Following successful testing of DSOC technology in Earth orbit and on the Moon, NASA is now using deep space optical communications technologies to test laser communications over increasingly greater distances. While aboard the agency’s Psyche mission, DSOC has already sent video via laser to Earth from 19 million miles (31 million kilometers) away and is aiming to prove that high-throughput data can be sent even from Mars.
NASA’s Psyche mission launched on October 13, 2023, with the goal of exploring what could be the ancient planet’s exposed metallic core. NASA’s Deep Space Optical Communications (DSOC) demonstration will test the use of lasers to transmit and receive more data from distant spacecraft than is possible with radio waves currently used.
Using a narrow laser beam to communicate with a spacecraft 300 million kilometers away is a challenge on both the interplanetary and quantum scales. However, if successful, the DSOC demonstration could open up a whole new world of possibilities for future deep space missions.
“Fiber optic technology on Earth has enabled incredible data transfer rates for applications such as the Internet,” says Clemens Hees, head of optical technology at ESA’s (European Space Agency) European Space Operations Center in Darmstadt, Germany. “However, data transmission from spacecraft over interplanetary distances is still limited to the use of radio waves.”
“We have already shown that optical communications can provide much higher data rates for Earth observation satellites and telecommunications satellites in low Earth orbits. But to use it at long distances in space, we need powerful, high-precision lasers and ultra-sensitive single-photon detectors, which simply do not yet exist with the required characteristics.”
Using pulses of light at a higher frequency than radio waves, optical communications can transmit more data in a given period of time. This higher data rate could allow future deep space missions at certain distances from Earth to use more sophisticated scientific instruments and return significantly more data than is currently possible.
However, testing new technology on a deep space mission, where every kilogram of payload must be carefully selected, is a rare opportunity. NASA’s DSOC is the first chance to build confidence in deep space optical communications and improve its readiness for use in space missions. ESA and NASA have a long-standing partnership in deep space communications and interoperability.
This collaboration allows ESA spacecraft to communicate with NASA ground stations and NASA missions to communicate with ESA Estrack stations, similar to how European mobile phones are compatible with cellular networks in the US and vice versa. This cross-compatible system enables seamless communications over vast interplanetary distances and symbolizes strong international cooperation in space exploration.
Both agencies are developing their own ground infrastructure to communicate with DSOC. This ground infrastructure must be built at high altitudes to avoid as much influence as possible from the Earth’s atmosphere and cloud cover. For example, NASA’s facility is located in the mountainous regions of California, which allows for clean atmospheric conditions there. ESA operates the 2.3-metre Aristarchus telescope located at 2,340m at the Chelmos Observatory in Greece.
Both observatories are owned and operated by the Institute of Astronomy and Astrophysics, Space Applications and Remote Sensing (IAASARS) of the National Observatory of Athens, a key partner in this demonstration of DSOC, the longest optical link ever carried out in Europe. ESA’s ground-based laser receiver for deep space communications will be a complex receiving unit known as an “optical bench”. This receiver will be securely mounted on the back of the Aristarchus telescope.
“The receiver’s detector must be very sensitive to detect individual quantum particles of light—photons—from the DSOC sent over hundreds of millions of kilometers,” says Sinda Mezhri, lead optical engineer for ESA’s ground-based laser receiver system. “To detect individual photons, the detector must be superconducting, meaning it can conduct electricity without any resistance. To do this, the receiver detector will be cooled to -272.15 degrees Celsius (1 Kelvin). Absorption of a photon disrupts the superconducting state of the detector, creating a measurable electrical pulse.”
The detector also faces a unique challenge: it must be cryogenically cooled but still be able to move as the telescope turns and follows the spacecraft across the sky. Cryogenic systems typically resist movement, and maintaining constant cooling while moving is another major technology challenge.
The terrestrial laser receiver also includes electronics to monitor signal strength from the DSOC. If the signal weakens, the system will automatically adjust the telescope’s position to maintain signal strength and transmit this information to a laser transmitter 37 km away, ensuring precise alignment. Such an installation requires the development of specialized software to effectively coordinate these operations.
“The laser must be so powerful that it would actually destroy the protective coating of its optical components and mirrors and melt conventional fiber optics if the necessary precautions were not taken during its design,” says ESA Ground Laser Transmitter lead optical engineer Andrea Di Mira. “And we combine up to seven separate beams that need to work together seamlessly.”
By combining seven beams, ESA’s laser will be able to transmit photons encoded with information bright enough for DSOC to detect them at a distance of about 1.5–2.5 astronomical units (220–370 million km) from Earth. These distances would be typical for a future mission to Mars, for example. NASA believes it can extend this technology to even greater distances. In addition to high brightness, the laser beam must be aimed precisely towards the distant spacecraft. The precision required is similar to pointing a laser pointer from Earth at a small crater on the Moon.
ESA’s participation in the DSOC demonstration was made possible by a consortium of European companies including qtlabs, Single Quantum, General Atomics Synopta, qssys, Safran Data Systems and NKT Photonics Ltd, as well as the National Observatory of Athens, which provides access to Helmos and the Kryoneri Observatory. The project is funded through the ESA General Technology Support Program and the Technology Development Element.
“With this project we are really challenging European industry,” says Cinda Mejri. “But they gladly accepted the challenge. The work they are doing here could also give them an advantage in developing important technologies for applications such as quantum key distribution, used for secure communications, and quantum imaging.”
ESA’s DSOC experiments will take place in 2025, when the spacecraft will be far enough from Earth to be representative of future deep space science and exploration missions. If successful, the demonstration could pave the way for a new generation of solar system exploration and the development of deep space optical communications stations on Earth.
DSOC operates alongside NASA’s Psyche mission, but will not transmit data to the Psyche mission. The main goal of the Psyche mission is to explore the mysterious metal-rich asteroid of the same name. Scientists believe rocky terrestrial planets like Earth contain metallic cores, but their location so deep below the surface makes them difficult to study. Asteroid Psyche provides a rare opportunity to study the history and formation of terrestrial planets.
Psyche was first discovered by Italian astronomer Annibale de Gasparis in 1852 and was the 16th asteroid ever discovered. Almost two centuries later, Italy is now home to ESA’s Planetary Protection Directorate, which is particularly excited to see the results of the Psyche mission. Humanity’s understanding of asteroids is growing rapidly: we are getting better at detecting small asteroids before they hit Earth, detecting ones that fly nearby, getting close to them to study with spacecraft, and even returning asteroid samples to Earth.
The Psyche mission and the accompanying DSOC technology demonstration will advance our understanding of the origins of our Universe and enhance our ability to transmit large volumes of scientific data back to Earth.
“DSN is the heart of NASA. It has the vital mission of ensuring the flow of data between Earth and space,” said Philip Baldwin, acting director of the SCaN Network Services Division at NASA Headquarters in Washington. “But to support our growing portfolio of robotic missions, and now the human Artemis mission to the Moon, we need to move forward with the next phase of DSN modernization.”
At the same time, “Laser communications could change the way NASA communicates with deep space missions,” said Amy Smith, deputy DSN project manager at the Jet Propulsion Laboratory. “NASA is proving that laser communications are viable, so we are now looking at ways to build optical terminals inside existing radio antennas. These hybrid antennas will still be able to transmit and receive radio frequencies, but will also support optical frequencies.”