NASA demonstrates laser communication between Earth and Lunar orbiter

Jan. 23, 2013
Greenbelt, MD--NASA Goddard Space Flight Center scientists beamed an image of the Mona Lisa to NASA's Lunar Reconnaissance Orbiter (LRO) a distance of 240,000 miles.

Greenbelt, MD--NASA Goddard Space Flight Center scientists beamed an image of the Mona Lisa to NASA's Lunar Reconnaissance Orbiter (LRO) a distance of 240,000 miles as part of the first demonstration of laser communicationalso typically called free-space optical communicationwith a satellite at the moon.

The iconic 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 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.

"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 (MIT; Cambridge, MA). "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."

Typically, satellites that go beyond Earth orbit use radio waves for tracking and communication. LRO is the only satellite in orbit around a body other than Earth to be tracked by laser as well. "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 (http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-2-1865) 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 x 200 pixels. Every pixel was converted into a shade of gray, represented by a number between zero and 4095. Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4096 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.

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 and DVDs. 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 demonstration 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.

The next step after LLCD is the Laser Communications Relay Demonstration (LCRD), NASA's first long-duration optical communications mission. LCRD will help develop concepts and deliver technologies applicable to near-Earth and deep-space communication.

SOURCE: NASA Goddard Space Flight Center; http://www.nasa.gov/mission_pages/LRO/news/mona-lisa.html

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.

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