Starting in 2019, NASA will begin using laser communications technology to "enable greater return of science data from space."
The reason is laser is more bandwidth-friendly than classic radio for data delivery, plus it's more secure, NASA says in a newly released explainer of its plans.
Laser signals from space will be much harder to hack than old-school radio because the signal is more concentrated, the agency says on its website. Plus, the higher frequencies provide more bandwidth — important for space data crunching. And laser equipment is lighter, allowing for longer missions, among other benefits.
“Laser beams, which are forms of light waves, expand at a much lower rate than the radio frequency waves that traditionally transport space data,” NASA’s Exploration and Space Communications arm says. “They, therefore, cover less surface area” and are thus harder to intercept.
NASA has started testing satellite payload for its project. The Laser Communications Relay Demonstration (LCRD) will pump data back to Earth at 10 to 100 times faster rates than existing radio, it says. That’s a nine-week data-send time from Mars rather than the current radio-based nine years — its estimate for a Google-style map of the entire planet surface.
The challenges of laser communications
Laser is not as easy as radio, though, NASA explains. That’s partly because the Earth’s rotation, coupled with the amount of time it takes data to reach the ground station from the spacecraft — albeit faster than radio — means tricky timing calculations are needed to determine where the narrower laser needs to hit. Traditional radio simply needs a data dump, from space, in the vicinity of the ground receiver, whereas laser needs to be continually connected during the transmission.
The agency intends to employ a special locking, pointing mechanism. The idea is that a pre-scheduled passing craft’s telescope picks up a finder-signal sent from the ground station. That allows the transmitter to lock on. Mirrors in the spacecraft’s laser modulator are driven by sensors, and they send the beam.
Using the LCRD, NASA is aiming for a 1.24 Gigabits per second, geosynchronous-to-ground optical link with two ground stations. The first flight, run by NASA's Goddard Space Flight Center in Greenbelt, Maryland, is expected to take place next year. The LCRD's 2019 experiment “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,” NASA said on its website.
Other applications for laser-based data transmission
Other organizations, such as Google-owner Alphabet’s subsidiary X, have expressed interest in using laser-based carriers but terrestrially. X, for example, is setting up as an ISP that — instead of using wireless and cables — places Free Space Optical Communications (FSOC) laser-containing boxes within line of sight every few miles.
Work has been wide-reaching and includes network development. One thrust has been in how to send the data over the difficult distances using low overheads and with no loss. I’ve written about the Disruption or Delay Tolerant Networking that’s being used, recently. The protocol is supposed to guarantee delivery when traffic gets kiboshed. Clouds can be an issue, for example. That networking idea could have uses in land-based internet, too — it works by storing data at nodes rather than at the originating transmitter.
“Testing laser communications in geostationary orbit, as LCRD will do, has practical applications for data transfer on Earth,” NASA says. In fact, X says its FSOC land ISP project is in part inspired by balloon-to-balloon internet FSOC tests in the stratosphere.