Space communications are progressing rapidly, pushing technological boundaries. The transmission of data over vast distances constitutes one of the major challenges for the exploration of the cosmos. A recent innovation in this area is capturing the attention of the scientific community and expanding the possibilities for future interplanetary missions.
A record for laser communication in deep space
NASA’s Deep Space Optical Communications technology demonstration reached a new threshold this summer. A laser signal was sent from Earth to the Psyche space probelocated approximately 460 million kilometers away. This technical feat is equivalent to communicating with Mars when the Red Planet is at its farthest point from Earth.
On July 29, 2024, shortly after reaching this milestone, the initial phase of operations for this technology demonstration concluded. The launch of the experiment was carried out on October 13, 2023, aboard the Psyche probe.
Meera Srinivasan, project operations manager at NASA’s Jet Propulsion Laboratory (JPL) in Southern California, explained: “The importance of this milestone is considerable. Laser communication requires a very high level of precision, and before launching with Psyche, the extent of performance degradation at our furthest distances remained unknown. Now, the techniques used for tracking and pointing have been validated, confirming that optical communications can provide a robust and transformative way to explore the solar system.»
A technology of the future for space exploration
The Deep Space Optical Communications Experiment, managed by JPL, consists of an onboard laser transceiver and two ground stations. The historic 5-meter aperture Hale Telescope at Caltech’s Palomar Observatory, located in San Diego County, California, serves as the downlink station. The laser transceiver sends its data there from deep space. The Optical Communications Telescope Laboratory, located at JPL’s Table Mountain facility near Wrightwood, California, serves as an uplink station. It can transmit 7 kilowatts of laser power to send data to the transceiver.
Lasers enable data transport at rates up to 100 times higher than radio frequencies. This capability makes it possible to transmit complex scientific information as well as high-definition images and videos. .
Performance exceeding expectations
Data from the technology demonstration is sent to and from Psyche as bits encoded in near-infrared light. The latter has a higher frequency than radio waves, allowing more data to be concentrated in a transmission and achieving significantly higher transfer rates.
Even when Psyche was about 53 million miles away – a distance comparable to Mars’ closest approach to Earth – the technology demonstration was able to transmit data at the system’s maximum rate of 267 megabits per second. This speed is similar to that of a high-speed Internet connection. As the probe moves further away, the rate at which it can send and receive data decreases, as predicted.
On June 24, 2024, when Psyche was approximately 390 million kilometers from Earth – more than 2.5 times the distance between our planet and the Sun – the project achieved a sustained downstream data rate of 6.25 megabits per second, with a peak rate of 8.3 megabits per second. Although this rate is significantly lower than the maximum of the experiment, it is still well above what a radio frequency communications system using comparable power can achieve over this distance.
A multifaceted experience
The goal of deep space optical communications is to demonstrate technology that can reliably transmit data at speeds greater than other space communications technologies, such as radio frequency systems. In pursuit of this goal, the project had the opportunity to test unique datasets such as artwork and high-definition videos, in addition to engineering data from the Psyche probe.
As an example, one downlink included digital versions of the artwork “Psyche Inspired» from Arizona State University, images of the team’s pets, as well as a 45-second ultra-high definition video parodying television patterns from the previous century and depicting scenes from the Earth and space.
The technology demonstration enabled the transmission of the first ultra-high definition video from space, featuring a cat named Taters, from the Psyche probe to Earth on December 11, 2023, at a distance of 19 million kilometers. The artwork, images and videos had been previously uploaded to Psyche and stored in its memory before launch.
Regarding the project objectives, Abi Biswas, Demonstration Project Technologist at JPL, said: “A key goal of the system was to prove that the reduction in data rate was proportional to the inverse square of the distance. This goal was achieved and huge amounts of test data were transferred to and from the Psyche probe by laser.» Nearly 11 terabits of data were transmitted downlink during the first phase of the demonstration.
The flight transceiver is currently turned off and will be turned back on on November 4, 2024. This activity will prove that the flight hardware can operate for at least one year.
Regarding next steps, Ken Andrews, project flight operations manager at JPL, concluded: “The flight laser transceiver will be powered on and a short operational check will be performed. Once this objective is achieved, the use of the transceiver at its maximum design capabilities during the post-conjunction phase, which will begin later in the year, can be considered.»
Illustration caption: NASA’s Psyche spacecraft receives a laser signal from the Deep Space Optical Communications (DSOC) uplink ground station at the Table Mountain Facility at JPL in this artist’s concept. The DSOC experiment consists of an uplink station and a downlink station, as well as a flying laser transceiver with Psyche. NASA/JPL-Caltech
Source : NASA
