On October 4th, 1957 a polished metal sphere, 58 cm in diameter, with four external radio antennas blasted into space from a Kazhak mountain range. Its name was Sputnik 1, it was the first artificial satellite, and its launch caused widespread panic throughout the U.S. that if the Soviet Union’s communistic ideology could win the space race, surely it could conquer the world?
60 years later a fight between a man that had never boxed professionally and the greatest living pugilist was beamed from Las Vegas across the globe thanks to satellite technology. The fighters are expected to earn more than $400m, for less than 30 minutes in the ring. It is safe to say capitalism won out.
The U.S. owns approximately a third of 1,400+ satellites orbiting the globe. Whether it is broadcasting sports, surveilling insurgents or monitoring weather, each satellite is transmitting and receiving information using radio frequencies (RF). The way satellites decide which frequencies to receive and transmit has largely remained the same for 50 years.
Metal RF filters allow frequencies from selected channels to pass through, rejecting the rest. A modern satellite like the Eutelsat KA-SAT manufactured by Airbus Defence and Space carries nearly 500 RF filters and 600 waveguides. There’s a trend in the space industry for increased capacity for multiple beams within a single satellite using tailored RF filters.
Adding more components means lightweighting has become ever more crucial. Blasting technology into space is not cheap; it takes as much as $20,000 per kilogram to send a vehicle into geostationary orbit. Added complexity and increasing weight saving? Sounds like a job for 3D printing.
The RF filter in situ
Using a 3D Systems ProX DMP 320, 3D Systems Leuven and Airbus Defence and Space have created the flight-worthy 3D printed RF filter that consolidates two parts, resulting in a 50% weight reduction at the same time as improving the RF performance.
The project built upon research funded by the European Space Agency (A0/1-6776/11/NL/GLC: Modelling and Design of Optimised Waveguide Components Utilising 3D Manufacturing Techniques).
Disruptive Design Innovation
RF filters are traditionally designed based on libraries of standardised elements, such as rectangular cavities and waveguide cross-sections with perpendicular bends. Shapes and connections are dictated by typical manufacturing processes such as milling and spark eroding. As a result, cavities for RF filters typically need to be machined from two halves bolted together. This increases weight, adds an assembly step to production time, and requires further quality assessment.
Designing the parts for 3D printing enabled Airbus Defence and Space to explore complex geometries at no additional manufacturing cost.
CST MWS, a standard 3D electromagnetic simulation software tool, was used to design the 3D printed RF filters, with little time spent on optimisation. The increased manufacturing flexibility enabled by 3D printing led to a design using a depressed super-ellipsoidal cavity. The unique shaping helped to channel RF currents and deliver the required tradeoffs between Q factor—a measure of a waveguide’s efficiency based on energy lost—and rejection of out-of-band signals.
“The disruptive innovation lies in the fact that pure functionality, not manufacturability, now determines how the hardware will be designed,” says Koen Huybrechts, project engineer for 3D Systems in Leuven. “This project is a classic example of ‘form follows function’.”
The new design for 3D printing with a depressed super-ellipsoidal cavity.
Eliminating Surface Concerns
Initially, the different surface topology in 3D printed metal parts was thought to be an issue, but extensive testing by Airbus Defence and Space eliminated those concerns.
“The microscopic topology is different in the 3D print-ed part than in a machined part,” says Paul Booth, the RF Engineer for Airbus Defence and Space in Stevenage, UK. “Machined surfaces have sharp peaks and troughs, while the 3D printed surface is spheroids melted together so there is less sharpness.”
“The spherical shape of the powder particles used in 3D metal printing lead to a certain waviness rather than steep transitions,” says Huybrechts, “but the ability to shape a part for more effective signal filtering more than overcomes any concerns with surface topology.”
“We were very pleased with the work that 3D Systems did for us and many inside Airbus have commented on how good the surface finish is,” says Booth. “We did some x-ray CT scans and have been impressed with the density of the part and the general surface quality.”
Three aluminium samples printed on the ProX DMP 320 using different processing paths were tested by Airbus Defence and Space at its Stevenage facilities. Tests mimicked conditions the parts would face during launch and orbit, including vibration, shock and thermal situations such as temperature extremes and vacuum conditions. All three samples met or exceeded requirements, with the best performance coming from a filter that was silver-plated via an electrolytic process.
Beyond 3D printing, 3D Systems delivered added value that is critical to this kind of project, including certified powder handling, process control for superior material density, proven post-processing, and reliable quality control.
Booth recognises that this added expertise played a key role in the project’s success: “We realise that this is not just down to using a good machine to manufacture the part but also the result of a good understanding by 3D Systems of the manufacturing process.”
