‘Finite element analysis of the Mercator telescope’s primary mirror’ is the title of the prize-winning work. There may not be a spontaneous association between telescopes and Electromechanics engineers, but the tale is different in the case of Bart and Wim. Both have been fascinated with astronomy, space exploration and science in general since childhood. When the Physics and Astronomy department from the K.U. Leuven Science & Technology Group appealed to upcoming master students through GROUP T’s website to realize a project that was clearly linked to astronomy, Bart and Wim immediately jumped at the opportunity. Prof. Guido Ceulemans, manager of the Energy & Technology unit, was approached as supervisor. Paul Bielen from the Physics and Astronomy department was prepared to act as the co-supervisor.
The object of study for both GROUP T students was the Mercator telescope. “The telescope is not set up in Leuven but rather on the island of La Palma where the observation conditions are more favorable,” Wim explains. “And such a telescope is not a small matter. The mirror alone has a 1.2-meter diameter and weighs no less than 400 kg. Not only do K.U. Leuven researchers use it, but also scientists from Switzerland and Spain regularly carry out measurements with it. There is also an identical copy of it in Chili: the Euler telescope.”
“The size and the weight of the mirror offer many benefits for the observation of the cosmos and everything in it but there is also a drawback,” Bart continues. “Because of gravity, the mirror bends under its own weight. Of course, this effect is minuscule – barely 1/50,000 of the cross-section of a human hair or the length your fingernail grows while you read this sentence – but still enough to affect the image quality and render the measurements less accurate. As a result of the deflection, the images get hazy and stretched and a star that is in position X according to the measurement may just as well be in position Y. Our assignment was to find a solution to this problem.”
“We opted for a finite element analysis to deal with this problem,” Bart relates. “This allows you to calculate the deflection very accurately. Essentially, we are using a Unigraphics NX program that we learned to use at GROUP T and allows us to solve mathematical formulas quickly and efficiently. By using the finite element analysis, it is also possible to verify the image degradation. By means of these measurements, the support of the mirror can subsequently be corrected.”
“We do not correct the images themselves,” Wim clarifies. “The focal point is the positioning of the mirror support points. You have to realize that such a large mirror is supported by no less than 15 manipulable pneumatic supports and three fixed ones. In addition, there are six supports on the sides. By changing the position of these supports as well as the pressure they exert it is possible to negate the deflection and obtain quality images and measurements again.”
In addition, the computer software provided by GROUP T was coupled to a pre- and postprocessor developed by both winners. “With the preprocessor we establish the finite-element model of the mirror,” says Bart. “Next, we use the NX solver to calculate the model, that is, the mathematical formulas that are associated with the various elements. And finally, we apply the postprocessor to the solutions we got from this which allows us, among other things, to visualize the results and, based on that, to qualify and quantify the image degradation and then to optimize the position of the support points.”
“Our proposed improvement of the mirror support can be used for all large telescopes in the world,” Bart confirms. “It comes down to entering the correct parameters, the analysis itself is identical.”
Experiments showed that the image degradation predicted by Bart and Wim’s software are correct. Consequently, they are very happy that their method will be applied to both the Mercator and the Euler telescopes.
Traditionally, the Barco/VIK awards target Electronics or ICT engineers. The fact that Electromechanics students have been pronounced the winners is highly unusual, although Bart suspects he may know why. Apparently, Barco is examining whether pneumatically steered mirrors can also be implemented in the large projectors the company produces. Perhaps the technology developed by Bart and Wim could help this along.
Consultant and student
In the meantime, Wim has been working as a consultant for the consultancy company Ascente since 1 September and, at the moment, he is working for a customer in Zaventem. The company develops and installs all manner of electronic payment systems for companies and organizations. “It will definitely be a job with much variety and many customer contacts,” he says.
Bart, in turn, has remained in Leuven. He is continuing his studies to become a civil engineer in Mechanical Engineering. His choice to major in aero- and astronautics was an obvious one. His dream? “To contribute to high-tech research, preferably with top organizations like CERN and ESA.” Bart’s future is literally and figuratively written in the stars.