UH Researcher Part of National Team Analyzing Infrasound Data in Columbia Shuttle DisasterUniversity of Hawaiʻi
Kristen Cabral, (808) 956-5039
Public Information Officer
Dr. Milton Garces, researcher at the Infrasound Laboratory of the University of Hawaiʻi, was part of a task team formed by the Department of Defense (DoD) to help analyze and interpret the wealth of infrasonic data associated with the February 1 disaster as well as other reentries with a similar orbital inclination.
"The complete approach path from California to Texas was recorded acoustically, and unambiguous warnings of imminent disaster were not evident from the complex sounds recorded by a network of acoustic stations in North America," said Garces. "This suggests that the thermal instability and possible shedding of small fragments of the shuttle did not significantly alter the flight dynamics during the reentry, and thus its catastrophic structural failure probably occurred rapidly. Had a meteor or lightning discharge created significant damage to the shuttle, we would have observed associated infrasonic signatures. We looked carefully at signals that may have corresponded to the offshore approach and did not find anything substantial, so we can discount those hypotheses."
Forensic studies of such energetic large-scale processes have only recently been made possible by a global network of infrasound stations that monitor atmospheric sound. Coverage over the United States is provided by the North American Infrasound Network (Figure 1). Stations in Hawaiʻi, Alaska, California and Canada are part of the International Monitoring System (IMS), and stations in Nevada, New Mexico, Wyoming, Utah, and Texas are operated by the U.S. Department of Energy. All infrasound stations are composed of multiple sensors that permit an estimate of the arrival azimuth and apparent propagation speed of a signal across the array.
Dr. Henry Bass, researcher at the University of Mississippi and team leader for the DoD Columbia team, states that "our infrasonic observations support NASA‘s working hypothesis to date. Although our infrasonic observations indicated that high intensity bursts may have originated near the California-Nevada border, where a flash may have been observed, such acoustic and visual phenomena may be caused by changes in the trajectory of the shuttle."
Researchers Michael Hedlin and Gerard D‘Spain at the University of California, San Diego, noted that the flash may correspond to a small aileron change. As time progresses, new information may still be obtained from the infrasonic observations. Dr. Eugene Herrin of Southern Methodist University considered the possibility that a small explosion may have caused some of the signals observed at the station in Texas. Due to the low density of the high atmosphere, a small burst can make a powerful infrasonic signal on the ground. Ongoing research on the acoustics of hypersonic sources may shed additional light on the last minutes of the Columbia‘s final flight.
Infrasounds have frequencies below the 20 cycles per second threshold of the human ear. Because they have very large wavelengths, they warp around mountains, bounce against earth and sea, and are turned by strong winds, propagating for hundreds to thousands of kilometers.
As the Columbia slammed into the lower thermosphere (~120 km height), the higher density of the atmosphere began to resist the hypersonic penetration of the craft. Air was compressed and heated ahead of the body to create a sharp shock front, known as a Mach cone. The craft was moving so much faster than the speed of sound (Mach 20) that the Mach cone appeared as a cylindrical sheath around the vessel, the intense heat rapidly dissipated by thermal tiles. As the shuttle roared over the United States, sensitive microphones first detect the jarring sonic boom. For the following hour, the atmosphere may reverberate with acoustic bursts corresponding to small changes in trajectory along the approach path. Although this is a common scenario for spacecraft reentry, on February 1, 2003, Columbia Shuttle flight STS-107 produced an unexpected series of explosive bursts associated with the violent disassembly in Texas that led to the tragic demise of its crew.
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Additional Points of Contact:
Henry Bass, University of Mississippi -- Email: firstname.lastname@example.org -- Cell phone: 662.816.0977
Michael Hedlin, University of California, San Diego -- Email: email@example.com -- Cell phone: 858.204.5375
For more information, visit: http://www.isla.hawaii.edu