It's been a full year of laser communications in space. In October and November, NASA launched two pilot demonstrations to test high-bandwidth optical communications links, and these technical demonstrations are now showing some preliminary results.
On December 11, a laser communications station aboard NASA's Psyche spacecraft en route to an asteroid was linked to a receiver in Southern California. The near-infrared laser beam contained a message encoded in the form of a 15-second high-definition video clip showing a cat jumping around a sofa, chasing the light of a store-bought laser toy.
Laser communications provide the benefit of transmitting data at a higher rate than can be achieved using traditional radio links. In fact, the Deep Space Optical Communications (DSOC) experiment aboard the Psyche spacecraft is testing technologies capable of transmitting data at rates 10 to 100 times greater than those possible in previous missions.
“We're looking to increase the amount of data we can send back to Earth, and that has a lot of advantages for us,” Jeff Volosin, acting deputy associate administrator for NASA's Communications and Astronautics Program, said before Psyche's launch. Earlier this year.
Now, DSOC has set a record for the furthest distance ever broadcast from space via high-definition video. At that time, Psyche was traveling 19 million miles (31 kilometers) from Earth, about 80 times the distance between Earth and the Moon. NASA said the video signal, which moves at the speed of light, took 101 seconds to reach Earth, and was transmitted at the system's maximum bit rate of 267 megabits per second.
After arriving at the receiver at Palomar Observatory in San Diego County, each video frame was sent “live” to NASA's Jet Propulsion Laboratory in Pasadena, California, where it was played back in real time, according to NASA.
“One goal is to demonstrate the ability to transmit large-scale video over millions of miles. Nothing on Psyche generates video data, so we typically send packets of generated test data,” Bill Klippstein, technology demonstration project manager at JPL, said in a statement. Randomly.” “But to make this milestone even more memorable, we decided to work with designers at JPL to create a fun video, which captures the essence of the demonstration as part of the Psyche mission.”
A video of Taters, an orange cat of a JPL employee, was recorded before Psyche's launch and was stored on the spacecraft for this demonstration. The robotic probe was launched on October 13 aboard a SpaceX Falcon Heavy rocket, with the primary goal of flying to the asteroid Psyche, a metal-rich world located in the asteroid belt between the orbits of Mars and Jupiter.
It will take the Psyche probe six years to reach its destination, and NASA has conducted a laser communications experiment to help keep the spacecraft occupied during the journey. Since launch in October, JPL ground teams have operated the Deep Space Optical Communications (DSOC) experiment and run it through some early tests.
One of the most important technical challenges involved in the DSOC experiment was aligning the 8.6-inch (22 cm) optical telescope aboard Psyche with a transmitter and receiver mounted on the ground-based telescopes in California and vice versa. Since Psyche is accelerating through deep space, this problem is like trying to hit a dime from a mile away as it moves, according to Abi Biswas, a DSOC project technologist at JPL.
“Once this feat is achieved, the signal received is still very weak, thus requiring highly sensitive detectors and electronic processing that can capture that signal and extract the information encoded in it,” Biswas said.
The telescope aboard Psyche is mounted on an isolation and guidance assembly to stabilize the optics and isolate them from spacecraft vibrations, according to NASA. This is necessary to eliminate tension that could prevent the stable laser from being locked between Earth and the Psyche spacecraft.
“What optical or laser communications allows is to achieve very high data rates, but on the downside, it is a very narrow laser beam that requires very precise pointing control,” Biswas told reporters before the launch. “For example, platform disturbance from a typical spacecraft can throw off the signal, so it needs to be isolated from or controlled.
“For near-Earth missions, you can only control them because you have enough control bandwidth,” he said. “From deep space, where the received signals are very weak, you don't have a lot of bandwidth to control, so you have to isolate from the disturbance.”
There is another drawback to direct laser communications from space to Earth. Cloud cover over transmitting and receiving telescopes on Earth can block signals, so an operational optical communications network would require several ground nodes in different locations around the world, ideally in areas known for clear skies.
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