NASA tests laser communications by sending Mona Lisa to space
NASA scientists usually use lasers to track the position of its Lunar Reconnaissance Orbiter (LRO) – the robotic spacecraft that creates gravitational maps of the moon. It collects the information then transmits it back to earth at a rate of 50 Mbs.Then NASA scientists had the bright idea of reversing the flow by beaming an image of the Mona Lisa to the LRO using lasers. "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."The picture was transmitted to the LRO spacecraft, because it is the only satellite that has a laser receiver.
Precise timing was the key to transmitting the simplified black and white image, because the laser pulse has to hit a small target a very very long way away. The first attempt to reassemble the image was not successful, the quality of the picture was significantly degraded. Atmospheric turbulence and a slight pause in transmission caused errors, making the resulting image grainy, distorted and incomplete. The scientists then applied the same kind of data correction methods used for CDs and DVDs, which substantially helped clear up the image.A data rate of 300 bits per second is woefully slow compared to what is possible with cables or radio, so NASA has come up with a new experimental laser they hope will be capable of transmitting 600 million bits per second. This system will be carried by the Lunar Atmosphere and Dust Environment Explorer satellite, which is to be launched in August. This is just one aspect of NASA’s planned research into laser communications. In 2017 it plans to start a new experiment called Laser Communications Radar Demonstration – a commercial satellite that is going to test beam-based communication systems. Theoretically the speed and volume of information that can the transferred by laser is an order of magnitude greater than the rates attainable with radio waves.