HOUSTON -- The Columbia Accident Investigation Board said Thursday that investigators are searching the area around Caliente, Nev., for what may be a piece of the space shuttle that was tracked by air traffic control radar as it fell to Earth on Feb. 1.
The Civil Air Patrol began searching the rugged desert and mountain area, and other means may be used in the search, the report said.
No piece of the shuttle has been found west of Fort Worth, and finding a piece of wreckage that separated from the shuttle early in its breakup, and was large enough to have been tracked by radar, could provide a significant clue as to what triggered the disaster.
Most wreckage has been located from Fort Worth to Louisiana so far, but witnesses and data suggest the breakup started much earlier, perhaps as the shuttle crossed the California coast.
The investigation board's status report, released late Thursday, said trajectory and ballistics experts pinpointed the Caliente area by using video imagery to analyze the trajectory of shuttle pieces. That information was then handed to the National Transportation Safety Board in Washington, which reviewed radar tapes from that area.
"The review resulted in what is believed to be a significant radar track of a piece of debris as it fell," the report said. Similar trajectory analysis is continuing, but no other search areas have been identified, the report said.
The board also said it is making "significant progress" in analyzing military and civilian video and photography that could help reveal what went wrong during Columbia's descent.
The material, which comes from several government agencies and members of the public, includes an analysis of sonic booms the shuttle made as it broke up, according to the Southern Methodist University Web site where the recording was posted: http://www.geology.smu.edu.
The analysis is based on an infrasound recording of as many as 12 shocks, most probably emanating "from a single explosive event," the site said.
An instrument in Lajitas, Texas -- about 500 miles south of Dallas -- recorded the sounds. The first came within a minute of the time when Mission Control in Houston lost contact with Columbia and continued for about 11 minutes.
The analysis indicates the main explosion took place about 8:59 a.m. EST about 39 miles above west Texas, between Lubbock and Amarillo.
Earlier in the day, NASA Administrator Sean O'Keefe said the space agency will decide within a few days whether to return a full three-astronaut crew to the international space station or to cut back to a smaller complement when the current crew returns in late April.
O'Keefe said during a news conference at NASA's Stennis Space Center in Mississippi that there is no danger to the space station crew, despite the grounding of the space shuttle program following the Columbia crash.