Large 3D metal printed parts save weight for satellites

| Manufacturing

Flight path improvements with better satellite comms
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Andy Pye explains how the feasibility of highly sophisticated and very large AM parts for applications in space has been achieved in the Koreasat-5A and 7 communications satellite project.

3D metal printing is pointing the way to a change in manufacturing strategies. The aerospace industry is driving forward innovation and acting as the spearhead for digital manufacturing. Thales Alenia Space, working in collaboration with the 3D printing service company Poly-Shape, has produced additively manufactured (AM) parts for the new Koreasat-5A and Koreasat-7 South Korean communications satellites.

Koreasat-7 is set to go into orbit in 2017 at position 116º East in order to provide coverage for South Korea, the Philippines, Indonesia and India. Koreasat-5A will cater for Korea, Japan, Indochina and the Middle East from the position 113° East. Koreasat-5A should be launched before 2017 second quarter.

The Koreasat-5A and Koreasat-7 antenna supports will be the largest volume parts so far produced by powder-bed-based laser melting of metals from Europe to be in orbit. With dimensions of 447 x 204.5 x 391mm3 – and weighing just 1.13kg these huge additively manufactured 3D components are being used as basic antenna supports for the communication with ground base. An identical part is installed in both satellites.

Manufactured by the French company Poly-Shape, the dimensions presented a real challenge for Thales Alenia Space, a joint venture between Thales (67%) and Finmeccanica (33%), and a key European player in space telecommunications, navigation, Earth observation, exploration and orbital infrastructures.

Due to its weight and thermal conductivity, aluminium is the material most commonly used for satellites. Florence Montredon, Head of AM at Thales Alenia Space, says: “As a rule of thumb, the actual costs of putting 1kg into orbit are around EUR 20,000. The starting weight of the two new satellites is around 3,500kg.”

AM’s potential for lightweight design was therefore a key reason to move away from the traditional methods. Applications in space demand high strength, rigidity and resistance to corrosion from the materials that are used and Thales Alenia Space chose an AISi7Mg alloy. The component validation process also revealed a low porosity rate on the finished component of <1%.

Mechanical tests also produced pleasing results. For example, fatigue tests have yielded values that significantly exceeded the specifications. Minor deviations in the geometry were corrected with simple reworking, as was a small crack which was revealed by the CT. Fairly small pores inside the geometry were accepted following localised mechanical analysis. Ultimately, the parts successfully passed the dynamic tests carried out at Thales.

“The effects were huge – a 22% weight saving for the bionic AM structure compared to a conventional structure,” adds Montredon. “A reduction in costs of around 30% is attributable to various factors: the redesign as an additive, bionic part replaced the number of parts that were previously produced from nine to one, done through one-shot manufacturing, without the previous outlay on assembly. Secondly, there was no need for mould construction, as casting would have needed to make the same part. Thirdly, the so-called time-to-fly is much reduced.”

Poly-Shape has 28 3D metal printing machines which have different sizes of build envelope. The largest build envelope dimension for 3D printing with aluminium at Poly-Shape is currently an X line 1000R from Concept Laser. It offers a build envelope of 630 x 400 x 500mm3 and has a closed system for reliable process and powder management in accordance with the ATEX directives. The X line 1000R also has a rotating mechanism which allows two build modules to be used reciprocally, thus guaranteeing constant production with no downtimes. This unique machine design not only results in greater availability, but also simple and above all secure handling when arming and disarming the machine.

The follow-up model, the X line 2000R, has an even bigger build envelope (800 x 400 x 500mm3), which is currently claimed to be unique in the world when it comes to powder-bed-based laser melting. The usable build volume is again increased by around 27%, in comparison to an X line 1000R, from 126 to 160 litres.

The LaserCUSING process technology from Concept Laser features so-called stochastic navigation of the slice segments (also referred to as “islands”) which are processed successively. This patented process ensures a significant reduction in stresses when manufacturing very large parts, helping to warping. In this process, fine metal powder is melted locally by a high-energy fibre laser. The material solidifies after cooling. The contour of the component is created by redirecting the laser beam using a mirror redirection unit (scanner). The component is built up layer by layer (with a layer thickness of 15 – 500μm) by lowering the bottom of the build chamber, applying more powder and then melted again.

The transition over to AM also meant rethinking the design to make full use of the potential offered by laser melting. CAE-CAD was used to trim the 3D components to a performance-focused geometry and lightweight design. The design was optimised through several transitions. In addition, there was fine-tuning in the area surrounding the satellite in order to guarantee a maximum precision fit.

Thales Alenia Space also incorporated layer-based manufacturing methods. “In the future, we would also like to incorporate thermal control technology or radio functions directly on or within the 3D structures, so functional integration is the next task,” says Montredon.

European aircraft to use satellite communication

The European aviation sector is planning to introduce satellite communication between aircraft and the ground, resulting in fewer zig-zag flight paths, reductions in CO2 emissions, and saved time and money. Norwegian researchers at SINTEF are looking into data security risks.

Today, most communication between an aircraft and air traffic controllers takes place verbally. But aircraft are also able to utilise a data link system for sending and receiving instructions and information via text messaging. However, this service has limited range and capacity because it utilises heavily-used radio frequency bands – so of the thousands of flights operating across Europe, only very few use data link communication.

The European Space Agency (ESA) has joined forces with the SESAR Joint Undertaking, an aviation framework programme, to ensure that the aviation sector can reap the full benefit of available satellite services. Last year, a demonstration project was completed during which a secure satellite data link (CPDLC) was established between an aircraft and an air traffic controller, providing both with continuous information updates.

Risk analysis

The drawback of the data link is that, as with all digital information, it is vulnerable to attack by hackers, who may, for example, want to send false information to the pilot. For this reason, SINTEF researchers have set in motion a highly detailed risk analysis of what might go wrong.

“We’re currently working closely with many organisations such as Inmarsat, Airbus, Boeing and Honeywell in order to acquire information”, says Karin Bernsmed at SINTEF. “All companies operate with their own security requirements, and our job is to look into the various threats that are giving them cause for concern. What kind of information can they send? Who has access to their systems? How can the code keys they use be best protected?”

Testing

SINTEF researchers have previously developed an authentication system that enables pilots and air traffic controllers to confirm with whom they are communicating. Moreover, they have also been responsible for implementing the proposed system and integrating it with a smart card supplied by the UK firm CGI.

The system is currently being tested and will soon be certified for operational use. “If you try to trick the system, you will be denied access to the service”, says Bernsmed.

The new study includes an assessment of how the authentication system can be expanded. For example, will the airlines get the opportunity to use it? SINTEF also recognises a need for more stringent security requirements. For example, confidentiality must be guaranteed when sensitive information is transmitted using the data link. The potential users of satellite communication are many, and achieving watertight security is a key element of the study.

Multiple applications

Because airline flight paths are closely linked to aviation corridors, pilots are in contact with several air traffic controllers, and in reality fly along a series of point-to-point sections. This means that flight paths may appear as “zig-zags”, and are not aerodynamically optimal.  Satellite communication is one of many initiatives that will make it possible to transmit more precise instructions from air traffic control centres and thus achieve smoother flight paths. This will reduce fuel use and environmentally-harmful emissions.

Bernsmed’s colleague at SINTEF, Hans Erik Swendgaard, says that flight safety will be greatly improved once it is possible to receive instructions and exchange information with air traffic controllers via a satellite data link across large expanses of ocean.

One area which gets relatively little attention concerns the internal text messages exchanged between an aircraft and the airline’s ground stations (ACARS). This system is used to exchange a great deal of information that enables pilots to keep to their departure and arrival schedules as cost-effectively as possible. A satellite data link enables them to exchange text messages over wide expanses of ocean and other areas where radio channels are unavailable.

When will the system be ready?

This year, an Airbus aircraft was the first to test the data link and smart card. The test was carried out as part of this project because it required the installation of dedicated on-board equipment.

The question now is how to get the ball rolling. How much pressure can the aviation authorities apply to the airlines to persuade them to utilise the system?

Researchers believe that the solution may involve a combination of aviation directives and pricing. However, when the satellite data link service is made available, there is reason to believe that many airlines will come to recognise the sound operative and commercial benefits it offers.

Others believe that routes to the Far East and across the Atlantic Ocean will be the first to take advantage of this new communications tool. It is they that will reap the benefit of the new technology – flying across wide expanses of ocean and land areas where the lack of ground stations generates problems today.

About Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.

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