2023 Issue One

1. Optical links for space: inter-spacecraft links and DTE links
(Source: Euroconsult’s Optical Communications Market report, 2023 edition)

The physical advantages of laser beams compared to RF have led to the hope that their propagation will help satisfy growing capacity needs and increasingly stringent security requirements while offering a solution to RF spectrum saturation in space. Indeed, for similar mass and volume, Laser Communication Terminals (LCTs) have a significantly higher throughput compared to RF antennas (between 10 and 1000 times depending on product type). As such, they can be made lighter, less power-hungry and less voluminous while still supporting identical or superior data rates than RF antennas. Their implementation in space communications, either as emitter, receptor or both, paves the way to several use cases improving on traditional RF links by satisfying growing throughput needs, especially for broadband connectivity and several time-sensitive applications. The smaller size and higher capacity of LCTs compared to RF antennas make them especially attractive for satellites lighter than 500kg, which have higher constraints in terms of mass, power and size.

Besides higher data rates, the narrowness of laser beams compared to RF beams makes them very hard to intercept – a laser beam is typically less than a few kilometres wide after travelling several thousands. This feature provides inherent protection against signal interception and eavesdropping in an increasingly contested space environment. Looking forward, a growing number of government communication projects aim at combining optical communications with quantum communication technology, which enables immediate detection of intrusion in a signal by exploiting photon entanglement.

Also due to their narrowness, laser beams have very little chance of crossing one-another and interfering as RF beams tend to do. As such, they offer a virtually unlimited amount of unregulated spectrum – at least in the foreseeable future –, as an alternative to radio communications in the current context of RF spectrum saturation.

Nevertheless, optical communications technology and use cases come with a set of new challenges, both technical and economic, compared to RF communications. Some apply to any optical communications use case, both in space and from space to ground. For instance, the inherent narrowness of optical beams makes beam pointing significantly more difficult, calling for high accuracy in pointing and target tracking. Furthermore, its implementation on satellites requires platform design adaptations to guarantee a wide field of view for the LCT – clearing it from the solar panels, complementary RF antennas, etc. Meanwhile, optical waves are subject to more perturbation than RF due to noise from external sources of light, requiring the ability of adapting the signal to different conditions.

Space-to-ground laser communications bring yet another set of challenges as visible light is highly affected by humidity and atmospheric turbulence and almost completely stopped by clouds. As such, in order to downlink data from space to the ground using optical links, one must plan several Optical Ground Stations (OGS) in meteorologically unrelated areas and low cloud probability to ensure continuity of service, hence driving up the cost of infrastructure. In this context, the emergence of space-to-ground optical communications will need to overcome a chicken-and-egg dilemma: operators will likely withhold implementing Direct-To-Earth LCTs on their satellites if there are not enough available OGS, but on the other hand it will be hard for actors to invest in OGS networks if there is not already a substantial amount of Direct-To-Earth LCTs in orbit.

One last challenge for space-based optical communications is the terminal cost which remains one of the main economic challenges ahead. Despite lower mass, LCT technology still has a higher price tag than RF antennas – around $500k per terminal for space-to-space LCTs based on SDA contracts. The ability to serially produce LCTs to drive their cost down through scale will be one of the main conditions to their large adoption.

Inter-Satellite Links (ISLs) are necessary for NGSO constellations operators wanting to provide services all over the world with additional features. However, Optical Inter-Satellite Links (OISL) are preferred over RF links as they allow lower latencies over long distances and more secured communications. Moreover, having OISLs is necessary for NGSO constellations meant to provide broadband internet services to its end-users as RF links speeds are not becoming fast enough to support many users at the same time. The increasing use of data-hungry applications such as streaming, video calls, etc., advocates the choice of OISLs over RF links for the constellation to be future-proof in terms of capacity delivered to the user.

The need for inter-satellite links is being further highlighted with the rise of NGSO constellations. As 70% of the globe is covered by water, NGSO satellites spend a significant amount of time over the oceans, polar regions and remote areas. Hence, being unable to constantly connect to the ground network instantly limits the data transfer. In its new market intelligence report about space-based Optical Communications, Euroconsult estimates that the total number of LCTs deployed will grow from less than a hundred in 2021 to approximately 62,000 by 2031. The majority of the growth is expected to transpire post-2025 when the existing NGSO constellation operators will deploy their next-generation satellites with LCTs onboard combined with the newly launched GEO and NGSO satellites for different applications. Even though the number of satellites deployed in the second generation might be limited because of the increased satellite size providing a higher capacity per satellite, the new constellations will compensate for the decrease. Consequently, the LCT market may depict limited growth towards the end of the decade.

2. Number of LCT terminal by mission
(Source: Euroconsult’s Optical Communications Market report, 2023 edition)

As most of the NGSO constellation operators will include LCTs onboard their upcoming satellites, a cyclic pattern is expected to be showcased in the number of LCTs launched per year. This cyclic nature of the market will mainly be driven by the ongoing completion of 1st generation of the constellation, mainly by Starlink with LCTs and then starting the replacement of gen-1 satellites without LCTs by new satellites equipped with LCTs, likely post-2024. It will then be followed by the launch of gen-2 satellites for Starlink and OneWeb constellations. Meanwhile, many other constellations are expected to launch their gen-1 satellites with LCTs such as GuoWang, Telesat Lightspeed, Kepler, Amazon Kuiper, etc.

The number of LCTs launched per year will be dominated by the mega-constellations for the satcom applications. Starlink, one of the forerunners of satcom LEO constellations operators has already launched at least ten satellites of their gen-1 with LCT prototype in 2021 and it is likely that all Starlink satellites launched in 2022 and to be launched after will embark LCTs.

3. LCTs launched per year by mission type
(Source: Euroconsult’s Optical Communications Market report, 2023 edition)

Low-Earth Orbit constellation satellites equipped with intra-constellation communication capabilities need to embark up to four LCTs per satellite. As a result, most of the market will be captured by one type of LCT which will be standardized. Such terminals will feature a data rate capability of around 2 Gbps. Current prices for such LCT are around $500k. These prices can be explained by the low volumes of production and the high labour costs associated. Euroconsult has conducted an estimation of the price evolution for this type of LCT.

Over the next three years, the Space Development Agency (SDA) constellation is expected to be one of the key elements to affect market prices. Indeed, this will allow manufacturers to produce LCTs in larger batches and according to some specific standards, increasing economies of scale for future products. The SDA publicly emphasized that it would make every Tranche of its constellation a competitive bid and thus this will allow several manufacturers to win contracts and influence the whole market. Furthermore, the goal of the agency to procure LCTs for its constellation at a price of $100,000 in the future reflects this expected downward trend.

Other large constellation projects will also further increase economies of scale from manufacturers. The second generation of OneWeb which will feature LCTs according to recent announcements can be cited as one of the major deals for manufacturers. Same for the European broadband constellation, IRIS², which could help European manufacturers, and more likely Mynaric which is part of the consortium UN:IO. Other constellation projects like Telesat Lightspeed and Starlink require all the production capabilities of their manufacturers to date but could lead to new LCT manufacturers entering the competition and thus further decrease the prices.

Moreover, technological advances are expected to put pressure on prices of LCTs delivering 2 Gbps of bandwidth as new generation LCTs can deliver up to 10 Gbps and could attain 100 Gbps in the future, further pushing down the prices.

However, it is important to remind that other types of LCTs will coexist on the market. As an example, several manufacturers are developing LCTs for Cubesats in LEO. Prices of such LCTs are also expected to decrease in the future and NASA’s TeraByte InfraRed Delivery (TBIRD) CubeSat to demonstrate fixed DTE optical links can be used as a reference with a 200 Gbps terminal costing $100,000.

4. Price estimation for an optical terminal in LEO with a data rate capability of 2 Gbps
(Source: Euroconsult’s Optical Communications Market report, 2023 edition)

As in most cases for nascent markets, stakeholders of the space-based optical communications market have some challenges from the perspective of technology, continuous investment and business expansion. For example, on October 31st 2022, SpaceLink announced that it would shut down its operations as its parent company, Electro Optic Systems Holdings Ltd, has declined in business. However, according to the recent contracts and main players’ activities, several trends can be extracted. Notably, most of the current LCT contracts apply to satellites with an average mass of about 200kg, either for intra-constellation links or for data relay applications. By the way, there are several clues indicating that future optical demand is quite strong for data relay constellations. However, setting them up requires a significant investment upfront. Last but not least, interoperability between LCTs from different manufacturers is key to support market growth. In that respect, one main purpose of the SDA program is to develop interoperability standards, which should foster developments for future commercial use.

In a nutshell, the optical communications market for space applications is on the edge of a revolutionary change that is expected to reshape and dynamize a full ecosystem.

Source: NSR

Influencing factors

In the wake of the war in Russia’s and the ensuing cyber-attacks on satellites, security is gaining higher priority for both commercial and government/military players. OSC has several advantages to help in that it offers anti-jamming and interference-resistant properties to tackle data security concerns. LCTs may be a more suitable solution as data volumes increase with higher resolution, hyperspectral, SAR imagery and video. Also, LCTs require less power and mass requirements compared to RF to achieve the same gain, offering a cost-efficient alternative to RF. Moreover, the lack of spectrum licensing reduces the setup costs and deployment timelines.

However, most of the demand for LCTs is from mega-constellations like Starlink, Kuiper who are developing the terminals in-house, minimizing the overall serviceable market opportunity and these players are considered a closed market. Additionally, the high cost per terminal of LCTs, due to the requirement for high precision optics and on-board processing technology, hinders wider adoption. While the Space Development Agency (SDA) in the U.S. has initiated standardization for Optical Communications Terminals (OCT), international standards do not exist. Furthermore, Earth Observation (EO) operators benefit from technological innovation such as cloud, ground system virtualization and dynamic network management solutions. These innovations can be easily integrated to RF systems at lower price compared to OCT infrastructure needs, and hence operators often prefer them.

Total Market Potential

NSR forecasts a cumulative opportunity of $2.6 billion from 2022-2032, with ISLs being a major driver. The market is equipment-centric, and successful demonstrations of ISLs and DTEs will boost demand and increase the technology readiness level of the product, which in turn increases the market readiness level. The initial demand is driven by the Gov/Mil segment, with constellation operators driving the demand. Players such as SpaceX’s Starshield and Spire are offering satellite-as-a-service models that include LCT terminals as offerings, further driving adoption of optical terminals in the market and positively impacting equipment revenues.

Source: NSR

ISLs: Unleashing Satellite Synergy.

The ISL’s market is expected to grow to 8,522 terminals cumulatively in next ten years. The highest demand comes from government and military sector in the short term. The communications vertical drives the majority of the demand, coming from large communications constellations, and commercial next generation constellation launches and replacements, is expected to peak in 2025.

Source: NSR

NSR forecasts total cumulative opportunity of LCT units for communications including constellations and data relay to be 95% of the total market opportunity. OneWeb, Kepler Communications, Telesat Lightspeed, SDA Transport Layer, Blackjack are some of the key high volume demand drivers in this segment for Non-GEO OISLs. Also, ISLs will be used for data relay applications to form ring and mesh networks in space. Launches for data relay applications are expected to begin in 2024 & 2025, which also contributes to the peak in 2025.

In the high growth scenario, ISL market is forecasted at 11,700+ terminals cumulatively in the next decade, with demand from VLEO Q/V band constellations, which adds to higher growth during the second half of the decade.

Space-to-Ground to Catch Up.

NSR forecasts 170+ DTE LCT units through the coming decade, with a cumulative opportunity of $24 million. This low volume market is an outcome of challenges associated with space-ground links. Atmospheric turbulence, resulting in lower link availability/reliability coupled with additional requirements onboard the satellite such as additional storage, onboard processing for network management and precision pointing limit the adoption of DTEs. This Demand is driven by higher data rates, improved security, and regulatory advantages.

Constellations based in North America such as Kepler Communications, have an impact on demand throughout the forecast period. The remainder of the equipment revenue opportunity comes from EO and data relay operators in North America, Latin America, and Asia, primarily for SAR, hyperspectral/ multispectral, TIR, or high-resolution optical data providers.

However, there are significant market restraints for the adoption of optical by EO due to fast-developing alternative technologies such as cloud-based processing/analytics, virtualized ground stations, the ubiquity of RF-based systems, and advancements in data throughputs with RF terminals. Overall, the space-to-space optical link segment is orders of magnitude higher in opportunity than the space-ground segment due to limited technological maturity and business viability factors.

Government: An Early Adopter

Globally, government and military customers are key enablers for the optical satellite communication market. National security concerns have drawn the attention of government and military players towards OSC technology, making them initial adopters of the market. Optical communications can provide higher security compared to RF due to their anti-jamming and minimum interception abilities. Government and military have awarded contracts to commercial players for optical terminals, making it easier for them to get into the market. For example, SDA signed manufacturing orders with Mynaric, SA Photonics, Skyloom and Tesat for OISLs for its Tranche 0 constellation.

Government and military players have also played a key role addressing the lack of standardisation across the terminals, as it often challenges the OSC adoption, due to the large and diverse options. As a result, SDA’s Optical Communication Terminal (OCT) Standard (Version 3.0) has been adopted by most players, filling the need for standardisation.

Government and military customers help to increase the adoption of ISLs across the satellite operators who focus on Defence and Intelligence applications, during the transition from RF terminals to hybrid systems. In the future, the range of cases ISLs can be applied is expected to increase, as government organizations eye opportunities in missile detection and threat monitoring. Also, with sponsoring research and development (R&D) contracts for technology development, they are enabling and setting the future of the market.

A similar picture can be observed in Asia where government agencies are leading the development of constellations, making it a sizeable market. Nonetheless, this market is closed off to commercial LCT vendors, which limits the number of long-term opportunities for commercial constellations in the region.

NAM Continues to Dominate

LCT demand is highest in North America due to government programs like SDA’s Transport and Tracking Layer, Space-BACN, and DARPA’s BlackJack that have led to widespread adoption of LCTs. Furthermore, the push for inter-operability has driven the adoption of SDA standards in the region.

Source: NSR

In the Asia region, China dominates the market with numerous constellation development and future plans supported by governmental agencies like CAST, CASC, CASIC etc. These large constellations, namely communication constellations like Hongyan, Hongyun and Xingyun are however considered closed market. The nation is witnessing the emergence of new commercial players, such as Hi Starlink, who are developing ISLs to address need for high speed data transmission.

Japan and South Korea are also developing constellations with potential LCT adoption. Large corporations such as Sony Space Communications and Canon are turning their attention to the optical communications market in Japan. New players such as Space Compass, a joint venture of NTT and SKY Perfect JSAT, have signed agreement with Skyloom to roll out GEO based data relay service across Asia. The initiative will tap into Skyloom’s communication and networking technologies to cater to the growing EO market by facilitating real-time, high-volume, and direct-to-cloud data transfer. The partners envision establishing the first network infrastructure node in Asia in 2024, with plans to scale the GEO constellation for increased capacity and global coverage by 2026.

In South Korea, commercial players are focused in EO applications. Ground station service providers such as Contec have secured funds up to $47.3M for its ground station network, which will include OGS. Increased activity is also observed in Singapore, India, and South Australia.

The Bottom Line

The adoption of OSC technology is witnessing a rapid surge, and the market is poised to experience steady growth after 2025, as it transitions from an initial equipment-centric phase to an emergent, robust ecosystem. The optical equipment’s high data rates and anti-jamming capabilities have drawn the attention of government and military organizations, resulting in an increased adoption of LCTs by these players.

The demand is primarily concentrated in the ISLs segment, driven mainly by communication constellations. In the short-term Gov/Mil will be key drivers of this market and by setting standards, commercial and R&D contracts, Gov/Mil will act as facilitator and accelerators for a market that near commercialisation.

Point to multipoint technology allows users to remain interconnected (courtesy by BridgeComm)

An evolution is occurring in the optical communications market

While many in the telecom and defense sectors are just starting to embrace its potential, an evolution is already taking place within optical wireless communications. Point-to-point optical wireless communication infrastructure solutions offer a new means of connectivity, bypassing the infrastructure and spectrum limitations that are becoming an issue within terrestrial communications as requirements for data-driven resources continue to grow exponentially. And yet, even as current optical wireless communications systems are beginning to offer this new form of connectivity, they remain constrained by communicating only between two points, making the deployment of large point-to-point systems expensive and cumbersome.

An appropriate analogy would be the use of the telegraph versus a broadcast radio system. With the telegraph, only two locations would be able to communicate with each other. When broadcast RF was developed, that limitation was eliminated, and information was able to be shared with a much larger audience.

Beyond cost, point-to-point systems suffer from all of the liabilities similar to the old telegraph system, including: limited functionality/flexibility, low resilience as a result of multiple single point of failure, lack of graceful degradation from the system, network and physical layers, along with high deployment costs.

Customers want a low-cost solution, high bandwidth, higher security, resilience, graceful degradation, and flexible networking capabilities so they can maximize revenues or ensure mission success. To shift the paradigm in communications infrastructure we need to move beyond the “telegraph,” or point-to-point optical wireless communications, and into multipoint optical wireless communications.

BridgeComm Optical Ground Station (courtesy by BridgeComm)

Point-to-Multipoint: Connectivity with unlimited flexibility, lower costs and increased resilience

Point-to-multipoint technology allows optical communications systems to act like broadcast RF, while still capturing the inherent benefits of optical communications in terms of offering higher resilience, security, more bandwidth, and lower cost.

For government and defense users, the result is that they can continue to operate in the same interconnected environment that is utilized today even when an adversary has eliminated RF communications from the battlefield. Multipoint optical communications technology allows defense users to remain interconnected across all the warfighting domains – including space, air, land and sea – through multiple points of communication simultaneously. The continuity of capability in operations is a significant enabler for defense users, and that is priceless.

Commercial aerospace operators will gain the following benefits from point-to-multipoint capabilities versus point-to-point:

• Tiered pricing structures enabled by advanced point-to-multipoint and full mesh network architectures will increase revenue and network utilization.
• Higher network resilience and reliability
• Non gimbaled beam steering
• Lower satellite bus costs
• More capable SmallSat offerings

For the telecommunications industry and operators, multi-point optical wireless technology enables them to deploy 5G capabilities to their customer base providing them the bandwidth they need to fully utilize the 5G standard. Additional benefits to the telecom industry are that the optical wireless communications spectrum is not yet regulated and there is no spectrum cost. Plus, OWC utilizes less power per bit transmitted, lowering power costs overall. Also, by utilizing OWC, telecom operators will no longer have to obtain landing rights, or licenses, to bury fiber optic cable, eliminating cost while speeding up network deployment times and in turn increasing customer satisfaction.

Optical wireless communications have an opportunity to fill connectivity gaps cost-effectively – be it in the air, on land, in space or at sea – and point-to-multipoint is a true game changer. As digital intelligence and data-driven everything continues to require greater, faster, and enhanced connectivity, the time to invest in multipoint optical communications is now.

Figure 1: Using laser communications, connectivity between air, space and the ground can be greatly increased helping to connect the un- or underconnected.

The use of laser communications in satellite networks is not a new concept. NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated laser communication between the Moon and Earth in 2013, achieving data rates of up to 622 megabits per second. Since then, several commercial companies and government agencies have completed additional demonstrations on Earth and on orbit to test the efficacy of the technology. Today, this technology can achieve hundreds of gigabits of data per second and lab models are seeking to reach data levels of 1 Terabit per second.

The Rapid Growth of Satellites

According to Euroconsult, 17,000 satellites are expected to be launched by 2030 representing a fourfold increase over the past decade. The Beyond Earth Institute, a public policy think tank, expects as many as 100,000 satellites in orbit by 2030. Over 80% of these satellites will be launched as part of satellite constellations and mostly by commercial players, such as OneWeb, SpaceX Starlink, Amazon Kuiper, Telesat Lightspeed, and others. This exponential growth of the satellite industry in the coming years will advance the need for satellite-to-satellite communications.

Not only will consumers, vehicles, devices and industry communicate with these in-orbit constellation satellites from Earth, but the satellites will need to “talk” to one another to increase network capacity, efficiency and reach. Inter-connected satellites will also serve as access points and provide connectivity services for other applications in space, such as Earth observation, data transmission and military surveillance. Laser communications technology has been proven to enable such high-speed and secure inter-satellite communication capabilities (see Figure 2).

Figure 2: Rendering demonstrating the inter-operability of satellites using laser communications technology.

Key Advantages of Laser Communications

One of the primary advantages of laser communications is its higher data rates compared to RF. Laser communication can provide data rates of hundreds of gigabits per second, which is much faster than the data rates of a few hundred megabits per second provided by RF. This high data rate is essential in transmitting large amounts of data, such as images and videos from Earth observation satellites.

Another advantage of laser communications is its improved security. Unlike RF, which can be intercepted and jammed, laser beams are tightly focused and difficult to intercept. Moreover, laser communications use a narrow beam, making it harder to intercept and harder to detect. This feature makes it an attractive option for military applications and other sensitive communications.

Laser communication is also less susceptible to interference from other sources, such as weather conditions and radio frequency noise, which can disrupt RF communications. In space, RF communication can be affected by solar flares, which can cause disruptions in the signal. On the other hand, laser communications are less affected by these conditions, making it a more reliable option for satellite communication.

Finally, laser communication technology is easy to deploy. Because there is no spectrum regulation for laser communications, frequency coordination which can take years to obtain using RF is not required.

Key Applications of Laser Communications

These planned mega constellations will be designed and deployed to create an “always on” connectivity infrastructure in space. Why space? Because space provides the most economical environment to create ubiquitous connectivity while avoiding common terrestrial barriers, such as topography and the expense of burying millions of miles of cable across Earth. We have witnessed how natural disasters, such as typhoons, hurricanes and volcanic activity can decimate terrestrial infrastructure. Building the communications infrastructure in space allows us to connect consumers, businesses, governments and industries in some of the most remote places on our planet and avoid the reliance on systems that can be damaged through natural disasters or human interference.

These proposed mega constellations will serve as data relay networks, powered by laser communications, to distribute and access unprecedented amounts of satellite data securely and globally with speeds of many Gigabits per second. We will be able to capture and transmit dynamic images of Earth in all sorts of spectra from satellites in real-time. The sheer size of the data files created by Earth observation technologies, like synthetic aperture radar, cannot be downloaded using RF.

And by using laser communications technology, we will be able to feed commercial satellite data directly in-orbit to government satellites avoiding the frequency bottlenecks and delays related to bringing satellite data down to Earth before relaying it further. The U.S. military is using commercial satellites for increased data and imagery and these needs will expand as more LEO satellites are launched.

Conclusion

Laser communications technology is becoming a critical part of large satellite networks due to its high data rates, increased security, and reliability. With the increasing demand for satellite connectivity, laser communication technology will play a significant role in enabling inter-satellite communication and providing global connectivity. Companies like Mynaric are at the forefront of developing and commercializing this technology, providing the means for satellite constellations to communicate with each other and with the ground.

At Mynaric, we are built on the power of laser communications technology. We have set out to not only provide optical communications terminals to ensure inter-satellite connectivity, but to package these capabilities in industrialized products suited for deployment as part of, and interoperable with, emerging satellite constellations.

Artists Impression of an optical laserlink between two satellites
(Photo courtesy Tesat-Spacecom)

ISLs can be addressed by traditional RF signals or by optical technologies, based on laser beams, so called optical inter-satellite links (OISLs). The major difference between RF and optical signals is the shorter wavelength of the laser light corresponding to a significantly higher frequency. As a consequence, optical antennas or telescopes can bundle the outgoing laser beam much better than the RF signals. Beam spot sizes of laser beams are typically in the order of 1 km after 45,000 km distance. The higher frequency range in the optics offers a higher bandwidth that can be used for data transmission. In summary, this leads to smaller dimensions and higher data rate capabilities for OISLs leading to smaller mass figures and lower power consumption. That’s why laser terminals were developed worldwide over the last decades. The breakthrough of the technology is driven by technological maturity combined with new applications that benefit exceptionally from the unique properties of OISLs. The number one application in this respect are satellite constellations.

Satellite constellations offer the possibility to connect people world-wide, especially in rural areas without terrestrial infrastructure. They also offer secure communications between two locations on ground with a known communication in between. With OISLs, satellite constellations turn into a meshed network in the sky. Several global satellite constellations in low earth orbit (LEO) are currently in planning and deployment. Besides LEO connectivity, multi-orbit connectivity towards MEO and GEO orbits are gaining more and more attention.

Artists Impression of an optical satellite network
(Photo courtesy Tesat-Spacecom)

Besides OISLs in constellations, there is also a need for OISLs in earth observation satellites. With ever more powerful sensors on board, the amount of data generated with earth observation satellites is continuously increasing. Direct-to-earth (DTE) optical communication links or data relay optical communication links via a data relay satellite provide a solution to get the increasing amount of data to ground. Data relay concepts can be applied over geostationary satellites. Alternatively, a LEO constellation can be used as a data relay layer to distribute the data.

As mentioned above, optical communication links are working with narrow beams, therefore the benefits of transferring the data via optical communication links are; high operational security and immunity to interferences while benefitting of a non-regulated optical frequency spectrum.

Because of these advantages, optical communication in space is very attractive for space applications. Research projects were running with various institutions. The technology has been extensively investigated and brought into orbit in several missions. In the following, an excerpt of in-orbit demonstration missions are listed, that helped to move the field forward. The list is not exhaustive and is intended to give an impression on how the technology was continuously matured worldwide.

In Japan optical communication technology has been intensively investigated over decades. The first laser communication link from space to ground was carried out in 1995 between the JAXA’s ETS-VI GEO satellite and an optical ground station at the National Institute of Information and Communications Technology (NICT)’s in Tokyo achieving 1 Mbit/s. This program was followed by the Japanese OICETS program, demonstrating LEO to ground optical data transmission to a NICT optical ground station.

The research activities in Europe reach well back into the 1980s. The European Space Agency (ESA) together with the German Space Agency (DLR) and the French Space Agency (CNES) had various technological research programs in the field of optical communication. The first European demonstration in orbit happened in 2001 with a laser inter-satellite link demonstration between the European Space Agency (ESA) satellite Artemis, and the CNES earth observation satellite SPOT 4. In this demonstration, a data rate of 50 Mbit/s was achieved over 40,000 km, the distance of a LEO-GEO link.

In the US, led by NASA, a remarkable optical inter-satellite link demonstration to the moon was performed in 2013. The mission, called LADEE (Lunar Atmosphere and Dust Environment Explorer) demonstrated optical data transmission from a satellite in an orbit around the moon to optical ground stations on earth. In 2014, optical communication links from the International Space Station (ISS) to ground were demonstrated in a project named OPALS.

In 2007, a LEO to LEO OISL demonstration experiment led by the German Space Agency (DLR) was launched. The two Optical Communication Terminals (OCTs) manufactured by TESAT in Germany, were launched on board of the US satellite American Near Field Infrared Experiment (NFIRE) and the German satellite TerraSAR-X. Data transmission of 5.6 Gbit/s was demonstrated for both OISLs and LEO to ground DTE links. The pointing, acquisition and tracking (PAT) algorithm was based on a so-called beaconless approach, a scheme that does not require a separate beacon to acquire the communication link. Instead, the communication beam is used in a spiralling scheme to set up the communication link. The related PAT algorithms were intensely investigated in orbit.

Artists Impression of an optical inter-satellite link between TerraSAR and NFIRE in 2008 at 5.6 Gbit/s.
(Photo courtesy Tesat-Spacecom)

After these intense research activities and various successful in orbit demonstrations, the very first commercial application of optical communication in space was realized, which is the European Data Relay System (EDRS). EDRS is a LEO to GEO data relay system which relies on TESATs’ optical ISLs at a data rate of 1.8 Gbit/s. As of today, there are three Laser Communication Terminals (LCTs) on board of GEO satellites and four LCTs on board of LEO satellites. The EDRS service is operative since end of 2016 and is continuously used to get real-time data from the Sentinel earth observation satellites to ground. As of now, 78,000 links have been performed at a rate of 1,000 links per month. EDRS demonstrated the benefit of OISLs in a commercial application, offering an additional data path to the ground increasing the overall satellite capacity. In addition, a near real time service is used to download satellite data to ground in occasions where no ground station is in sight of the LEO satellite.

Based on these in-orbit experiences over decades, TESAT has built a broad portfolio of optical communication solutions, ranging from powerful GEO-to-GEO long-distance ISLs to small, low complex DTE solutions for CubeSat missions. The Scalable Optical Terminal (SCOT) family from TESAT currently consists of three new models. The SCOT20 is optimized for SmallSat and CubeSat applications, the SCOT 80 is designed for LEO constellations whereas the focus of the SCOT135 is on MEO and LEO orbit connections.

Artists Impression of TESAT’s OCT family incl. LCT135, SmartLCT70, SCOT80, SCOT20, T-OSIRIS
(courtesy by Tesat-Spacecom)

But not only in Europe has the potential of optical communications been identified as a game-changer for satellite communication. Also the US is intensively expanding the use of optical communication technology for ISLs.

Thus the Space Development Agency (SDA), who will launch their first constellation in March 2023, relies on OISLs for both transport and tracking layer. In order to reduce development and production costs SDA has set a standard for optical communications, allowing interoperability between terminals of different suppliers. This approach transformed the industry and allowing companies like TESAT to grow its production for optical communication terminals.

In summary, after an intense research phase and successful demonstrations in orbit, the Optical Inter-Satellite Link (OISL) technology is now ready for use. The intense investigations of the terminals in orbit provided valuable insights to further mature the technology. The need for OISLs in constellation applications pushed the industrialization and the commercialization of the Optical Communication Terminals forward. Therefore, the future is bright for this exciting new technology.