Designed to fulfill a critical inspection need for the Space Shuttle Program, the EVA IR Camera System can detect crack and subsurface defects in the Reinforced Carbon-Carbon (RCC) sections of the Space Shuttle's Thermal Protection System (TPS). The EVA IR Camera performs this detection by taking advantage of the natural thermal gradients induced in the RCC by solar flux and thermal emission from the Earth.
This instrument is a compact, low-mass, low-power solution (1.2cm3, 1.5kg, 5.0W) for TPS inspection that exceeds existing requirements for feature detection. Taking advantage of ground-based IR thermography techniques, the EVA IR Camera System provides the Space Shuttle program with a solution that can be accommodated by the existing inspection system. The EVA IR Camera System augments the visible and laser inspection systems and finds cracks and subsurface damage that is not measurable by the other sensors, and thus fills a critical gap in the Space Shuttle's inspection needs. This paper discusses the on-orbit RCC inspection measurement concept and requirements, and then presents a detailed description of the EVA IR Camera System design.
Designed to fulfill a critical inspection need for the Space Shuttle Program, the Infrared On-orbit RCC Inspection System (IORIS) can detect crack and surface defects in the Reinforced Carbon-Carbon (RCC) sections of the Space Shuttle’s Thermal Protection System (TPS). IORIS performs this detection by taking advantage of the natural thermal gradients induced in the RCC by solar flux and thermal emission from the Earth. IORIS is a compact, low-mass, low-power solution (1.2cm3, 1.5kg, 5.0W) for TPS inspection that exceeds existing requirements for feature detection. Taking advantage of ground-based IR thermography techniques, IORIS provides the Space Shuttle program with a solution that can be accommodated by the existing inspection system. IORIS augments the visible and laser inspection systems and finds cracks that are not easily measurable by the other sensors, and thus fills a critical gap in the Space Shuttle’s inspection needs. Based on crack IR signature predictions and on-orbit gradient expectations, IORIS can achieve crack detection over approximately 96% of the wing-leading edge RCC (using multiple inspections in an orbit period). This paper discusses the on-orbit RCC inspection measurement concept and requirements, and then presents a detailed description of the IORIS design.
One of NASA’s Space Shuttle Return-to-Flight (RTF) efforts has been to develop thermography for the on-orbit inspection of the Reinforced Carbon Carbon (RCC) portion of the Orbiter Wing Leading Edge (WLE). This paper addresses the capability of thermography to detect cracks in RCC by using in-plane thermal gradients that naturally occur on-orbit. Crack damage, which can result from launch debris impact, is a detection challenge for other on-orbit sensors under consideration for RTF, such as the Intensified Television Camera and Laser Dynamic Range Imager. We studied various cracks in RCC, both natural and simulated, along with material characteristics, such as emissivity uniformity, in steady-state thermography. Severity of crack, such as those likely and unlikely to cause burn through were tested, both in-air and in-vacuum, and the goal of this procedure was to assure crew and vehicle safety during re-entry by identification and quantification of a damage condition while on-orbit. Expected thermal conditions are presented in typical shuttle orbits, and the expected damage signatures for each scenario are presented. Finally, through statistical signal detection, our results show that even at very low in-plane thermal gradients, we are able to detect damage at or below the threshold for fatality in the most critical sections of the WLE, with a confidence exceeding 1 in 10,000 probability of false negative.
At the conclusion of the Columbia Accident Investigation, one of the recommendations of the Columbia Accident Investigation Board (CAIB) was that NASA develop and implement an inspection plan for the Reinforced Carbon-Carbon (RCC) system components. To address these issues, a group of scientists and engineers at NASA Langley Research Center proposed the use of an IR camera to inspect the RCC. Any crack in an RCC panel changes the thermal resistance of the material in the direction perpendicular to the crack. The change in thermal resistance can be made visible by introducing a heat flow across the crack and using an IR camera to image the resulting surface temperature distribution. The temperature difference across the crack depends on the change in the thermal resistance, the length of the crack, the local thermal gradient, and the rate of radiation exchange with the environment. The current paper describes how the authors derived the minimum thermal gradient detectability limits for a through crack in an RCC panel. This paper will also show, through the use of a transient, 3-dimensional, finite element model, that these minimum gradients naturally exist on-orbit. The results from the finite element model showed that there exists sufficient thermal gradient to detect a crack on 96% of the RCC leading edge.
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