Maxim Kravchenko, a graduate of Novosibirsk State Technical University (NETI), took a key part in the development of a measuring complex for non-contact precision control of objects' deformations when simulating the conditions of outer space.
The complex was created at the SB RAS Design and Technology Institute of Scientific Instrumentation. It is designed to monitor structures at extreme temperatures and pressures. Such conditions are simulated inside a thermal vacuum chamber. The complex is based on the method of digital electronic speckle interferometry. It captures interference patterns of laser radiation scattered by the rough surface of an object, allowing micro-displacements and deformations to be recorded, said Maxim Kravchenko, one of the developers, a graduate of the Faculty of Physics and Technology of NSTU-NETI (Department of Optical Information Technologies), a researcher at the laboratory of KTI NP SB RAS. The work was conducted under the guidance of Peter Zavyalov, a lecturer at the Department of Optical Information Technology.
The objects of control are large-sized elements of spacecraft, primarily parts of the mirror systems of telescopes, antennas and satellites, where even micron deformations are unacceptable. They lead to distortion of the wavefront, loss of focus and, as a result, a decrease in image/signal quality. So, in telescopes, image distortion can manifest itself in the form of blurring, loss of contrast. This limits the resolution and degrades the detail of the observed objects. That is why minimizing micron deformations is an important task in the design of such systems.
"In the thermal vacuum chamber where the controlled object is located, the conditions of outer space are simulated - deep vacuum, extreme temperature changes. Traditional measurement systems do not work in such conditions. A monitoring device based on digital speckle interferometry provides non-contact measurement by digitally processing interference signals that occur when a laser beam is reflected from an object. Surface deformations are calculated using the interferogram with an accuracy of 1 micrometer. This way we can understand what will happen to the object in extreme conditions," explains Maxim Kravchenko.
The measuring complex is located near the thermal vacuum chamber. The laser illuminates the object through an optical porthole. The scattered radiation is detected by the photodetector unit. The data obtained is analyzed to identify deformations.
"As part of the project, I performed a computer simulation of the operation of a speckle interferometer, and with my participation, a methodology for analyzing the metrological characteristics of a speckle interferometer was developed. He carried out the design and assembly of the entire optoelectronic measuring complex - from the development of an optical circuit to the final device, including the creation of specialized software," said Maxim Kravchenko.
In addition, the developer performed unique measurements of deformations in a thermal vacuum chamber, statistical analysis of the data obtained and comparative analysis of the results of speckle interferometric measurements with data from alternative control methods.
Tests of the developed device were carried out. Three carbon fiber objects were studied, which were prototypes of reflectors, had parabolic and hyperbolic surface shapes and differed in diameter. Based on real measurements in a thermovacuum chamber, the values of deformations of objects at all stages of thermal cycling (drying, heating, cooling) were obtained. The results suggest the possibility of using the measuring complex for precision control of deformations of large-sized objects, such as reflectors and elements of spacecraft mirror systems in conditions of simulated outer space.
It should be recalled that NSTU-NETI is also developing a hardware and software complex for measuring residual technological stresses in metal products. The speckle interferometry method is at the heart of the equipment.