In December 2023, a small satellite covered in gold broadcasted a video clip of an orange cat named Taters chasing a laser pointer up and down the couch. If you thought you couldn’t stop bragging about your pets, Taters’ adventure was broadcasted, lasting 15 seconds from a distance of 19 million miles from Earth. A few months later, images and videos of NASA employees’ pets were flying through space, packed precisely inside laser beams that took 101 seconds to travel back to Earth at the speed of light.
Regardless of every pet owner’s superiority on Earth, NASA’s demonstration was designed to test optical communications systems as a way to transmit data to distant spacecraft much faster than radio waves. Mira Srivastava, the Deep Space Optical Communications (DSOC) operations lead at NASA’s Jet Propulsion Laboratory (JPL), told Gizmodo: “This has been in the works for decades.” “We needed to develop that technology and make it suitable for operations, especially in the space environment.”
A New Era of Space Communications
Years of research and smaller technology demonstrations that sent data across shorter distances, such as from Earth to the Moon, were necessary before DSOC was ready to fly. The laser transmitter and receiver device for DSOC was launched in October 2023, connected to the spacecraft Psyche (which is conducting its own mission to explore an asteroid with the same name).
While Psyche relies on traditional wireless communications, the DSOC laser transmitter and receiver device is the first for optical communication from far distances like Mars. In November, the tool saw its first encrypted optical and radial data from a near-infrared laser beam from a distance of approximately 10 million miles from Earth.
Yes, we are talking about invisible rays traveling at the speed of light, carrying high-definition data from deep space to Earth. Here’s how it works: optical communication systems convert data into light wave oscillations in laser beams, leading to message encryption into an optical signal that is transmitted to the receiver device through near-infrared rays that are invisible to the human eye.
How Optical Communication Works
Since the launch of the first satellite in the 1950s, NASA and other space agencies have relied on radio frequency communications to send data to and from space. Both radio and laser signals are part of the electromagnetic spectrum and travel at the same speed, but they have different wavelengths. The laser transmits data in the near-infrared part of the electromagnetic spectrum, making its wavelength shorter and its frequency higher. This means that there are longer wavelengths for infrared rays compared to radio waves at a certain distance, allowing more data to be gathered within infrared waves.
Srivastava said, ‘It affects the amount of data you can absorb.’ ‘Obviously, what that does is it allows higher resolution data because you can send a lot of bits in the same time window.’ DSOC’s experiment aims to demonstrate data transfer rates 10 to 100 times greater than current radio frequency systems used by spacecraft today, according to NASA.
If you’re thinking about the feisty cat video, Psyche’s traditional wireless transmitter, which has a data rate of 360 kilobits per second, would take 426 seconds to transmit the video. At the same time, the DSOC laser transmitter and receiver device only took 0.58 seconds to transmit the video at a data rate of 267 megabits per second. However, both radio and laser signals would take the same amount of time to reach Earth at the speed of light.
Srivastava said, “With optical communications, you’re using telescopes and lasers to communicate predominantly, and you’re pulsing these laser beams.” The DSOC experiment includes a laser transceiver device for flying and two ground stations: the 200-inch aperture Hale Telescope at the Palomar Observatory operated by the California Institute of Technology in San Diego, which serves as the downward link station, and the Optical Communications Telescope Laboratory at the Jet Propulsion Laboratory facility in California, serving as the transmitter station.
The upward link station sends pulsed laser signals to the spacecraft equipped with a camera capable of counting individual photons. The flying station uses the ground transmitter device as a beacon, where it is mounted to aim the laser beam. Using the ground transmitter device, the flying station sends its data as laser pulses as a downward link to Earth.
Challenges and the Future of Laser Space Communications
It may seem somewhat straightforward, so why hasn’t NASA relied on space laser beams all this time? Well, optical communications are not without challenges. When the laser beam reaches Earth, it is much narrower than its radio counterpart, with a width of only a few miles compared to a radio signal with a width of about 1.5 million miles. Its narrow width requires greater accuracy to reach the receiving station on Earth, where the laser beam is directed to the point where the ground telescope will be in the planet’s orbit when the signal reaches it.
Optical communication has been used to transmit data from Earth orbit to the Moon, but the recent test represents the farthest distance covered by laser beams, as NASA seeks to enhance its communication skills before missions to deep space. However, longer distances make it difficult for space laser beams to accurately hit a target on Earth, which is the biggest challenge NASA faces in fully relying on lasers to download data from deep space.
As the spacecraft Psyche continues its journey of 2.2 billion miles to the asteroid belt, the DSOC engineering team will continue to conduct communication system tests and weekly surveys using the laser transmitter and receiver device. As Psyche travels farther on its way to its asteroid target, the laser photon signal becomes dimmer.
So far, the experiment has broken records as it approaches Earth. In July, DSOC sent a laser signal from Earth to the spacecraft Psyche from a distance of about 290 million miles, the same distance between Earth and Mars when the two planets are far apart.
Srivastava from NASA expects missions to start relying on lasers within the next decade or so, highlighting the need to build dedicated telescopes for optical communications to provide a range of ground locations capable of receiving data.
She said, ‘I think it’s going to be a complement to both (wireless and laser communications).’ ‘With laser communications, it’s a high-data rate channel used for high-definition videos, richer scientific data, and so on, but there will always be a place for radio frequency communications.’
