Laser - The future for space communications and connectivity

Show me the Moon

When NASA returns to the moon with its Artemis III mission in 2025, we can expect to see live video images beamed back to Earth in 4K ultra-high-definition quality, a far cry from the grainy greyscale images from the Apollo 11 landing in 1969. The difference is thanks to the development of wireless laser communications, also known as Free-space optical (FSO) communications offering much higher bandwidth than that achieved with traditional radio spectrums.  Laser or FSO communications is technology that uses photons moving in free space (air, vacuum or outer space) to wirelessly transmit optically encoded digital data. Laser communications will enable 100 times more data to be transmitted back to Earth than current radio frequency systems.

Gigs in Space

My research into LEO satellite connectivity at Forrester last year didn’t specifically cover laser communications – as we won’t be expecting to see fibre to the premise offerings as we get for terrestrial communications today (more on that later). But space users are experiencing other benefits of laser communications. Newer satellites launched into low-orbit, such as those from Starlink, are now being equipped with fibre-optical terminals. Satellites in the constellation will comprise optical inter-satellite links (OISLs) to create a huge resilient mesh network in space. Telesat plan to include optical satellite links when it fully launches its LightSpeed constellation and OneWeb is planning to include optical links in its phase two deployment. Amazon’s Kuiper constellation will (eventually) launch with inter-satellite links enabled by design from the outset.

Manufacturers such as CACI, Mynarmic and Tesat offer speeds of 10-20Gbps and are promising up to 100-200Gbps with upcoming product developments.  NASA has already transmitted data from low orbit to Earth at 100Gbps (see below) and the ESA (European Space Agency) is undertaking a project with the ambition to hit up to 1 terabit per second speed, way surpassing broadband speeds achievable over radio spectrum.  The evolution of satellite communications has always been the search for more bandwidth. Laser technology, with its higher frequencies and short wavelength allowing greater data encoding, has been around since the 1970s but the sector was not ready for the paradigm shift. That’s changed alongside the other developments in space commercialisation. With the increasing adoption of synthetic aperture radar (SAR) for earth observation via Low-Earth Orbit (LEO) satellites, using radio spectrum for downloads will not be scalable. Analysts are now projecting the market for satellite laser communications will be worth $3 billion to $4 billion over the next ten years.

Something in the air

For space there are two main scenarios, 1) space to space communication, such as inter-satellite links and 2) Space to ground communication, where satellites equipped with laser communications connect with strategically located optical ground stations to support high data transmissions for use cases such as earth observation and imaging. Mynaric are also planning laser solutions for air to air and air to ground communications with terminals deployed on airplanes, drones and even balloons. They offer some interesting use cases if they can overcome the challenge of atmospheric distortions due to cloud, fog and bad weather conditions for the downlinks to Earth. These include network coverage in a disaster relief scenarios, surveillance and high-speed in-flight Wi-Fi services.

Down to Earth – Cutting through the ups and downs

While American chemist and materials scientist, Mark Ratner is quoted as saying "Lasers are like magic wands. You can do almost anything with them." like any technology innovation, there are constraints and challenges such as the aforementioned issue with atmospheric distortion.

The laser communications telescope pointing from a satellite to a ground station must be exact especially when beaming from a distance of thousands of miles away. A deviation of even a fraction of a degree can result in the laser missing its target entirely. Complications also arise because the beam must stay focused on the ground site as the satellite passes over it, remembering its path will change slightly with each pass, because the Earth is constantly rotating. And, although laser light can travel long distances in space, laser beams can be distorted on Earth due to atmospheric effects, cloud, fog and bad weather conditions. This distortion causes the beam to experience power loss, resulting in data loss.

The location of optical ground stations to receive the laser signals from space to Earth is critical. For example NASA located their optical ground station on Table Mountain, California, where most weather takes place below the mountain's summit making for a clearer sky.  The ground station uses adaptive optics to correct for distortions caused by atmospheric turbulence. The system measures the distortion and then sends the signal through a deformable mirror that changes its shape to take out any aberrations that the atmosphere induces to improve the signal quality. Subsystems are also required for signal acquisition, tracking and error detection and correction.  Selecting optical ground stations is easier for GEO satellite connectivity but with LEO constellations, a larger network of optical ground stations is needed to enable seamless and global coverage of optical satellite-to-ground communications. While the ideal location for clearer skies is at high altitudes in remote locations, ground network infrastructure connectivity and ground station maintenance requirements must also be considered. These dependencies make laser communications to the home unfeasible.

For LEO satellites using OISLs, optical communication relies on precision pointing of the narrow beams as the satellites are travelling at 28000km/hour and are subject to vibration, extreme thermal conditions and radiation. Interoperability is another key challenge. To date, there are no specifically agreed standards, although vendors state they are adopting existing fibre optical protocols.

Focusing on the pluses

Despite these challenges, there are clear advantages of laser to spotlight in addition to its ultra-high data rates. Radio is susceptible to interference due to congestion from adjacent carriers so needs to be licensed and regulated. Laser’s narrow beam and point-to-point communications avoids interference with other systems meaning restrictive and costly regulation is not needed. Its small beam size also makes it less demanding on power, critical for systems deployed on satellites in orbit. Because it is point to point with a narrow beam, only the designated receiver can detect the transmitted beam making it undetectable to adversaries. Radio, with its wide signal spread in multiple directions is more easily intercepted and subject to jamming and eavesdropping.

The maximum distance depends on factors such as the power of the laser, the sensitivity of the receiving equipment, atmospheric conditions, and the diameter of the beam. With more compact design and greater energy efficiency in converting electricity supplied into light energy, it is feasible to establish links at distances greater than 40,000 km in space. NASA achieved the record distance for laser communication back in October 2013, transmitting data from lunar orbit to Earth at a rate of 622Mbps, a distance of 239,000 miles or 385,000km. All is looking good for the Artemis III moon mission.

For LEO satellite connectivity to be viable in the long-term, the ability to inter-connect satellites is a critical dependency for a scalable and resilient high-speed, low latency service. OISL with AI algorithms to determine the most efficient path for data routing combine to make LEO satellite constellations into self-governing networks. Rather than bringing data to the ground immediately, and paying terrestrial network providers to move it to the end user, the smart mesh in space will move data around in orbit and bring it to Earth via the ground station closest to the end user.

Beaming ahead

Ultimately the real benefits with laser communications are space-based where the likes of NASA, DARPA (Defense Advanced Research Projects Agency), SDA (Space Development Agency) and ESA are beaming ahead in addition to commercial ventures.

NASA is leading several initiatives exploring the future of laser communications. In December 2021 NASA launched its first two-way optical communications relay system – the Laser Communications Relay Demonstration (LCRD) mission. LCRD is a relay satellite in geosynchronous orbit (GEO) capable of sending data from its GEO orbit to Earth at 1.2Gbps.  Missions in space can send their data over laser links to LCRD, which will then transmit the data down to optical ground stations on Earth. In May 2022, NASA certified that LCRD is ready for its plans to conduct hundreds of experiments. The first experiment will be NASA's Integrated LCRD Low-Earth-Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) mission, targeted to launch later in 2023. This will provide astronauts and scientists aboard the International Space Station with enhanced data capabilities.

NASA’s TBIRD (TeraByte InfraRed Delivery) mission, launched in May 2022 is testing laser communications in Low-Earth Orbit on a small satellite (the size of a tissue box). The goal is to demonstrate a downlink of 200 gigabits per second. In November 2022 the mission achieved a record for optical communications in space. The satellite downlinked 1.4 terabytes of data at 100Gbps in a single pass that lasted about five minutes.  NASA’s Artemis II moon orbit mission, planned for 2024, will demonstrate laser communications, sending data to Earth with a downlink rate of up to 260Mbps.

DARPA in partnership with SDA is testing laser communications as part of its Blackjack defence program to develop and demonstrate the critical elements needed for a global high-speed, resilient and secure defence network in low Earth orbit. OISL communication between two satellites was successfully tested in May 2022 and they are now focusing on space to ground laser tests. They also kicked off a program in August 2022 to investigate interoperability for free space optical communications. SDA is also leading a program for the United States Department of Defense’s plans for a new network of low-cost missile tracking satellites where encrypted optical inter-satellite links are seen as critical to the design of the constellation.

ESA’s HydRON program (High-thRoughput Optical space Network) will link satellites in low orbit to optical-fibre networks on the ground, enabling reliable, instant connectivity anywhere on Earth. HydRON forms part of ESA's ScyLight program (Secure and Laser communication technology). Both programs are still in early studies and contract award for projects stages. ESA also partners with Airbus for the Space Data Highway (SDH) laser communication infrastructure.  SDH enables users to transfer data over laser from LEO satellites and airborne platforms via two geostationary satellites to receiving ground stations in Europe.

Not light years away

The future of free space optical communications is very encouraging, as ongoing research and development efforts focus on improving the technology and expanding its capabilities. Laser promises hundreds of gigabits per second and potentially terabits per second data rates. This will be critical for future deep space missions. With the anticipated huge growth of data from more and more earth observation and imaging solutions, optical links will also be critical to deal with the sheer volumes of data needed to come back down to Earth. Of course, like any technology, it will always be constrained by physics. While we can anticipate high-definition images from the Artemis moon mission in 2025, expect approximately two seconds of latency given the distance. As a trade-off though, the benefits are hugely significant. Ongoing research and development will continue to design more compact, efficient, reliable and resilient laser communication systems and expand the range and coverage and flexibility of laser communications interfaces and networks. We can certainly look forward to some magic laser innovations from space in the years ahead.