In September 2024, the New York Times published a report on a spectacular flight by a SpaceX capsule carrying two private astronauts. The crew performed the first-ever commercial spacewalk, among a few other headline-grabbing feats. Courtesy of ESA/P. Carril. Notably, the last sentence of the article read: “They have also tested laser communications between the Crew Dragon and SpaceX’s constellation of Starlink internet satellites”1. So far, most satellites in operation send and receive information via radio waves or microwaves. They use radio frequencies between 3 and 31 GHz (superhigh frequency) from the S-band to the Ka-band. Starlink, the company that runs the largest satellite configuration in existence, was granted permission to use V-band frequencies between 40 and 50 GHz. The higher the frequency, or the shorter the wavelength, the more data that can be carried on a signal. In this respect, the move to laser communications is a game changer. Telecom wavelengths of ~1.5 μm have frequencies of ~10,000× higher than Ka-band radio waves. Lasers and electronics for telecom wavelengths are available in large numbers and have a high level of technological readiness. Although it took several decades to bring laser communication terminals (LCTs) to maturity, the technology has arrived. It has not been without major technical challenges, such as the issue of pointing accuracy from one satellite to another — it is not easy to hit a receiver terminal on a satellite flying at a speed of 30,000 km/h with a narrow laser spot. But this problem has been solved, and today the small diameter of the laser spot has in fact turned from a challenge into a selling point, because it is much harder to eavesdrop on such a beam than to scoop radio waves. Even though additional obstacles pose more recent problems, such as the micro vibration generated by reaction wheels and solar panel movements, NASA summarized the major benefits of LCTs in one sentence: “[It] weighs less, uses less power, and occupies less space than a comparable [radio frequency] system”2. How laser terminals work The development of LCTs began in the 1970s. Significant advancements in several technologies, including lasers, were required to make LCTs the off-the-shelf products that they are today. The laser source is one of the main components of an LCT. The others include a beam pointing and tracking system; a telescope to send and receive optical signals; and a detector to convert the optical signals into electronic information. The onboard laser source generates high-power laser beams, often operating in the NIR spectrum at 1064 nm or 1550 nm. The beam pointing and tracking system ensures that these beams are precisely directed at receivers, even across tens of thousands of kilometers. Coarse pointing is often performed by gimbals to steer the beam in the general direction of the receiver. The precision here is better than 1°. Fine steering optics compensate for vibrations, jitter, and relative motion, achieving microradian alignment accuracy. Most often, piezos are applied to realize fast steering with a microrad precision. Beacon beams may be used to support the pointing and tracking system. The telescope is the largest component of an LCT, and its size determines both the overall shape of the system and its range. Even a laser beam diverges over a long distance, meaning that the telescope for geostationary satellite links must be larger than that for an intersatellite link in low Earth orbit (LEO) only, which is on the order of several hundred kilometers. Accordingly, major LCT suppliers have developed a range of systems of different sizes, for different purposes (see the table below). On the receiving end, photodetectors, such as avalanche photodiodes and/or advanced single-photon detectors, convert optical signals into electrical signals. Data processing units handle signal modulation, error correction, and encryption, which ensures reliable and secure communication. To establish a connection, the transmitting terminal starts with a spiral beam movement. Initial random “hits” are used to calculate the optimal direction. The challenge is to reconcile the different inertial systems: coarse and fine pointing mirrors; Earth; the sun; and the orbital position and attitude of the sending and the receiving satellite. Of course, each possesses its own coordinate system(s). Stepping toward the space laser network The first intersatellite laser link was established in November 2001 when the European geostationary satellite Artemis connected with the Earth observation satellite SPOT 4 (see Reference 3). The system used a 60-mW laser diode with a 25-cm telescope aperture to achieve 50 Mbit/s. The system’s total weight was 160 kg, and it consumed 150 W of power. Technical Data of Laser Communication Terminals from Manufacturer TESAT LCTs have been used in defense applications from some of the early stages of their development. In February 2008, a German LCT was used onboard the U.S. Missile Defense Agency’s NFIRE satellite. It was designed to accelerate the transmission of missile tracking information, especially over long distances. NASA commenced laser communications in 2013 with its Lunar Laser Communication Demonstration (LLCD) (Figure 1). The LLCD consisted of a space terminal on the LADEE spacecraft and three ground terminals on Earth. Together they demonstrated that it is possible to transmit up to 622 Mbps of data over a distance of 385,000 km between a spacecraft and a ground station on Earth using a space terminal2. The same year, the geostationary orbit (GEO) satellite Alphasat was launched to demonstrate GEO-to-ground and GEO-to-LEO laser communication links. In 2014, the Optical Payload for Lasercomm Science (OPALS) was tested onboard the International Space Station. It downlinked a video of the 1969 Apollo 11 moon landing in merely 7 s, compared with 12 h using existing radio links. Figure 1. A computer rendering of NASA’s Lunar Laser Communication Demonstration (LLCD) optical module. It includes a 0.5-W laser transmitter, with the optical module mounted to the exterior of the LADEE spacecraft, and consists of a 4-in.-diameter telescope on a two-axis gimbal. The entire system weighs ~65 lbs. Courtesy of NASA. The next major steps in LCT history were the integration of LCTs on the LEO satellites Sentinel 1 and 2 and the GEO satellites European Data Relay Satellite (EDRS)-A and -C. These satellites are part of the Space Data Highway, which was established to transfer data from LEO satellites to ground stations via GEO satellites. The data transfer between LEO and GEO over >35,000 km is performed by intersatellite links with LCTs. The data rate from space to ground amounts to 1.8 Gbps. Sentinel 1A was launched in 2014, and EDRS-A in 2016 (Figure 2). The Space Data Highway has been in regular operation since the launches. Figure 2. European Data Relay Satellite (EDRS)-A is the first node of the EDRS. Courtesy of ESA. NASA has its own plans with its Laser Communications Relay Demonstration (LCRD) (Figure 3). Launched in 2021 to a GEO orbit, NASA tested communications to several ground terminals. With LCRD, NASA engineers also proved that laser communications systems can enable more precise navigation capabilities. An ongoing navigation experiment has already shown that engineers can receive more precise location data over a laser link than over standard radio waves. Figure 3. The Laser Communications Relay Demonstration (LCRD) payload is attached to the LCRD Support Assembly Flight (LSAF). Attached to the LSAF are the two optical modules, which generate the IR lasers that transmit data to and from Earth. Courtesy of NASA's Goddard Space Flight Center. LCRD became instrumental as a relay station in 2023, when the Integrated LCRD Low Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) was sent to the International Space Station to establish a two-way laser connection. The latest record in space communication meanwhile was set when NASA’s Psyche mission transmitted video over 31 million km from deep space to Earth in a demonstration that serves to enable future human missions beyond Earth orbit. Capable of sending and receiving NIR signals, the instrument used an encoded NIR laser to transmit 267 Mbps to the Hale Telescope at Caltech’s Palomar Observatory in California. SpaceX began to deploy LCTs in 2022; its Starlink satellites were originally designed to receive signals from a portable terminal on the ground and to relay these signals to the next ground station with internet connection. By enabling communications from one satellite to another on the same or adjacent orbital plane, a ground station does not need to be in the same satellite footprint as user terminals. This is poised to be a major change to Starlink operation. LCT developers Until recently, LCT installations were test deployments. Only a few systems, such as EDRS, were used for regular data transmission. But this has changed, and LEO constellation operators have started to place orders for large batches of LCTs. Accordingly, LCT market leader TESAT opened a production facility with a capacity of 100 LCTs per month. The opening in August 2024 followed TESAT’s launch of a production facility on Florida’s Space Coast in 2023. At that time, TESAT said in a press release, “With more than 500,000 h of operation and 10 optical communication terminals in space, TESAT is the only provider worldwide for in-orbit-verified optical communication terminals.” TESAT-Spacecom was founded in 2001 in Backnang, near Stuttgart, Germany. The company formed as a rebrand of an established player in the field of satellite payloads and has become a market leader. The company has roots in AEG Telefunken, which was forced to flee Berlin in 1949. It ultimately changed names and ownership several times until 2001, when EADS Astrium (now part of Airbus Defence and Space) acquired TESAT and kept it as a separate company. Today, TESAT employs approximately 1100 people, primarily in Backnang. The promising market has yielded a strong competitor: In March 2024, SpaceX President Gwynne Shotwell announced that the company had started to sell LCTs. News on this has been quiet since. When SpaceX promoted a successful test of a laser link on two satellites built for the U.S. Space Development Agency in September 2024, it used TESAT terminals. The successful test involved two of the four SpaceX satellites equipped with Leidos IR sensors and TESAT terminals. Meanwhile, other LCT providers are evolving. In June 2024, the U.S. Space Systems Command announced that it had awarded contracts to four companies to develop prototypes for laser communication terminals, kicking off the first phase of the $100 million Enterprise Space Terminal program. The four companies contracted are Blue Origin, CACI International, General Atomics, and Viasat. German competitor Mynaric previously won an order from Northrop Grumman as the sole supplier of optical communications terminals for the Space Development Agency’s Tranche 1 Transport and Tracking Layer programs. It was one of several contracts for the company, whose CEO left the firm in the summer of 2024 because the ramp-up of LCT production was not going to plan. Mynaric lost most of its valuation, though ramp-up has nevertheless continued for the firm. LCT technology has additionally become a military priority, spurring activities around the world. China successfully deployed its first two-way LCT into orbit in February 2024. Shenzhen, China-based HiStarlink developed the terminal in collaboration with AdaSpace, a satellite maker from Chengdu, China. The terminal has a maximum transmission speed of 10 Gbps, according to China Daily. China had previously launched a research satellite with optical connection in 2016, called Micius. It established the first quantum encrypted connection from a satellite by sending entangled photon pairs to ground stations. In Japan, NEC partnered with California-based Skyloom Global Corporation, and the collaborators are aiming to develop LCTs by 2025. In Europe, defense contractors Thales Alenia Space and Hensoldt joined the pack: While the former started LCT development for quantum communication, the latter promotes LCT even for submarines. Laser connections to the ground are still seen as special and impressive accomplishments, because the presence of clouds, fog, and air turbulence can always reduce the transmission capacity. It therefore seems likely that such stations would be located in high mountains or arid regions, similar to astronomical telescopes. And they might borrow unblurring techniques such as adaptive optics from neighboring technologies. Cailabs has suggested another approach. The French laser developer and manufacturer proposes spatial composition/decomposition (demux) of the optical field for turbulence mitigation at high data rates. Cailabs’ proprietary optics can handle up to 45 modes for multiplexing/demux and up to 100 W per channel. The company currently runs several test lines of up to 10 km on the ground. What’s next It is doubtless that the large satellite constellations hold the most promise for LCT manufacturers. For example, Starlink plans to have 12,000 satellites in space; Project Kuiper (Amazon) has discussed 3000+; and Qianfan’s Spacesail constellation aims to rival Starlink with an additional 15,000 satellites. If each of these carries two or four LCTs, then thousands of LCTs will be needed per year. So far, launch capacity seems to be the biggest limit for LCT deployment. And LEO satellites have a lifetime of about 7 years, which necessitates ongoing demand. Assuming unit prices are to be below $1 million, one can make a rough estimate of a new market on the order of $1 billion annually. This estimate deserves scrutiny far beyond the scope of this article. So far, the largest constellations have been planned for end user service. Rivada Space Networks, a German-American constellation, adds a commercial dimension; its planned constellation of 600 satellites is intended to serve the maritime, telecom, enterprise, energy, and government services markets. Rivada has not yet launched a single satellite, though it said in a November 2024 press release that it had secured more than $13 billion of business for its LEO network. Such markets — the maritime, telecom, enterprise, energy, and government services, for example — could further influence the growth and deployment of this technology. Starlink has shown impressive numbers with its latest generation of user terminals, which could be used on cars and ships. And certainly, stationary terminals in underserved regions, such as the Brazilian jungle or Australian Outback, hold opportunity. The staunchest believers in the promise of the Internet of Things are eager to discuss the promise of a fast uplink everywhere, at any time. Internet on airplanes may require more sophisticated solutions, and certainly, governmental agencies will ensure that the uplinks reach to their jets, rockets, submarines, and more. This will drive more encryption technology. The first quantum encrypted satellite connections have been demonstrated already, and much more is in the pipeline. German company MO-SPACE is developing a laser and quantum communication network with airships in the stratosphere. This idea has a range of benefits. For one, airships are cheaper to launch than spaceships and easier to recover. They can serve as relay stations between satellites and ground stations; offer redundancy related to space debris risks; and do not contribute to environmental issues caused by disintegrating satellites in the stratosphere (Figure 4). Figure 4. Stationary airships in the stratosphere could be a cost-efficient alternative to low Earth orbit (LEO) satellites for free space data transmission. Courtesy of MO-SPACE. Compared to satellites, airships can also be stationary with low latencies, thereby bypassing the issue of beam-blocking clouds. Finally, airships can support direct smartphone links much more easily than satellites. Although airships have an exotic touch, the idea is expanding. For example, Sceye, headquartered outside of Albuquerque, New Mexico, is also preparing airships with LCTs. The future is now LCTs have been discussed for at least 40 years. Now, they are reality, and hundreds of systems have been ordered from LEO satellite constellations already. LCTs possess a technology readiness level 9. And given price and order estimations, one can see a hardware market (for LCTs only) evolving toward a volume of $1 billion per year. Should the technology meet this projection, it will serve as the backbone of global satellite fleets with low latency internet connections. Internet access anywhere, anytime, with a kitchen plate-size antenna is just the beginning. Direct smartphone connections will follow, and improved GPS precision through optical signals is one more application. More ideas are abundant, and rapid technological progress will bring such innovations to daily life. Meet the authors Andreas Thoss, Ph.D., is a laser physicist, founder of THOSS Media, and a contributing editor to Photonics Spectra. He has been writing and editing technical texts, with a focus on the field of photonics, for two decades; email: th@thoss-media.de. Spacecraft engineer Michael Ullrich has worked at spacecraft companies for more than 20 years. He headed the EDRS-A satellite test team and founded MO-SPACE in 2022. MO-SPACE develops quantum key distribution and laser communication networks with high-altitude platform systems, airships, and satellites; email: michael.ullrich@mo-space.de. References 1. K. Chang. First Private Spacewalk in SpaceX Capsule Achieves New Milestone. The New York Times, Sept. 11, 2024. 2. NASA (2013). Lunar Laser Communications Demonstration. LLCD Project Summary. https://www.nasa.gov/mission/lunar-laser-communications-demonstration-llcd/. 3. The European Space Agency (Nov. 22, 2001). A world first: Data transmission between European satellites using laser light. www.esa.int/Applications/Connectivi-ty_and_Secure_Communications/A_world_first_Data_transmission_between_European_satellites_using_laser_light.