© Fraunhofer / Thomas Straub
Security
Web special Fraunhofer magazine 3.2023
It began with the internet in Ukraine. When the network collapsed under the force of Russian attacks, nationwide digital communication was restored with the help of a private satellite network. In Europe, relief over US entrepreneur Elon Musk quickly providing help via Starlink soon changed to unease: It seemed no European state was in a position to support Ukraine with this strategically important issue. The war highlighted two problems: How vulnerable terrestrial infrastructure is without backup from space, and how dependent Europe is on third parties when it comes to space technologies and satellite-supported communication.
The EU now wants to change this. By 2027, a constellation of up to 200 satellites should guarantee Europe’s sovereignty in space and, by extension, on the ground. IRIS² (Infrastructure for Resilience, Interconnectivity and Security by Satellite) is a large-scale project aimed at not only securely networking critical infrastructures and creating resilient crisis management methods for governments, but also ensuring comprehensive broadband connectivity across Europe, especially in previously underserved regions. The EU wants to open this up to private technological initiatives: Apart from Starlink – which currently has about 4,000 satellites at an altitude of 500 to 550 kilometers, with 8,000 more to come – another supplier active in space is the British company OneWeb, which has 600 satellites. Amazon has announced news of another mega-constellation in the form of its Project Kuiper. China, too, is already planning a network numbered in the five digits.
“More and more countries want to increase their sovereignty by having their own satellite constellations,” observes Dr. Nadya Ben Bekhti-Winkel. As acting head of the Space technology area, part of the Fraunhofer AVIATION & SPACE alliance, she has joined 14 organizations from five countries in participating in a feasibility and concept study for a European broadband satellite constellation. The goal: to develop, analyze and evaluate new ideas and technologies for this purpose. This involves four key areas: First, robust, resilient communication between the satellites that combines radio signals with optical, laser-based technologies. Second, quantum encryption, to make it as tap-proof as possible. Third, GPS-independent satellite operation, as well as interoperability with existing European systems such as Galileo and Copernicus. “And fourth,” adds the space expert, “the scalability of the entire system.” The consortium also carried out customer analyses to determine the benefits to state organizations, industry and private households, and to establish the relevant business cases.
These days, profitability is key, even in space: Welcome to the New Space age! While satellite projects were formerly driven and exclusively financed by state bodies, these days we are seeing ever-increasing involvement from private enterprises. Industrial companies and start-ups will be providing the lion’s share of the space applications we need – and they will also reap the financial rewards. Rather than large systems with sophisticated technology, New Space will feature small satellites communicating with each other to form powerful networks. “Small satellites are cheaper and quicker to manufacture than conventional large satellites. This means companies can react more quickly to the needs of the market. The possibility of cheaper mass production would enable construction of large satellite constellations for entirely new commercial services and scientific applications. This brings about exciting research questions for Fraunhofer in areas such as intelligent systems, innovative payloads and modern manufacturing processes, right through to application development,” says Prof. Frank Schäfer, head of the Space business unit at the Fraunhofer Institute for High-Speed Dynamics EMI, based at the Ernst-Mach-Institut in Freiburg. His institute researches and develops technologies for New Space and has built ERNST, Fraunhofer’s first research satellite, which is scheduled for launch in 2024.
Built with research funding from the German Federal Armed Forces (Bundeswehr), the role of ERNST is to detect missile launches from anywhere in the world from a low Earth orbit. Its built-in infrared camera can recognize the heat emitted by hot rocket engines. However, this nanosatellite half the size of a beer crate also lends itself to other important tasks: spotting forest fires, detecting greenhouse gases and measuring sea temperatures. As a modular platform, it offers important experiential data on how to design a satellite that can accommodate as much productive payload as possible within a small space. “ERNST offers us entirely new opportunities to research a wide variety of technologies on our own satellite platform,” says Prof. Schäfer. “These findings are being included in the plans for more small satellite constellations in the future.”
Seeing as many small satellites in lower Earth orbits circle the Earth more frequently, constellations of these kinds of nanosatellites lend themselves to Earth observation, which requires as many images of a location as possible – to document local changes, for example. As they are permanently available, they could also guarantee comprehensive internet access if fitted with the right equipment. Compared to the tally of satellites owned by private networks, numbering in the four digits, IRIS², with its approximately 200 individual satellites, is on a more manageable scale. These satellites should be carefully distributed across multiple orbits, as orbiting at higher altitude allows them to cover wider areas.
In the case of satellite swarms spanning multiple orbits, the most crucial factor is communication with ground stations. IRIS² aims to harness the latest radio and laser-based optical technologies. “One of the greatest challenges when constructing a new satellite constellation is the availability of radio frequencies,” says Dr. Ben Bekhti-Winkel. “The electromagnetic spectrum is very limited, and with the ever-increasing numbers of satellites in orbit, it is important that radio ranges from various services do not cause interference for each other. They must therefore be well shielded; compatibility studies must be used to prove that there is no overlap.” In Germany, the German Federal Network Agency is responsible for the restrictive allocation of frequencies as well as for regulating them, both within the country and internationally.
Satellite communications must therefore use the available frequencies as efficiently as possible. Rainer Wansch, head of the RF and SatCom Systems department, and his team at the Fraunhofer Institute for Integrated Circuits IIS in Erlangen, are working on this. These researchers already played a part in the standardization of DVB-S2X, the most advanced satellite communications standard to date. They use beam hopping, a new concept that allows data transmission via satellite to be flexibly adapted to the variable levels of data demand in different areas. “Up until now, a satellite would supply static levels of data to certain areas. Beam hopping means the satellite switches back and forth between different coverage areas – based on a schedule that takes into account the required data rates at a given time,” explains Mr. Wansch. “This means one antenna can cover multiple areas – and the transmission capacity is always available in full bandwidth exactly where it is needed.” This requires the satellites to be equipped with modular phased array antennas. Their individual beams can be electronically controlled, making them much more flexible than the mechanically controlled antennas that were previously used.
For global cellular coverage to function reliably, satellite communications must be integrated into terrestrial communications such as the 5G network. In the future, user equipment should also be able to directly communicate with satellites – even when there is no terrestrial base station nearby, which has been an indispensable requirement up until now. In the future, depending on whether they have reception, smartphones or even autonomous vehicles could be able to establish a 5G connection either via a terrestrial station or directly via satellite. This flexible combination of fiber-optic and satellite internet would enable complete network coverage across Germany – bidding goodbye to mobile dead spots. In 2021, Mr. Wansch’s team of researchers at Fraunhofer IIS used a geostationary satellite in orbit above a fixed location on the Earth’s surface to successfully demonstrate the first direct communication between satellites and 5G-enabled user equipment in a non-terrestrial network (NTN).
To trial these NTNs, along with efficient transmission concepts and other satellite technology, radio experts developed the Fraunhofer On-Board Processor (FOBP), a type of satellite communications laboratory that can be booked by those in research and industry for experimental purposes. This flying laboratory went into space this summer on board the communications satellite Heinrich Hertz (H2Sat), and took on the job of processing its digital signals. “Up to now, communications satellites have just acted as relays that receive signals from Earth, amplify them and transmit them to other ground stations, where the signals are processed,” explains Mr. Wansch. “Onboard processors allow the signals to be processed directly within the satellites. So the satellites themselves become intelligent network components that can control data streams as needed.” As the processor can be adapted to new communication standards from the ground at any time, it lends itself to a diverse range of experiments and applications.
More and more data, limited radio frequencies – but at the end of the tunnel there is: light! Light can also be used for communication between satellites and ground stations. Transmitting constantly increasing amounts of data at the speed of light across ever-expanding distances through space is one area that optics experts are researching at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena. They are developing laser sources for generating light, as well as optical amplifiers to maximize the range of these lasers.
One of their solutions is the wavelength division multiplexer: a device that combines multiple laser beams of different wavelengths. Every individual laser beam with its own specific wavelength represents a single channel, each of which can transmit data and generates 20 watts of power. This multi-channel approach enables high data transmission rates. The multiplexer combines these channels into a single, more powerful signal. Superimposing five channels achieves a total of 100 watts of optical power and thus a very long range. This raises the prospect of an optical link that could reach as far as the moon. Satellites distributed across multiple orbits could use light to communicate seamlessly with ground stations. Researchers are currently working on a system with 1,000 watts of power, which should be scalable up to 10,000 watts in the future. This would make it possible to transmit data from Earth as far as Mars.
Light offers one further advantage, apart from range and capacity: Entangled light particles make data exchange particularly secure – which is vital in today’s uncertain global situation. Critical information belonging to state or military bodies must be reliably protected from unauthorized access. The EU therefore wants to be among the first to back the principle of quantum key distribution (QKD). This could prove to offer a real advantage over Starlink and other commercial networks. The aim is to supply secret symmetric keys to two partners, no matter how far apart they are. This can be achieved using entangled light particles. The characteristics of these photons are so closely linked that measuring just one of the particles also immediately determines the state of the other. Any unauthorized interference immediately breaks this connection, which makes it practically impossible to tap. QKD would secure this communication even from quantum computers, which could well be capable of cracking many of the classic encryption methods before long.
Quantum keys can already be seamlessly exchanged over shorter distances at ground level. However, global quantum communication would require longer ranges that could span continents. This remains a challenge − too many of the fragile light particles go astray. At Fraunhofer IOF, Dr. Fabian Steinlechner and his team are working on multiple parallel projects in search of some solutions. For example, they are developing space-suitable miniaturized photon sources the size of a milk carton − these act as a transmitter on board satellites, generating entangled light rays and sending them to Earth. These rays are received at the ground station by optical reflecting telescopes the size of a TV satellite dish. From there, they enter the fiber optic network to be distributed to the receivers. The optics experts are working with eight European and Canadian research partners to further develop quantum communication via free beam into scalable global quantum networks. “In the Hyperspace project, we’re creating preliminary designs for transmitting entangled photons over longer distances of 6,000 kilometers and more. This includes, for example, noise-resistant quantum state encoding, as well as hyperentanglement, where the particles are mutually entangled across not one, but multiple characteristics. That could make information transfer both quicker and more efficient.”
However, optical communication via satellite faces three hurdles: sunlight, clouds and atmospheric turbulence. These can significantly reduce the quality of light signals or diminish visibility. To receive usable signals even during daylight hours, the quantum experts apply various filters: “Because we know the direction and point in time from which the data signals were transmitted, we can use spatial and temporal filters to distinguish them from sunlight and filter them out,” explains Dr. Steinlechner. “In addition, spectral filters allow the spectrum to be narrowed to the relevant wavelengths.”
Light rays distorted by turbulence can be corrected using adaptive optics (AO). Picture these like small, flexible deformable mirrors located within the receiving telescopes − they are reshaped using multiple positioning elements to precisely align the light ray so that it can be received by the telescope. These AO mirrors allow the light to be focused even more exactly and directed into a fiber optic cable about two millimeters in diameter. The biggest challenge yet to be resolved is that of clouds, as they often completely block the optical signals. According to Dr. Steinlechner, it could help to include redundancies in the form of other technologies such as radio or diversions to other satellites positioned over cloud-free regions. The quantum keys can also be created in advance so that secure communication is not necessarily dependent on cloud cover.
All of this means quantum communication is still too technologically complex to provide secure universal broadband connections. “Just as quantum computers are not going to replace smartphones, quantum communication will not replace conventional communication technologies,” says the researcher. He believes the technology will reach sufficient maturity by 2027, when IRIS2 will launched, but only for specific areas of application. For example, European satellites could be used to create a temporary high-security internet for especially security- critical applications or events such as the G7 summit. The research team recently demonstrated how this can be done by carrying out a key experiment as part of the QuNet initiative, which is funded by the German Federal Ministry of Education and Research (BMBF). The experiment involved creating an ad-hoc network between three locations in Jena, through which they were able to establish tap-proof communication.
The private satellite networks are still a few years ahead of the European network in their development. However, there is one other area, apart from the application of quantum technology, where IRIS² could still take a pioneering role: this constellation will be more sustainable than others. The plan is to minimize greenhouse gas emissions at every stage of the development process. Light pollution is a problem that has not been adequately addressed to date. For some time now, the night sky has been illuminated not only by stars, but by a great many satellites – and their number keeps growing. The International Astronomical Union is concerned about the impact of satellite constellations, as they reflect sunlight and so interfere with astronomical observations. “In IRIS2, we therefore also intend to reduce the visual brightness of the satellites using methods such as special non-reflective coatings,” explains Dr. Ben Bekhti-Winkel.
Then there is the enormous issue of leaving behind undesirable legacies: More satellites will potentially lead to more space debris in the form of detached parts, or defective or decommissioned objects. This increases the risk of collisions. According to the ESA, about 30,000 objects measuring larger than ten centimeters, and more than a million measuring between one and ten centimeters, are currently hurtling around the Earth at speeds of up to 50,000 kilometers per hour. The impact of even one tiny fragment of debris can equal the force of a hand grenade. Researchers at Fraunhofer EMI are conducting laboratory experiments to investigate the effects of such impacts on satellites. They use in-house software to carry out risk analyses with the aim of identifying vulnerabilities right from the satellites’ design phases, and building in protective shields. Many manufacturers also equip their satellites with thrusters so that they can evade large pieces of debris and flying objects with measurable trajectories.
To increase sustainability in space, as well as security on the ground, satellites must be able to burn up without trace when they reenter the Earth’s atmosphere at the end of their lifespan – this feature must be built into satellites during their construction. The problem is, at an altitude of 600 kilometers, space debris circulates for about 25 years before its velocity reduces to a point where it can burn up in the atmosphere. At an altitude of 800 kilometers, this can take as long as 150 years. France is a trailblazer when it comes to solving the problem of debris: French law dictates that satellites must be disposed of at the end of their mission. ERNST is also working in earnest to protect the space environment: At the end of the operating period, a braking sail measuring 1.6 meters x 1.6 meters is unfurled, meaning Fraunhofer nanosatellites linger at an altitude of 500 kilometers for only a few months, instead of a few years.
As low Earth orbit becomes more crowded, it is becoming more important that we maintain the most comprehensive and up-to-date overview possible − especially considering there is no single worldwide institution or international agreements that regulate or monitor who is sending satellites into orbit, and how many. When it comes to systematic space surveillance, Germany has so far relied on data from US authorities, which may sometimes have different priorities, or choose not to disclose certain information. In recent years, an awareness has grown that in this crucial area, Germany needs to become less dependent on data from third parties. This has led to the establishment of GESTRA (German Experimental Space Surveillance and Tracking Radar), a domestically owned space surveillance system. It uses the most up-todate radar technology to observe objects at an altitude of 300 to 3,000 kilometers. The German Space Situational Awareness Centre calculates orbit data for all detected objects, which are recorded in the form of a giant roadmap called the orbit data catalog. This catalog offers a basis for assessing any collision risks. Various influences can sometimes cause the objects to change their orbit, so they must be continuously monitored and the map must be constantly adjusted.
GESTRA was developed by the Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR in Wachtberg, near Bonn, for the German Space Agency at the German Aerospace Center (DLR). It is currently undergoing test operations at the Schmidtenhöhe military training facility near Koblenz, but will be handed over to the DLR as soon as possible. “What is special about GESTRA is its phased array technology,” explains Dr. Lars Fuhrmann, head of the Radar for Space Situational Awareness (RWL) section at Fraunhofer FHR. “It generates radar beams that can be electronically pivoted to stretch like a giant fence across a wide area. Any objects that pass through this fence are detected. The radar covers an area of sky of up to 90° x 15°. To contextualize that, the diameter of the moon in the sky, as viewed from Earth, equates to about half of one degree. And area of the GESTRA search fence in the sky is equivalent to around 180 x 30 moon diameters.”
GESTRA is also unique worldwide as it is extremely compact and partially mobile – its components can fit inside a few containers. This not only makes it easy to transport the system to other locations to cover other areas of sky, but also makes it scalable. The future could see systems positioned in multiple locations around the world to gather even more precise data by observing the same object from multiple different angles, for example. With this goal in mind, Fraunhofer FHR is collaborating with Hensoldt AG, which wants to convert the space surveillance radar into a system that is ready to go into production and operation.
While it is important to have a comprehensive overview of what is happening in near Earth space, sometimes more detailed information is needed on a particular object – be it an active satellite or space debris. This is a job for the TIRA (Tracking and Imaging Radar) space reconnaissance sensor. This radar system, also developed and operated at Fraunhofer FHR, is housed within a spherical white radome in Wachtberg, near Bonn, about 60 kilometers away from the GESTRA location. As of yet, it is the only system outside the USA that allows a very high degree of precision in measuring space objects’ orbits from ground level and produces high-resolution images of satellites.
While GESTRA gives an overview of the bigger picture, TIRA takes a closer look: What are the object’s characteristics? Has a satellite been damaged in a collision? How is the object’s trajectory or rotation changing? When and how will the object reenter the Earth’s atmosphere? To answer questions such as these, the TIRA system uses both a high-powered radar to precisely track the objects and a high-resolution radar to generate a detailed image of the object. Both are integrated into the large antenna, which has a diameter of 34 meters.
Tracking fast-moving satellites or pieces of debris requires speed and precision above all, as these objects usually disappear behind the curvature of the Earth within a few minutes. And TIRA is fast: The system’s enormous antenna, weighing about 240 tons, can complete one full rotation within 15 seconds. “That’s a world record,” says Dr. Fuhrmann. He goes on to explain: “The system combines highly precise positioning and sensitivity. At a distance of 1,000 kilometers, the tracking radar’s beam can be trained on an object to an accuracy of three meters. At the same distance, we can simultaneously detect pieces of debris measuring as little as two centimeters in size.”
TIRA is also used as an experimental system for developing new space observation techniques, both at Fraunhofer FHR and in collaboration with space organizations such as the ESA and DLR. “Its areas of application range from precise orbit calculations right up to highly technical analyses of suspicious or otherwise interesting satellites,” explains Dr. Fuhrmann. “We compile series of high-resolution radar images to investigate factors such as the stability level and rotational characteristics of disabled satellites.” To assist with preparations for the first European ClearSpace mission scheduled for 2025, TIRA experts helped with object characterization during the process of selecting suitable objects for retrieval. One possible candidate for a future mission is Envisat, the ESA earth observation satellite, which has been circling through space as a ghost satellite ever since it was decommissioned in 2012. It would take 150 years for it to lose enough speed to independently enter the Earth’s atmosphere and burn up. As it weighs eight tons and measures 25 meters in diameter, it would pose a significant risk to other satellites during this period. In the case of a collision, the resulting debris cloud could trigger a devastating chain reaction.
To assess which of the available capture technologies – such as nets or magnetic field technology – are most suitable for capturing such a colossus, as well as deciding on the best way to approach it, the experts are using TIRA to observe the satellite over months and years, meticulously recording its rotational parameters and speed. This data could be used to prepare for a retrieval mission. The goal is to deliberately let the decommissioned satellites burn up, thus ensuring they end their lives in a sustainable manner. TIRA’s special features have earned it a great reputation worldwide. In fact, the research team is currently supporting the Japanese space agency with similar retrieval activities.
One other challenge remains largely unresolved: How will the European satellites actually get into space? Since the EU still has neither the necessary modern rocket technology nor the capacity, this is where sovereignty reaches its limits. After the Ukraine war rendered Russian carrier rockets and launch sites unusable, European missions turned to businesses such as Elon Musk’s US-based company SpaceX. But despite SpaceX’s large number of flights, the waitlists are long. In 2022, Falcon rockets launched 60 times, in contrast to the European Ariane 5, which launched only twice.
While the much-postponed launch of Ariane 6, Europe’s most powerful carrier rocket to date, is now scheduled to happen in French Guiana in late 2023, a question still hangs over whether its capacity will suffice for the growing satellite business. The reason is that in contrast to the reusable SpaceX carrier rockets, which can be relaunched, Ariane will remain a single-use rocket for the time being. Sustainability just wasn’t on the table during the initial planning process at Arianespace back in 2014.
However, there is hope − many recently founded New Space start-ups are now working with public decision-makers to expand EU space capacity. Even Prof. Schäfer of Fraunhofer EMI is convinced: “In Europe as well as at Fraunhofer, there is a huge amount of know-how around relevant technologies, whether in satellite construction or in communication, quantum and radar technologies. This will help us succeed in establishing our own reliable infrastructure in space and release us from our previous dependency on the USA and Russia.”
Fraunhofer-Gesellschaft