In internet engineering, there’s a problem called the “last half mile," which looks at how to connect users to high-speed fiber optic networks without going through old-fashioned copper wires that can slow data down to a crawl. NASA has more of a “last 250 miles” problem in making data connections with the International Space Station (ISS). The upcoming Optical Payload for Lasercomm Science (OPALS) project is an optical technology demonstration for using lasers to improve communications with the ISS and other spacecraft in hopes of boosting connection speeds by a factor of 10 to 100.
You’d think that lasers and space travel would go together like Captain Kirk and phasers, but aside from zapping rocks on Mars, they don’t get much of a look in – at least, in terms of shooting them across thousands of miles. True, scientists bounced a laser off the Moon in 1962 and they've been aiming them at reflectors set up on the lunar surface by the Apollo astronauts, or in geodetic satellites, but otherwise all the long distance stuff has been pretty much left to the radio bands.
Space travel is currently undergoing something of a renaissance, however, as commercial companies take a greater interest in the final frontier. The problem is that as technology becomes more sophisticated and the missions more ambitious, the communications systems need to keep up with an ever increasing flow of information. Conventional radio links are like hooking an old telephone line to a fiber optic cable, so something better is needed. In the case of OPALS, it’s lasers.
"OPALS represents a tangible stepping stone for laser communications, and the International Space Station is a great platform for an experiment like this," says Michael Kokorowski, OPALS project manager at the Jet Propulsion Laboratory (JPL) in Pasadena, California. "Future operational laser communication systems will have the ability to transmit more data from spacecraft down to the ground than they currently do, mitigating a significant bottleneck for scientific investigations and commercial ventures."
OPALS consists of a sealed container holding the avionics in a pressurized environment. This is connected to an optical gimbal transceiver, an uplink camera and a laser collimator. The package will be sent to the ISS in December aboard a Dragon supply ship and will be mounted outside the station where it will run for 90 days.
Back on Earth, JPL’s Optical Communications Telescope Laboratory in Wrightwood, California will shoot out a laser beacon through its telescope in the direction of the ISS. The OPALS package will home in on this and lock on using a closed loop control system and a two-axis gimbal. When the line of sight is clear, the system will download a formatted video using a laser beam for 100 seconds.
"It's like aiming a laser pointer continuously for two minutes at a dot the diameter of a human hair from 30 feet away while you're walking," says OPALS systems engineer Bogdan Oaida of JPL.
Since a laser has much greater bandwidth than a radio transmission, success should greatly increase the download speed.