Synthesis Report


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The 17th “European Conference on Spacecraft Structures, Materials and Environmental Testing” brought together some 475 participants from 30 countries, mostly European. Although few in number (10%), there were also representatives from countries outside Europe (America, Asia, Oceania).

The Conference was jointly organized by CNES, DLR and ESA. The official opening was announced by Dr. Jean-Claude SOUYRIS, Deputy Director of CNES Technology and Digital Directorate.

The 200 papers (174 oral presentations and 25 posters) were divided into 40 sessions and the themes covered revealed to be in good continuity with the previous conference organized in 2021 by DLR.

Most papers discussed scientific and application satellite and launcher projects, mainly covering the design, development, manufacture and testing.

The presentations and discussions allowed to assess the technical state reached in the various areas relating to mechanics, together with the changes needed to meet the objectives of future missions.

ALM (8 sessions)

Advanced manufacturing including additive manufacturing was the most widely discussed topic during ECSSMET 2023 with in total 11 splinter sessions, 34 papers and 4 posters. The presented work covers the whole value cycle from raw materials in both powder and wire form up to printed metallic and non-metallic material properties, innovative design processes and manufacturing processes, applications in diverse fields and finally the topic related to qualification and acceptance of parts.

Small cubesat structures up to XXL structural panels with integrated thermal functions have been designed, printed and tested. The use cases illustrate the benefits of additive manufacturing by integrating different functionalities such as thermal, optical and electrical functions into structural parts.

Topological optimization has been widely used for a few years and ALM technologies made it possible to manufacture the parts designed by topological optimization. For the first time, during ECSSMET 2023 several papers presented trending topics in big data such as machine learning, artificial intelligence and genetic algorithms. One presentation demonstrated the use of AI tools Stable Diffusion for topological optimization and ChatGPT for generating code for Nastran analysis and post treatment providing support to mechanical and design engineers.

The presented additive manufacturing process work covered ALM technologies and other advanced manufacturing technologies such as cold spray technology, plasma metal deposition technology, friction stir welding to assemble parts that were made by ALM, application of coatings to functionalize surfaces, solutions to produce fiber reinforced polymers or metal matrix composites. Direct energy deposition technologies are capable of manufacturing very large and thick structures while powder bed fusion technology is capable of manufacturing parts with more precision and even very thin walls if process parameters are adapted. Most papers focus on on-earth manufacturing processes while a few papers are dealing with manufacturing in space dealing with vacuum and microgravity issues.

All types of materials are studied for additive manufacturing from classical metallic materials to non-metallic such as polymers, ceramics, multi materials, composites and even 4D materials. The TA6V titanium alloy (5 papers) and Scalmalloy aluminum alloy (4 papers) are the most cited materials for additive manufacturing during the conference.

ALM is still facing cost issue mainly coming from workmanship tests, preventing a wider use of the techno.

Lattice structures (3 sessions)

A number of papers presented lattice structures built with additive manufacturing, but also using composites.

A special interest was identified for the launcher industry with a limited number of interfaces compared to satellite applications.

Composites (7 sessions)

The number of sessions dedicated to composite materials experienced a considerable boom this year with a total of 7 sessions compared to only 2 sessions during the 15th and 16th ECSSMET conferences, hence competing with ALM. In total 30 papers and 1 poster were presented covering a wide range of subjects – design, modelization, manufacturing and testing – and a wide range of applications – satellite structures, tanks and launcher structures.

Whereas composite manufacturing of spacecraft structures used to be very manual in the past, we see an increase of robotic processes even for smaller parts like booms. Innovative processes were also presented like the “GRAM” technology which consists in winding resin pre-impregnated carbon fiber filament around interfaces before curing. A significant amount of papers dealt with composite grid structures which allow mass and cost reduction compared to the existing honeycomb sandwich structures.

Some papers also focused on reducing the environmental footprint of the composite materials at different stages and tackling evolution of REACH regulation: at matrix level, by using bio based epoxy or replacing thermoset by reusable thermoplastics, or at manufacturing level by using a sustainable material like salt for molds. At material level, it was also mentioned that the use of specific resin based on Vitrimers for the production of composite enables new functionalities like self-bonding and offers good recycling capabilities. Such new approaches that combine bio based thermoset, recycling and repairing capabilities will have a great impact on the entire composite industries. Most of the new thermoset materials presented are fully compatible with the existing industrial processes, which is very important to foster adoption.

Furthermore, a couple of papers focused on Metal Matrix Composite structures. Although the presentations contained mixed results, it is an interesting development for composites.

Two sessions were dedicated to failure analysis and numerical methods, showing the importance of predicting the behavior of the composite structures. This is especially true for tanks with several presentations on the modelization of crack propagation in cryogenic environments. Also the cost of testing remains very high, and one presentation even addressed the use of simulation to qualify composite launcher structures.

Environmental Testing (6 sessions)

The session on acoustic noise test has been particularly popular. 5 papers were presented with main focus on direct acoustic field approach, which is a very active area of research and development. There, new metric to quantify the uniformity and diffusiveness of the pressure field was proposed; advancement of MIMO test control performance was demonstrated via detailed assessment of test data, complemented by the high fidelity simulation developed specifically for this purpose.

We can notice that there is still some work to do on the launcher acoustic field representativeness.

Another presenter showed an end-to-end validation covering test and simulation tools based on a different acoustic noise control and generation system. Notwithstanding the progress shown on direct acoustic field approach in practice, one presenter has highlighted the fundamental aspect on wave incidence which is important in both the understanding and correct simulation of the field and structural responses.

On the more conventional acoustic noise test approach in a reverberant chamber, the last paper of the session rightly highlighted the need to account for the influence of sound absorption of the test article to ensure the safety and needed performance are reached.

The Mechanical test campaign session provided an overview of the verification tests performed on a number of Earth Observation spacecrafts (EarthCare, FLEX and Sentinel 6), as well as scientific (PLATO), but also a very specific application with the International Berthing and Docking Mechanism for ISS. Presenters covered a wide range of topics, from remarking the importance of refined test predictions and advanced check of test instrumentation response (e.g. via auto-MAC calculation tool), to highlighting the option of qualifying versus quasi-static loads in the frame of sine vibration test (with QSL limits reached in a frequency range below the first mode), to implementation of a random environment verification approach to cope with launcher requirements defined late in the development.

At the session dedicated to launchers, several presentations were dedicated to re-usable launchers which is now an important topic for the European community. The challenges of developing such a system were described for the Calisto vehicle and in particular the qualification wrt the dynamic environment. For re-usable vehicles, structural health monitoring could be a great asset in order to improve their reliability and efficiency. A system was tested to demonstrate it could withstand all the environmental conditions it could face on a re-usable launcher.

Other types of mechanical environment on launchers were discussed: first the methodologies needed to optimise acoustic fairing protections in order to offer a better comfort to the payloads, and a study on the correlation of assembly fluxes (created when 2 interfaces with imperfect geometries are bolted together) which need to be taken into account for structure sizing.

The session on thermal test means included the presentation of specific thermal test facilities, like the large cryogenic facility in CSL, used to cycle solar arrays for Jupiter missions, or a specific facility for mechanical testing of adhesive at cryogenic temperatures. Instrumentation techniques were also presented, in particular the development of infrared thermography at low temperature. Development of a new test facility in IABG to support optical tests was also presented.

Multi-axis vibration was presented as a promising new approach, with comparison between responses obtained in one axis, 3 axes and 6 degrees of freedom vibration. Vibration testing with empty tanks was also presented with the experience of JUICE testing, including discussion of the conditions under which such approach can be acceptable in terms of model correlation, sensitivity analyses to demonstrate robustness, and verification at lower level of integration (structure, tanks, …).

Analysis & Design (3 sessions)

Several examples of spacecraft or payload development were presented. Most of them show the need and the methods to reduce safety factors and uncertainties in order to avoid over-sizing and over-testing. This has been achieved by using either more often CLA when significant design or environment evolutions are available, or system level analyses and tests in the case of payloads with complex interfaces. These solutions required good collaboration between all project partners to share specifications, models and methods, which has proved efficient to reach good results.

Deployable Structures (4 sessions)

Development of deployable antennas for large satellites is an activity in progress. The problematics of the repeatability of the deployment was also addressed during the session. The majority of papers focused on the development of deployable antennas for cubesats and minisats, some with several meters in dimensions. These antennas will allow cubesats extending their functional capabilities, and most probably replacing larger satellites in the near future.

Dynamics Analyses (2 sessions)

Those sessions covered a wide scope and addressed several subjects: (non-linear) structural dynamics, aero elasticity, damping, acoustics… The main common point is the willingness to develop new methods for reducing computational costs and to capture new complex physics.

Isolation and damping (1 session)

Over the years, new innovative damping technologies are continuously being developed, proof that reducing mechanical loads on sensitive structures and payloads is still a main concern and that no universal solution has been found yet.

The proposed damped solutions in this session are based on passive elastomer solutions or on more nonlinear physics such as particles. All show interesting potential but are not done yet with the development and qualification process.

A very interesting work presented the effect of acoustic black hole damping effect presenting simulation and experimental results of the phenomenon. Due to its nonlinear nature the effect could be interesting for high intensity vibrations/ shock damping for launcher applications.

Thermoelastic (2 sessions)

Activities are mostly related to performance (pointing / distortion) rather than strength. In this view, the European Guidelines for Thermo-Elastic Verification was presented. This guideline gathers the widely accepted and validated methods for thermo-elastic verification originating from several thermo-elastic workshops held during previous ECSSMET conferences, a European thermo-elastic working group and an ESA funded study dedicated to the preparation of this Guideline.

The two thermos-elastic sessions also presented specific examples of thermo-elastic verification at instrument or satellite level including detailed thermal cartographies and uncertainty analyses.

Space Sustainability (1 session)

The space sustainability problem is a recent topic for the ECSSMET conferences. The first paper presented a selection of Design for Demise and Design for Containment in order to reduce the on-ground casualty area. The other ones presented various aspects of structure resistance against hypervelocity impacts of debris.

Space debris still not the highest priority with increasing number of satellite (constellations); waiting on politics for pushing the subject stronger.

Microvibrations (1 session)

The micro vibration session dealt with its 3 main topics: the sources of micro vibrations, the system mechanical paths, and the studied performance susceptibility. Concerning the sources, a complex detailed numerical study showed how critical ball bearing manufacturing accuracy can affect the induced loads of reaction wheels. Then, other presentation provided a picture of test facilities associated with this topic, with an interesting analysis on the difficulty to remove analytically the test hardware contribution from the measured mechanical behavior when performing micro vibration tests. Finally, two papers dealt with the thermal performance impact of micro vibration on a cryogenic instrument with complex interfaces definition, which is quite unusual compared to the more common line-of-sight stability performance on Earth observation instruments.

We can see through these papers a global need to decrease the micro vibrations environment due to the increasing instrument performance that we foresee. The usual principle of isolating the sources may no longer be sufficient in the future and more complex analysis/test procedures seems to be required to face this challenge.

Shock (2 sessions)

The shock environment is still a challenge for all the community as it was demonstrated by the intensity of the discussions during the shock sessions. Various different approaches to the shock prediction were presented (shock specification using extrapolation from a shock database, use of ECSS standard rules and numerical analysis). The numerical simulations presented reveal some progress in the understanding and simulation of the shock environment. Effort must be maintained to continue to improve the methods, understanding and accuracy of the simulations. From the experimental point of view, various interesting examples and analyses of shock failures were presented, which showed once again the complexity of this environment and the need for better understanding. Also, an application of DIC to shock test measurement was presented and demonstrated the feasibility of the approach although it requires some further evaluation and calibration.

One presentation introduced a shock database similar to Viborspec for acoustic. There is also an interest in “big data” to extract trends, statistics and reduce margins.

To conclude

The Conference gave specialists in the area a real opportunity to get up-to-date information on the most recent advances and share the experience acquired.

The Conference Chairmen:

Pierre-Yves TOURNEAU – CNES | Christian HÜHNE – DLR | Tommaso GHIDINI – ESA