NDT of dielectric materials and constructions in aerospace industry by means of holographic subsurface radar

Head of the project: Sergey Ivashov, sivashov@rslab.ru.

Accidents during spacecraft launching spacecraft quite often occur in different countries. They cause considerable direct material losses. In addition, countries with high accidents rate also carry indirect losses in the form of increased insurance premiums for the insurance of subsequent launches, and many customers are beginning to refuse to launch their satellites on unreliable rockets. One of the means to improve reliability of the rocket and space industry production is the non-destructive testing of the manufactured products.

This project focus on the development and introduction of a new holographic subsurface radar technology as a nondestructive testing technique of dielectric products and coatings.

The Space Shuttle Columbia disaster occurred a few tears ado, killing all seven crew members. This and other incidents which fortunately did not lead to such catastrophic consequences have aroused interest in the development of new methods for non-destructive testing of insulation and thermal protection coatings on spacecraft and fuel tanks. In the opinion of NASA investigators that was published in Aviation Week & Space Technology, one of the causes of the Columbia disaster was voids in the thermal protection coating on the shuttle’s external fuel tank. The external tank contains liquid oxygen and hydrogen propellants stored at minus 183 and minus 253 degrees Celsius respectively. To reduce fuel vaporization and prevent icing of tank surface that could fragment and damage the shuttle, the tank is covered with insulating polyurethane foam. The thickness of the foam is within the range of 25 mm to 50 mm. If the super-cold external tank is not sufficiently insulated from the ambient warm and moist air, atmospheric water vapor condenses inside the foam voids. According to this hypothesis, during the launch of Columbia’s 28th mission, water that had condensed inside voids rapidly vaporized (boiled) as result of lowering pressure with increasing altitude following launch. As a result of this explosive boiling, a piece of foam insulation broke off from the external tank and struck the left wing, damaging heat protective leading edge panel. When Columbia reentered the atmosphere after the mission, this damage allowed plasma (produced ahead of the craft during its flight in stratosphere) to penetrate and destroy the wing structure, causing the spacecraft to break up. Most previous shuttle launches had seen similar, but more minor, damage and foam shedding, but the risks were deemed acceptable.

It is well-known that the tiled thermal protection coating of return vehicles like the Space Shuttle is exposed to high mechanical, and especially thermal, influence on reentry. In fact, after the first flight of Columbia (April 12, 1981) 16 tiles were lost and 148 tiles were damaged. Similar problems with more serious after-effects arose after the first and only flight of Buran (November 15, 1988). Post-flight inspection showed partial destruction to complete loss of thermal shielding tiles after 21st section of leading edge. Such damage could lead to a repeat of the Columbia disaster in its possible future missions.

In the Remote Sensing Laboratory, Bauman Moscow State University has been developed a new technology of holographic subsurface radar, which has no analogues in the world. For the development of this technology and the launch on its base the production of holographic subsurface radar of RASCAN type, the laboratory’s staff was awarded a Russian Federation Government’s prize in the field of science and technology. The design of the device is protected by several patents of the Russian Federation, as well as the RASCAN radars are supplied to domestic consumers, and in many countries around the world. The main destination of RASCAN radars is diagnostics of building structures. In this connection, the radar operating frequency range, which depends on the device modification, lies in the range of 1.6 through 6.8 GHz (http://www.rslab.ru/english/product/ ). A further increase in the frequency does not have sense because of the nonlinear increase of attenuation of electromagnetic waves in building structures and errors arising during manual scanning.

It is worth noting that for a long time there was widespread opinion that due to strong attenuation in typical media, and the inapplicability of time-varying gain to continues-wave radar returns, holographic subsurface radar was unlikely to find any significant application in practice. However, the recent development of RASCAN radars, their commercial production, and sufficiently wide practical applications have shown that for examination of low electrical conductivity media at shallow depths, this type of device has many advantages including real-time imaging plan-view, and high resolution in plan of scanning. Design details of RASCAN radars and fields of their applications are presented in http://www.rslab.ru/downloads/A0065.pdf and http://www.rslab.ru/downloads/hsrrt.pdf .

The main peculiarity of thermal protection and thermal insulation materials such as polyurethane foam or sintered silica fiber, which are used in the rocket and space industry, is a low level of attenuation of microwave waves. This allows the use of higher frequency band to improve the radar spatial resolution and sensitivity for detection of heterogeneities and defects. Another peculiarity in the diagnosis of coatings is that they, as a rule, are glued onto the metal surface of the spacecraft, which is a perfect mirror for microwave waves. This fact needs to be taken into account especially in the reconstruction of recorded microwave holograms.

Preliminary studies showed that the frequency range of the serial RASCAN radar does not provide sensitivity and resolution required to detect typical defects encountered in polyurethane coatings. It was necessary to increase the frequency range and replace manual scanning with electromechanical one. At the first stage, an experimental setup was designed that included a vector network analyzer Rohde & Schwarz ZVA 24 with operating frequency range from 10 MHz to 24 GHz, an electromechanical scanner and a set of antennas operating in different frequency bands. Then, in agreement with FSUE “NPO Technomash” (Roscosmos State Corporation for Space Activities), a compact experimental device with operating frequency range of 22.6-26.4 GHz was developed, which allowed increasing the sensitivity of measurements and obtaining satisfactory results. Experiments to determine the coatings defects were carried out with samples provided by FSUE “NPO Tekhnomash”, FSUE “Khrunichev State Research and Production Space Center”, RSC “Energia” and Vikram Sarabhai Space Center, India.

The device needs be improved in order to increase its sensitivity and provide wireless communication with the data processing computer, as well as new software will be developed automatizing the recorded information processing and detecting the construction defects. Particular attention is paid to conducting experiments on the same samples to identify defects by various methods: microwave holography, X-rays, ultrasound and infrared thermography. This allows comparing the effectiveness of these methods, identifying their advantages and disadvantages, and the preferred areas of application. The possibility of the combined use of different diagnostic methods will be also studied. This problem has not been carefully considered up-to-date.

One of the tasks is assessing the possibility of detecting moisture penetrating the composite structures, which can lead to their destruction, especially when the temperature fluctuates around zero degrees Celsius. This task is especially important in post-flight inspection of reusable descent modules.

Result of the project is designing a compact holographic subsurface radar that can be used in real production lines. The work was carried out with the assistance and consultations with the Russian enterprises of the Roskosmos system, aviation industry, and participation of Vikram Sarabhai Space Center, India.

Another task is the investigation of the possibility of examining the Cheops’ (Khufu’s) Pyramid, Egypt in the radio range using the developed methods of non-destructive testing. This task became relevant after the appearance in 2017 report of an international collaboration on the possible discovery of previously unknown voids in the Great Pyramid using muon sensors. Using the independent method proposed in the project will give a possibility to confirm or deny the presence of unknown voids in the Pyramid.

Considering the complexity of the emerging tasks, colleagues from Bulgaria, the USA and Italy are also involved in the project.


  1. Bugaev À.S., Ivashov S.I., Razevig V.V., Chizh Ì.À. Comparison of microwave diagnostics with other non-destructive testing methods for composite products. Achievements of modern radioelectronics. 2020. V. 74. No. 4–5. P. 19–38 [in Russian]. DOI: 10.18127/j20700784-202004-02
  2. V.V. Chapurskii, V.I. Kalinin, A.S. Bugaev, and V.V. Razevig, Method for Recirculation of Signals in the Problem of Observation of a Point Object above a Metal Surface // Technical Physics, 2019, Vol. 64, No. 8, pp. 1189–1193. DOI: 10.1134/S1063784219080048
  3. Sergey Ivashov, Andrey Zhuravlev, Vladimir Razevig, Margarita Chizh, Timothy Bechtel, Lorenzo Capineri, Binu Thomas, "Frequency Influence in Microwave Subsurface Holography for Composite Materials Testing," Proceedings of the 17th International Conference on Ground Penetrating Radar, GPR 2018, Rapperswil, Switzerland, June 18–21, 2018, pp. 98-103. DOI: 10.1109/ICGPR.2018.8441592
  4. Vladimir Razevig, Sergey Ivashov, Margarita Chizh, Andrey Zhuravlev, Lorenzo Capineri, Influence of Electrical Properties of Media on Reconstruction of Microwave Holograms Recorded by a Subsurface Radar, 2019 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS 2019), Tel-Aviv, Israel, 4-6 November 2019.
  5. Lorenzo Capineri, Margarita Chizh, Andrey Zhuravlev, Vladimir Razevig, Sergey Ivashov, Pierluigi Falorni, Defects investigation in thermal insulation coatings with microwave imaging based on a 22 GHz holographic radar, NDT and E International 2019,109 (2020) 102191, pp. 1-8. DOI: 10.1016/j.ndteint.2019.102191, ISSN: 0963-8695
  6. Margarita Chizh, Andrey Zhuravlev, Vladimir Razevig, and Sergey Ivashov, Detection of Water Inclusions in Honeycomb Composite Products by a Holographic Radar, 2019 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS 2019), Tel-Aviv, Israel, 4-6 November 2019.
  7. S. Ivashov, L. Capineri, T. Bechtel, V. Razevig, A. Zhuravlev, and P. Falorni, Use of holographic subsurface radar analysis in the preservation and restoration of cultural heritage objects, Surface Topography: Metrology and Properties, 2019, 7 045017, pp. 1-11. DOI: 10.1088/2051-672X/ab4fa2, ISSN 2051-672X
  8. Sergey I. Ivashov, Vladimir V. Razevig, Andrey V. Zhuravlev, Timothy Bechtel, and Margarita A. Chizh, Comparison of Different NDT Methods in Diagnostics of Rocket Cryogenic Tanks Thermal Protection Coating, 2019 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS 2019), Tel-Aviv, Israel, 4-6 November 2019.
  9. S. I. Ivashov, A. S. Bugaev, A. V. Zhuravlev, V. V. Razevig, M. A. Chizh, and A. I. Ivashov, Holographic Subsurface Radar Technique for Nondestructive Testing of Dielectric Structures, Technical Physics, 2018, Vol. 63, No. 2, pp. 260-267. ISSN: 1063-7842 (Print), 1090-6525 (Online), DOI: 10.1134/S1063784218020184
  10. Andrey Zhuravlev, Vladimir Razevig, Margarita Chizh, and Sergey Ivashov, Non-Destructive Testing of Foam Insulation by Holographic Subsurface Radar, 9th International Workshop on Advanced Ground Penetrating Radar, IWAGPR 2017, Edinburgh, UK, 28-30 June 2017, DOI: 10.1109/IWAGPR.2017.7996087
  11. L. Capineri, P. Falorni , T. Becthel, S. Ivashov , V. Razevig and A. Zhuravlev, Water detection in thermal insulating materials by high resolution imaging with holographic radar, Measurement Science and Technology, Special Issue, Vol. 28, No. 1, 2017, pp. 1-6. doi:10.1088/1361-6501/28/1/014008
    (PDF, 1.7 Mb)
  12. Margarita A. Chizh, Andrey V. Zhuravlev, Vladimir V. Razevig, and Sergey I. Ivashov, Experimental validation of sparse sensing technique in subsurface microwave holography, Proceedings of Progress In Electromagnetics Research Symposium (PIERS 2016), Shanghai, China, 8-11 August, 2016.
    (PDF, 1.5 Mb)
  13. S. Ivashov, A. Zhuravlev, M. Chizh, and V. Razevig, High Resolution MW Holographic System for NDT of Dielectric Materials and Details, Proceedings of the 16th International Conference of Ground Penetrating Radar 2016, Session # 9.5 Material properties, Hong Kong, Polytechnic University, 13-16 June 2016.
    (PDF, 300 Kb)
  14. A. Zhuravlev, V. Razevig, M. Chizh, S. Ivashov, and A. Bugaev, Non-destructive Testing at Microwaves Using a Vector Network Analyzer and a Two-coordinate Mechanical Scanner, Proceedings of the 16th International Conference of Ground Penetrating Radar 2016, Session 4D System and Antenna Design, Hong Kong, Polytechnic University, 13-16 June 2016.
    (PDF, 600 Kb)
  15. Sergey I. Ivashov, Vladimir V. Razevig, Timothy D. Bechtel, Igor A. Vasiliev, Lorenzo Capineri, and Andrey V. Zhuravlev, Microwave Holography for NDT of Dielectric Structures, Proceedings of the IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS 2015), Tel-Aviv, Israel, 2-4 November 2015, 978-1-4799-7473-3/15/$31.00 ©2015 IEEE, DOI: 10.1109/COMCAS.2015.7360372
    (PDF, 600 Kb)

  16. Andrey V. Zhuravlev, Vladimir V. Razevig, Sergey I. Ivashov, and Alexander S. Bugaev, Experimental Comparison of Multi-Static and Mono-Static Antenna Arrays for Subsurface Radar Imaging, Proceedings of the IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS 2015), Tel-Aviv, Israel, 2-4 November 2015, pp. 1-4, 978-1-4799-7473-3/15/$31.00 ©2015 IEEE. DOI: 10.1109/COMCAS.2015.7360380
    (PDF, 2.3 Mb)

  17. S. Ivashov, V. Razevig, I. Vasiliev, T. Bechtel, L. Capineri, Holographic subsurface radar for diagnostics of cryogenic fuel tank thermal insulation of space vehicles, NDT & E International, Vol. 69, January 2015, Pages 48-54.
    (PDF, 2 Mb)

  18. S. Ivashov's presentation at the IEEE COMCAS 2015, Tel Aviv, Israel, 2-4 November, 2015, Holographic Subsurface Radar for NDT Diagnostics in Aerospace Industry.
    (PPT, 22 Mb)
  19. T. Lu, C. Snapp, T.-H. Chao, A. Thakoor, T. Bechtel, S. Ivashov, I. Vasiliev. Evaluation of holographic subsurface radar for NDE of space shuttle thermal protection tiles, Sensors and Systems for Space Applications. Proceedings of SPIE, Volume 6555, 2007.
  20. S.I. Ivashov, I.A. Vasiliev, T.D. Bechtel, C. Snapp, Comparison between Impulse and Holographic Subsurface Radar for NDT of Space Vehicle Structural Materials, Progress in Electromagnetics Research Symposium 2007, Beijing, China, March 26-30, 2007, pp. 1816-1819.
  21. Experimental installation for NDT&E of dielectric materials and structures.

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