of the Optics Express paper which describes the experiment.
The image was 152 pixels by 200 pixels in size, and converted into shades of grey. To compensate for transmission errors caused by turbulence in Earth's atmosphere, the scientists used Reed-Solomon coding, the same process used for CDs and DVDs. The data rate for transmission was about 300 bits per second.
The technology will be used in the next planned lunar mission, the Lunar Atmosphere and Dust Environment Explorer (LADEE).
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