NASA has made its first step beyond its more than 50 year-old radio wave-based Deep Space Network (DSN), to communicate with spacecraft.
The organization said that it successfully demonstrated that data can piggyback on its tracking lasers and transmit information at "planetary distances".
The demonstration consisted of individual pixels of an image, the portrait of Mona Lisa, that were sent via light impulses to the Lunar Reconnaissance Orbiter (LRO), which travels about 240,000 miles away from Earth. By knowing the location of the LRO via a tracking beam, NASA was able to use the laser simultaneously for data communication and tracking.
"This is the first time anyone has achieved one-way laser communication at planetary distances," said Lunar Orbiter Laser Altimeter'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."
The data transmission required the image to be reconstructed and corrected by the LRO, but the complete image was eventually received. The image had a resolution of 152 pixels by 200 pixels. "Every pixel was converted into a shade of gray, represented by a number between zero and 4,095," NASA said. "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 achieved data transmission rate was 300 bits per second.
Current radio transmission data rates heavily depend on the distance the signal has to travel. For example, signals from Voyager 1, the spacecraft currently farthest away from the distance, need more than 30 hours to reach Earth. The DSN is said, however, to deliver a "few megabits per second" of bandwidth at this time with more modern devices, such as the Mars rovers. In the future, NASA hopes to achieve as much as 600 Mb/s bandwidth with its space network.