Photogrammetry Measurements During a Tanking Test on the Space Shuttle External Tank, ET-137

Abstract

On November 5, 2010, a significant foam liberation threat was observed as the Space Shuttle STS-133 launch effort was scrubbed because of a hydrogen leak at the ground umbilical carrier plate. Further investigation revealed the presence of multiple cracks at the tops of stringers in the intertank region of the Space Shuttle External Tank. As part of an instrumented tanking test conducted on December 17, 2010, a three dimensional digital image correlation photogrammetry system was used to measure radial deflections and overall deformations of a section of the intertank region. This paper will describe the experimental challenges that were overcome in order to implement the photogrammetry measurements for the tanking test in support of STS-133. The technique consisted of configuring and installing two pairs of custom stereo camera bars containing calibrated cameras on the 215-ft level of the fixed service structure of Launch Pad 39-A. The cameras were remotely operated from the Launch Control Center 3.5 miles away during the 8 hour duration test, which began before sunrise and lasted through sunset.The complete deformation time history was successfully computed from the acquired images and would prove to play a crucial role in the computer modeling validation efforts supporting the successful completion of the root cause analysis of the cracked stringer problem by the Space Shuttle Program. The resulting data generated included full field fringe plots, data extraction time history analysis, section line spatial analyses and differential stringer peak-valley motion. Some of the sample results are included with discussion. The resulting data showed that new stringer crack formation did not occur for the panel examined, and that large amounts of displacement in the external tank occurred because of the loads derived from its filling. The measurements acquired were also used to validate computer modeling efforts completed by NASA Marshall Space Flight Center (MSFC). Background

STS-133/ET-137 Tanking Test Photogrammetry Assessment

“…For more imformation on the photogrammetry aspects of the tanking test, including set-up, calibration, operational challenges, and results, refer to Ref. 3.…”

Stress Analysis and Testing at the Marshall Space Flight Center to Study Cause and Corrective Action of Space Shuttle External Tank Stringer Failures

“…Since the SOFI was required to be in place during the tanking test, the photogrammetry required painting a speckle (dot) pattern on the external surface of the foam (Figure 15). Approval was granted to try photogrammetry on two regions of the intertank on approximately opposite sides of the intertank from each other [8]. The field of view of the camera systems limited both regions of study to the forward ends of several stringers and the adjacent LOX tank area.…”