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Media & Public Relations
University of Mississippi

06/04/2003

Acoustics Research Provides Insight to Cause of Shuttle Loss
By Mitchell Diggs

UNIVERSITY, Miss. -- The "sound" from Shuttle Columbia's reentry Feb.
1 was "different," say scientists analyzing low-frequency signals
from listening posts across western North America.

The infrasound signal was much longer than those associated with
other shuttle reentries to Earth's atmosphere, lasting almost an hour
after the sonic boom, the scientists reported today while meeting at
the University of Mississippi. 

"We're still not clear why this is the case," said Henry Bass, leader
of the infrasound team that studied the data. "We're not sure if this
indicates something about the fragments or pieces that were actually
flying along with the shuttle or not. Given all the other things that
affect the received signal, we really don't have enough experience
with this to sort it all out." 

Bass is director of the National Center for Physical Acoustics at UM.
His team reported its findings to the U.S. Department of Defense at
the end of March. The report is being released to the public this
week.

Infrasound is the part of the audio spectrum too low in frequency for
humans to hear. From major events such as explosions or volcano
eruptions, infrasound can travel thousands of miles, making it an
effective detection tool for nuclear tests. 

Scientists have analyzed recordings made at 13 sites the morning of
Feb. 1 and compared them with observations during three earlier
shuttle reentries. Data contains hints of a catastrophic event near
the California-Nevada border, but early reports that stations heard
an explosion aboard Columbia were premature, said Bass.

"It's really not clear to us if there was an explosion," he said.
"The breakup may or may not have been explosive in nature."

More analysis will be necessary to determine exactly what the sound
data means, Bass said. Comparing data from Columbia with earlier
reentries is difficult because most of the infrasound stations are
relatively new and because Columbia returned to earth on a trajectory
last used by a shuttle in 1998. 

In addition to Columbia's lengthy reentry sound, researchers are
analyzing spikes in the sound signal near the time when NASA lost
radio contact with the shuttle. The report concludes that although
the data could be interpreted as indicating an explosion or other
catastrophic event, it also could indicate a change in the shuttle's
angle. 

Ruling out potential causes is one of the data's biggest
contributions, Bass said. The infrasound data discounted "extraneous
claims," such as the shuttle's being struck by a meteor or bolide, or
lightning. 

Bringing together a diverse group of people to examine the data, with
a high level of cooperation between agencies, bodes well for the
future, Bass said. "We now know how to pull this team together to get
definitive results." 

Five of the locations recording Columbia's infrasound are part of the 
International Monitoring System, a 60-station network to monitor
compliance with the Comprehensive Test Ban Treaty. Data also was
obtained from stations funded by the U.S. departments of Defense and
Energy, the National Oceanic and Atmospheric Administration, and the
U.S. Army Research Laboratory. 

Besides NCPA, team members also included representatives from BBN
Technologies Inc., the Center for Monitoring Research, Los Alamos
National Laboratory, NOAA Environmental Technology Laboratory, U.S.
Naval Research Laboratory, the Laboratory for Atmospheric Acoustics
at the University of California-San Diego and the University of
Hawaii's Infrasound Laboratory. 

IMS stations providing data for the study are in Pinon Flat, Calif.;
Fairbanks, Alaska; Kona, Hawaii; Newport, Wash.; and Lac du Bonnet,
Manitoba. Data also was from stations in St. George, Utah; Los
Alamos, N.M.; Pinedale, Wyo.; Mina, Nev.; Lajita, Texas; Boulder,
Colo.; and White Sands Missile Range in New Mexico. Except for Alaska
and Hawaii, all locations recorded clear signals from the shuttle
reentry.

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