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The Japanese technology leading the way to making the "spaceified internet" a reality
Shiro Yamakawa, JAXA JDRS Project ManagerHiroaki Miyoshi, NEC Fellow
Earth observation satellites capture images of the Earth and relay the data back to the ground in real time via a relay satellite. In January of this year, Japan Aerospace Exploration Agency (JAXA) successfully completed an on-orbit trial for a project it has been working on since 2015—the Laser Utilizing Communication System (LUCAS) project involving an optical inter-satellite system for achieving high-volume, high-speed data transmission. NEC has supported the development and testing of this system every step of the way. We sat down with Shiro Yamakawa, JAXA JDRS Project Manager, who has conducted the development of LUCAS, and Hiroaki Miyoshi, the leader of the NEC team, to learn why this project was a success and ask them to share their visions for the future.
Transmitting large volumes of data to the Earth in real time
──On September 28, 2024, JAXA and NEC successfully performed inter-satellite optical communication between the DAICHI-4 Earth observation satellite and an optical data relay satellite. This was the exact moment in which the LUCAS project became a success. Could you please tell us how you felt in that moment?
JAXA JDRS Project Manager
Yamakawa: I was overwhelmed with emotion. The optical data relay satellite was launched in November 2020, and DAICHI-4 was launched in July 2024. In the two months following DAICHI-4’s launch into space, we verified the initial functions and confirmed the operation of communication devices one by one, making minor adjustments along the way. Once communication proved successful, I knew our hard work had paid off.
Miyoshi: The LUCAS project has been challenging because many things can only be tested in space. The distance between DAICHI-4 and the optical data relay satellite is around 40,000 km, and it is impossible to perform communication testing over that great of a distance here on Earth. Therefore, our only option was to put two satellites into space and conduct the testing there. Since this was a first for us, there were many uncertainties that we had to clear one by one over those two months.
Yamakawa: The data captured by DAICHI-4, which orbits at a low altitude of around 600 km, is transmitted to an optical data relay satellite in geostationary orbit at an altitude of 36,000 km above the equator and then sent to a ground station. Instructions from the ground are also sent to the optical data relay satellite and shared with DAICHI-4. Optical communication, which enables high-capacity, high-speed transmission, is used for inter-satellite communication. That’s where LUCAS comes in. On January 10, we successfully used this system to transmit large volumes of data.
──What specific data did you obtain?
Yamakawa: DAICHI-4 orbits the Earth in approximately 100 minutes. The images captured of the Earth’s surface back in January from this orbit are of the Arctic Ocean, Europe, and Africa. This series of images captured over a 35-minute period were sent in real time to a ground station in Japan via an optical data relay satellite.
What makes LUCAS groundbreaking?
──Could you explain what makes LUCAS groundbreaking?
Yamakawa: There are two main reasons. The first is that it uses a data relay satellite to transmit data rather than transmitting data directly from the observation satellite to the Earth. When observed data is directly sent to the ground, the time in which communication with the ground station is possible is limited to around 10 minutes per 100-minute orbit of the Earth. Meanwhile, communication with the ground station can be extended up to 40 minutes per orbit via an optical data relay satellite that is in constant communication with the ground. During that time, an extensive area covering approximately one-third of the earth can be observed. This is the first reason LUCAS is groundbreaking.
NEC Fellow
Miyoshi: On a per day basis, this equates to a nine-fold increase in the amount of time that can be spent observing the Earth’s surface. A simple calculation tells us that this results in the amount of area growing nine-fold as well.
The visibility range of a data relay satellite in geostationary orbit covers approximately one-third of the Earth’s surface. Therefore, if we were to use multiple Earth observation satellites to orbit the Earth, the entire surface of the Earth could be captured in real time. We believe a system like this will become a reality in the not-so-distant future.
Yamakawa: The other reason LUCAS is groundbreaking is that it uses optical communication to transmit data. This has four major benefits.
The first is that it enables high-speed transmission of high-capacity data. In the past, radio frequencies were used for inter-satellite communication. With optical communication, data can be transmitted at a data rate more than seven times faster than radio frequency communication. As a result, the amount of data that can be transmitted also increases dramatically.
The second is that it makes it possible to reduce the size and lighten the weight of antennas mounted on satellites. While the diameter of radio frequency antennas is 3.6 m, that for optical antennas is a mere 15 cm. This significantly decreases the load on satellites.
The third is that the spread of communication waves is minimal. Communication waves spread as they travel through the air over long distances. The distance between an observation satellite and an optical data relay satellite can be as far as 40,000 km. The beam diameter of a radio wave can expand up to several tens of kilometers as it covers that distance. Meanwhile, the spread of an optical beam diameter is just under 600 m. This smaller beam spread also means that interference with other communication waves is unlikely to occur.
The fourth and final benefit is also related to the spread of communication waves. The smaller the beam diameter, the more difficult it is to interfere with or intercept communications. As a result, data confidentiality can be ensured.
The challenge faced in the final phase of the project
──When did JAXA and NEC start their partnership in the domain of inter-satellite optical communication?
Yamakawa: Although the LUCAS project officially began in 2015, the partnership between JAXA and NEC goes back even further. Japan’s first optical inter-satellite communication experiment was conducted in 2005. This was an experiment jointly conducted by Japan and Europe, with JAXA and NEC participating from Japan, and the European Space Agency (ESA) and a French company participating from Europe. Over the course of this endeavor, JAXA and NEC built a solid partnership. The strength of this partnership has also been demonstrated through the LUCAS project. I would even venture to say that this project would not have been possible without NEC’s participation.
──Please tell us why NEC was the perfect partner for this project.
Yamakawa: Japan launched its first artificial satellite, OHSUMI, in 1970, and it was NEC who was responsible for its development. NEC has now been involved in the space business for over half a century. In addition, NEC has extensive experience in the optical communication infrastructure business. These are the two biggest reasons. In reality, NEC is the only company in Japan that can be called an expert in space and optical communication.
I think another crucial factor is NEC’s integrity. In response to our requests, they would tell us outright if they couldn’t do something. This integrity is what mattered most to us. It would be pointless for them to tell us they could do something even though they couldn’t if it would later result in problems. However, they wouldn’t just tell us that they were unable to do something. Instead, they would offer proposals for what they could do. In this way, I have always found everyone at NEC to be incredibly trustworthy.
──Did you encounter any serious situations over the course of this project spanning ten years?
Miyoshi: While we faced numerous hardships along the way, the optical fiber amplifier was the biggest hurdle we found ourselves up against in the final phase of the project. The wavelength used with LUCAS was the 1.5 micrometer (C band) band. This is the laser wavelength utilized for terrestrial optical fiber communications, and we anticipate it being the standard for space in the future as well.
The problem that arises is that laser power at a wavelength of 1.5 μm is weak. Repeaters are installed approximately every 100 km for the submarine cables used to connect continents, thereby making it possible to amplify power while covering long distances. However, this is not an option in outer space.
This is what led us to employ a method using a component called an optical fiber amplifier to boost laser power. To realize this component, a signal light with power output as high as 3W must be passed through a fiber core with a diameter measuring 10 μm, which is far thinner than even a human hair. This was a challenge that had not yet been tackled by anyone in the world because it is an unnecessary technology here on Earth, where repeaters can be installed.
Bringing this optical fiber amplifier to fruition was not an easy task. There were times when the heat generated by the light would cause the fiber to burn. After about a year of addressing each problem, we finally perfected it.
Yamakawa: The project would have come to a screeching halt if we hadn’t brought the optical fiber amplifier to fruition. Since everyone at NEC made such a concerted effort under Mr. Miyoshi’s leadership, we trusted that they would guide us to a definitive solution.
Miyoshi: We couldn’t betray the trust that JAXA and Mr. Yamakawa had placed in us. We wanted to do everything in our power to meet their expectations, and it was this strong desire that spurred NEC’s engineers and technicians to do everything they possibly could. It was truly a testament to their dedication and hard work.
The future charted by space technology
──Exactly what will the realization of inter-satellite optical communication make it possible to do?
Miyoshi: An inter-satellite optical communication system will make it possible to send large amounts of data in real time, such as terrestrial imageries taken by remote sensing satellites, to the ground. This will aid in not only preventing disasters but also facilitating emergency responses when they do occur. That is primarily what we envision using this system for.
Beyond that, there is a broad array of possible applications. Once optical communication becomes possible in outer space, we will have expanded the Internet network we use here on earth to space. Think about how the number of things we were able to do increased exponentially once the entire world became connected via the Internet in the 1990s. Now imagine the same thing happening in outer space.
Having said that, there is no reason to venture into space to do what can be done right here on Earth. In the past, we had to use broadcast satellites (BS) or communication satellites (CS) to watch TV programs on anything other than terrestrial broadcast. However, now that submarine cable networks have been installed, most video content can be viewed via Internet streaming. This is one example of a system that was once “spaceified” but has now been “terrestrialized.”
Conversely, there are many technologies that will not become a reality until they have been spaceified. It will be impossible to monitor extensive areas and transform inaccessible areas into places of economic activity without a system for acquiring terrestrial data from space and a communication network for transmitting that data.
Applications of the so-called "spaceified internet" are expected to be wide-ranging. For example, to allow systems for the autonomous operation of vehicles and vessels to take root as part of our social infrastructure, we must improve security and networking. However, there are limits to this if you are using terrestrial-based sensing and network technologies. It will be necessary to have a system with which you can monitor the driving of vehicles and the operation of vessels from space, and instantly deliver information to the ground in times of danger. It should also be possible to use the spaceified internet for this.
Yamakawa: JAXA and NASA are currently collaborating with other countries on the Artemis program aimed at completing a manned moon landing. I believe optical communication technology will prove to be very useful in international projects like this one as well.
Miyoshi: We view the optical communication technology in outer space realized through LUCAS as an enabler; that is, “a means by which to achieve what has up until now been impossible.” So what can we do with this enabler? We need to find colleagues in different fields and industries who will not only contribute ideas, technologies, and funds but also join us in our efforts to create new value. This is what we need to be working on going forward. I’d like to see us expand the ecosystem and promote the social implementation of optical communication technology in space.
──Having achieved this success in optical communication, is it safe to say that the LUCAS project has reached the point of completion?
Yamakawa: The lifespan of a satellite that has been launched into space is about 10 years. While satellites remain in operation until they reach the end of their lifespan, I would say that we have completed the research and development phase. The inter-satellite optical communication trial period will continue until July 2025, after which we will finally enter the actual operation phase.
──Could you please leave us with a few words about your aspirations going forward?
Miyoshi: Japan was the fourth country to successfully launch a satellite into space. We have a long history of space development, advanced technologies, and many outstanding engineers. To harness that potential, we need a goal or vision that can be shared by many people.
What can we achieve by using space technology? How can we utilize space technology to make the world safer and encourage economic development? What kind of future can we chart with space technology? My goal moving forward is to work together with everyone at JAXA, the members of NEC, and people in Japan and around the world to share this vision with society at large.
Yamakawa: I think it is safe to say that Japan is a step ahead of other countries in the inter-satellite optical communication domain. Speed is the key to capitalizing on this first-mover advantage. I would like to contribute to the generation of solid value by achieving the social implementation of this technology early on.
Space offers infinite potential to take on new challenges. If younger generations take a keen interest in space and the number of people who would like to be involved in the space business increases, I think Japan will continue to be the top runner in space development. NEC would like to see this vision become a reality.
