Plenary Event
Monday Plenary Session
13 April 2026 • 13:30 - 15:15 CEST | Auditorium Erasme (Niveau/Level 0)
13:30 – 13:40 hrs CEST
Welcome and Opening Remarks
13:40-13:45 hrs CEST
Speaker Introduction
13:45-14:30 hrs
The active alignment of large astronomical telescopes with 3D metrology tools
The 20th and early 21st centuries have seen significant growth in the physical size and complexity of astronomical land-based telescopes. These scale increases, combined with tighter image-quality requirements arising from a combination of scientific demands and improvements in technology, have led to the development of active optics for telescope control, where wavefront sensors combine with actuators to drive the shape and position of optics in closed loop, correcting for deflections caused by gravity orientation and temperature changes. Active optics for large telescopes was conceived and developed in the late 1970s, 1980s, and 1990s, and, arguably, only brought to full maturity in the early 2000s.
At this point in time, we stand poised on the brink of the Extremely Large Telescope (ELT) era, where apertures in the 10 m range from the 1990s generation of optical–infrared telescopes have leaped by factors of two to four in the upcoming generation of telescopes. At this scale, optical flexures and deflections are amplified compared to the current generation of telescopes, and the combination of open-loop modelling for initial optics positions and shapes, and wavefront sensing for closed-loop control and convergence, is seriously challenged. Since the late 2000s, a new approach, based on the direct metrology of optical components and instrument interfaces, has been developed. Direct metrology offers an interesting intermediate alignment stage between open-loop modelling of positions and closed-loop wavefront sensing. This paper discusses the development and application of these approaches to a range of large telescopes, including optical and radio telescopes.
Dr. Andrew Rakich has spent a lifetime working with and using astronomical telescopes. As a teenage amateur telescope maker, Andrew developed the “aperture bug,” producing first a 200 mm diameter mirror and later a 550 mm paraboloid mirror for Newtonian telescopes. This early passion led to advanced degrees in optics and aberration theory, and to a career in which he has served as optics lead for, or otherwise worked at, several of the world’s major observatories, including the Large Binocular Telescope Observatory, the European Southern Observatory, and the Giant Magellan Telescope Observatory.
Andrew has published numerous papers and one book on optical aberration theory, optical fabrication, alignment, and design. He was an early pioneer in the application of 3-D direct-metrology techniques to the active alignment of telescopes, and continues to work actively in this field on a number of projects. He is currently the Director of his own consulting company, Mersenne Optical Consulting, and the Chief Technical Officer of the optical-fabrication company KiwiStar Optics.
14:30 - 15:15 hrs
Future ESA Earth observation missions
This presentation will provide a comprehensive overview of European Space Agency (ESA) ongoing efforts to prepare for the next generation of optical Earth Observation missions. First, we will present the science-driven Earth Explorers and Scout missions addressing key scientific issues, followed by an update on preparations for future Meteorology and Copernicus missions. Second, we will present the pre-development activities of innovative instrumental concepts and associated technologies engaged to prepare the future of Earth Observation optical missions. Finally, we will highlight the activities focused on the preparation of compact optical payloads for small satellites.
Dr Christophe Buisset holds a PhD in Optical Instrumentation and he is the Head of the Optical Instruments Section at the European Space Agency, where he leads a team of engineers developing advanced optical payloads for space missions. With over 20 years of experience, Dr Buisset has overseen the design, performance estimation, and risk management of cutting-edge space and ground-based instruments for Earth observation and astronomy. Before joining ESA, Dr Buisset established and directed a laboratory in Thailand dedicated to the development of optical technologies, building a team of engineers and researchers and developing state-of-the-art facilities. His career spans leadership roles in both industry and research institutes, numerous patents and publications, and a strong record of fostering international collaborations.
Welcome and Opening Remarks
 |
Thierry Lépine
Institut d’Optique & Hubert Curien Lab (France) 2026 Symposium Chair |
 |
Julie Bentley
University of Rochester (United States) SPIE President |
13:40-13:45 hrs CEST
Speaker Introduction
 |
Marta C. de la Fuente
ASE Optics Europe (Spain) 2026 Symposium Chair |
13:45-14:30 hrs
The active alignment of large astronomical telescopes with 3D metrology tools
 |
Andrew Rakich
Mersenne Optical Consulting (New Zealand) Kiwistar Optics (New Zealand) |
The 20th and early 21st centuries have seen significant growth in the physical size and complexity of astronomical land-based telescopes. These scale increases, combined with tighter image-quality requirements arising from a combination of scientific demands and improvements in technology, have led to the development of active optics for telescope control, where wavefront sensors combine with actuators to drive the shape and position of optics in closed loop, correcting for deflections caused by gravity orientation and temperature changes. Active optics for large telescopes was conceived and developed in the late 1970s, 1980s, and 1990s, and, arguably, only brought to full maturity in the early 2000s.
At this point in time, we stand poised on the brink of the Extremely Large Telescope (ELT) era, where apertures in the 10 m range from the 1990s generation of optical–infrared telescopes have leaped by factors of two to four in the upcoming generation of telescopes. At this scale, optical flexures and deflections are amplified compared to the current generation of telescopes, and the combination of open-loop modelling for initial optics positions and shapes, and wavefront sensing for closed-loop control and convergence, is seriously challenged. Since the late 2000s, a new approach, based on the direct metrology of optical components and instrument interfaces, has been developed. Direct metrology offers an interesting intermediate alignment stage between open-loop modelling of positions and closed-loop wavefront sensing. This paper discusses the development and application of these approaches to a range of large telescopes, including optical and radio telescopes.
Dr. Andrew Rakich has spent a lifetime working with and using astronomical telescopes. As a teenage amateur telescope maker, Andrew developed the “aperture bug,” producing first a 200 mm diameter mirror and later a 550 mm paraboloid mirror for Newtonian telescopes. This early passion led to advanced degrees in optics and aberration theory, and to a career in which he has served as optics lead for, or otherwise worked at, several of the world’s major observatories, including the Large Binocular Telescope Observatory, the European Southern Observatory, and the Giant Magellan Telescope Observatory.
Andrew has published numerous papers and one book on optical aberration theory, optical fabrication, alignment, and design. He was an early pioneer in the application of 3-D direct-metrology techniques to the active alignment of telescopes, and continues to work actively in this field on a number of projects. He is currently the Director of his own consulting company, Mersenne Optical Consulting, and the Chief Technical Officer of the optical-fabrication company KiwiStar Optics.
14:30 - 15:15 hrs
Future ESA Earth observation missions
 |
Christophe Buisset
European Space Agency (Netherlands) |
This presentation will provide a comprehensive overview of European Space Agency (ESA) ongoing efforts to prepare for the next generation of optical Earth Observation missions. First, we will present the science-driven Earth Explorers and Scout missions addressing key scientific issues, followed by an update on preparations for future Meteorology and Copernicus missions. Second, we will present the pre-development activities of innovative instrumental concepts and associated technologies engaged to prepare the future of Earth Observation optical missions. Finally, we will highlight the activities focused on the preparation of compact optical payloads for small satellites.
Dr Christophe Buisset holds a PhD in Optical Instrumentation and he is the Head of the Optical Instruments Section at the European Space Agency, where he leads a team of engineers developing advanced optical payloads for space missions. With over 20 years of experience, Dr Buisset has overseen the design, performance estimation, and risk management of cutting-edge space and ground-based instruments for Earth observation and astronomy. Before joining ESA, Dr Buisset established and directed a laboratory in Thailand dedicated to the development of optical technologies, building a team of engineers and researchers and developing state-of-the-art facilities. His career spans leadership roles in both industry and research institutes, numerous patents and publications, and a strong record of fostering international collaborations.