Scientists with NASA's Lunar Reconnaissance Orbiter (LRO) - the only satellite in orbit around a body other than
Earth to be tracked by laser - beamed an image of the Mona Lisa to the spacecraft from Earth.
The image traveled nearly 240,000 miles in digital form from the Next Generation Satellite Laser Ranging
(NGSLR) station at NASA's Goddard Space Flight Center in Greenbelt, Md., to the Lunar Orbiter Laser Altimeter
(LOLA) instrument on the spacecraft.
By transmitting the image piggyback on laser pulses that are routinely
sent to track LOLA's position, the team achieved simultaneous laser communication and tracking.
Click on image to enlarge
To clean up transmission errors introduced by Earth's atmosphere (left), Goddard scientists applied Reed-Solomon
error correction (right), which is commonly used in CDs and DVDs. Typical errors include missing pixels (white) and
false signals (black). The white stripe indicates a brief period when transmission was paused. Image courtesy: Xiaoli Sun, NASA Goddard
"This is the first time anyone has achieved one-way laser communication at planetary distances," says
LOLA's principal investigator, David Smith of the Massachusetts Institute of Technology.
"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."
NASA Goddard scientists transmitted an image of the Mona Lisa from Earth to the Lunar Reconnaissance
Orbiter at the moon by piggybacking on laser pulses that routinely track the spacecraft.
Credit: NASA's Goddard Space Flight Center
"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," says Xiaoli Sun, a LOLA scientist at NASA Goddard
and lead author of the Optics Express paper, posted online today, that describes the work.
Precise timing was the key to transmitting the image. Sun and colleagues divided the Mona Lisa image into an array
of 152 pixels by 200 pixels. Every pixel was converted into a shade of gray, represented by a number between zero
Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4,096 possible time
slots during a brief time window allotted for laser tracking. The complete image was transmitted at a data rate of
about 300 bits per second.
The laser pulses were received by LRO's LOLA instrument, which reconstructed the image based on the arrival times
of the laser pulses from Earth. This was accomplished without interfering with LOLA's primary task of mapping the
moon's elevation and terrain and NGSLR's primary task of tracking LRO.
The success of the laser transmission was verified by returning the image to Earth using the spacecraft's radio
Turbulence in Earth's atmosphere introduced transmission errors even when the sky was clear. To overcome these effects,
Sun and colleagues employed Reed-Solomon coding, which is the same type of error-correction code commonly used in CDs
The experiments also provided statistics on the signal fluctuations due to Earth's atmosphere.
"This pathfinding achievement sets the stage for the Lunar Laser Communications Demonstration (LLCD), a high data rate
laser-communication demonstrations that will be a central feature of NASA's next moon mission, the Lunar Atmosphere
and Dust Environment Explorer (LADEE)," says Goddard's Richard Vondrak, the LRO deputy project scientist.