Application of a Near Infrared Imaging System for Thermographic Imaging of the Space Shuttle during Hypersonic Re-Entry

Abstract

High resolution calibrated near infrared (NIR) imagery was obtained of the Space Shuttle's reentry during STS-119, STS-125, and STS-128 missions. The infrared imagery was collected using a US Navy NP-3D Orion aircraft using a long-range infrared optical package referred to as Cast Glance. The slant ranges between the Space Shuttle and Cast Glance were approximately 26-41 nautical miles at point of closest approach. The Hypersonic Thermodynamic Infrared Measurements (HYTHIRM) project was a NASA Langley led endeavor sponsored by the NASA Engineering Safety Center, the Space Shuttle Program Office and the NASA Aeronautics Research Mission Directorate to demonstrate a quantitative thermal imaging capability. HYTHIRM required several mission tools to acquire the imagery. These tools include pre-mission acquisition simulations of the Shuttle trajectory in relationship to the Cast Glance aircraft flight path, radiance modeling to predict the infrared response of the Shuttle, and post mission analysis tools to process the infrared imagery to quantitative temperature maps. The spatially resolved global thermal measurements made during the Shuttle's hypersonic reentry provides valuable flight data for reducing the uncertainty associated with present day ground-toflight extrapolation techniques and current state-of-the-art empirical boundary-layer transition or turbulent heating prediction methods. Laminar and turbulent flight data is considered critical for the development of turbulence models supporting NASA's next-generation spacecraft. This paper will provide the motivation and details behind the use of an upgraded NIR imaging system used onboard a Navy Cast Glance aircraft and describe the characterizations and procedures performed to obtain quantitative temperature maps. A brief description and assessment will be provided of the previously used analog NIR camera along with image examples from Shuttle missions STS-121, STS-115, and solar tower test. These thermal observations confirmed the challenge of a long-range acquisition during re-entry. These challenges are due to unknown atmospheric conditions, image saturation, vibration etc. This provides the motivation for the use of a digital NIR sensor. The characterizations performed on the digital NIR sensor included radiometric, spatial, and spectral measurements using blackbody radiation sources and known targets. An assessment of the collected data for three Space Shuttle atmospheric re-entries, STS-119, STS-125, and STS-128, are provided along with a description of various events of interest captured using the digital NIR imaging system such as RCS firings and boundary layer transitions. Lastly the process used to convert the raw image counts to quantitative temperatures is presented along with comparisons to the Space Shuttle's onboard thermocouples.

Mass Efficiency Considerations for Thermally Insulated Structural Skin of an Aerospace Vehicle

“…3,4 It is interesting to note the variation in the equivalent square heating pulses that occur over just the windward surface in a single flight. The last three heating histories were predicted for a single point on the windward surface of three different proposed reusable launch vehicles.…”

Thermographic imaging of the space shuttle during re-entry using a near-infrared sensor

“…Frame acquisition time is stamped and the value is stored in the frame header. Custom data acquisition software was developed to control the camera's integration time in steps down to 10 µsec [12]. The characterizations performed on the digital NIR system included radiometric, spatial, and spectral measurements using blackbody radiation sources and known targets.…”

“…Implementation of the digital NIR camera system has resulted in NIR imagery with improved dynamic range, instantaneous field of view, and signal to noise [8][9][10][11]. The characterizations performed on the digital NIR system included radiometric, spatial, and spectral measurements using blackbody radiation sources and known targets [12,13]. An assessment of the collected data, using the digital NIR imaging sensor, for STS-119, STS-125, STS-128, STS-131, STS-132, STS-133, and STS-134 missions, is presented.…”

“…Nevertheless, excellent imagery is obtained, by selecting or "cherry picking" the best images. A histogram method is used to analyze the thermal imagery to determine the images of interest [12]. The histogram analysis method determines image saturation, frame dropouts and signal loss due to vignetting distortion.…”

Recommendations for Hypersonic Boundary Layer Transition Flight Testing

“…[30][31][32][33][34][35][36] Starting with STS-119 in March of 2009 and continuing through with a majority of the final flights, including all of the BLT FE flights, the HYTHIRM team has utilized a mix of airborne and ground based imaging platforms to view the Shuttle at hypersonic conditions. Each deployment of the HYTHIRM team has added to the collection of calibrated thermal imagery, at Mach numbers ranging from 8 to 18, suitable for processing and comparison with computational models and wind tunnel data.…”