Working from moon? Forget dial-up speeds. A team of MIT and NASA researchers is demonstrating a laser-based data communication technology that provides space workers (or maybe even dwellers) with the connectivity we have on Earth. That means large data transfers and high-definition video streaming from and on the lunar surface.
Last fall, the on-orbit performance of their moon-to-Earth uplink shattered previous transmission speed records. Now they’ve got the underlying physics sorted out, and they think the technology could even extend into deep-space missions to Mars.
The Lunar Laser Communication Demonstration (LLCD) transmitted over 384,633 kilometers between here and the moon at a download rate of 622 megabits per second. They also sent data from Earth to the moon at 19.44 megabits per second. That’s 4,800 times faster than the best radio frequency uplink ever used.
“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,” Mark Stevens of MIT Lincoln Laboratory says in a news release. “It’s doubly difficult going through the atmosphere, because turbulence can bend light -- causing rapid fading or dropouts of the signal at the receiver.”
To avoid a fading signal over such a distance, they employed several techniques to help overcome a wide range of atmospheric conditions, in both darkness and light, and through clouds in our atmosphere.
A ground terminal (pictured below) at White Sands, New Mexico, uses four telescopes to send the uplink signal to the moon. Each telescope is about 15 centimeters in diameter and fed by a laser transmitter that sends information coded as pulses of infrared light. The four separate transmitters combined results in 40 watts of power.
Each telescope transmits light through a different column of air experiencing different bending effects from the atmosphere. This increases the chance that at least one of the laser beams will interact with the receiver mounted on a satellite that’s orbiting the moon.
The receiver (top photo) collects the light using a narrow telescope. The light is focused into an optical fiber (like the ones used in our fiber optic networks), and the signal is amplified 30,000 times. The pulses of light are converted into electrical pulses, and these, finally, are converted into data bit patterns that carry the transmitted message.
Of the 40-watt signals sent by the transmitters, less than a billionth of a watt is received at the satellite. “But that’s still about 10 times the signal necessary to achieve error-free communication,” Stevens says.
The work will be presented at the Conference on Lasers and Electro-Optics (CLEO) next month.
[Via The Optical Society]
Images: NASA (top) & Robert LaFon, NASA/GSFC (middle)