International Edition 2024 / ISSN 0173-6264 B 13716 / EUR 5,– / CHF 9.– Luft- & Raumfahrt The Aerospace Magazine of the German Society for Aeronautics und Astronautics International Edition Shaping the future of aviation with cleaner aircraft Space sustainability and space debris – Imagine a mega-constellation, 200 years from now Bridging the gap to 2050 – How can aviation be decarbonised faster? A beacon of European space exploration – The history of Ariane 5 

TABLE OF CONTENTS Luft- und Raumfahrt, Int. Edition 2024 Clean Aviation p. 8 – 9 Sustainable Aero Lab 10 – 13 Hydrogen Aviation Lab p. 14 – 17 Multimodal mobility p. 18 – 21 Sustainable Aviation Fuels p. 22 – 25 Space sustainability p. 26 – 29 The story of Ariane 5 p. 30 – 35 EnMAP p. 36 – 39 JUICE p. 40 – 43 Heinrich Hertz p. 44 – 47 

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7 S o u r c e : v a r f l o l o m e y / s t o c k a d o b e c o m . . ABOUT DGLR Luft- und Raumfahrt, Int. Edition 2024 The German Society for Aeronautics and Astronautics (Deut sche Gesellschaft für Luft- und Raumfahrt; DGLR) is the oldest institution in Germany to offer a common forum for those with a private or professional interest in aero- nautics and spaceflight� The Society offers a network for knowl- edge exchange about the aerospace sector; current projects and developments are presented, and good ideas are nurtured and rewarded� Inform, network, promote DGLR is the only technical and scientific association for aviation and spaceflight in Germany. Its members represent industry, government, education and research institutions. It acts as a link between every discipline and hence encourages a comprehensive exchange of information and experience. Beyond its function as a provider of information for its members, DGLR acts as a repre- sentative of aeronautics and spaceflight for the general public – nationally and internationally. DGLR is as multifaceted as its members – it combines varying areas of expertise and specialist committees into a structured network of skill sets. Here, members can pursue their individual areas of interest and discover like-minded people. Regional groups offer the option of networking at a local level. At events, members have the opportunity to network and catch up on recent developments. For example, every year the German Aerospace Congress (Deutsche Luft- und Raumfahrtkongress; DLRK) acts as a central national forum for aeronautics and spaceflight. Encouragement of new talent in science and technology is a core objective of DGLR. Through the Skyfuture online information portal, it offers contacts and guidance in training, study and ca- reer options in the aerospace sector. DGLR also helps student trainee groups carry out their own projects at universities. Information Stay informed on the latest aerospace news – Member magazine ‘Luft- und Raumfahrt’ – Weekly newsletter ‘Inforadar’ – Special newsletter ‘Infoflash’ – Access to Skyfuture – DGLR’s youth portal offering career and study advice – Access to DGLR’s library Networking Make use of the largest scientific and technical aerospace net- work in Germany – DGLR’s competent expert committees – DGLR’s district groups across Germany – DGLR’s student trainee groups – Contact to over 3,000 colleagues & experts – Connections to the industry via international partnerships – Symposia and congresses such as the annual German Become a member! Aerospace Congress (DLRK) Any person interested in aerospace can become a member of DGLR and take full advantage of the Society’s wide range of services. Promotion Industrial companies, associations, societies and other organisa- tions that deal with aerospace are invited to become part of a large network as a corporate member of DGLR. Benefit from personal promotions – Awards and honours – Young talent awards – Publication service via the German National Library • S o u r c e s : D G L R 

AERONAUTICS – Clean Aviation Luft- und Raumfahrt, Int. Edition 2024 9 S o u r c e : H E R A Aviation must bring significantly cleaner aircraft into service by 2035 if it is to meet its climate neu- trality goals by 2050� The Clean Aviation programme, a wide-ranging collaborative research project of the European Union and Europe’s aeronautics industry, is de- livering game-changing aircraft technol- ogies to achieve this transformation� We need to innovate, accelerate and, most importantly, collaborate� But there is even more at stake, because aviation is one of Europe’s strategic industrial sectors and plays a key role in job creation across the continent� In fact, aviation represents 3�6 per cent of all employment in Europe and 4�4 per cent of European GDP� Ensur- ing the long-term viability of this sector is imperative for retaining highly qualified competencies and jobs, which in turn safeguard European research and engi- neering capabilities� Where are the opportunities to make avia- tion climate-neutral? Currently, the greatest opportunities to make aviation more environmentally friendly lie with short/medium-range and regional aircraft. As roughly 55 per cent of aviation emissions are produced on routes below 4,000 kilometres in length (approx. Brussels-Cairo), it is precisely within the regional and short/medium-range com- mercial aircraft sectors where Clean Avia- tion is directing its efforts. With a total budget of 4.1 billion euros, of which 1.7 bil- lion in EU funding comes through the Horizon Europe programme, our new set of projects will target novel aircraft con- cepts, innovative propulsion architectures and new fuselage and wing designs. Those new aircraft will enter service by 2035 and reduce fuel consumption by at least 30 per cent owing to new aircraft technology. Moreover, replacing kerosene with SAF (Sustainable Aviation Fuel) or hydrogen will reduce the CO2 emissions of these aircraft by 80 to 100 per cent, de- pending on the fuel used. Which technologies is Clean Aviation fo- cusing on? In the upcoming years, Clean Aviation’s 28 ongoing projects will delve into new electric and hybrid electric concepts, ul- tra-efficient short/medium-range aircraft The HERA project aims to develop a concept of a hybrid-electric regional aircraft architectures and disruptive hydrogen- powered technologies. Our efforts are directed towards accelerating the matura- tion of these technologies, for demonstra- tion by 2028/2029. In practical terms, this means that airlines will be offered new aircraft featuring Clean Aviation technologies throughout the pro- gramme’s lifetime. The focus on combined technological and industrial readiness will enable replacement of 75 per cent of the world’s civil aviation fleet by 2050. But back to the here and now, Clean Avia- tion is focusing on technologies applicable to aircraft in the short/medium-haul sec- tor. Whilst some of those technologies have the scope to be scaled up for use in larger aircraft, others need to be devel- oped specifically for the long-haul sector, which accounts for approximately 45 per cent of current aviation CO2 emissions – an important challenge not to be forgotten! text to harness expertise and resources from both the public and private sectors. At Clean Aviation, we bring together hun- dreds of European entities, representing 24 different countries from across the aeronautical community. This builds on intensive cooperation between large in- dustrial entities, SMEs, research institu- tions and universities, and the European Aviation Safety Agency (EASA). The entire aviation sector needs to find new ways to collaborate to make sustain- able aviation a reality. This effort spans the complete ecosystem: airlines, airports, policymakers, regulators, manufacturers, energy producers, scientists, innovators and other partners. Their active involve- ment and contribution is paramount. Our 28 Clean Aviation projects are important pieces in this puzzle, because only through joint efforts can we achieve a future of clean flying. Let’s make it happen together! • What are the key success factors? The current decade offers an unprecedent- ed opportunity to redefine the aerospace industry with the convergence of height- ened environmental awareness and tech- nological breakthroughs. The key to suc- cess in the journey towards sustainable aviation lies in close cooperation and align- ment between all aviation stakeholders to reach our shared climate neutrality goals. Public-private partnerships like Clean Aviation are crucial in the European con- THE AUTHOR Axel Krein is the Executive Director of the Clean Aviation Joint Undertaking. He is the chief executive responsible for the implementation of the Joint Undertaking, in accordance with the decisions of the Governing Board. Together with the Programme Office he is in charge of the day-to-day manage- ment and implementation of the Stra- tegic Research and Innovation Agenda. 

AERONAUTICS – Sustainable Aero Lab Luft- und Raumfahrt, Int. Edition 2024 11 11 y d u t S 0 5 0 2 t n o p y a W G A T A i : e c r u o S Even the most pessimistic forecasts predict that the number of passenger-kilometres flown will double The aviation industry has irrevocably shaped our world� Flying is an essential component of modern life and a cor nerstone of our globalised society� Despite a tempo- rary decline linked to the coronavirus pandemic, the number of individuals travelling in aircraft continues to rise� Simultaneously, aviation is facing an escalating challenge: with increasing air traffic comes a corresponding surge in emissions� Failure to address decarbonisation substantially and promptly imperils the very basis of this key industry’s business model� Enter the Sustainable Aero Lab, established in early 2021 and now recognised as the premier fast-track initiative dedicated to accelerating sustainable aviation start-ups worldwide. Over the past two years, it has collaborated with pioneering companies at the forefront of decarbonising aviation. By fostering alliances with experienced mentors and investors, the organisation opens doors to opportunities by helping to find customers, identify new products and cultivate partnerships. The programme is centred on five key areas of development: Sustainable Aviation Fuels (SAFs), hydrogen, electrification, novel designs and materials, and enhanced operational efficiency. Through this collaborative . . m o c e b o d a k c o t s - y k s p a a : e c r u o S Accelerating the introduction of Sustainable Aviation Fuels (SAFs) can fast-track the decarbonisation of aviation SUSTAINABLE AERO LAB The Sustainable Aero Lab stands as the premier start-up accelerator dedicated to sustainable aviation worldwide. Since its establishment in early 2021, the programme has provided support to over 50 companies, guided by more than 60 men- tors hailing from the aviation sector, related industries and venture capital. Additionally, the Lab serves as a vital platform for fostering public discourse and advancing the promotion of zero-emission aviation technologies. This initiative is sup- ported by Breakthrough Energy, whose founders include Bill Gates� sustainable�aero effort, a wealth of insights into the imminent future of aviation has emerged. Insights into the future of aviation eVTOLs and other battery-powered aircraft will not be a panacea for decarbonising commercial aviation While promising, Electric Vertical Take-Off and Landing aircraft (eVTOLs) lack the range and capacity to replace conventional commercial aeroplanes from major manufacturers like Airbus and Boeing. The weight of batteries required to meet the consider- able energy demands of flight render eVTOLs impractical for operational ranges exceeding 100 kilometres. This is very differ- ent than the automotive sector, where electrification has proven effective because while the combustion engine is around 25 per cent efficient, braking in traffic can reduce the efficiency of the overall system to five per cent. The most modern aircraft, on the other hand, already convert 50 per cent of their fuel energy into thrust. Hydrogen will not help us – at least not yet The prospect of commercial hydrogen-powered aircraft by the 2030s is promising. But these aircraft will probably be turboprops with less than 100 seats, which are a long way from the segment that accounts for 96 per cent of emissions. Moreover, the exten- sive infrastructure required for hydrogen implementation, both in flight and on the ground, suggests a timeline spanning dec- ades. While hydrogen may eventually emerge as a pivotal solution for emission-free aviation, its practical application is unlikely to materialise before 2050. The aircraft of the future are in production today The world’s active fleet consists of some 25,000 aircraft that are in the air every day. And nearly 2,000 more come off the produc- tion lines every year. Aircraft typically remain in service for 25 years before being scrapped. All commercial aircraft with more than 100 seats built in the next 15 years will be conventional. For long-haul aircraft, which consume around two-thirds of all fuel, the switch to new technology will take considerably longer. This replacement timetable means that today’s aircraft models will still make up the majority of the global fleet in 2050. 

AERONAUTICS – Sustainable Aero Lab Luft- und Raumfahrt, Int. Edition 2024 13 to operate, the Sustainable Aero Lab advocates the imposition of restrictions on carbon dioxide emissions per tonne of freight. Currently, the majority of active commercial aircraft belong to the single aisle narrowbody category, particularly the Airbus A320 and Boeing 737 families. The latest versions of these popular models reduce fuel consumption per seat kilometre by up to 20 per cent. Implementing concrete and long-term incentives for airlines to transition to newer generations could have a substan- tial impact on overall emissions. The same is true for long-haul aircraft. Such a strategy would mirror the German government’s actions for the automotive sector during the 2008/2009 financial crisis, which encouraged citizens to replace their old cars with more modern alternatives. Cornerstones of implementation Political incentives Currently, production costs for SAFs are, on average, two to four times higher than for conventional fuels. Until the market is further developed and production costs fall, government support and incentives will be required. This also applies to any emissions tax. Airlines and airports cannot take this important step alone because they would lose their competitiveness. Within Europe, this discussion needs to take place primarily at the transnational level. On the production side, investments need to be mobilised for the development of several new large-scale facilities to increase the production of SAFs, meet the additional demand and reduce production costs. The USA has already taken a major step in this direction with the Inflation Reduction Act. Coalitions of the willing The aviation industry does not yet speak with a common voice. Despite having institutions such as the International Air Trans- port Association (IATA), various interest groups have mainly focused on their own goals. To truly drive decarbonisation efforts, a more open and hands-on mentality needs to be established where airlines, airports, fuel suppliers and manufacturers world- wide work closely and visibly together towards the same goal. Research and development In addition to longer-term technologies such as hydrogen, more research and development needs to be focused on reducing SAF production costs and finding ways to efficiently scale its produc- tion. This path is the most promising solution for the next 20 years, and research and funding activities should reflect this. There is still great potential in these areas over the next two decades. S o u r c e : l W E F C e a n S k i s o f T o m o r r o w R e p o r t HEFA-based SAFs will be the only relevant sustainable fuels in the coming years deliver benefits in a reasonable timeframe. The ReFuelEU deci- sion is at least a significant step in the right direction. Public awareness So far, the aviation industry has failed to involve the general public in its strategies to make flying ‘greener’. Indeed, some question- able greenwashing activities in the past have had the opposite effect. The aviation industry needs to make people more aware that it is working hard to decarbonise air transport and that pas- sengers can already play an active role in reducing their carbon footprint. The addition of information on carbon dioxide emissions in Google Flights search is an excellent example of how awareness can be raised. However, it was a technology company that took this step, not the aviation industry. Adding a ‘green’ option or class at the time of booking is another great example of how a SAF or offset option can be offered during the booking process – just like adding baggage. If a particularly efficient aircraft flies on a particular route, why is this not presented in a way that is understandable to the average person? The three measures mentioned above could be implemented relatively quickly. If we are determined to do it, we can collec- tively reduce emissions from the aviation industry by 2050. There is nothing stopping us from starting immediately. • Regulatory support THE AUTHOR An unclear regulatory situation is one of the reasons why invest- ment in SAFs is still progressing relatively slowly. In a nutshell, it is often not clear which type of SAF and which production process will be considered by authorities and regulators for a ‘sustainable’ label. This confusion slows down innovation and needs to be resolved quickly. A global certification and framework system is needed NOW to avoid misdirected investments. Capital should only be available for labelled technologies; that is, those that can Lukas Kaestner serves as the co-founder and Chief Com- mercial Officer of the Sustainable Aero Lab, as well as the Chief Development Officer of the ZAL Center for Applied Aeronautical Research in Hamburg. Prior to his current roles, he amassed many years of experience at the Hamburg Aviation Cluster of Excellence and with the international Crystal Cabin Award. 

AERONAUTICS – Hydrogen Aviation Lab Luft- und Raumfahrt, Int. Edition 2024 15 Aircraft manufacturer Airbus plans to launch the first commercial hydrogen-powered aircraft, called ZEROe, by 2035� But before any hydrogen- powered aircraft can enter commercial service, much research is needed into the technology of hydrogen propulsion and, critically, into the ground infrastructure that will support it� Otherwise, a new gen- eration of high-tech aircraft will be effec- tively stranded at airports which are un- able to service and refuel them� To fill this knowledge gap, a decommissioned Airbus A320 is being converted for a new life as the Hydrogen Aviation Lab in Hamburg, where extensive maintenance and ground processes for hydrogen technology will be developed and tested over the next few years� The stationary laboratory is a project of Lufthansa Technik, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), the ZAL- Center of Applied Aeronautical Research and Hamburg Airport� It is funded by the City of Hamburg� In this interview, Hans Bernd Aringhoff, Head of Corporate Inno- vation at Lufthansa Technik, discusses the status of the project and the challen- ges it aims to address� Mr Aringhoff, the old A320 found a new home at the Lufthansa Technik site last year. What are you working on at the moment? We have already made a few modifications. First, we cleared the rear section of the aircraft, removing components like the auxiliary power unit and part of the cabin. This is where our test setup will be installed: the tanks, the fuel cell, the pipes and all the other necessary components, such as con- trol and regulating valves or safety devices. There are also sensors that check whether the corresponding safety valves close. This is not a flying hydrogen aircraft; it is a labo- ratory – so the entire research infrastruc- ture has to be accommodated. We are currently assembling the hardware step by step. The aircraft will be fuelled with liquid hydrogen, which has a much higher energy density volume than gase- ous hydrogen. However, the fuel cell needs gaseous hydrogen, so we must vaporise the liquid hydrogen before it reaches the fuel cell. The fuel cell generates electrical energy that must be supplied to the vari- ous consumers in the aircraft, such as the on-board electronics. At the same time, the control system for the entire labora- tory setup has to be programmed. This is how we will be able to control our experi- ments later on. Over time, we want to expand our labora- tory step by step with new partners and research projects. That way we should end up with a setup that is very close to a future airworthy model. i G A k n h c e T a s n a h t f u L : e c r u o S Working container with hydrogen tank for refuelling the laboratory S o u r c e : L u f t h a n s a T e c h n k A G i Hans Bernd Aringhoff has been Head of Corporate Innovation at Lufthansa Technik since September 2022 But it is not meant to fly? This A320 will remain grounded – and that gives us a huge administrative advantage. If it were an operational aircraft, the as- sociated costs would be much higher. All modifications would have to be conducted and documented in such a way that the licence would not be invalidated, requiring time-consuming coordination with the licensing authorities and the aircraft man- ufacturer. This way we are much more flex- ible. We can try things out quickly and discard them again without having to worry about jeopardising the aircraft’s certification. What is the progress on developing the ground infrastructure? A large hydrogen storage tank with a refuelling system is being built while the aircraft is being modified. All the com- ponents that will not be in a hydrogen- powered aircraft are being built outside our test aircraft. This includes, for exam- ple, the measuring instruments. There is a mobile container near the laboratory, in which a workstation has been set up for our research colleagues. What is next? In autumn, we began to assemble every- thing in the aircraft to start the systems for the first time. Everything will be ramped up to assess functionality. At the same 

AERONAUTICS – Hydrogen Aviation Lab Luft- und Raumfahrt, Int. Edition 2024 17 tions. Secondly, there is the question of supply. We need to look at the supply chains. Will the hydrogen be produced close to the airport, or will it have to be transported over long distances? Is it transported by pipeline or by tanker truck? Solutions need to be found here, too. Hydrogen-powered aircraft will require huge amounts of liquid hydrogen, which will require a whole new infrastructure. Are there existing methods to speed up refuelling? There are two ways to get a certain amount of mass into a specified volume more quickly. One way is to enlarge the cross-section – by increasing the diame- ter of the fuelling nozzle, hydrogen can pass through more rapidly. However, this approach makes the tank nozzles heavier and puts more heat into the liquid hydro- gen because there is more surface area. The alternative is to accelerate the mass flow. This can be done with pumps or with pressure differences between the source and destination. Both approaches are be- ing investigated at the Hydrogen Aviation Lab. We are looking at what works best given the prevailing conditions and com- paring costs. We are also evaluating their practicality; ultimately, the technology will have to be introduced at all airports. For either approach there are no existing com- ponents or suppliers. Consequently, we are having to do a lot of development and adaptation ourselves. The announcement of large hydrogen air- craft slated for the mid-2030s prompts the question: will we be able to adapt the ground infrastructure in time? Indeed, it is feasible. We still have twelve years. But we need this time. Just getting the necessary licences to start this hydro- gen trial near the airport has taken a year. Consequently, the infrastructure setup must be tailored extensively to local regu- lations and environmental conditions. The immediate priority lies in swiftly defin- ing standards. Critical questions need to be addressed: What does the refuelling process entail? Which couplings are to be used? What storage procedures are opti- mal? And what safety protocols must be strictly adhered to? The answers to these questions will determine the configuration S o u r c e : L u f t h a n s a T e c h n k A G i The refuelling system and the fuel cell are to be housed in the rear part of the aircraft of the entire infrastructure. The introduc- tion of SAFs, for instance, faces hurdles due to the absence of globally binding stand- ards. The establishment of such standards for hydrogen will consequently be a focal point of research in the coming years. How will ground handling procedures have to change to accommodate liquid hydro- gen? Hamburg Airport’s involvement in the pro- ject is very important in this regard. All technical personnel have to be trained to handle hydrogen-powered aircraft, to un- derstand operational protocols, and to identify safety risks and implement pre- ventive measures. We are actively driving this aspect forward here. Currently, our aircraft is undergoing an intensive main- tenance programme. Selected colleagues have been selected to oversee the entire process from step one. They are actively participating in tests and will subsequent- ly assume responsibility for the mainte- nance and safety evaluations of hydrogen components at our Hydrogen Aviation Lab. The goal is to build up the corre- sponding qualifications within our opera- tions. In addition to developing the ground infra- structure, there is a plan to create a digital twin of the A320. What exactly does that entail? want to simulate and test, and discuss our experiments, in parallel within a digital environment. This approach will reduce the risk of actually building something, only to discover later that it is not feasible. We want to plan the experiments as pre- cisely and effectively as possible right from the start. Furthermore, the digital twin will serve as a visualisation tool for the public. While only trained personnel can conduct the experiments themselves, 3D models and visualisations will make the research more accessible and comprehensible to a broad audience. What is the timeframe for the project? The initial construction of the hydrogen laboratory is set to be completed this year. Concurrently, we have developed several research projects and submitted them for approval. Right now, a number of topics are in the preparatory stages, involving collaboration with academic and indus- trial partners, all geared towards the re- alisation of an aircraft capable of flight using hydrogen propulsion. As progress unfolds, expect to hear more from us in the coming years. • Thank you for your insights, Mr Aringhoff! THE AUTHOR Every aircraft is unique. The A320 in ques- tion is 32 years old and has undergone numerous modifications and changes over its lifetime. That is why we want to create a digital model, to capture both its geo- metric and functional aspects. We always Alisa Griebler coordinates the commu- nication activities of the German Soci- ety for Aeronautics and Astronautics (DGLR). She is the spokesperson for the DGLR and editor-in-chief of the ‘Luft- und Raumfahrt’ magazine. 

AERONAUTICS – Multimodal mobility Luft- und Raumfahrt, Int. Edition 2024 19 S o u r c e : i i i N c k Z g c o n P x a b a y i Air transport as part of the multimodal door-to-door travel chain The topics of multimodality, passenger experience and creating a seamless mobility system that meets the goals of the Paris Climate Agreement are high on the agenda for shaping the future European transport system� Europe’s long-term vision for aviation research, described in the Flight- path 2050 and the new Fly the Green Deal publications, envi- sions a future in which aviation becomes an integrated part of multimodal transport� In parallel, the European Commission’s Sustainable and Smart Mobility Strategy has defined several goals and respective flagship programmes that pave the way towards zero-emission, resilient and integrated mobility, creat- ing seamless and efficient connectivity with better connections between European regions� One of the goals is a stronger focus on multimodality, which is the combination of different modes of transport to improve overall convenience, speed, cost, reliability and predictability – cycling to the station to catch a train to the airport, for example� By better supporting multimodal journeys, the overall transport system can deliver faster, more efficient and more reliable door- to-door mobility on a local or even European level. But to achieve this goal while reducing transport sector emissions, several critical factors must be considered: – enabling seamless passenger journeys with single ticketing; – ensuring fair and efficient pricing across all transport modes; – establishing a true multimodal framework with respect for passenger rights; and, – identifying and developing new business models that enable multimodal transport. There are many challenges ahead and a wide range of innovative ideas and solutions already available. In this article, we discuss some ideas from different European projects, with a particular focus on the role of and opportunities for the aviation sector. i y a b a x P n o n n a m t l A d r e G : e c r u o S Multimodality encompasses the combined use of different modes of transport with regard to various factors Understanding (future) traveller behaviour Travellers have unique preferences, requirements and needs. Different groups may prioritise different aspects of a journey: overall travel time, ticket price, travel time reliability, time of day, frequency of service, convenience, comfort or quality of service. Thinking beyond leisure and business travellers or those visiting friends and relatives to consider more diverse traveller personas or user segments can help us to take a more passen- ger-centric view and better understand decision-making factors. This approach focuses on passenger characteristics such as socio-demographic profile, household size and income, purpose of travel, frequency of travel, the size of travel groups, the amount of luggage and the destination. Understanding travel behaviour and decision-making is necessary for segmenting passenger flows and modelling modal and route choice, as well as trip start times (which depend on the buffer times required by each type of passenger), which in turn drive door-to-door travel times. This distinction is even more important in light of trends that may influence current and future traveller behaviour. 

AERONAUTICS – Multimodal mobility Luft- und Raumfahrt, Int. Edition 2024 21 variety of multimodal routing options, which can enable mode substitution and/or passenger rerouting in response to severe disruptions. Resilience indicators are therefore particularly rel- evant for the assessment of multimodal solutions and the door- to-door travel time impact of disruptions such as missed con- nections or cancellations. The Sustainable and Smart Mobility Strategy highlights the need for sustainable mobility within a fully integrated network. One example would be using high-speed rail connections on short-haul routes to complement long-haul air transport. Europe-wide network effects could be mapped by applying demand-driven optimisation and data-driven models and algorithms that consider multimodal integration, as in the Modus and MultiModX projects. A seamless passenger experi- ence and interoperability between different transport providers and modes may hence be enabled by integrating airports as multimodal nodes in the air traffic management (ATM) network, contributing to increasing network resilience and the reliability and predictability of journeys. S o u r c e : M o d u s / S E S A R Leveraging big data and data analytics Requirements for a multimodal mobility system according to Modus The impact of multimodal solutions depends on how they are aligned with passenger needs. In a context of dynamic passenger demand and changing transport systems, the aviation sector requires up-to-date and fine-grained information on passenger behaviour. Passenger surveys provide valuable data, but are often costly and limited in sample size, and so do not provide detailed measures of passenger behaviour. making. Key enablers and requirements for a truly multimodal mobility system within Europe include: – close cooperation between air and rail mobility providers to ensure seamless door-to-door journeys (including data availability and sharing, integration of privacy require- ments); – comprehensive assessment of different modes to meet Geolocation data, which exploits the digital traces passively generated by passengers along their journeys, have opened new opportunities for understanding passenger needs. The anonymised records collected by mobile network operators from the interaction between mobile devices and network antennas are particularly interesting as they enable a detailed analysis and reconstruction of the door-to-door journeys of large passenger samples (as applied in the TRANSIT project). This mobile net- work data (MND) can be used to identify the location and dura- tion of door-to-door trips and the pauses between trip legs. In combination with transport supply information, it is also possible to identify the mode and route chosen in medium- and long- distance trips. However, contrary to passenger surveys, MND is passively collected and lacks key sociodemographic information about passengers such as age, gender, or income, and relevant journey attributes including private vehicle availability, group travelling or luggage carried. Also, MND is in general not suited to international travel analyses. Therefore, the most recent research has focused on data fusion techniques that combine MND with sources such as surveys or censuses to classify sam- ple users according to these types of variables. Moving towards multimodality There are various essential requirements and key enablers to foster multimodality in Europe. Among all these recommenda- tions, it is important to consider different scenarios, use cases and developments in long-term planning, while considering uncer- tain economic or social developments. Scenarios can help to make sense of the future and to structure decision- and policy- climate goals, including transparency of all costs; – integration of remote regions, to ensure their connectivity and accessibility takes into account diverse traveller needs; – emergence of new actors in the mobility market, and new business models which may originate outside the transport sector; – legislation, regulations, policies and incentives that foster cooperation across modes and across national borders, and are tailored to specific regions and routes; and – infrastructure investments to enhance integration of different modes along the travel chain. Integrated, multimodal mobility concepts will enable us to travel seamlessly, comfortably, easily, efficiently and flexibly in the future – without having to rely on private cars, for example, and with a low ecological footprint. • THE AUTHORS Dr Annika Paul is the deputy head of the area Air Transport System at the German Society for Aeronautics and Astronau- tics, and a member of the Advisory Council for Aviation Research and Innovation in Europe (ACARE), which considers the requirements of various air traffic participants and solu- tions for the air traffic system. Dr Kay Plötner heads the Economics and Transport team at Bauhaus Luftfahrt. One of his main areas of research is region- al air transport and how new technologies and concepts may enhance its market potential. 

AERONAUTICS – Sustainable Aviation Fuels Luft- und Raumfahrt, Int. Edition 2024 23 S o u r c e : A i r b u s / S . R a m a d e r i The DLR research aircraft Falcon 20E measures the emissions in the exhaust jet of an Airbus A350, which flies on 100 per cent sustainable fuel Producing low-cost synthetic kerosene is key to reducing emissions from aviation� Securing low-cost, carbon neu- tral electricity is of great importance to the large-scale production of such Sustainable Aviation Fuel (SAF). Yet, the critical role of carbon efficiency is less acknowledged� Hydrogen has emerged as a prospective energy source that might curb the carbon dioxide (CO2) emissions of short- and medium- haul flights in the future. For long-haul flights, there is probably no alternative to synthetic kerosene. The key challenge is to reduce the cost of SAF production in order to speed up its mar- ket entry. SAF can be produced using various technologies. Currently, the economical production of climate-neutral hydrogen required for SAF synthesis is considered the main lever to reduce costs. This hydrogen must come from electricity that does not emit CO2 to the atmosphere. However, it is frequently overlooked that SAF synthesis requires both a hydrogen and a carbon source. The uncertain future cost of carbon in a low-carbon energy system is a notable risk for predicting future SAF costs. Thus, it is vital to take a closer look at carbon efficiency as an indicator of potential cost risks when SAF production increases. Where does carbon come from? Public statements on carbon for fuel synthesis are a prime exam- ple of misleading science communication. Frequently, the amount of greenhouse gases linked to biomass are neglected, industrial emissions are misrepresented as everlasting sources of carbon, and the costs associated with direct air capture (DAC) are not transparently declared. Consequently, carbon sources and the reasons for their scarcity must be clearly communicated in analyses of SAF potentials. In a hypothetical CO2-neutral energy system, there are three pri- mary sources of carbon: biomass, point sources and air. Each of these sources entails availability and cost risks. Biomass sour ces have the advantage of containing both hydrogen and carbon. However, biomass derived from crop production is currently not climate neutral, as fertilisers are predominantly produced from ‘grey hydrogen’ – de facto produced from fossil fuels. This green- house gas footprint is made even larger by nitrous oxide emis- sions from soil, by farm machinery and transportation. In a decar- bonised energy system, agricultural biomass that relies on green hydrogen for fertiliser production will likely be expensive. Large- scale point sources of CO2, such as blast furnaces or coal-fired power plants, have high concentrations of CO2. However, they will not be available in a carbon-neutral energy system. Captur- ing carbon from the air is currently not competitive, costing around 1,000 euros per tonne of CO2. There are also no reliable ways to lower these costs to less than 100 euros per tonne of CO2 at the moment, mainly due to the high energy requirements of DAC. In addition, DAC is not CO2-neutral with Germany’s current electri city mix, for instance. This illustrates that low-cost and climate-neutral carbon will be a scarce commodity in the future. Synthesis technologies will quickly become less expensive if they make the most efficient use of this scarce resource. What is carbon efficiency? Carbon efficiency is the ratio of the number of carbon atoms in a final product relative to the source, ranging from zero to 100 per cent. A carbon efficiency close to 100 per cent means that most of the carbon atoms of the feedstock will end up in the final prod- uct, and the carbon resource is therefore well utilised. In future markets, the price per kilogram of SAF and the green- house gas emission savings per kilogram of kerosene are cru- cial. Why is it still important to consider carbon efficiency in ‘techno-economic’ analyses? As carbon is likely to be a scarce S o u r c e : D L R Carbon efficiency illustration using the example of synthetic kerosene produced from biomass. The definition can be applied by analogy to carbon atoms from industrial waste gases and CO2 capture from the air. In this illustration, the carbon efficiency is 60 per c ent 

AERONAUTICS – Sustainable Aviation Fuels Luft- und Raumfahrt, Int. Edition 2024 25 S o u r c e : H a b e r m e y e r e t a l . 2 0 2 3 Comparison of the potential for producing SAF from BtL and PBtL. The high carbon efficiency of PBtL entails that the EU’s aviation fuel needs could, in principle, be m et ‘staged fixed bed’ gasifier and subsequent ‘Fischer-Tropsch’ syn- thesis. parity emphasises the superior ability of PBtL to optimise utilisa- tion of scarce biomass resources. When comparing the carbon efficiency values, it is evident that the PBtL process has about one and a half times the carbon effi- ciency of the BtL process because of the hydrogen supply. This implies that producers of SAF using PBtL will be less impacted by increasing carbon prices compared to BtL producers. The disparity in energy efficiency between the two processes is mar- ginal, differing by only four percentage points, and thus can be considered roughly equivalent. Since PBtL requires less biomass and more electricity than BtL, PBtL would benefit to a higher degree if the price of carbon-neutral electricity decreases in the future. The production costs of the two synthesis processes are comparable, only differing by a few percentage points, and are calculated at around one euro per litre. This is significantly low- er than for e-fuels, which were calculated at 3.38 euros per kilo- gram (2.38 euros per litre) in 2016, as outlined in a dissertation by Daniel König at the Institute of Engineering Thermodynamics at the German Aerospace Center (DLR) – assuming offshore wind power costs of 14 euros per megawatt hour and a CO2 purchase price of 1.72 euros per tonne. The notable difference in global warming potential, which is approximately twice as high for the PBtL process compared to BtL, can be attributed to the global warming potential of the Finnish electricity grid considered in the project. As the BtL process requires only 15 per cent of the electrical energy of the PBtL process, the global warming poten- tial of electricity has a more significant impact on the latter. Potential for PBtL kerosene To reduce emissions in European aviation, it is important to ana- lyse the potential of domestic SAF production. The higher carbon efficiency of PBtL compared to BtL has a favourable effect on the potential production volume of SAF. External studies suggest that approximately 40 million tonnes per year of forestry residues and 139 million tonnes per year of agricultural residues could be utilised to produce SAF in the EU. Using the PBtL process, this translates to 63 million tonnes of SAF per year, which would effec- tively meet the EU’s estimated kerosene demand for 2030. The BtL process, on the other hand, would meet just over half of the estimated demand due to its lower carbon efficiency. This dis- How to make air transport greener In principle, there are two options to mitigate CO2 emissions from aviation: flying with synthetic kerosene or using climate-neutral hydrogen. In the case of SAF, the carbon source and the carbon efficiency of the production process are pivotal for indicating future cost trends. This significantly shapes the outlook for SAF. Given that significant point sources of CO2 will be scarce in a post-fossil energy system, and there is no viable technology path- way for direct air capture at a competitive price – below 100 euros per tonne of CO2 – biomass is poised to take a critical role as a feedstock for SAF synthesis. When forecasting the cost development of SAF, it is important to consider both energy and carbon costs. Biomass derived from agricultural sources is expected to become more expensive in a carbon-neutral energy system because fertilisers would have to be produced from green ammonia in the future. When it comes to the potential of biomass sourced from forestry, its climate neutrality and large-scale utilisation are subject of debate among experts. In the long term, synthesis processes with high energy and carbon efficiency offer both commercial advantages and faster time to market. • THE AUTHORS The authors hold the following positions at the Institute of Engineering Thermodynamics at the German Aerospace Center: Prof� Dr André D� Thess (Institute Director), Julia Weyand (PhD student), Felix Habermeyer (PhD student), Dr Ralph-Uwe Dietrich (Team Leader Techno-Economic Analy sis). A bibliography is available on request from Prof� Dr André Thess (andre.thess@dlr.de). 

ASTRONAUTICS – Space sustainability Luft- und Raumfahrt, Int. Edition 2024 27 To really understand and tackle space debris today and in the future, we fundamentally need to know how much there is and where it is located� Through observations, models, simulations and on-ground tests, we can then see into different future scenarios – how will the state of Earth’s orbit vary depending on today’s actions? The majority of debris objects reside in low-Earth orbit, with the highest density at around 800 kilometres above Earth. This orbit is crucial for space activities like Earth observation and satellite internet constellations. While ground-based sensors track larger objects, significant gaps persist in assessing smaller objects down to the centimetre range, including at higher altitudes up to geosynchronous orbit. Closing these gaps requires modelling the space debris environment, which means a combination of statis- tics and ‘deterministic’ orbital mechanics calculations. The result- ing debris population is then compared with available data for a realistic depiction. Current trends in spaceflight activities, such as mega constella- tions and increased rocket launches, contribute to a growing number of objects in Earth’s orbit, escalating collision risks. Ensur- ing safe space operations near Earth hinges on maintaining pre- cise knowledge of the space environment, including continuous updates to global catalogues through sensor-based observations. Additionally, assessing the risk posed by reentering space debris on Earth’s surface is imperative. Space debris poses a significant challenge to space operations and so our future in orbit. The distribution of orbital debris Objects larger than one centimetre are the largest contributors to space debris, created primarily when bodies in orbit explode and, to a lesser extent but still critical when objects catastroph- ically collide. ‘Slag’ particles released by solid rocket motors – those in upper rocket stages or apogee kick motors – also make a significant contribution, but this is diminishing as solid motors are replaced by liquid thrusters. Another unusual contributor is liquid metal droplets consisting of sodium and potassium from the cooling systems of Soviet nuclear reactors. The most concerning space debris are those objects larger than one centimetre in size. Between 200 and 2,000 kilometres above Earth, the ‘spatial density’ of this debris peaks at around 800 kilometres – where many Earth observation satellites reside in Sun-synchronous orbits. Sustainable space traffic management is key to the debris prob- lem and requires observations, sensors and sensor network sim- ulations, realistic modelling of our skies, simulation of long-term debris evolution and of course risk assessment and mitigation for re-entering pieces of debris. Effective management requires not only observational capabilities but also a significant amount of scientific background expertise. Simulation and modelling Catalogues and networks of sensors, like the US Space Force’s Space Surveillance Network, make observations that form the foundation of our knowledge of the space debris environment. With the increasing number of objects requiring observation, it is even more important to maximise the efficiency of existing sensor networks. Maintaining and updating our current compre- hensive object catalogues is vital, and research is also underway to explore their efficient operation – from maximising the data sensors’ yield through clever planning and optimally distributing tasks based on the location of the sensor, debris and other fac- tors. Every year, numerous orbital fragmentation events occur in Earth’s orbit involving human-made objects – for instance, they explode, collide or disintegrate. These events generate thousands to tens of thousands of fragments larger than one centimetre which are dispersed along various trajectories, potentially influ- encing a wide area and increasing the risk of further collisions. In the worst-case scenario, this could trigger the Kessler Syn- drome – the tipping point when collisions in orbit create cascades of further debris and so more chance of collisions. The spatial density of all objects larger than one centimetre on Low Earth Orbits (LEO) divided into the four most important contributions, consist- ing of Launch and Mission-Related Objects (LMRO), fragments, Solid Rocket Motor Slag (SRMS), and sodium-potassium droplets (NaK) as of November 2016 To ensure that active satellites and space stations continue to provide essential services, it is crucial to assess the impact of new fragmentation events on their space environment. This includes estimating the necessity of additional collision avoidance i g e w h c s n u a r B U T : e c r u o S 

ASTRONAUTICS – Space sustainability Luft- und Raumfahrt, Int. Edition 2024 29 S o u r c e : i S t o c k c o m . / j o h a n 6 3 Artist’s impression of space debris in Earth orbit ESA and other international bodies, even before an object is launched. A recent example is the 2�6-tonne battery pallet that plummet- ed to Earth from the International Space Station in March 2024. Roughly 350 extremely durable steel battery cylinders descend- ed from the pallet, the majority of which survived re-entry. Approx- imately 130 fragments remain, highlighting how risk not only increases with mass, but quantity. Within satellites, only a few components are capable of surviving re-entry, such as tanks, flywheels and optical parts. It is clear that from the outset, satellites, rockets and their parts should be designed to entirely disintegrate during re-entry. Various methods are currently being examined for constructing satellites and influencing how they can disintegrate most opti- mally during re-entry into Earth’s atmosphere. This entails scrutinising typical satellite construction materials such as aluminium, titanium and CFRP in a hypersonic wind tunnel – under conditions akin to those encountered during re-entry through Earth’s atmosphere. risks, necessitating sustainable space traffic management. Sensor simulation plays a crucial role here, in enhancing observation capabilities, optimising sensor networks, and maintaining comprehensive object catalogues. Modelling fragmentation events is essential for assessing collision risks and mitigating the chances of the Kessler Syndrome. Long-term simulations help evaluate the stability of mega-constellations and inform altitude selection and disposal operations to minimise collision risks. The risk posed by re-entering objects is also a growing concern, particularly with the expected increase in satellites being launched. Developing software to calculate the trajectories and ground risks of returning objects is imperative for ensuring safe- ty. Ongoing research aims to advance our understanding of the dynamics of space debris as it enters Earth’s atmosphere and develop strategies to ensure nothing reaches the ground. By integrating observational data, advanced modelling techniques and innovative spacecraft design principles, the scientific com- munity is striving to ensure the sustainability of space activities in the face of growing debris. • Aiming for a safer space THE AUTHORS Space debris poses a significant challenge to space operations and so our future in orbit. Tackling the problem requires a com- prehensive understanding of the quantity, distribution and asso- ciated risks of space debris. It is vital to measure and character- ise space debris, particularly in low-Earth orbit where most objects reside. While larger debris is generally well-tracked, there are significant gaps in monitoring smaller objects, highlighting the need for advanced modelling techniques to complement obser- vational data. Current trends in space exploration, such as the proliferation of mega-constellations and more rocket launches, increase collision The authors hold the following positions at the Institute of Space Systems of the Technical University of Braunschweig: Carsten Wiedemann (Senior Academic Councillor), Manuel Schubert, Daniel Wacker, Lorenz Böttcher (all of the working group Space Debris) and Simona Silvestri (Institute Director). The author Tobias Lips is CEO of the Hyperschall Technologie Göttingen GmbH (HTG). This article provides an overview of previously published research findings. The results mentioned have been previ- ously disseminated in reports, articles, or presentations. For further information please contact the editing team. 

ASTRONAUTICS – The story of Ariane 5 Luft- und Raumfahrt, Int. Edition 2024 31 S o u r c e A r i a n e G r o u p / S w e e t p u n k The James Webb Space Telescope embarked on its mission aboard an Ariane 5 It ferried James Webb into space with such precision that the telescope can now use its extra fuel to work for years longer than planned� Thanks to Ariane 5, human technology landed on a comet� Its 117th and final flight marked its 100th consecutive successful launch� The life of the Ariane 5 launcher illustrates the evolution of Europe’s technological and spacefaring prowess – this is a story of constant progress� ing the telescope into the designated orbit on Christmas Day 2021 with remarkable accuracy. A margin of error of six per cent had been planned for, but Ariane 5 put the telescope into an orbit just one per cent from perfect. The more precisely the launch vehicle flies, the longer the released telescope has the energy to investigate the galaxy. When the James Webb Space Telescope (JWST) reached its destination on 24 January 2022, approximately one and a half million kilometres from Earth, astonishment struck as the fuel gauge indicated an unexpected surplus. The JWST – the largest, most powerful and complex telescope in human his- tory – relies on fuel throughout the life of its mission. But fuel was also set aside for the final part of its journey into orbit, after it was first transported into space. Before its launch, the US National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA) had forecast that the telescope would have an opera- tional life of ten years. However, when engineers analysed the fuel on board after reaching Lagrange point two (L2), they real- ised there was much more of the original 240 litres of hydrazine propellant and dinitrogen tetroxide oxidiser in the tank than anticipated. James Webb had enough fuel on board to last 20 years. Why? Ariane 5 performed its job with unparalleled precision, deposit- Ariane 5 – a continuing legacy That JWST flight is a testament to the entire story of Ariane 5, which ended with its final flight on 5 July 2023 after 117 launch- es and 236 satellites being escorted to space. All of this paved the way for its successor, Ariane 6. Continuity is a hallmark of Europe’s space launch vehicle: engineers’ efforts on the models before seamlessly feed into the development of those that come next. The evolution and enhancement of the European Ariane launcher are grounded in decades of experience. Ariane 5’s conception can be traced back to the European Con- ference of Science Ministers in Brussels in 1972, when a collec- tive European space programme was conceived. In 1980, Ariane- space was established and it has been responsible for marketing and launching the carrier rockets ever since. Today, the majority ownership of Arianespace lies with ArianeGroup, established in 2015 as a collaboration between the European aerospace com- pany Airbus and the French group Safran. 

ASTRONAUTICS – The story of Ariane 5 Luft- und Raumfahrt, Int. Edition 2024 33 E A - S E N C - A S E : e c r u o S S o u r c e E S A - C N E S - A E / C S G S e r v i c e O p t i q u e Ariane 5 ES launched five ATVs into space Integration of two Galileo satellites into the upper stage of an Ariane 5 ES upper stage. A unique variant, Ariane 5 ES ATV, carried the 21 tonne European Automated Transfer Vehicle (ATV) into low- Earth orbit to rendezvous with the International Space Station (ISS). The upper stage could ignite three times in this configura- tion: first, after the first stage had burnt out; second, after the ballistic flight phase in transfer orbit switched it to an almost circular Earth orbit, and the third time to slow down the stage following the release of the ATV. The ATV then propelled itself to the ISS using its own engines. Another specialised version for navigation satellites, Ariane 5 ES Galileo, used the EPC-H173 first stage equipped with the Vulcain 2 engine, along with two EAP- 241 boosters and a modified EPS upper stage featuring an Aestus engine. Four Galileo satellites would be paired up during assem- bly and subsequently released once they reached their orbit, before Ariane deactivated its upper stage. In the early 2000s, the Ariane 5 Plus programme was initiated to enhance the thrust of the Vulcain engine and develop a new cryogenic upper-stage engine, Vinci. Vinci was designed to make the upper stage reusable at a later stage of development. In November 2008, the ESA Council of Ministers approved the development of the ever more powerful Ariane 5 ME (Midlife Evolution). The rocket was highly competitive at launching mis- sions into geostationary transfer orbit because of its high per- formance, dual launch capacity and its multiple ignition upper stage. Consequently, Ariane 5 could even position satellites direct- ly into geostationary orbit without the need for the transfer orbit which consumes valuable fuel to ‘circularise’ the orbit. This is precisely the ability that gave the James Webb Space Telescope its ‘extra’ fuel. S o u r c e : A r i a n e G r o u p / A R T O N D e s i g n The Ariane family of launchers 

i G S C u d o é d v e u q i t p O / E C A P S E N A R A - S E N C - A S E I : e c r u o S p u o r G e n a i r A : e c r u o S ASTRONAUTICS – The story of Ariane 5 Luft- und Raumfahrt, Int. Edition 2024 35 S o u r c e : I E S A - C N E S - A R A N E S P A C E - A r i a n e G r o u p / O p t i q u e v d é o d u C S G i Ariane 5’s most recent launch included the German Heinrich Hertz satellite Ariane 6 on the launch pad before the first hot fire tests One of the consequences of the 2002 accident was an indus- trial reorganisation. In the summer of 2003, service providers Astrium from Germany and the French company EADS Launch Vehicles merged to form a joint general contractor for the production and development of Ariane 5. This merger not only reduced the complexity and susceptibility to errors of the rocket, but also significantly lowered its price. As chapter 5 ends, 6 begins That was Ariane 5’s final disaster, which was followed by 100 suc- cessful launches in a row, with the very last launch in the early hours of 6 July 2023. On board were the German telecommuni- cations satellite Heinrich Hertz and the French military satellite Syracuse 4B – as well as a wealth of experience for the next rocket model. With Ariane 6, engineers are focussing on flexibility. The new rocket should be able to launch payloads of any kind into any The first Ariane 5 rocket exploded 37 seconds after launch orbit, one payload or multiple, deploying satellites and spacecraft with electric propulsion or launching multiple into large con- stellations. This is thanks in large part to the upper stage’s re- igni table Vince engine. The launcher will be available in two versions: Ariane 64 with four boosters will be able to launch more than twelve tonnes into geostationary orbit, and the Ariane 62 with two boosters will be able to launch up to 4.5 tonnes. As when the James Webb Space Telescope was launched, but with added flexibility, Ariane 6 will be able to precisely transport its cargo into near-perfect orbit, ensuring they can live long and perform brilliant science. • THE AUTHORS The monumental moment that humankind first stepped on the Moon propelled Jens Laßmann towards a career in space exploration, after completing his studies in aerospace engi- neering in Berlin. Since then, the Ariane rocket has remained his focus. As project manager, Laßmann played a pivotal role in developing Ariane 5’s cryogenic upper stage. He is now site manager at ArianeGroup’s largest facility in Germany, located in Bremen, and remains an integral part of the Ariane family. Maximilian Gaub’s fascination with space began early. When the first Ariane launched in 1979, he could be found painting rockets and constructing LEGO spaceships, inspired. His early passion evolved into a career in journalism, where Gaub reported on the Mars Exploration Rover mission in 2003. Today, his enduring love for space exploration permeates his role as a communications strategist for ArianeGroup, comple- mented by numerous hours spent indulging in his favourite series, ‘The Expanse’. 

ASTRONAUTICS – EnMAP Luft- und Raumfahrt, Int. Edition 2024 37 S o u r c e : D L R Every material on Earth’s surface reflects sunlight differently, leaving behind what is known as a spectral signature. EnMAP can recognise, distinguish and map this ‘coloured fingerprint’ using its high-resolution measuring instrument Spectroscopy provides essential information about space� By measuring the interactions between electromagnetic energy and matter with optical instruments such as spec- trometers, we can observe the life cycles of stars light years away, or analyse the chemical composition of atmospheres of distant planets and draw conclusions about their habitability� Our interest in exploring such exciting questions has been the main reason why our spectrometers have primarily been used to observe the vastness of space in recent decades� However, the massive stresses placed on Earth’s environment by popula- tion growth, urbanisation, pollution and climate change make it an urgent priority that we pay more attention to our home planet� The German Environmental Mapping and Analysis Pro- gram (EnMAP) mission is an important step in this direction� With a successful SpaceX launch from Cape Canaveral, Florida on 1 April 2022, the EnMAP hyperspectral satellite was placed precisely into a Sun-synchronous orbit at 640 kilometres – and one of the first high-quality imaging spectrometers specifi- cally dedicated to Earth observation went into operation� Hyperspectral systems are characterised by a large number of narrow spectral bands and continuous spectral coverage of a broad wavelength range. With its two complementary spectrom- eters, the EnMAP hyperspectral instrument analyses the solar radiation reflected from Earth’s surface in wavelengths ranging from visible light to short-wave infrared, corresponding to a wave- length range of approximately 400 to 2,500 nanometres. Within this range, EnMAP covers more than 250 spectral bands at a resolution far exceeding current multispectral Earth observation instruments. Within a single image, the EnMAP satellite covers 900 square kilometres with a spatial resolution of 30 metres. This allows for a precise assessment of the state of Earth’s surface, addressing research questions in environmental domains such as near-natural ecosystems, agriculture and forestry, land use, water management and quality, mineralogy and geology. Acrobatics at 640 kilometres above sea level During an overflight, EnMAP records a 30 kilometre-wide obser- vation strip along its ground track, which is normally truncated after 30 kilometres to form a square – a so-called tile. In order to cover larger contiguous areas, several neighbouring observation strips would have to be combined to form a mosaic. However, EnMAP was not designed to provide wall-to-wall mapping of the Earth’s surface. Rather, the aim of the mission is to observe selected areas with high spectral resolution and, for example, to investigate temporally dynamic processes such as vegetation growth in different regions, thus using a hyperspectral spotlight to complement spatially continuous multispectral Earth observa- tion systems. Theoretically, EnMAP repeatedly passes every part of Earth in a constant rhythm of 27 days. To speed up the repeated observation of a selected point on the surface, the satellite can be rotated in its orbit so that instead of observing our planet directly from above – in nadir view – the instrument looks to the side. Using the full tilting range of +/- 30 degrees, this oblique viewing capability makes it theoretically possible to observe the same area every four days. Measuring the same area repeatedly over time has been pos- sible for many years, for example with the help of airborne mis- sions. However, ground-based and airborne sensors and meas- uring instruments only provide very limited data sets of small areas. And global comparison of evaluation methods was often not feasible because the spectrometers used at different loca- tions around the world were too different and attempts at cross-calibrating these sensitive instruments often failed due to logistical reasons. Only with the use of satellite-based spa- ceborne sensors such as EnMAP is it possible to measure the solar radiation reflected by the Earth’s surface worldwide with the same instrument and thus maintain consistent measuring conditions globally. 

ASTRONAUTICS – EnMAP Luft- und Raumfahrt, Int. Edition 2024 39 Remote sensing of atmospheric gases The state of the atmosphere is just as responsible for the devel- opment of the climate as the state of the land surface. Luckily, EnMAP can also provide support in that respect. The satellite is used, for example, to determine the concentration of important climate-effective gasses such as water vapour, methane or carbon dioxide. Due to its limited spatial coverage at the global level, EnMAP is less suitable for measuring rapidly diffusing gasses, but it can be applied to detect local emissions, for example of methane, or regional phenomena such as mineral and fine dust clouds. Natural hazards and environmental disasters Like many Earth observation systems, EnMAP also supports the observation of natural hazards and environmental disasters: landslides, soil erosion, permafrost disturbances, floods, droughts, volcanic eruptions, land degradation, etc. However, EnMAP’s high spectral resolution can be particularly useful for the detection of pollution. By analysing narrow absorptions, it is possible to meas- ure the characteristics of oil emulsions in the sea up to a maxi- mum thickness of around eight millimetres. Plastic waste can also be detected in the short-wave infrared due to the specific absorp- tion of plastics – at least as long as the plastics float on the surface. Information-based agriculture Another important application for EnMAP is in information-based precision agriculture. Here, the satellite contributes to the devel- opment and improvement of accurate, robust and reliable meth- ods for determining biophysical and biochemical variables. For example, information on crop type, leaf area, absorbed photo- synthetically active radiation, chlorophyll and water content of the plants, and the geometric structure of the crop (such as the leaf angle), can be quantitatively measured. Current state-of-the- art methods for deriving information from spectroscopic data increasingly use reflectance models that are parameterised to compile large training databases. These training databases, which then purely consist of simulated data, are in turn used to train machine learning algorithms that can extract the required infor- mation from EnMAP data. This method of using reflectance mod- els and machine learning in a combined way enables the deriva- tion of advanced and more complex agriculturally relevant information. This so-called hybrid approach makes it possible, for example, to measure the nitrogen and carbon content in the above-ground biomass. The nitrogen content of a crop is key to monitoring nitrogen use efficiency, which is a major driver of farm economy and ecology. The nitrogen use efficiency describes the ratio between the nitrogen fertiliser input and the nitrogen con- tent achieved in the harvested parts of the biomass, which de- termines the yield quality of the crops and thus the price of the harvested crop. Time-series observations, which can only be reliably obtained from satellite platforms, are of great importance for monitoring stressors in agricultural crops, such as nitrogen deficiency or lack of other micro or macronutrients, plant diseases, insect S o u r c e : S p a c e X On 1 April 2022 at 18:24 CEST (12:24 local time), the first hyperspectral satellite built and developed in Germany, EnMAP, was launched into space from Cape Canaveral, Florida on board a SpaceX Falcon 9 rocket i nfestation or drought stress. Information about the spatial and temporal dynamics of stressors can serve as a basis for inte- grated, information-driven agricultural management systems and provide well-founded decision support. Current research in the field of agriculture is concerned, for example, with the use of EnMAP data to measure the gradual accumulation of organic carbon in the soil as part of carbon farming, a concept of regen- erative agriculture, or with the measurement of carbon that is bound to the surface in the form of non-photosynthetic plant tissue such as in crop residues. The various examples above show that EnMAP’s areas of applica- tion are extremely diverse and cover a broad range of environ- mental domains. The German satellite has been designed as a scientific precursor to future satellite missions that will extend the idea of hyperspectral environmental observation to the glob- al level. The European Space Agency (ESA) is preparing the Copernicus Hyperspectral Imaging Mission for the Environment (CHIME), which is set to follow in EnMAP’s footsteps from 2028. • THE AUTHOR Prof� Dr Tobias Hank is a researcher and teacher at the Department of Geography of the Ludwig-Maximilians-Univer- sity in Munich, Germany. His studies of physical geography have contributed to the development of airborne spectrom- eters and environmental spectroscopy. As a member of the EnMAP Scientific Advisory Group, he is now working on hyperspectral applications for agriculture and vegetation research. He has been involved in the EnMAP mission from its earliest stages. 

ASTRONAUTICS – JUICE Luft- und Raumfahrt, Int. Edition 2024 41 A remarkable eight-year journey began in Kourou, French Guiana on 14 April 2023, at 14:14 Central European Sum- mer Time� Propelled by an Ariane 5 launcher, the Euro- pean Space Agency’s (ESA) JUpiter ICy moons Explorer (JUICE) spacecraft set off on an ambitious voyage to explore Jupiter and its icy moons� The precision of the rocket was paramount in putting JUICE on the correct interplanetary trajectory, requir- ing accuracy down to the second� Meticulous planning paid off, and the scheduled course correction manoeu vre, scheduled to take place one month later, was rendered un necessary, leaving extra fuel for future mission operations� A launch attempt was made the day before but was aborted due to bad weather and the chance that lightning could strike the launcher� Since Ariane 5’s propulsion capacity was not enough to launch JUICE directly to Jupiter, a complex series of gravity-assist manoeuvres have been meticulously designed for the journey. During each one, JUICE gets relatively close to a moon or planet, using its gravitational field to alter its orbit around the Sun by either gaining orbital energy or losing it. The planet’s orbit is also altered by this exchange with the tiny spacecraft, but the effect is minute due to its far greater mass. As it launched, JUICE sur- passed the escape velocity required to leave Earth and enter an orbit around the Sun, with the next step being a gravity assist of the Moon and Earth in August 2024. Subsequent assists will take place with Venus in 2025, and more with Earth in 2026 and 2029, ultimately redirecting JUICE towards Jupiter. The spacecraft is expected to reach Jupiter in July 2031. Then it will employ its 400-Newton main engine to navigate the Jupi- ter system and decelerate the spacecraft by 900 metres per second. A gravity-assist manoeuvre with the moon Ganymede will then further decelerate JUICE and save about 300 kilograms of fuel. JUICE has a dry mass of 2,420 kilograms and carried an additional 3,650 kilograms of fuel when it launched. The space- craft is equipped with 20 thrusters for three-axis attitude control, in conjunction with momentum wheels. ) I c S T S ( e l a u q s a P e D . J , ) y e l e k r e B C U ( g n o W . H . M , ) C F S G - A S A N ( n o m S i . A , I c S T S , A S E , A S A N : e c r u o S Image of Jupiter and its moon Ganymede, taken by the Hubble Space Telescope on 6 January 2023 S o u r c e : E S A / A T G m e d a i l a b Artist’s impression of JUICE in front of Jupiter’s moon Ganymede, with the gas giant in the background Jupiter and its many moons The primary scientific objective of the JUICE mission is to thoroughly explore the largest planet in the Solar System, along- side its three largest icy moons: Europa, Callisto and Ganymede. Together with Io, which orbits closer to the planet and boasts active volcanoes, these are Jupiter’s four largest moons. Com- monly referred to as the Galilean moons, they were first observed by Galileo Galilei in 1610 when he glimpsed four diminutive ‘stars’ in proximity to Jupiter through his telescope. Over the course of several days, he noted their shifting positions, leading him to deduce that they were in fact Jupiter’s moons. Today, the Jupiter system is known to harbour 95 moons. Gany- mede takes the crown as the largest – and the ninth largest object in the Solar System – with a diameter of 3,100 kilometres. Jupi- ter’s smallest natural satellites measure only a few kilometres across and are believed to be captured asteroids. The arrange- ment of the Jupiter system mirrors that of a miniature Solar System, providing a valuable model for studying the evolution of our own system and facilitating comparisons with other extra- solar planetary systems. Life beneath the ice The question of whether life on Earth is an extraordinary one off, or if it has arisen elsewhere in the Solar System and beyond, has long captivated humanity. Water is a fundamental requirement for life as we know it, and it could plausibly exist on the three icy moons that JUICE is set to explore. It is thought that these like- ly harbour subterranean oceans of liquid water beneath their thick ice crusts, providing potential environments where life may have emerged. JUICE will investigate these promising leads by gauging the movements of their ice crusts to ascertain their thickness and the scale of the oceans beneath. Essentially, JUICE promises to greatly add to our understanding of the Jupiter system. The spacecraft is not equipped with a lander. As such, it cannot directly detect traces of life on Jupiter’s moons, but it can amass vital data during its many flybys. To do this, the probe will employ an array of tools including cameras, spectrometers, particle sen- sors, radar and a laser altimeter, allowing for comprehensive observations of Jupiter, Europa, Callisto and Ganymede. 

ASTRONAUTICS – JUICE Luft- und Raumfahrt, Int. Edition 2024 43 Moreover, transmitting collected data and sending commands across the vast expanse between the spacecraft and Earth takes between 30 and 50 minutes, due to Jupiter’s average distance from Earth – spanning between 600 and 800 million kilometres. The 2.5-metre diameter transmitting antenna is expected to deliver over two gigabytes of data per day to ESA ground anten- nas: a noteworthy feat over such staggering distances. Adding to the challenge, sunlight at Jupiter is approximately 27 times weaker than at Earth. To compensate, ten solar panels with a vast surface area of 85 square metres provide approxi- mately 700 to 900 watts of electrical power. On-board batteries enable the space probe to survive for up to five hours in the shade cast by orbiting moons and planets. In preparation for the mis- sion, extensive simulations and tests were conducted to mitigate interference between the 16-metre RIME antenna, the 10.6-metre J-MAG magnetometer boom and the 27-metre solar panels. Given the potential for these parts of the spacecraft to interfere with each other, precise calculations and measurements were vital to ensuring uninterrupted measurements can be taken throughout the mission. Upon arrival at Jupiter, JUICE will encounter the most potent radiation field in the entire Solar System. Jupiter’s formidable magnetic field captures and accelerates charged particles – such as protons, electrons and ions – from both the solar wind and the volcanic eruptions of its moon Io, creating what is known as particle radiation. This poses a significant threat to its on-board electronics. Data from previous missions made it possible to pre- pare for this and design the instruments in such a way that they remain operational. Science on arrival after long journey JUICE is set to arrive at Jupiter in July 2031, when it will be just over 600 million kilometres away from Earth’s orbit. Upon reach- ing Jupiter, the probe will enter into orbit and conduct a total of 35 close flybys of its icy moons; two of Europa, 21 of Callisto and 12 of Ganymede, all before November 2034. In December 2034, JUICE will become the first spacecraft to orbit a moon of the outer planets. At this point, its instruments will primarily scour Ganymede’s icy shell for signs of an ocean. S P M : e c r u o S SWI telescope and receiver unit S o u r c e : i E S A / J u c e / J M C ( C C B Y - S A 3 0 . I G O ) After its launch, JUICE took a few pictures of Earth At the same time, NASA’s Europa Clipper probe, slated for launch in October 2024, will also be exploring the Jupiter system, focus- sing particularly on the icy world of Europa. European and Amer- ican scientists are already coordinating their efforts in order to obtain even greater benefits from the measurements taken by both probes, allowing the two missions to complement each other perfectly. Crash landing on Ganymede JUICE’s mission is scheduled to come to an end in September 2035. At this point, the probe will use the last of its fuel to decel- erate, ending with a controlled impact on Ganymede’s surface. The possibility of contaminating the Jovian moon with terres- trial life forms is deemed negligible, as there are no indications that the deep subsurface ocean can be in contact with the moons’ surface before the impact site is sterilised by the prevailing intense radiation. JUICE, ESA’s most expansive planetary mission to date, is now en route to the largest planet in the Solar System. During the eight-year journey, scientists and engineers will meticulously assess its instruments during the commissioning phase, address any issues that arise, refine software for instrument operations, finalise the setup of data centres and plan the detailed mission operations to come at the Jupiter system. There are many captivating and complex years ahead, even before JUICE arrives. • THE AUTHORS Christian Chlebek, Dr Claudia Dreyer, Dietmar Friedrichs and Dr Christian Gritzner managed the funding projects for the German Space Agency at DLR, Bonn, during the development phase and will continue to support the instrument teams dur- ing the operational phase. Their role also involves represent- ing German interests in the JUICE mission with ESA and the other partners. 

ASTRONAUTICS – Heinrich Hertz Luft- und Raumfahrt, Int. Edition 2024 45 At midnight Central European Summer Time on 6 July 2023, the final Ariane 5 rocket (VA261) lifted off from the launch pad at Europe’s Spaceport in French Guiana� On board was a notable payload; sharing the ride with a French military communications satellite, Syracuse 4B, was Germany’s Heinrich Hertz technology demonstrator and communications satellite� This launch marked Germany’s return to system capability in the domain of geostationary telecommunications satellites, 20 years after the end of the DFS-3 Kopernikus mis- sion, which was launched on 12 October 1992 and decommis- sioned in February 2003� Despite some remaining gaps in network coverage, most people in Germany now take the consistent availability of telecommuni- cations bandwidth for granted. Information, entertainment and long-distance communication have become easily accessible, whether at home or while travelling, through a simple search query or phone call. Globally, people, businesses and machines are increasingly interconnected and exchanging data – with geo- stationary telecommunications satellites serving as a pivotal component of this network. The transformative impact of these spacecraft was demonstrated in 1964 when Syncom 3 became the first communications satellite in geostationary orbit – just in time to transmit television images of the Summer Olympics in Tokyo to over four million viewers. While satellite television is gradually being supplanted by streaming services, geostationary telecommunications satellites remain indispensable for ensuring stable connections to aircraft in flight, ships at sea and remote terrestrial locations. Beyond commercial services, these satellites play a crucial role in facilitating secure and encrypted government communica- tions. Demand escalates during crises such as wars, environmen- tal disasters and border security events. Geostationary telecommunications satellites are also valuable for transmitting data between space and Earth. Satellite missions equipped with high-resolution sensors in low orbits are collect- ing ever-increasing volumes of data, and transmission to Earth is becoming a bottleneck. This issue will only get worse with burgeoning demand for high-precision weather, environment and climate data. Geostationary telecommunications satellites can help by serving as intermediaries. B H O : e c r u o S Artist’s impression of Heinrich Hertz S o u r c e : A r i a n e s p a c e ‘Family photo’ of the teams from French space agency CNES, Arianespace, DLR, OHB and ArianeGroup in the S5C integration facility at Europe’s Spaceport in French Guiana In short, constant and ubiquitous communication services with high bandwidth and vast data volumes have become a critical infrastructure. As time goes on, society will only become more reliant on this capability. Heinrich Hertz as a German satellite mission To address the escalating demands on satellite communications infrastructure, the German Space Agency at the German Aero- space Center (DLR) is delivering the Heinrich Hertz national satellite mission on behalf of the Federal Ministry for Economic Affairs and Climate Action (BMWK) and in collaboration with the Federal Ministry of Defence. This mission is a test platform for an array of new payload and platform technologies positioned in geostationary orbit, laying the groundwork for future communi- cations satellites. Alongside its scientific and technical objectives, the Federal Ministry of Defence is using additional payload capacity on the satellite for its own communications requirements, as part of a cooperative effort with the BMWK. The scientific and military payloads are entirely independent of each other and can be opera- ted autonomously. WHO IS HEINRICH HERTZ? The mission is named after the German physicist Heinrich Rudolf Hertz (born 22 February 1857 in Hamburg, died 1 Jan- uary 1894 in Bonn). He is credited as the discoverer of elec- tromagnetic waves. In 1886, Hertz became the first person to experimentally detect electromagnetic waves and transmit them from a transmitter to a receiver. This pioneering work laid the foundation for modern telecommunications. In recognition of his groundbreaking achievement, Heinrich Hertz’s name features in the metric system of units. The unit of frequency was named after him in 1930; one hertz (1 Hz) is defined as one oscillation per second. 

ASTRONAUTICS – Heinrich Hertz Luft- und Raumfahrt, Int. Edition 2024 47 A notable feature of the Heinrich Hertz mission is that the IOV payload is designed as a regenerative payload. The on-board processors enable direct processing of information on the satel- lite, facilitating post-launch software configuration changes and testing of future, as yet undefined, payload operation modes. This flexibility should prove to be a significant advantage over Heinrich Hertz’s anticipated 15-year operational lifespan, during which technical requirements for the satellite are expected to evolve. The second function of Heinrich Hertz is to provide satellite- based communications capacity for the German armed forces. Relay station in geostationary orbit Heinrich Hertz has been positioned in geostationary orbit, circling the equator at an altitude of approximately 36,000 kilometres� At this altitude, a satellite’s orbital period matches the Earth’s rotation, so as viewed from the ground it remains at a fixed point in the sky – 0.5 degrees east, in this case – facilitating radio com- munication with roughly a third of the Earth’s surface. This posi- tioning also enables Heinrich Hertz to function as a relay station for satellites operating at lower altitudes. Satellites in lower orbits typically have limited windows for transmitting data back to Earth, usually less than ten minutes per orbit, as they pass over suitable ground stations. However, Heinrich Hertz offers a substantial advantage; low Earth orbit satellites remain within its line of sight for a generous 40-minute period. This extended radio contact duration allows for the transmission of significantly larger volumes of data. Third satellite in the SmallGEO family Following H36W-1 and EDRS-C, Heinrich Hertz is the third com- munications satellite based on the SmallGEO platform, developed under OHB’s leadership as part of the European Space Agency’s ARTES-11 programme. Thanks to the platform’s modular struc- ture, a significant portion of the satellite’s design has been inher- ited from the H36W-1 and EDRS-C missions. However, Heinrich Hertz possesses distinct features that set it apart from its pre- decessors. For instance, the satellite boasts a total of eight swivelling anten- nas, four of which will be used for scientific and technical exper- iments. The primary focus of coverage is Germany and Central Europe, while a dedicated antenna is reserved for communication with lower-flying satellites. Heinrich Hertz is also pioneering with regard to its propulsion system. In addition to the experimental HEMPT ion beam system, the satellite is equipped with flight-proven Hall-effect electric thrusters and an additional chemical propulsion system. Electric propulsion is very efficient, so combining it with a chemical sys- tem can reduce overall fuel consumption and thus leave more of the spacecraft’s mass for payload capacity. The inclusion of two redundant electric propulsion systems, based on different phys- ical principles, is owing to the experimental nature of the HEMPT system; should it fail, the backup, Hall-effect system can assume control. S o u r c e : A r i a n e s p a c e Ariane 5 awaits its final launch from French Guiana The launch mass of the Heinrich Hertz satellite was 3,450 kilo- grams, including about 1,600 kilograms of propellant (220 kilo- grams of xenon and 1,380 kilograms of chemical propellant). The satellite can generate up to 6.6 kilowatts of electrical power at the beginning of the mission, with a guaranteed 3.7 kilowatts for the payload until the end of its nominal 15-year service life. The satellite stands 4.6 metres tall, up to six metres wide in its final flight configuration with the antenna reflectors deployed, and nearly 22 metres long with the solar panels extended. Alongside the space segment, a distinct ground segment has been estab- lished, comprising an indepen dent satellite control centre and two antenna sites dedicated to Heinrich Hertz. The Heinrich Hertz project is being executed by a predominantly German industrial consortium led by OHB System. • THE AUTHORS Pia Bausch has a master’s degree in biomimetics and works in corporate communications at OHB SE. Dr Alexander Schneider is Programme Manager of the Hein- rich Hertz mission and heads the telecommunications projects in phases C/D at OHB System AG in Bremen. Dr Siegfried Voigt is Head of the National Programme in the Satellite Communications Department of the German Space Agency at the German Aerospace Center (DLR). 

F U T U R E . S P A C E B W A d v e r t i s e m e n t SPACEFLIGHT 49 CONFERENCE th 20 24 5 NOVEMBER 2024 HAUS DER WIRTSCHAFT BADEN-WUERTTEMBERG STUTTGART (GERMANY) RAUMFAHRTKONFERENZ.DE 

A d v e r t i s e m e n t 73rd GERMAN AEROSPACE C O N G R E S S 30 SEP – 02 OCT 2024 HAMBURG (GERMANY) 4 2 0 2 O N E H U N D R E D S T U D E N T S PARTICIPATION CAMPAIGN POWERED BY: Rolls-Royce Germany and the German Society for Aeronautics and Astronautics are enabling 100 students from a University in Germany to attend the German Aerospace Congress (DLRK) 2024 from 30 September till 2 October 2024 in Hamburg free of charge. Students from all german-speaking universities with an aerospace or aeronautics background are invited to apply for the student participation campaign. Those students who win a ticket will receive a code for free registration. The ticket entitles the holder to attend the entire scientific programme of the German Aerospace Congress 2024. Rolls-Royce Germany is also inviting the winners to a special presentation followed by a question and answer session. Here you will have the opportunity to network with experts from Rolls-Royce Germany. Further information and the terms and conditions for participation can be found on the campaign website. AND NOW? GO TO THE WEBSITE https://dlrk2024.dglr.de/programm/100_studierenden_aktion AND APPLY UNTIL 31 JULY 2024!