Laser communications, an ever so important factor for the future of space exploration, has seen some important steps forward recently. Two test missions are on the way to provide important information, and a third one is planned for next year.
The Integrated LCRD LEO User Modem and Amplifier Terminal (ILLUMA-T), which flew to the International Space Station (ISS) by CRS-29 on Nov. 9, has been successfully installed at the Japanese Experiment Module – Exposed Facility. After check-outs were performed for nearly a month, the first data exchange was made between ILLUMA-T and NASA´s Laser Communications Relay Demonstration (LCRD) satellite on Dec. 5.
The Psyche spacecraft was launched at the beginning of October to the asteroid of the same name, which orbits the Sun between Mars and Jupiter. It is fitted with the DSOC (Deep Space Optical Communications) system and exchanged data with the ground for the first time from a distance of nearly 10 million miles (16 million kilometers) away on Nov. 14 – the farthest-ever demonstration of optical communications thus far.
The upcoming Artemis II mission, expected to launch at the end of 2024, will carry the Optical Communications System (O2O) in the Orion spacecraft. If successful, the crew, led by Commander Reid Wiseman, will be able to transmit live footage from cis-lunar space like never before.
Until now, space communication has relied on radio waves in low-Earth orbit, mainly through Tracking and Data Relay Satellites, and the Deep Space Network. But with the rising number of missions and the amount of data needed to be transferred, both networks are reaching their capacity limits or sometimes overloaded.
During Artemis I, for example, a lot of data transfer from robotic missions and deep space probes had to be radically reduced to make room for the needs of the Orion spacecraft.
The new near-infrared laser communication experiment also uses electromagnetic waves for data transmission but with a much higher capacity thanks to significantly shorter wavelengths, which allows ground stations to receive more data.
NASA assumes a 10 to 100-fold increase in data volume with new laser communication systems. This, in turn, will help with future human and robotic missions and allow scientific instruments to feature components that perform measurements in higher resolutions. ILLUMA-T can transmit more than 1.2 gigabytes per second, which is excellent, especially compared to higher home internet rates on Earth.
“Future missions have potentially exceptionally large data needs, and so we have to think about how we’re going to meet those needs,” said Dr. Jason Mitchell, director of the Advanced Communications and Navigation Technologies division within NASA´s Space Communications and Navigation program at NASA Headquarters, which funds ILLUMA-T and all the other new optical communication programs.
According to acting ILLUMA-T project manager Glenn Jackson at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, laser systems are smaller, more lightweight, and use less power than radio systems. The smaller size frees up more room for instruments, reduces launch costs, and results in less drain on spacecraft batteries.
ILLUMA-T is participating in a technology demonstration to provide high data-transmission rates from the ISS to NASA’s Laser Communications Relay Demonstration (LCRD) satellite in geosynchronous orbit (GEO) and ultimately to ground stations on Earth, and also from the ground back up to the ISS.
LCRD launched in December 2021 and has been waiting for ILLUMA-T’s installation ever since. After receiving ISS data, LCRD beams it to optical ground stations in Haleakala, Hawaii, and Table Mountain, California.
Once the data reaches these ground stations, it will be sent to the LCRD Mission Operations Center at NASA’s White Sands Complex in Las Cruces, New Mexico. After this, the data will be sent to the ILLUMA-T ground operations teams at the agency’s Goddard Space Flight Center.
The “heart” of the system, designed by the Massachusetts Institute of Technology Lincoln Laboratory, is called MAScOT (for Modular, Agile, Scalable Optical Terminal), which will also be used for O2O on Artemis II. It is comprised of a telescope and a two-axis gimbal, which allows the pointing and tracking of LCRD in geosynchronous orbit. The optical module is about the size of a microwave.
Together with a modem, it forms ILLUMA-T, which is connected via ethernet to the ISS local area network, which computers and other experiments plug into. This allows ILLUMA-T to send various kinds of data from the ISS, such as scientific measurements and system health and status indicators.
With all the advantages of the new technology, integrating it into an already-existing complex system like the ISS is an additional challenge. Manish Khatri, Chief of NASA’s Flight Operations Safety Office, highlighted this when he mentioned that laser communications could not be upheld at all times at the ISS.
Gigabit speeds for the ISS!
— Manish Khatri (@SpaceManish) October 29, 2023
The system might interfere with approaching or departing vehicles’ navigation sensors, and he and his team had worked intensively to determine when it has to be switched off to prevent any risk of a collision.
The DSOC experiment on Psyche does not have to worry about this, but as the first demonstration of optical communication from deep space, it is facing different challenges. In its first contact, it sent data to the Hale Telescope from a distance of about 40 times farther than the Moon is from Earth to the Hale Telescope at Caltech’s Palomar Observatory in San Diego County, California. Recently, contact was made from even 79 times the distance to the moon (0.2 astronomical units).
Like using a laser pointer to track a moving dime from a mile away, aiming a laser beam over millions of miles requires extremely precise “pointing.” So, the transceiver must be isolated from the spacecraft vibrations, which would otherwise nudge the laser beam off target.
The demonstration also needs to compensate for the time it takes for light to travel from the spacecraft to Earth over vast distances. In the first DSOC test, the near-infrared photons took about 50 seconds to travel from the probe to Earth. Once the probe arrives at the asteroid, the transmission time will be extended to 20 minutes. In that time, both the spacecraft and the planet will have moved, and the uplink and downlink lasers will have to be adjusted accordingly.
The receiving Hale Telescope is also specially equipped for laser communications. Integrated into it is a cryogenically cooled superconducting nanowire photon-counting array receiver developed by NASA’s Jet Propulsion Laboratory in California. High-speed electronics can record the arrival time of single photons so that the signal can be decoded. The DSOC team even developed new signal-processing techniques to squeeze information out of the weak laser signals that will have been transmitted over tens to hundreds to millions of miles.
The DSOC’s first contact was a highlight for the whole team. “Achieving first light is one of many critical DSOC milestones in the coming months, paving the way toward higher-data-rate communications capable of sending scientific information, high-definition imagery, and streaming video in support of humanity’s next giant leap: sending humans to Mars,” said Trudy Kortes, director of Technology Demonstrations for the Space Technology Mission Directorate at NASA Headquarters in Washington.
For Dr. Jason Mitchell, DSOC is an essential part of the planned Moon to Mars architecture: “If we want to be able to really think about exploring more, we have to make sure that we understand what it’s going to take to have high-rate capability.” Not only for data but also for humans: “If we’re going to have humans, humans have to be connected to home, right?”
Dr. Mitchell feels that this point is sometimes glossed over or not discussed. But it’s absolutely necessary to ensure that ground teams and astronaut crews can react if there is an issue onboard the spacecraft with the crew: “Maybe they have a portable small X-ray or CT scan capability. That’s a lot of data you’ve got to get back, and you have to have that pipe to do it. But you also want to make sure that you can send them a lot of data because you like to make sure that they remain connected to home, feel connected to home, and don’t feel isolated during that long journey.”
(Lead image: Artist’s illustration showing the LCRD mission. Credit: NASA)