CAPE CANAVERAL, Fla. -- NASA engineers on Sunday began assembling a grim jigsaw puzzle, taking precise satellite measurements of where Columbia debris landed to learn why the nation's oldest space shuttle disintegrated just minutes from home.
NASA chief Sean O'Keefe named a former Navy admiral to oversee an independent review of the accident, and said investigators initially would focus on whether insulation from a phased-out fuel tank caused damage that ultimately doomed the shuttle.
"That's one of the earliest indications. It's one of the areas we're looking at first, early, to make sure that the investigative team is concentrating on that theory," O'Keefe said as he vowed a thorough investigation during a round of appearances on Sunday talk shows.
The focus for now is whether insulation that broke loose from a fuel tank during the shuttle Columbia's ascent on Jan. 16 damaged heat-protecting tiles, ultimately dooming the shuttle's return to earth 16 days later.
The manufacturer of the fuel tank disclosed Sunday that NASA used an older version of the tank, which the space agency began phasing out in 2000. NASA's preflight press information stated the shuttle was using one of the newer super-lightweight fuel tanks.
Harry Wadsworth, a spokesman for Lockheed, the tank maker, said most shuttle launches use the "super-lightweight" tank and the older version is no longer made. Wadsworth said he did not know if there was a difference in how insulation was installed on the two types of tanks.
O'Keefe emphasized that the space agency was being careful not to lock onto any one theory too soon. He vowed to "leave absolutely no stone unturned."
For a second day, searchers scoured forests and rural areas over 500 square miles of East Texas and western Louisiana for bits of metal, ceramic tiles, computer chips and insulation from the shattered spacecraft. State and federal officials, treating the investigation like a multi-county crime scene, were protecting the debris until it can be catalogued, carefully collected and then trucked to Barksdale Air Force Base in Louisiana.
The effort to reconstruct what is left of Columbia into a rough outline of the shuttle will be tedious and painstaking.
When a shuttle piece was located this weekend, searchers left it in place until a precise global position satellite reading could be taken. Each shuttle part is numbered; NASA officials say experts hope to trace the falling path of each recovered piece and learn when in the fiery re-entry it came off of the spacecraft.
The goal is to establish a sequence of how parts were ripped off Columbia as it endured the intense heat and pressure of the high-speed re-entry into the atmosphere.
At least 20 engineers from United Space Alliance, a key NASA contractor for the shuttle program, were dispatched to Barksdale for what is expected to be a round-the-clock investigation.
Other experts, including metallurgists and forensic medicine specialists, are expected to join the investigation. Their focus will be on a microscopic examination of debris and remains that could elicit clues such as how hot the metal became, how it twisted and which parts flew off first.
In addition to NASA's investigation, O'Keefe named an independent panel to be headed by retired Navy admiral Harold W. Gehman Jr., who previously helped investigate the 2000 terrorist attack on the USS Cole.
Gehman's panel will also sift through the Columbia wreckage, and come to its own conclusions about what happened. O'Keefe described Gehman as "well-versed in understanding exactly how to look about the forensics in these cases and coming up with the causal effects of what could occur."
Joining Gehman on the commission are four other military officers and two federal aviation safety officials.
Officials used horses and four-wheel-drive vehicles to find and recover the shuttle pieces. Divers were being called in to search the floor of Toledo Bend Reservoir, on the Texas-Louisiana border, for a car-sized piece seen slamming into the water.
Some body parts from the seven-member astronaut crew have been recovered and are being sent to a military morgue in Dover, Del.
Columbia came apart 200,000 feet over Texas while it was streaking at more than 12,000 miles an hour toward the Kennedy Space Center. A long vapor trail across the sky marked the rain of debris over the heavily forested Texas and Louisiana countryside.