Greenbelt, MD--Hosted aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) in lunar orbit, NASA's Lunar Laser Communication Demonstration (LLCD) confirmed laser communication capabilities from a distance of 400,000 km. In addition to demonstrating data download and upload speeds to the moon at 622 Mbit/s and 20 Mbit/s, respectively, the LLCD showed it could operate well under seemingly difficult conditions.
For example, the LLCD demonstrated error-free communications in broad daylight, including operating when the moon was to within 3º of the sun as seen from Earth. LLCD also demonstrated error-free communications when the moon was low on the horizon (less than 4º as seen from the ground station), which also showed that wind and atmospheric turbulence did not significantly impact the system. LLCD was even able to communicate through thin clouds, an unexpected bonus.
Operationally, LLCD demonstrated the ability to download data from the LADEE spacecraft itself. "We were able to download LADEE's entire stored science and spacecraft data [1 GB] in less than five minutes, which was only limited to our 40 Mbit/s connection to that data within LADEE," says Don Cornwell, LLCD mission manager at NASA's Goddard Space Flight Center. Using LADEE's onboard radio system would take several days to complete a download of the same stored data.
LLCD also demonstrated the ability to "hand-off" the laser connection from one ground station to another, just as a cellphone does a hand-off from one cell tower to another. An additional achievement was the ability to operate LLCD without using LADEE's radio at all. "We were able to program LADEE to awaken the LLCD space terminal and have it automatically point and communicate to the ground station at a specific time without radio commands," says Cornwell. "This demonstrates that this technology could serve as the primary communications system for future NASA missions."
Cornwell credits the work of Don Boroson and his team at the Massachusetts Institute of Technology's Lincoln Laboratory (MIT/LL; Lexington, MA) for developing and operating both the space and ground laser communications terminals for LLCD.
NASA's follow-on mission for laser communications will be the Laser Communications Relay Demonstration (LRCD). Also managed at Goddard, LCRD will demonstrate continuous laser relay communication capabilities at greater than 1 Gbit/s between two Earth stations using a satellite in geosynchronous orbit. The system also will support communications with Earth-orbiting satellites. More importantly, LCRD will demonstrate this operational capability for as long as five years, thus building more confidence in the reliability of this laser technology.
For more information about LLCD, see http://llcd.gsfc.nasa.gov
For more information about LCRD, see http://esc.gsfc.nasa.gov/267/LCRD.html
