Microwave Components Group (MCG) Etiqueta

Jabir Hussain, Ph.D. Fellow/ Early Stage Researcher (TESLA project H2020-MSCA-ITN) at the Microwave Components Group (MCG), Department of Electrical, Electronic and Communications Engineering, Public University of Navarre (UPNA)

What is Additive Manufacturing?

According to the International Organisation for Standardisation (ISO), additive manufacturing is a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies.
Let us break it down to have a better understanding.

• joining materials – instead of cutting the bulk raw material into the desired shape and size, the raw materials in powdered form or sheets are fused or bonded together.
• 3D model data – the object to be built is designed using computer-aided-design (CAD) software and the data is fed to the manufacturing machine.
• layer-upon-layer – the objects are build using a bottom-up approach.

We can use the analogy of ice-sculpting for the traditional subtracting manufacturing techniques such as the conventional machining techniques like milling or electro-erosion, whereas additive manufacturing can be thought of as using LEGO® blocks to build the objects.

  

In common parlance, additive manufacturing (AM) is most widely known as 3D-printing. Though technically 3D-printing is one of the many ways of AM, the term has become almost synonymous with AM and is used interchangeably. At the same time, AM is just a class of the new Advanced Manufacturing procedures currently being developed and used across industry sectors.

Additive Manufacturing dates back to the early 1980s for rapid prototyping and it has since then increasingly found its way into commercial and consumer markets as well as into the challenging sectors like the healthcare, automobile, and aerospace industries. Starting from the basic stereolithography (SLA) process, AM technology has evolved into wide variety of processes like Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS) and Direct Metal Laser Sintering (DMLS). However, the general workflow of the process remains the same: to build layer by layer.

Why do we need it in space?

Going by very rough estimates, the cost to launch one kilogram to space (for instance onboard the European Ariane 5 or the future Ariane 6) averages about €20,000. Also, any rocket system designed for space is constrained (Tsiolkovsky’s rocket equation) to have at least 85 percent of its total weight to be the fuel propellant and only the remaining 15 percent to be the actual rocket structure and satellite payload system.

Ariane 5 ECA flight VA214, Alphasat (Credit: ESA)

Thus, one of the key challenges in space industry is to reduce the weight of the rocket-payload system, and additive manufacturing provides the right tools of engineering to achieve this goal. By incorporating novel organic and lattice structures into the design philosophy as well as using lightweight and dense materials (which are not quite suitable for machining), a weight reduction of 30 to 60 percent is possible using additive manufacturing. Apart from the advantage of weight reduction, additive manufacturing also has the following benefits:

• Rapid prototyping, meaning a prototype of the object can be tested and verified without restructuring and/or retooling the manufacturing process.
• Devices with complex geometries can be easily fabricated as compared to traditional techniques. This design freedom allows us also to envisage new forms that could not be manufactured with traditional techniques.
• Structures can be built with fewer functional parts, sometimes in one single piece (with any points of weaknesses removed and without needing screws for instance), thereby improving structural integrity, and reducing assembly and logistics cost.
• Freedom in part design allows also on-demand build in required quantity (low-volume), which also increases cost-efficiency.
• Reduced use of raw materials (due to adding and not removing) results in increased environmental benefits (waste management) as well as cost-benefits.

In the future context of global broadband communications using a space segment consisting of constellations of hundreds or even thousands of mini-satellites, AM promises to be a turning point for flexible, cost-effective satellite production. Another potential issue of consequence in the space industry is the requirement of high data rates for the next generation of large geostationary telecommunication satellites along with the increase in capability to support a greater number of users. These requirements, i.e., high data rates and more users, produces the need to design satellite payload components like antennas, filters, etc., with very high-power handling capability. Conventionally designed filters have reached a sort-of theoretical limit to support high-power, and so the need of novel designed filters less prone to high-power effects such as multipactor have arisen. Smooth-profiled rectangular waveguide filters such as those developed by the Microwave Components Group at UPNA are an excellent example of this new generation of power resistant devices and additive manufacturing is the ideal approach for fabrication.

Challenges of AM in space

Additive manufacturing opens up new possibilities in fabricating devices for the next generation telecommunication satellites. However, there are a few technical barriers and bottlenecks that it has to overcome in order for it to become a standard for space industry. A few of these are listed below:
• There is an inherent variability due to factors such as material powder distribution, flow of melt pools or alignment of build platforms. As such there are issues with reproducibility, reliability, and accuracy. This also hinders its application in mass production.
• As objects are build layer-by-layer from bottom-up, some angled-structures requires the need of supports which needs to be removed after printing.
• Postprocessing treatments like polishing and silver-plating to improve surface roughness and RF performance respectively are required.
• The need to develop new standards and verification methodologies for 3D-printed parts.

Current state-of-the-art of AM in space and how UPNA is forging ahead?

Additive manufacturing capability has been successfully demonstrated in building components for both rocket launch systems as well as satellite payload systems.
Under rocket launch systems, spacecraft support structures such as wing systems, nozzles, combustion chambers etc. have been additively manufactured. The advantages reported were fewer part counts, reduced complexity, and reduced weight. Because additive manufacturing builds objects from bottom-up, it allows the use of new materials with improved thermal and mechanical properties like cooper alloys, polymer-ceramic composites, and high temperature plastics (PEEK, PEI).
ESA under its AMTAC project developed the world’s first spacecraft thruster with 3D-printed platinum-rhodium alloy combustion chamber and nozzle. In recent news, the coaxial injector head of a liquid rocket engine was manufactured using laser beam melting (a process of AM) under the EU project SMILE (SMall Innovative Launcher for Europe).

In addition to this, there has been a massive push for what is known as “in-space” additive manufacturing. The International Space Station is equipped with a 3D-printer capable of printing polymer-based tools and hardware components on demand – without the need of waiting for a visiting vehicle to deliver a required component.
When it comes to satellite payload systems, additive manufacturing is still in a nascent stage. Heavy metal components like filters, antennas, diplexers, etc., have very stringent specifications and the low tolerances of AM fabrication coupled with non-standardisation of processes proves a barrier for it to be adopted by the space industry.

As such, low tolerance structures like antenna supports or placeholders for waveguides and cavity filters have been extensively built using AM and deployed in space missions. In 2018, Hispasat in partnership with SSL launched its HISPASAT 30W-6 satellite with the largest and most complex antenna support structure till date having more than 200 additively manufactured metal and polymer components.

In recent years however, building on previous research, ESA in partnership with Airbus DS and 3D Systems has developed a 3D-printed RF waveguide filter and tested and validated for use in commercial telecommunication satellites. ESA has also developed and tested a 3D-printed dual-reflector antenna which was built as a single piece of polymer and then coated with copper.

Under its ARTES 5.1 programme, ESA, in collaboration with leading space companies such as Airbus DS, Thales Alenia Space, RUAG or TESAT, and other players such as various research institutes in the TESLA network, has been massively driving the R&D in regards to manufacturing and optimizing RF components using AM.

In this regard, UPNA has been a forefront in the research and development of new technologies benefitting the rise of additive manufacturing. The Institute of Advanced Materials (InaMat) is working on developing microreactors for photocatalytic applications using 3D printing directly or 3D printing as a manufacturing tool. The Institute of Smart Cities (ISC), by means of the Microwave Components Group, is a beneficiary of the TESLA project under which one of the aims is to build new design techniques for telecommunication payloads of space systems suitable for additive manufacturing in the context of large platforms. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 811232. The project will entail manufacturing RF passive components using additive manufacturing processes in both metals as well as ceramics. This is a pan-European project collaborating with various research institutes in Europe as well as various partner organisations in space and additive manufacturing industries.