Wireless broadband service went cosmic in a demo conducted by the Massachusetts Institute of Technology's (MIT) Lincoln Laboratory and NASA, in which a laser-based communication uplink between the moon and earth beat the previous record transmission speed by a factor of 4,800.
The ground terminal, with the sun reflecting off of the solar windows of the uplink telescopes. (Photo by Robert LaFon, NASA/GSFC)
The demo proved that "a data communication technology exists that can provide space dwellers with the connectivity we all enjoy here on earth, enabling large data transfers and even high-definition video streaming," MIT said. It added that this technology is extendable to deep-space missions to Mars and the outer planets.
The demo was conducted last fall, and MIT is finally releasing details of the implementation at the CLEO: 2014 event, which will be held June 8-13 in San Jose, Calif.
The team's Lunar Laser Communication Demonstration (LLCD) transmitted data over the 384,633 kilometers between the moon and earth at a download rate of 622 Mbps. In addition, data was transmitted from the earth to the moon at 19.44 Mbps, a factor 4,800 times faster than the best radio-frequency uplink ever used, MIT said.
"Communicating at high data rates from earth to the moon with laser beams is challenging because of the 400,000-kilometer distance spreading out the light beam," said Mark Stevens of MIT Lincoln Laboratory. "It's doubly difficult going through the atmosphere, because turbulence can bend light--causing rapid fading or dropouts of the signal at the receiver."
The demo employed several techniques over a wide range of optically challenging atmospheric conditions in both darkness and bright sunlight, MIT said.
A ground terminal at White Sands, N.M., used four separate telescopes, each about six inches in diameter, to send the uplink signal to the moon. Each telescope was fed by a laser transmitter that sent information coded as pulses of invisible infrared light.
Four telescopes were needed because each one transmitted light through a separate column of air that experienced different bending effects from the atmosphere, Stevens said, increasing the chance that at least one of the laser beams would interact with the receiver mounted on a satellite orbiting the moon. The receiver used a slightly narrower telescope to collect the light, which then focused into an optical fiber.
At that point, the signal in the fiber was amplified some 30,000 times. A photo-detector converted the pulses of light into electrical pulses, which were converted into data bit patterns that carry the transmitted message.
MIT said its upcoming presentation will also describe how the large margins in received signal level can allow the system to operate through partly transparent thin clouds in the earth's atmosphere.
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