Processing near-infrared imagery of hypersonic space shuttle reentries

Abstract

High-resolution, calibrated, near-infrared imagery of the Space Shuttle during reentry has been obtained by a US Navy NP-3D Orion aircraft as part of NASA's HYTHIRM (Hypersonic Thermodynamic InfraRed Measurements) project. The long-range optical sensor package is called Cast Glance. Three sets of imagery have been processed thus far: 1) STS-119 when Shuttle Discovery was at 52 km away at Mach 8.4, 2) STS-125 when Shuttle Atlantis was 71 km away at Mach 14.3, and 3) STS-128 when Shuttle Discovery was at 80 km away at Mach 14.7. The challenges presented in processing a manually-tracked high-angular rate, air-to-air image data collection include management of significant frame-to-frame motions, motion-induced blurring, changing orientations and ranges, daylight conditions, and sky backgrounds (including some cirrus clouds). This paper describes processing the imagery to estimate Shuttle surface temperatures. Our goal is to reduce the detrimental effects due to motions (sensor and Shuttle), vibration, and atmospherics for image quality improvement, without compromising the quantitative integrity of the data, especially local intensity variations. Our approach is to select and utilize only the highest quality images, register many cotemporal image frames to a single image frame, and then add the registered frames to improve image quality and reduce noise. These registered and averaged intensity images are converted to temperatures on the Shuttle's windward surface using a series of steps starting with preflight calibration data. Comparisons with thermocouples at different points along the space Shuttle and between the three reentries will be shown.

Boundary Layer Transition Flight Experiment Overview

“…Detailed information on the STS-119 flight can be found in reference 15. A post-flight review of the thermocouple data showed a relatively early (~Mach 11.5) asymmetric BLT event on the starboard side of the Orbiter during re-entry, observed in HYTHIRM imagery 18,19 as shown in Figure 5 (near Mach 9). Thermocouple 1 (hereafter referred to as TC 1), located at the center of the predicted flight experiment wedge, showed the earliest sign of BLT at Mach 15.6.…”

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

“…Figure 8 shows the frame-by-frame variation in the image sharpness due to the blurring as previously discussed. Approximately two-thirds or less of the collected images are typically not selected or considered for subsequent processing [20]. Another benefit of this technique is viewing a series of images.…”

“…Similarly, a blurred image would increase the number of pixels above the threshold, because the light would be spread over more pixels, however the intensity would decrease thus lowering the total pixels. Image selection based on sharpness was done previously using a feature-based approach where the wing leading edges, nose, and body flap were used to determine sharpness [20,21]. Because STS-134 data collect provided imagery at a much higher resolution, a eigenvalue value decomposition technique was used to determine sharpness.…”

A Vision of Quantitative Imaging Technology for the Validation of Advanced Flight Technologies

“…As summarized by Horvath 9 , the early attempts at observations were largely unsuccessful suffering from challenges primarily associated with preflight planning, communications, hardware, tracking and the general inability to respond to inherent cross range uncertainties associated with a Shuttle reentry. The success rate of data collection by the HYTHIRM team at the close of the Shuttle program, are attributed to addressing these shortfalls via rigorous mission planning and operations 8,7,3 ; trained and skilled asset personnel 2 ; and advancements in infrared detector technology and image analysis techniques 6 . The use of a highly proficient crew on board a Navy aircraft has provided the flexibility required to respond to cross range (ground track) and weather uncertainties.…”

“…Quantitative thermal imagery obtained by the Hypersonic Thermodynamic Infrared Measurements (HYTHIRM) team has provided a unique and never before observed perspective on the global distribution of surface temperature and the state of the boundary layer (i.e., laminar/turbulent) over the entire windward surface of the Shuttle during portions of hypersonic re-entry [1][2][3][4][5][6][7][8] . Sponsored by the Space Shuttle Program, observations made over a period of approximately 2.5 years spanning seven Shuttle missions have covered the Mach range from 6.2 to 18.1.…”