NASA’s innovative experiment aboard its Psyche spacecraft has achieved a milestone by sending a laser-beamed message across the vast expanse of space. The remarkable transmission, dubbed “first light,” is the farthest-ever demonstration of optical communications to date. It is an essential step toward enabling mission data rates 10 to 100 times higher than current radio-telecommunications systems that power current spacecraft, paving the way for high-definition images and other critical science information for future human and robotic exploration missions, and even supporting our eventual human-crewed mission to Mars.
The Deep Space Optical Communications (DSOC) experiment successfully transmitted a near-infrared laser beam encoded with test data from nearly 10 million miles—approximately 40 times the distance between Earth and its moon—to the Hale Telescope located at Caltech’s Palomar Observatory in San Diego County, California. DSOC is the first of a series of technology demonstrations to be performed as part of the spacecraft’s two-year journey to study the metal asteroid 16 Psyche in the central asteroid belt between Mars and Jupiter. The Jet Propulsion Laboratory at Caltech in Pasadena manages the DSOC and Psyche mission for NASA.
Unlike traditional radio signals, which use electromagnetic waves, near-infrared laser communications encode data into photons — or individual particles of light — transmitted in a narrow pulse. The pulses are then detected by receivers, which decode the information into bits that computers can send and receive. The longer the pulses of light travel, the fainter they become, making it difficult to track their arrival precisely. This requires susceptible photon-counting cameras that can discern just a single photon.
To overcome this challenge, the DSOC ground and flight system uses cutting-edge technologies to ensure the lasers are on target. Earth and Psyche’s positions constantly change as the laser photons travel, so the pointing systems need to compensate, directing the transmitters to where they will be when the photons arrive.
At Psyche’s farthest distance from Earth, it will take 20 minutes for the photons to reach us, and the system will need to track and follow the signal accurately. This will require tremendously precise pointing, like a laser pointer tracking a dime at a mile’s distance.
Whether the lasers are aiming at a dime or a metallic asteroid, the goal is to achieve a continuous flow of data that enables NASA’s future missions to take full advantage of this revolutionary technology. The upcoming demonstrations will culminate in a high-data-rate communication link between DSOC and Psyche, capable of streaming scientific data at the level of HD video. The earliest of these milestones, to be completed in June 2018, will allow DSOC to receive a complete set of Psyche’s science data. That, in turn, will allow the team to understand better Psyche and the other metal asteroids in the central belt and help DSOC and Psyche prepare for the more ambitious transmissions planned for 2020 and beyond.
