Two upcoming projects will demonstrate the feasibility of high-speed, long-distance laser communications.
Communications engineers have learned over the last several decades how to squeeze the maximum amount of bandwidth out of radio waves. But soaring data volumes and crowded spectrum are creating logjams that have prompted new efforts ranging from spectrum sharing technologies to laser communications.
NASA is preparing its next steps in its effort to demonstrate the feasibility of using high-capacity laser communications in space.
The Laser Communications Relay Demonstration (LCRD), scheduled to launch in 2019, will beam laser signals almost 25,000 miles from a ground station in California to a satellite in geostationary orbit, then relay that signal to another ground station.
Meanwhile, the Deep Space Optical Communications project is scheduled to launch in 2023 as part of an upcoming NASA Discovery mission. That mission will fly to a metallic asteroid, testing laser communications from a much greater distance than LCRD, program officials said.
In 2013, NASA demonstrated high-rate data transmission to the moon and back during its Lunar Laser Communication Demonstration. A NASA lunar orbiter, successfully sent data at a record rate of 622 megabit/sec, or six times the bandwidth of standard RF communications networks now used for space communications. The two-way optical system also delivered an error-free upload rate of 20 megabit/sec.
Lasers appear to be an ideal means of communicating in the vacuum of space. However, the optical technology remains prone to interference from clouds or atmospheric disturbances. As a result, planners note, ground stations would have to be designed and built in reliably clear areas. RF communications would serve as backups for low-data-rate spacecraft communications.The upcoming relay demonstrations "will allow us to test the performance over all different weather conditions and times of day and learn how to make the most of laser communications," said Dave Israel, space communications architect at NASA Goddard and principal investigator on LCRD.
A broadband communications pipe delivering higher-frequency laser communications promises to boost the amount and speed of data transmissions, making possible space applications such as real-time video links.
NASA also hopes to demonstrate that data can be relayed between optical links. Two ground stations would "work on the whole hand-over aspect" of the demonstration, Israel said. Other planned experiments include multiplexing data for use by multiple users at different locations and demonstrating a DVR-like "store/forward" capability that would allow video, for example, to be stored and relayed later at lower data rates.
It’s not just space researchers who stand to gain from faster communications, however. Such a capability would be of great interest to the military as it struggles to squeeze more bandwidth out of crowded electromagnetic spectrum for its unmanned platforms, sensors and other devices delivering real-time video and other large data sets.
The NASA laser relay demonstration will be carried to geosynchronous orbit as a hosted payload aboard a commercial communications satellite being built by Space Systems/Loral. MIT Lincoln Laboratories, which provided optical modules for the first laser communications demonstration, also is working on the upcoming relay demonstration.
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