(under preparation)

Small sats and CubeSats are proving to be very useful for in-orbit demonstration as well as dedicated space missions. Supporting their development ESA encourage a new approach to spacecraft integration and highlights an affordable way to deploy small payloads.

ESA has been globally pioneering the approach to a sustainable space environment. Following earlier studies and developments, since 2009 ESA's CleanSpace initiative develops European wide technology developments, standards, concepts and missions. One of the four targets of ESA's Technology Strategy is to invert Europe’s contribution to space debris by 2030, and ESA's Zero Debris approach aims to totally stop the generation of debris in valuable orbits by 2030.   

This approach has been initiated by the Agency in response to the catastrophic degradation of the Low-Earth Orbit environment. Indeed, space debris experts have already announced that the point of no return has been reached and that the debris population will keep growing even if we would totally stop launching objects in space, although at a far reduced rate. Thus, we must promptly act to mitigate this urgent issue.

The Zero Debris approach shows the Agency’s ambition to leave our precious space environment in a clean state.

ESA has a number of ambitious activities ongoing, including the application of a new ESA Space Debris Mitigation policy, which will make the new ESA standard ESSB-U-ST-007 applicable to ESA mission not having yet completed SRR. This ambitious standard materialises the first step towards a full implementation of Zero Debris approach to ESA missions by 2030.

In parallel, to support the transition of European space sector to develop product lines to be compliant with short and long-term Zero Debris goals, technical activities are being put in place though different ESA technology programmes. They focus on the swift progress on topics such as:

• Maturation of best practices and technical standards;
• promote evolution of European product lines for spacecraft of different classes;
• demonstration of safe and affordable active debris removal and in-orbit servicing;
• improvement of operational procedures, collision avoidance and technologies to support space traffic coordination.

ESA specifically welcomes new ideas and concepts from industry and academia to achieve this objective. This cluster provides a list of Discovery element activities addressing this objective.

 

What are solar power satellites or space-based solar power stations?

The concept of space-based solar power uses the wireless transmission of solar energy collected in space by solar power satellites, for use on Earth, on the Moon or on other planets. Solar power satellites can benefit from higher solar illumination, unfiltered by atmospheres, or even permanent sunlight in some orbits. They therefore offer the possibility to transmit clean energy, in a flexible way, to different remote users in space, on Earth or on the surfaces of the Moon and Mars.

In the long term, solar power satellites have the potential to mitigate climate change through the provision of clean energy. Earlier applications might be in space, for example to support exploration of the Moon and Mars. Compared to energy collection on the surface of a planet, a satellite’s solar collectors have the benefit of being unobstructed by a planet's atmosphere or local topography and can operate independently of a planet's tilt or rotation.

This concept was first described by Tsiolkovsky 100 years ago and first proposed as an engineering concept by Glaser in 1968. The development of various technological building blocks has progressed since then, and over the years many approaches to SPS technology have been proposed, from mirror satellites(1)(2)(3), to microwave beaming(4)(5), to laser technologies(6) To date, only select subsystems have been realized(7), but more and more solutions are being proposed for the near- to mid-term(8)(9)(10)(11). 

Why are solar power satellites not yet a reality?

Solar power satellites are by design relatively large structures and require advances in a number of key technical areas that push the boundaries of what is currently feasible in space. Some of these current technological bottlenecks include, but are not limited to:

• Very large structures (manufacturing, deployment)
• Construction (materials, modularity, in-orbit manufacturing, robotics...)
• Power generation and onboard energy conversion (high voltages, efficient solar to electric and electric to microwave/laser conversions)
• Thermal systems (efficient large radiators and distributed thermal subsystems)
• Wireless power transmission systems (laser/microwave generation, control, focusing, pointing...)
• Microwave/laser to electric conversion at receiving site(s)
• Operations (station keeping, autonomy, safety, resilience and redundancy, maintenance and servicing, re-fuelling including with in-space resources)
• Control (structures, formations, wireless power transmission beams)

Background and Motivation

Efforts towards human exploration beyond Earth are seeing a remarkable resurgence, with an increasing number of robotic missions to the surfaces of the Moon and Mars and plans to send humans to these destinations in the near future [1], [2]. Private entities are also formulating long-term visions and developing associated nearer-term technologies for enabling sustained human presence and activities on the lunar and Martian surfaces [3], [4].

Such objectives can only be realised with the appropriate infrastructure to support human presence [5]. This includes infrastructure to shield the crew and equipment from environmental conditions (e.g. habitat structure, berms), enable crew mobility (e.g. roads, landing pads), generate energy (e.g. solar energy equipment, energy storage) and facilitate communications (e.g. antenna towers).

Local sourcing of materials

Relying solely on the shipment of materials, equipment and supplies from Earth to build and maintain such infrastructure would likely make long-term exploration missions prohibitively expensive. The ability to produce the required infrastructure elements and associated equipment on site – by maximising the use of in-situ resources and minimising the use of supplies from Earth – appears essential to enable sustainable and economically viable long-term human activities. Manufacturing and construction using in-situ resources is inscribed in ESA’s Space Resources Strategy [6], as a field of application of local resources on the Moon, as well as a key technology area for development on Earth and further maturation for space.

Past efforts have been dedicated to proposing and demonstrating concepts for in-situ fabrication and construction of infrastructure elements, using a combination of resources found on the exploration site – such as regolith – and materials brought from Earth [7], [8]. Previously proposed technologies were developed up to the feasibility demonstration stage, focusing on the development of processes to obtain construction materials, [9]–[16], the construction of large-scale or miniature infrastructure element demonstrators [17]–[22], or the manufacturing of small, high-resolution hardware [23]–[25].  

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1. The Global Exploration Roadmap, January 2018, https://www.nasa.gov/sites/default/files/atoms/files/ger_2018_small_mobile.pdf
2. Gibney, Elizabeth. "How to build a moon base Researchers are ramping up plans for living on the Moon." Nature 562.7728 (2018): 474-+
3. SpaceX, Starship Update, 28 September 2019, https://www.youtube.com/watch?v=sOpMrVnjYeY
4. Blue Origin, “Going to Space to Benefit Earth”, 9 May 2019, https://www.youtube.com/watch?time_continue=2201&v=GQ98hGUe6FM
5. D. Binns et al, “Review and Analysis of (European) Building Blocks for a Future Moon Village”, IAC-17-D.1.7, 68th International Astronautical Congress (IAC), Adelaide, Australia, 25-29 September 2017
6. ESA Space Resources Strategy, 23 May 2019, https://sci.esa.int/documents/34161/35992/1567260390250-ESA_Space_Resources_Strategy.pdf
7. Lim, Sungwoo, et al. Extra-terrestrial construction processes–Advancements, opportunities and challenges. Advances in Space Research, 2017, 60.7: 1413-1429
8. Naser, M.Z., “Extraterrestrial construction materials”, Progress in Materials Science Volume 105, August 2019, 100577
9. Meurisse, Alexandre, et al. "Solar 3D printing of lunar regolith." Acta Astronautica 152 (2018): 800-810.
10. Mueller, Robert P., et al. "Additive construction using basalt regolith fines." Earth and Space 2014. 2014. 394-403.
11. Goulas, Athanasios, Russell A. Harris, and Ross J. Friel. "Additive manufacturing of physical assets by using ceramic multicomponent extra-terrestrial materials." Additive Manufacturing 10 (2016): 36-42.
12. Chen, Tzehan, et al. "Formation of polymer micro-agglomerations in ultralow-binder-content composite based on lunar soil simulant." Advances in Space Research 61.3 (2018): 830-836.
13. Chow, Brian J., et al. "Direct formation of structural components using a martian soil simulant." Scientific reports 7.1 (2017): 1151.
14. Wan, Lin, Roman Wendner, and Gianluca Cusatis. "A novel material for in situ construction on Mars: experiments and numerical simulations." Construction and Building Materials 120 (2016): 222-231.
15. Arnhof, M., S. Pilehvar, A.-L. Kjøniksen, and I. Cheibas. 2019. “Basalt Fibre Reinforced Geopolymer Made from Lunar Regolith Simulant.” In 8th European Conference for Aeronautics and Space Sciences, EUCASS, Madrid, Spain.
16. Lakk, H., Krijgsheld, P., Montalti, M., and Woesten, H., “Fungal Based Biocomposite for Habitat Structures on the Moon and Mars”, International Astronautical Congress, 2018. 
17. Cesaretti, Giovanni, et al. "Building components for an outpost on the Lunar soil by means of a novel 3D printing technology." Acta Astronautica 93 (2014): 430-450.
18. Werkheiser, Mary J., et al. "On the development of additive construction technologies for application to development of lunar/martian surface structures using in-situ materials." AIAA SPACE 2015 conference and exposition. 2015.
19. Buchner, Christoph, et al. "A new planetary structure fabrication process using phosphoric acid." Acta Astronautica 143 (2018): 272-284.
20. Zhang, Jing, and Behrokh Khoshnevis. "Selective Separation Sintering (SSS) A New Layer Based Additive Manufacturing Approach for Metals and Ceramics." University of Southern California, Department of Industrial and Systems Engineering (2015): 71-79.
21. Lakk, H., Schleppi, J., Cowley, A., Vasey, L., Yablonina, M., and Menges, A., “Fibrous Habitat Structure from Lunar Basalt Fibre”, International Astronautical Congress, 2018.
22. Imhof, Barbara, et al. "Advancing Solar Sintering for Building A Base On The Moon." 68th International Astronautical Congress (IAC), Adelaide, Australia. 2017.
23. Fateri, Miranda, and Andreas Gebhardt. "Process Parameters Development of Selective Laser Melting of Lunar Regolith for On‐Site Manufacturing Applications." International Journal of Applied Ceramic Technology 12.1 (2015): 46-52.
24. ESA, “3D-printed ceramic parts made from lunar regolith”, 14 November 2018, http://www.esa.int/spaceinimages/Images/2018/11/3D-printed_ceramic_parts_made_from_lunar_regolith
25. Jakus, Adam E., et al. "Robust and elastic lunar and martian structures from 3D-printed regolith inks." Scientific reports 7 (2017): 44931.

In the overall digitalisation context, i.e. having computers assisting all our tasks, it is difficult for a computer to understand the content of a document. To do so, the information that is in the document must be expressed in a different way, more structured (diagrams, tables), or with less expressive power but with stronger grammatical rules than the natural language. This way of expressing information is called a model in this context. The goal of MBSE is to replace most of the documents by models. And therefore to replace document editors with model editors, which are specific of the topic that the model is about. And finally to transfer these models from tools to tools, all along the project development, and to enrich them, e.g. from requirements models, to architectural models, to design models, to test models, etc.

The ability to create a flow of information transported from model to model, and from tool to tool, is called Digital Continuity. The fact that the tool can exchange models and understand the model of another tool is called interoperability of tools. The information included in the document has a meaning, which is called its semantic. Likewise, the meaning of models is also called their semantic. Semantic can also be represented by a model, in this case it is called a "conceptual data model" , or an ontology. An ontology is a representation of the concepts that are used by information, and of the relationship between the concepts. It gives a (semantic) structure to the information. It is not possible to create a simple and complete ontology able to describe the information contained in a document written in free natural language. But, as a model is a specific part of the information, it is possible to create an ontology for a particular (set of) models.

Tools can exchange information by pure item-to-item translation of the content. If we compare to language translation, the english (shooting in one's foot) will be translated in a foreign language by a gun sending a bullet in a foot: the tools will not be interoperable. Instead, if the two tools share the concept (in their own ontology) of "making a mistake that backfire on yourself", then the translation will go up to the ontology level to translate forth and back the right expression in the right language. This is called semantic interoperability.

 

THE CHALLENGE

ESA has set out strong ambitions for the European space industry in its latest Technology Strategy, including a 30% schedule reduction, and one order of magnitude of cost efficiency improvement. These targets cannot easily be reached solely through product technology improvement. Process change is needed!

Digital continuity is considered to be a major technique to enable:

• a continuous flow of information to reduce source of errors throughout the life cycle;
• the connection of all the engineering data to improve traceability, allowing change impact analysis and assessment of the impact of non-compliance to be performed more quickly; 
• the availability of a single source of truth for each engineering data to allow system engineers to make accurate and up-to-date system trade-offs, avoiding late system changes and reducing cost;
• the interface to many system design analysers to increase the proportion of verification by design, reducing the amount of testing required, and decreasing the overall project timeline.

 

WHAT IS MODEL BASED SYSTEM ENGINEERING?

It is System Engineering which is using preferably models rather than documents. It is a set of modelling techniques (methods, languages, tools). It is used to build a product, and describes all the facets of the product. Therefore, all the elements describing the product (its artifacts) can be manipulated by computers at a low level of details. The computer can therefore make all sorts of detailed relationships between the products artifacts. It can relate together two different disciplines using the same data (mass is defined by mechanical people and used by software people), it can relate a requirement with its implementation and with its test , it can relate a customer need with a supplier solution.

There are existing tools which are called Product Lifecycle Management (PLM) and Product Data Management (PDM). They  manage the products through their artifacts (“business objects”), but only globally. These tools do not enter into the artifacts, nor capture their relationship. For example, a functional model is identified as an artifact, but its relationship with e.g. the Computer Aided Design model, or the avionics architecture, is not addressed.

It is the role (and added value) of MBSE to make these links, and to look inside the artifacts. By doing so, MBSE transforms the product data into information.

Digital Continuity

Commercial tools start to address some of these problems through PLM and PDM, but in their own context, which does not offer the required industrial interoperability across tools, and may create unwanted vendor lock-in. The challenge is to implement digital continuity, which aims to create the above-mentioned links between the artefacts, across heterogeneous tools, by use of model-based techniques. These links need to be created in the three dimensions of system engineering:

• across disciplines
• throughout the life cycle
• along the supply chain

It is important to note that, in MBSE, SE (system engineering) must remain the objective, MB (model-based) is ‘only’ an enabler. Therefore, the technology must be thought as ‘MB for SE’, considering model-based engineering as a lever for system engineering.

 

GETTING TO THE SYSTEM ENGINEERING OF TOMORROW

System engineering is the art to define, design, realise and verify a system in a three dimensional space: across disciplines, along the lifecycle, through the supply chain (ECSS-E-ST-10C)[1].

Mastering system complexity is at the root of our needs. Initially manageable by a single or a small team of system engineers, the complexity of some of our space systems starts to exceed what can be thoroughly encompassed by a human team. Moreover, some traditional assumptions (e.g. the a priori separation into two predefined space and ground segment), may not hold anymore, thus creating even bigger systems. System complexity includes architectural complexity (due to multiple configured, tightly coupled elements), functional complexity (due to a high number of interrelated mission requirements), organisational complexity (due to the number of distributed actors). This complexity cannot be handled any more via documents.

 

CHALLENGES FACED BY OUR SYSTEM ENGINEERS

Because the functions become extremely complex, entangled, and full of exception and dependencies, or because the concept of operation has significant system implications, textual descriptions quickly become inadequate to describe the system behaviour completely and consistently.

->The system engineer needs formal representations beyond textual descriptions

The amount of information contained in the recent systems cannot be manually distributed across disciplines and along the supply chain.

-> The system engineer needs a controlled exchange of data supported by automated mechanisms.

Change impact, traceability and relationships between the various elements or aspects of a system cannot be achieved through an unorganised set of information.

-> The system engineer needs a structured knowledge of their system

The exchange of system data by documentation, email, or individual files makes it impossible to provide the right version of the right information to the right person at the right time.

-> The system engineer needs a single source of truth, consistent by construction, from which appropriate viewpoints may be extracted to communicate about the system.

The evolution of the system becomes more and more difficult to predict, as the evolution of key data may not be visible.

-> The system engineer needs, for progress monitoring, a dashboard with system engineering information such as main budgets (mass, power, link, etc.), key parameters, coverage statistics, trends, etc.

The history of the system elaboration is sometimes lost, and the lack of traceability does not allow, at the end of a project, requirement rationales or trade-off justifications to be recalled.

-> The system engineer needs traceability across the system of both formal derivation, satisfaction and justification of requirements versus design, as well as links to collaborative and informal aspects such as design and trade-off decisions at review milestones. 

The amount of interface with other stakeholders, customers and suppliers is increasing and cannot be handled only by loosely coupled documents.

-> The system engineer needs to create consistent baselines of system engineering data for communicating with customers (e.g. reviews) and suppliers (e.g. subcontracting a system element) and a mechanism to allow for the distribution of reduced models to external parties to protect intellectual properties.

The reuse of elements from previous projects is difficult when done from documentation, and the changes needed to adapt products to new requirements are spread over unidentified pages of documentation.

-> The system engineer must be able to initialise a system with a reusable set of consistent data (libraries), or add reused data during the project, with the capability to identify the required deviations and branches.

In the early stages of a project (i.e. Phases A, B1 and B2), the lack of an (as much as possible) exhaustive relationship model (dependencies) among all entities of the project and system, and the lack of the level of maturity of the represented/available information, quite often push the decision making process towards expensive and complex solutions. Such solutions might be even revisited and/or disregarded in later phases of a project (Phase CD).

->The system engineer must be able to grasp all relationships (even though they are not yet defined/consolidated) among all entities of the system (incl. entities of the project) and their maturity, in order to build a proper risk assessment and decision-making process.

 

WHAT IS SPECIFIC TO THE SPACE SECTOR?

The space domain has some particularity that can make the deployment of MBSE difficult:

• The projects are performed by wide consortia involving various industries, themselves sometimes made up of other consortia (for example, the Galileo 2G project includes 11 consortia). This may be due to geographical return constraints, European commission context, ‘best practice’ constraints, industrial product policy for dual sourcing, etc.
• Each space actor may or may not be trained in MBSE.
• Each space actor may or may not have its own MBSE standard/formalism.

Integrators and suppliers do not necessarily share the same modelling levels, the same modelling goals, nor the same engineering constraints. This results in possible large differences and needs in terms of methods, semantics, model usage, modelling concepts, rules, practices, and tooling.

Sharing technology would be obviously the most efficient way, as all the engineering stakeholders would use the same methods and tools to fulfil their needs. Unfortunately, the diversity of engineering needs, and the heritage in technology investments of all the stakeholders, make such a situation unrealistic.

The next technical solution is to bring together formalism, languages, and even meta-models. But this is not sufficient, because it often happens that the model building and conformance rules are different, the semantics have discrepancies, and the process or the tools generate constraints. In addition, the space engineering community will never be able to converge on a ‘one size fits all’ metamodel that covers all concepts and is accepted by all space stakeholders.

Instead, semantic interoperability should be targeted, rather than shared formalism, standards or languages, sometimes leading to impoverishment of the engineering quality. It is ultimately more efficient to rely on automatic transformation tools than on modelling constraints on both sides. Native entity practices and methods should be preserved so as not to hinder engineering quality.

WHAT are COTS?

Commercial Off The Shelf (COTS) components and modules are assemblies, modules or parts designed for commercial applications for which the item manufacturer or vendor solely establishes and controls the specifications for performance, configuration, and reliability (including design, materials, processes, and testing) without additional requirements imposed by users and external organisations.

COTS for space

Space is becoming a more and more competitive sector, asking continuously for higher performance figures while reducing the overall cost from mission inception up to end of life decommissioning. This has consequences at all levels down to the selection and procurement of individual building blocks and components.

In parallel to this trend, electrical, electronic and electromechanical (EEE) parts designed for terrestrial applications such as automotive and other industrial sectors show high reliability when produced in massive quantities and while being subject to other industrial qualification schemes (for example, AEC-Q automotive standards).

Although some solutions matching space needs already exist, there is still a gap between space and terrestrial applications of components, and proper methodologies have yet to be developed and approved to allow a more systematic usage of COTS components and modules for space applications.

COTS for institutional space applications — the expected advantages

The expected advantages of COTS for institutional space applications are:

1. Performance: where equivalent performance is not obtainable by classical high-reliability (Hi-Rel) components
2. New Capabilities: where Hi-Rel components for performing a specific function don't exist yet
3. Cost: typically for large volumes or low reliability/low radiation application where important risks might be taken
4. Availability: benefit from production capability of supply chains for terrestrial use (in terms of modules)
5. Time: shorter lead times and lower risk of part unavailability (though this advantage might not be always clear, depending on procurement scheme, taking into account of quick obsolescence cycle of COTS components and their limited shelf life)

COTS for institutional space applications — the challenge

The volume of COTS procurement for a specific spacecraft project is typically low and it is difficult to guarantee full traceability of the components. Radiation performance of the component in particular can differ substantially between the procurement lots even if the component type is the same. In this scenario, reproducibility of the radiation test results is challenging.

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related ESA links, publications and webstories:

• From custom-made to commercial: how ESA is changing the way that spacecraft are built, 09/06/2020
• Related Discovery element campaign on OSIP: (link)

 

In 2019, ESA launched a Discovery Element campaign on marine litter, asking for ideas to detect and track seaborne plastic litter using satellites. Based on these ideas, all submitted via the then brand new Open Space Innovation Platform, 26 innovative projects have been kicked off in 2020 to together better map the direction humanity should take to achieve this ambition.

The campaign and the resulting activities were overseen by ESA's Paolo Corradi.

The activities list on the right here provide the status and results of these activities.

Related events:

• Workshop on Remote Sensing of Marine Litter, 16 - 17 October 2023 | ESA-ESTEC | Netherlands: https://atpi.eventsair.com/remote-sensing-of-marine-litter/