A NASA experiment on the Psyche spacecraft has beamed back a near-infrared laser that contains test data from almost 16 million kilometres away. The distance is 40 times that between the Moon and the Earth and is the farthest-ever demonstration of optical communications, according to the space agency.
NASA’s Deep Space Optical Communications (DSOC) experiment is riding aboard the Psyche spacecraft, which was launched recently. DSOC will be used to send high-bandwidth test data to our planet as psyche travels to the main asteroid belt between Mars and Jupiter.
The space agency announced last week that the technological demonstration achieved “first light” in the early hours of November 14 after its flight laser transceiver, locked onto a powerful uplink laser beacon transmitted from the Optical Communications Telescope Laboratory at NASA’s Table Mountain Facility in California.
The transceiver is a high-tech instrument on Psyche that is capable of sending and receiving near-infrared signals. It was able to aim its downlink laser back to Palomar, which is about 130 kilometres south of Table Mountain, with help from the uplink beacon. Automated systems on the transceiver and ground station fine-tuned the pointing and receiving of the laser communication.
Optical communications have been demonstrated previously in low-Earth orbit and even to the Moon, but DSOC is the first test in deep space. Imagine using a laser to track a one rupee coin that is moving very fast about a kilometre away. Using lasers to communicate with a spacecraft in deep space millions of kilometres away is many orders of magnitude more difficult than that, requiring very precise “pointing.”
The pointers and the receivers also need to compensate for the time that light takes to travel such vast distances. At Psyche’s farthest distance from our planet, the near-infrared laser rays will take about 20 minutes to travel to our planet. In that time, both the spacecraft and the planet will have moved relative to each other. This means that the uplink and downlink lasers will have to point to where the spacecraft and planet will be at that point in time, instead of where it is at the moment of transmission.
