Alexander Lewis
Nov 21, 2023
NASA's Psyche spacecraft, carrying out a deep space experiment, has achieved a remarkable feat by transmitting a message via laser to Earth from a distance surpassing anything previously accomplished.
The Deep Space Optical Communications (DSOC) project achieved a groundbreaking demonstration of optical communication. It successfully beamed a near-infrared laser carrying encoded test data from its location approximately 16 million kilometres away — nearly 40 times farther than the Moon's distance from Earth — to the Hale Telescope situated at Caltech's Palomar Observatory in California.
This significant milestone in optical communication was achieved during the DSOC's two-year technology demonstration aboard the Psyche spacecraft en route to its primary target, asteroid Psyche.
NASA's Jet Propulsion Laboratory (JPL), overseeing both missions, confirmed the "first light" event on November 14. This triumph was made possible through a meticulously precise manoeuvre where the DSOC's laser transceiver aligned with JPL's powerful uplink laser beacon at the Table Mountain Observatory, enabling the DSOC to direct its downlink laser to Caltech's observatory located 130 kilometres away.
While optical communications have been utilised from Earth's orbit previously, this latest feat marks an unprecedented distance covered by laser beams. Laser communication involves the transmission of data-packed photons travelling in sync and sharing the same wavelength. This method enables the encoding of an optical signal in infrared (invisible to humans) beams, delivering messages to a receiver.
NASA typically employs radio waves to communicate with missions beyond the Moon. However, the advantage of laser beams lies in their ability to carry substantially more data within tighter waves. The DSOC tech demo aims to demonstrate transmission rates 10-100 times faster than current top radio communication systems.
Enhanced data transmission capacity will enable future missions to accommodate higher-resolution scientific instruments and facilitate faster communications in potential deep space missions — potentially allowing live video streams from the surface of Mars.
However, there are challenges to overcome. As the distance for optical communication increases, precision in aiming the laser beam becomes more demanding. Additionally, the signal carried by photons weakens over longer distances, resulting in increased communication delays.
During the November 14 test, the photons took around 50 seconds to travel from Psyche to Earth. As Psyche moves farther away, the time for the photons to return is estimated to reach around 20 minutes, necessitating adjustments in the lasers' positions on both Earth and the spacecraft.
