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NASA preps laser demo, expects to break 622Mbit/s record

Posted: 12 May 2014 ?? ?Print Version ?Bookmark and Share

Keywords:NASA? LLCD? data transmission? laser communication? optical relay network?

NASA is yet again raising the bar on data transmission with another laser communications relay demonstration scheduled in 2017, following a successful high-rate data transmission to the moon and back last year. NASA claims that its success will lay the groundwork for an optical relay network that could power an interplanetary Internet with data rates that are a hundred fold higher than conventional communication satellites with the same mass and potential.

The Lunar Laser Communication Demonstration (LLCD) carried aboard a NASA lunar orbiter successfully transmitted data at a record rate of 622Mbit/s on October 17, 2013. The optical system delivered six times the bandwidth of standard radio-frequency communications networks now used for space communications. The two-way optical system also demonstrated an error-free upload rate of 20Mbit/s.

The download rate of the 0.5W laser system used in the lunar demonstration is roughly equivalent to streaming 30 HDTV channels simultaneously, program managers said. Measured another way, they said a Google map of Mars using current communications technology would require nine years. A future laser communications network could reduce mapping time to nine weeks.

NASA Administrator Charles Boldin noted in a message transmitted to the moon via the laser system that the trial was a precursor to a more ambitious demonstration later in the decade called the Laser Communications Relay Demonstration. "With optical communications, we'll be able to transmit more data so that future rovers on other planets and human missions to an asteroid and Mars will enjoy Internet-like connections," he claimed.

Clouds happen

Along with reducing power consumption and weight, laser-communications research has focused on correcting for the effects of atmospheric turbulence. Cloud cover was an issue during the October demonstration. During 50 test passes, clouds sometimes obscured the primary ground station at White Sands, N.M. Mission managers were able to shift operations to a Jet Propulsion Laboratory facility at Table Mountain, Calif. Another option in Spain at 4,267.2m was well above the cloud deck.

On April 17, 2014, between 21:30 and 22:22 PDT, NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft successfully completed a planned de-orbit, bringing an end to the mission to study the structure and composition of the thin lunar atmosphere.

NASA managers have already launched an effort to make future laser-based space networks "delay- and disruption-tolerant." The reason, acknowledged David Israel, NASA's principle investigator for the laser relay demonstration, is simple: "Clouds happen."

"The real trick was pointing a very narrow laser beam from 239,000 miles away to a four-mile area," at the White Sands ground station, added LLCD mission manager Don Cornwell. The initial challenge in pointing a laser in lunar orbit was accounting for the 1.5 second time difference it takes for a beam of light to reach Earth from the moon. Hence, controllers at NASA's Goddard Space Flight Centre in Maryland had to point the laser slightly ahead of the ground stations, much as a quarterback leads a receiver on a long pass.

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