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Additive manufacturing at ESA, the alpha and omega

AM has allowed us to get closer than ever to space. Dr. Tommaso Ghidini, Head of the ESA Structures, Mechanisms & Materials Division, explains how

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Space is the initial frontier for additive manufacturing. It is where AM makes the most sense and where it has made the most sense from the very start. As Head of the Structures, Mechanisms and Materials Division at the European Space Agency, Dr. Tommaso Ghidini is in charge of identifying and maturing additive manufacturing at ESA for use in space exploration.

His division provides engineering support to all missions that are currently flying, from telecommunication satellites to scientific missions in deep space, to exploration missions on other planets, to human space flight, to rockets bringing payloads and astronauts into space. Before ESA, Dr. Ghidini worked for Airbus on all major civil and military programs of the European aeronautical industry, including the A380, A350 and A400M aircraft.

This experience was instrumental in running a very large number of additive manufacturing programs and tests over the past decade. As Dr. Ghidini explains in this exclusive and quite extensive interview, the moment ESA scientists and engineers understood what they could do with AM, a universe of possibilities opened up. Additive manufacturing at ESA is one of the enabling technologies that will make human space travel first more accessible and then more affordable. From Earth up to orbit, from orbit into deep space, and then onto the surface of other planets.

The Structures, Mechanisms and Materials Division is the largest division within ESA, with more than a hundred people working within it. Additive manufacturing at ESA receives a significant portion of the funding with all 22 member states that support ESA clearly understanding its importance. The division’s work is expansive and starts in the mission design phase. As the required physical hardware for a particular mission is defined, the division provides support, engineering services and sophisticated numerical and experimental analysis on a large number of hardware interactions and on all possible systems and subsystems.

“Once the design is ‘blessed’, we start on manufacturing it,” Dr. Ghidini tells 3dpbm. This means supporting manufacturers in qualifying all the materials, processes, systems, subsystems and electronic equipment of any structure. “Should something go wrong – because sometimes things do go wrong – we act as a completely independent and impartial authority to perform a tailored failure investigation, kind of like the ‘CSI of space’,” he explains.

additive manufacturing at ESA
ESA, ArianeGroup and DLR German Aerospace Center have built and hot-fire tested a fully additively manufactured thrust chamber. © ArianeGroup GmbH

Once the spacecraft has been built and all possible failures have been resolved, comes the moment of truth: full-scale testing. “In the past, our responsibilities ended with the launch phases and operations. We have now added ‘design for demise’ capabilities, which means we need to ensure not only that a spacecraft can carry out the mission – launching, reaching space or a planet and operating for whatever number of years it is required – but also guaranteeing that the spacecraft will disintegrate on the descent back to Earth.”

In addition to day-to-day activities, Dr. Ghidini’s division works to identify the technologies that can enable future missions. “We screen the market to identify the technologies and then we mature them for space applications.” That’s how AM came into the picture. If you like additive and you are fascinated by space, strap in, and get comfortable: it’s going to be a ride out of this world.

From case studies to standardization

How AM began its journey at ESA is a fascinating story, one that many AM adopters can relate to. “It dates back to 2006 and it started with a failure,” Dr. Ghidini tells us. “We had a major anomaly in the International Space Station (ISS). A water pump’s on/off valve in the Columbus module failed. That valve is extremely important because it regulates temperature. The ISS goes from +180°C when it’s exposed to the Sun, to -180°C when it is in the shadow of the Earth: a 360°C thermal gradient. We need to keep the temperature inside the station at 22°C to be comfortable for the astronauts on board. So, we had the Space Shuttle bring the valve back to Earth and to our laboratory for investigation. We understood the problem and fixed it. That’s it. Nothing to do with additive. What it did have to do with additive is that that particular valve was, from a manufacturing point of view, an ideal case study to try out this new technology.”

additive manufacturing
This organically-styled bracket, designed for the interior of an Ariane launcher, was 3D printed in space-worthy titanium alloy for an R&D project. © ESA–A. Abel

At the time, plastic Additive manufacturing at ESA was being used for prototypes but metal AM was still in its early days. ESA teamed up with Airbus and decided to use this as a case study. “We were shocked by the results. Going from subtractive to additive, we reduced material waste from 75% to 5%. Using so much less material, it made economic sense to move from stainless steel to titanium, which is more expensive but also has a superior weight-to-strength ratio.” The part’s weight was reduced by 50% and manufacturing time by several hours. Instead of welding two pieces together, which would require additional inspections, it was built in one go. “So, in a way, we won. But,” Dr. Ghidini concedes, ”we did not.”

This is the story of the second failure: a common mistake when approaching 3D printing. “We just replicated an old design,” Dr. Ghidini says. “We reproduced the valve as it was. To really benefit from AM, especially in space applications, you need to design for AM.”

Dr. Ghidini continues: “As we learned our lesson, we realized that, for the very first time, we had access to a manufacturing technology that enabled us to move from design for manufacturing to design for performance: growing parts like Mother Nature does. We realized we could distribute the material to where the loads are. And we understood that we could dramatically reduce mass, which is a key priority for any part that needs to be lifted into orbit.”

Every kilogram of mass launched into space can cost between tens of thousands up to a hundred thousand dollars, depending on the distance from Earth. In addition, a launcher has limited space available. So, the smaller the parts are, the better. However, making small parts also means more intricate geometries and a harder time procuring materials.

“The material supply chain is very challenging for us because we require extremely high performances and very small quantities,” Dr. Ghidini explains. “We are flying to the Sun and to the outer planets. We are landing on other planets. We have missions that need to operate in incredibly aggressive environments for many years. And we have a very limited production scale. Furthermore, there are few manufacturing processes that can achieve the performances we want, combined with very high reliability. Once a part is in space, it’s gone. And it may have to function continuously for decades without any maintenance or repair.”

Twin robotic arms work together as part of a project to construct what will be the largest, most complex object ever 3D printed in titanium: a test version of the 3m diameter ‘optic bench’ at the heart of ESA’s Athena X-ray observatory. © The Fraunhofer Institute for Material and Beam Technology IWS

Additive provided a possible solution to all of these challenges. First, because it works well on a small series of complex parts. It also works with a large variety of materials: from metals and polymers, to composites and ceramics, to food, cells (with bioprinting), concretes and geopolymers. You can now use AM on structures ranging in size from micrometers to meters. AM has enabled weight savings up to 90% and lead time reductions of several weeks, with a compressed manufacturing chain on very complex assemblies. By removing bolts and welds, it is now possible to produce structures that were not possible using traditional manufacturing, even embedding new capabilities, such as thermal functions, into a structure.

“Consider, for example, that a thruster today is made of almost 200 parts that need to be assembled,” Dr. Ghidini says. “Now you can have a thruster done in one piece.” But not everything that shines is gold. “As we saw the tremendous benefits, we also started to identify the possible issues,” he adds. “One is that wanting to use additive for everything is counter-productive. So, a big part of our job is to decide where it makes sense to use it.”

Roadmap to space

It took some time to ensure that AM was reliable for space. Having a rocket blow up or a satellite lost because of an additive manufacturing failure would have killed the technology in the early days. Today additive parts are flying, as ESA has successfully moved from demonstrators to flight missions. But the path was not so clear cut. “In the beginning, we saw a frightening mushrooming effect: everyone proposed themselves as AM experts. We realized we needed to have a centralized strategy in Europe, so we created the European Roadmap for Additive Manufacturing for Space Applications. All European partners contributed, and ESA chaired it.”

This roadmap details timelines and requirements needed for safe use of additive manufacturing [download PDF]. It also addresses the major issues to be resolved, such as dimensional and design challenges. “We noted that we had no design guidelines and no end-to-end tools to go from CAD to CAE to topology optimization and then on to manufacturing, taking into consideration complexity as well as residual stresses and build strategies.”  Another challenge was material-related: powder quality control, supply chain and reproducible quality of the powder. “We needed to guarantee a harmonized standard quality from our manufacturing partners,” Dr. Ghidini says. “Then we moved to the manufacturing challenges: process monitoring, processing strategy, post-processing such as surface treatment and surface engineering.”

additive manufacturing at ESA
A titanium 3D printed prototype of a deployment mechanism for satellite solar panels, by Thales Alenia Space. © ESA – A. Le Flock

Making additive manufacturing at ESA work

Another key issue is the qualification and verification strategy, including mechanical characterization, numerical predictions, fatigue analysis and non-destructive investigations (NDI). “Once we defined our strategy to qualify parts, we moved on to standardization,” Dr. Ghidini explains. “We leveraged ECSS, the European Consortium for Space Standardization. This AM standard for space is something that my division has led and we will publish this year.”

Any industry can adopt these standards. Requirements can be downgraded for less extreme conditions, but the document provides a clear guide on how to use and test AM parts. “It can be useful to have a standard procedure,” he adds. “We provide an ideal approach that can be tailored to specific needs and will help further the AM market uptake.”

In order to implement the roadmap through a centralized, consolidated and strategic approach, ESA created two ESA Additive Manufacturing Benchmarking Centers: one is at the MTC in Coventry, UK. The other one is in Dresden, Germany, at the Fraunhofer Institute. “We address all the fundamental challenges that need to be solved for a specific use,” Dr. Ghidini states. “If you are a company in the space industry and want to implement AM, you can find a center that has all the machines, all the technologies, all the materials to help you mature your process or application for space.”

Dr. Ghidini’s division also created a map of the AM powder producers in Europe. “We checked the quality they were able to achieve in terms of reproducibility, size, shape and composition of the powder. Then, on the same machine, with the same parameters, we produced the same samples to see how the different powders behave for each different material. We came up with this set of procurement specifications for space-grade additive manufacturing powder.” Another tool made available is a fractography atlas of additive manufacturing parts based on known modes of rupture, such as static overload, fatigue, corrosion and stress corrosion cracking. “For this, we systematically took pictures of the fracture surface so as to guide engineers as we open a completely new chapter of metallurgy.”

Taking additive manufacturing at ESA to new worlds

ESA was systematic in defining the possible applications for AM in space, dividing them into three domains. The first is additive manufacturing on Earth. That is, the production of optimized parts for spacecraft and rockets here on Earth. The second is additive manufacturing in orbit – on the ISS, for example. Finally, is additive manufacturing on other worlds (such as the Moon or Mars). Each has very different requirements but sometimes there are opportunities for cross-fertilization.

Taking advantage of additive manufacturing, the Solar Orbiter Sun Sensor Bracket was re-designed using a lattice geometry. © ESA – A. Le Flock

The first applications to consider are structural applications. This is where Dr. Ghidini’s division works to reduce the buy-to-fly ratio dramatically while increasing mechanical performances. “We started with secondary structures, which do not cause catastrophic loss if they fail, such as brackets,” he tells 3dpbm. “Now we are getting more confident and are addressing primary structures as well.”

In order to further develop lattice structures for weight optimization, the first step ESA took was to ask Airbus to review an entire rocket series, Ariane, and identify where to apply AM. The results pointed to 20 to 25 brackets in each launcher, for a total of over 30% in cost savings. Then the agency looked at space propulsion. This is where additive manufacturing at ESA can bring the most benefits, by dramatically reducing part count (from almost 200 to just one in case of thrusters) and by producing very intricate structures, such as injector heads with channels that no traditional manufacturing process can produce, or exhaust cones with embedded radiators for optimal heat dissipation.

In 2015, ESA and Airbus produced the first 3D printed platinum combustion chamber ever. Platinum is an ideal material for propulsion, however, it is impractical to use in traditional manufacturing, because of material waste (and relative cost), and because it is very difficult to forge and treat. Another key space application for AM is radio-frequency (RF) equipment. Advantages include a mass reduction (up to 50%) and eliminating the need for subassemblies. “The key aspect to consider is geometry,” Dr. Ghidini adds. “Antennas used to transmit data should not have sharp edges. With AM we can build the antenna in one go and with the ideal geometry for optimal RF performance.”

Moving to primary structures, ESA is collaborating with the Fraunhofer Institute to investigate the possibility of using AM parts for the mirror structure of the Athena X-ray observatory, a super telescope for space investigation due to launch in 2031. He says: “We tested a hybrid rapid plasma deposition (RPD) technology, a type of wire arc additive manufacturing (WAAM) process, and combined it with a subtractive system to produce meter-long parts.”

AM parts are now baselined for a number of ESA missions. The first satellites that integrate additive parts include Sentinel-4, the Quantum telecommunications satellite, and Electra, a geostationary satellite using only electric propulsion. There soon will be parts flying on the JUICE (JUpiter ICy moons Explorer) mission, launching to the Jovian system in 2022 (and arriving in 2029). The Vega -E, Ariane6 and Ariane5 rockets also integrate AM parts. The very first part, installed on an Ariane5 in 2016, was a cardan cross: this is a structural part in the exhaust lines of the Vulcain 2 cryogenic engine of Ariane5’s first stage. The VEGA E development has successfully fire tested an AM thrust chamber that is fed by liquid oxygen–methane propellants.

ESA successfully tested 3D printing with simulated Lunar and Martian regolith. This 1.5 tonne 3D printed structure is proof of concept for the building block of a future Moon base. © ESA–G. Porter

3D printing to stay in space

Additive manufacturing for space is quickly becoming a reality and the most logical next step is using it in orbit. Why? “Look at Apollo 13,” Dr. Ghidini replies. “If they had a 3D printer on board, they could have printed an adapter for the CO2 filter and everything would have been much easier. They managed, of course, but the issue of replacement parts for long-term missions remains.” For the past few years, two polymeric extrusion 3D printers have been in operation on the ISS. ESA is building a metal 3D printer for space as well. “Polymers make sense, since you have no loads in zero-G, but we also want to have metal printing capabilities,” Dr. Ghidini points out. “Metal spacecraft parts do fail, and we need to have repair opportunities.” These capabilities will be particularly important for missions such as the Deep Space Gateway (now known as the Lunar Orbital Platform-Gateway or LOP-G), which is the space station orbiting the Moon, that will be ready in 2024 – so practically tomorrow – and then the crewed mission to Mars.

A selection of 3D printed ceramic parts made from a simulated lunar regolith material. © ESA–G. Porter

Deep space missions would be unthinkable without 3D printing capabilities. “It’s a completely enabling technology—especially for metals—because it’s not possible to bring all spare parts along and because astronauts may need tools to address specific and unpredictable situations where the damage is such that standard tools don’t work,” he adds. “On the ISS, metal 3D printing could also imply the ability to build satellites directly in orbit instead of launching them. We could produce and deploy cubesats without the cost of launching them from Earth. And even expand structures that are already in orbit.”

While the German Aerospace Center is currently researching a metal PBF 3D printer for space, the metal powder does bring a whole set of challenges and considerations. That’s why Dr. Ghidini’s team is also working on a metal wire-based 3D printer that will launch next year. The idea is to build samples on Earth, then send the printer to space and print the same parts with the same parameters. By comparing the parts, it will be possible to understand the quality that can be achieved in orbit. “This is really something that would change our way of doing space in the long run,” he concludes.

Out of Earth Manufacturing

Out of Earth Manufacturing is a program that encompasses everything that can be produced off our planet: on the Moon, on satellites, or on Mars. This is the program that includes the bases that will be built out of Martian and Lunar regolith, bringing us to the third domain for space AM applications: on-planet manufacturing. Dr. Ghidini’s team conducted tests on both Martian and Lunar regolith simulants. For the Moonbase, they built a 1.5-ton demonstrator, and are considering two possible approaches: using the Sun to sinter the regolith powder or phosphoric acid to bind it. Phosphoric acid is available on Mars but not on the Moon. And that’s not nearly all.

Lunar regolith has been investigated for 3D printing as a ceramic but Dr. Ghidini’s lab also found that aluminum, titanium, steel and silicon can be extracted from it, releasing oxygen. “Which, of course, is not a byproduct, as much as it is a fundamental product in space,” Dr. Ghidini says. “Imagine having an unlimited supply of titanium, a very noble metal that you can build structures with; aluminum, also very noble; iron; and silicon for electronic components production. It means having manufacturing capabilities and resources available on location while producing oxygen for the astronauts to breathe.”

Dr. Ghidini’s team is also researching extraction, intended as a form of circular production. “A planetary lander exhausts its functions after landing,” he explains. “It becomes a piece of junk on the planet’s surface. We can extract all metals and all polymers from it to recycle and reprint them into new structures to use in a new phase of the mission. The properties of the materials will decay,” he points out. “But that doesn’t matter as long as we take this into account when we engineer the new structures.”

The last family of materials to consider for “Out of Earth Manufacturing”, and perhaps the most important is biomaterials. Using stem cells, a team in Dr. Ghidini’s division bioprinted skin, bone tissue and vasculature at minus one-G conditions (upside down), to demonstrate that the process could also work in zero-G. “The binder we used to hold the cells together is alginate, which comes from algae,” he says, pointing out that it can be produced from plants grown on the way to Mars or on the Red Planet directly. The astronauts’ stem cells will also be used to manufacture tissues and expose them to the same high levels of radiation they would receive on the trip to Mars, for even longer periods of time, to characterize their response without exposing them to any risks. This information will be used to develop drugs to cure cellular damage, through a personalized medicine approach, which is a strong trend on Earth as well.

Bioprinting human tissue could help keep astronauts healthy all the way to Mars. An ESA project has produced its first bioprinted skin and bone samples. © ESA – SJM Photography

Printing bones and skin will also be necessary to cure the astronauts if they hurt themselves during extravehicular activity (EVA) on the Martian surface, or to treat burns caused by an accidental fire on board. Because of astrodynamics, the mission to Mars cannot be aborted: once it takes off, the astronauts will have to go for the full two-year tour, which means that if they get hurt, they will need to be able to fix themselves.

Mass production: the final frontier

For the more immediate future, ESA is working on evolving current AM processes and implementing future AM applications. “We will continue to work on fully integrated design and manufacturing tools, to go from CAD to topology optimization and through the AM process, considering all the limitations in terms of manufacturability, support structures, residual stresses and building strategy. We want to work on design guidelines and handbooks to help designers. On the material side, we will continue the work on feedstock, powder and supply chain control. We want to introduce metal powder recycling in space AM, something we will need to address to further improve cost-efficiency,” Dr. Ghidini explains.

New material development will be more AM-specific. For example, making aluminum cheaper, stronger, as well as stress-corrosion-cracking resistant. Or developing aluminum with up to 40-50% silicon content for mirrors and other high-stability structures. AM-specific titanium alloys will be developed to become stronger during the 3D printing process. Copper alloys are being studied for cryogenics as well as chemical propulsion applications, using green lasers to process them. An entirely new area for AM is metallic glass composites. “These are very promising materials for space, for their stability and stiffness,” Dr. Ghidini says. “We want to make them available for additive manufacturing and use them in very long-lasting mechanisms, aiming at ‘infinite life’.”

As the line between science and fiction thins, Dr. Ghidini’s team is now looking to develop compliance mechanisms and actuators through the use of 4D printing. “That’s a big step,” he concedes. “We can 3D print shape memory alloys that are activated by temperature. This would allow us to launch a folded structure that could easily be contained in a small space so that it would unfold once it reaches the required temperature. By comparison, in order to deploy complex structures in space, today we use expensive and heavy motors or dangerous pyrotechnics. These systems depend on their reliability, and they could fail. On the other hand, memory alloy will always work because they only depend on physics.”

3D printed CubeSat with electrically conductive lines that have been laid down using ‘doped’ PEEK plastic feedstock. © ESA–G. Porter

The final area is mass production. Space became a first adopter of AM because of very limited batch requirements. But that is changing as satellite networks become larger constellations. “Not as large as automotive but closer to aeronautics volumes,” Dr. Ghidini admits. This opens up a whole new range of challenges and opportunities that take ESA closer to earthly AM challenges. “We are going to need more advanced AI to implement machine learning in-process monitoring, as well as more advanced NDI capabilities, all to be combined with more stringent requirements on Cyber-Security in manufacturing,” he adds. Standardization will also become increasingly important.

Post-processing, surface engineering, the use of 3D printing for the repair of both AM and non-AM parts, finishing capabilities for very complex parts: these are all key areas of focus at ESA. “My dream is to have a machine evaluate—during the process – the impact on the fatigue life of a component and decide whether to go for a repair or to accept the part as it is.” This is made possible by the introduction of a probabilistic approach in part evaluation. “Together with Milan Polytechnic University, we developed a software called ProFACE that we will use for structural evaluation of additively manufactured parts,” Dr. Ghidini says. “It starts with probable defects of an AM part and assesses the life of the components based on the probability of a failure. It’s a very new way of doing numerical assessment.”

To boldly go where no AM part has gone before, ESA will look to the industry for faster machines, smart manufacturing and digital twin capabilities, modeling simulations and automated inspections. That’s a story the entire AM industry can relate to as it evolves to help humans achieve one of the most exciting milestones of all: human settlement in space.

*This article first appeared in 3dpbm‘s AM Focus eBook on Aerospace AM. Read the entire issue here.

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