For many people, talking of the infinite vastness of the universe conjures up stories of science fiction, usually told by a Hollywood film studio. However, in real life, more than in any other area, it is arguably in space travel that a strong will and clear vision are vital for creating the necessary technology and readying it for deployment in the cosmos. This was the challenge faced by Swiss technology group RUAG in the construction of its Sentinel satellite, designed for observing our planet from on high. Even here, beyond the Earth’s atmosphere, Additive Manufacturing is playing a key role.
Need for optimal design
According to reports by the German Centre for Aerospace (DLR) from 2016, the mission costs of space exploration per kilogram of transported payload are upwards of € 20,000. Every single gram saved reduces total launch costs, as the system requires less fuel for the ascent. As a result, aerospace engineers need to shave every possible gram from every component as excess weight accumulates rapidly. In this case, the Swiss RUAG group was in need of an optimally designed antenna bracket.
Yet weight optimisation alone is not enough. During a rocket launch, the payload gets well and truly shaken up and the level of vibration is considerable. Also, the enormous speeds of several thousand kilometres per hour, not to mention the high G-forces, mean that the flight will not be as smooth as you would expect on a passenger jet. Stability and rigidity form a second essential on any specification sheet. Unfortunately, this requirement is usually diametrically opposed to the need for lightweight design.
Engineers employ complex structures to identify a workable level compromise between form and weight. The RUAG team sought the optimum combination of strength and weight for the structure of its antenna bracket, as conventional manufacturing methods had been exhausted. Thankfully, Additive Manufacturing provided the perfect possibility of
achieving the necessary freedom of design. Component testing represented a particular challenge, not least because of the aforementioned vibration. In outer space, reliability counts, as repairs are generally not possible. This also explains why the authorisation of such components is such a protracted and complex process. Every certification represents an accolade for the engineers who have achieved it.
AM enables design freedom
In such cases, the complete production chain plays an important role, particularly in the aerospace sector. “Obviously, the immense advantages of producing components using Additive Manufacturing was of great interest to us,” explained Franck Mouriaux, General Manager of Structures at RUAG. “For example, design freedom and complex components help us to save weight. The ability to integrate functions is also very helpful. In the end, however, it is a case of identifying these potential advantages, implementing them in an ideal fashion and acquiring the necessary corresponding authorisation. The simplest component serves no purpose if it cannot be used.”
Fundamental suitability and rigidity testing formed the starting point of the antenna bracket’s design. The next step comprised the selection of material, definition of processes and initial basic tests in respect of the material characteristics. The initial test structures then constructed to serve as the starting point for the topological optimisation of the component. RUAG was eventually able to achieve the theoretically perfect form for the antenna bracket, through a combination of intensive work with a CAD and FEM system from Altair and guidance from EOS on design and construction using Additive Manufacturing.
Production of antenna bracket
The approximately 40 cm long antenna bracket was produced by citim GmbH from Barleben in Germany using the EOS M 400. With a construction volume of 400 x 400 x 400 mm, it was possible to produce two antennas, 30 tensile test piecesand various test items in a single construction order. The construction time was approximately 80 hours. The parameter set used was for a layer thickness of 60 μm, optimised for surface quality and productivity.
The aluminium alloy used, EOS Aluminium AlSi10Mg, is characterised by high strength and strong resistance to dynamic stress, making the material perfectly suited for use with high-stress components. Comprehensive tests were carried out to demonstrate the required characteristics in the aerospace sector, these comprise up to 80% of the total scope
of a project. Specially manufactured structures were used for testing. Among other things, engineers examined the brackets in computer tomographs. Various mechanical and physical procedures were also performed. At times, the stresses brought to bear on the component deliberately exceeded the load limits, ultimately leading to the destruction of the test pieces.
The use of Additive Manufacturing in space
The result of these efforts was that the new antenna bracket for the Sentinel satellites exceeded all expectations. The component was awarded certification and with that, the approval for its utilisation in outer space. The achievement is all the more remarkable considering that the use of Additive Manufacturing in space is still in its infancy.
For example, the component’s minimum rigidity requirements were exceeded by more than 30% – a margin that is easily sufficient to ensure that even after a turbulent flight, an ideal antenna position could be attained and radio communication with Earth guaranteed. The required level of stability was achieved, in part because of the highly uniform stress distribution. Moreover, the use of Additive Manufacturing led to a significant reduction in the weight of the final component: down to 940 g from 1.6 kg, representing a saving of over 40%. In this instance, the use of innovative technology succeeded in achieving an unlikely combination: improved component characteristics and lower system costs.
“We are very happy with the results of this project. We entered unchartered territory on the process side and were rewarded with a stable, lightweight component,” says Aerospace Engineer Mouriaux. “Additive Manufacturing has shown that it can fulfill the fundamental procedural demands of space travel. The multiple design advantages and the characteristics of the component itself have certainly proven this. I see great potential for this technology going forward.” So, while Hollywood tells exciting stories, innovative technology continues to live them every day, extending the frontiers of design and construction. ☐Courtesy: EOS