The Active Phasing Experiment (APE), a European Union Framework Program 6 project, was chosen as the subject of the SE2 Challenge Team. Many technical products in the telescope domain show an increasing integration of mechanics with electronics, information processing, and also optics, and can therefore be rightly considered as optomechatronic systems. Our system case study is the Active Phasing Experiment technology demonstrator for the future European Extremely Large Telescope, which is a high-tech, interdisciplinary optomechatronical system in operation at the Paranal observatory.
The next generation of telescopes needs to collect significantly more light than current telescopes, therefore requiring larger reflecting surfaces that consist of many individual mirror segments. Due to different disturbances (such as vibrations, wind, and gravity), the segments must be actively controlled to provide a continuous mirror surface with a phasing error of only a few nanometers over the main mirror’s diameter of 42 m. The main challenge is to correctly detect the positioning errors of the segments via specific phasing sensors in order to create a continuous mirror surface.
APE was developed to evaluate those sensors, and was installed on one of the 8 m telescopes that constitutes part of the Very Large Telescope in Chile (VLT) for sky tests. For the installation at the telescope it had to comply with various mechanical, electrical, optical, and software interfaces. APE consists of about two hundred sensors and actuators such as wheels, translation stages, lenses, detectors, mirrors, light sources, an interferometer, and twelve computing nodes for control. Since APE had to be deployed in the test lab and in an already existing telescope, for each context it was necessary to model variants of function, interfaces, and structure. All of these characteristics made APE well suited to evaluate the potential of SysML in tackling similar issues.
The introductory presentation provides information on context, goals, and results of the Challenge team.