Columbia was flying at 17,500 mph, tail-first and upside down, its open cargo bay pointing toward the planet below.
It twirled and twinkled as it fell to Earth.
Apparently unseen by human eyes, it was recorded by military radar and stored in a computer.
There the reading stayed until after the accident, when Air Force technicians discovered it among thousands of automatic radar sweeps of Columbia in space.
In the surveillance files of the Air Force 21st Space Wing, the electronic traces of the mysterious object amounted to little more than squirts of static.
Had something drifted out of the open cargo bay on Jan. 17?
NASA investigators checked the lost-and-found log at Kennedy Space Center and discovered seven missing tools — an Allen wrench, screwdrivers, a flashlight and pliers.
Had the shuttle been hit by something in orbit?
Investigators checked mission records to see if Columbia had shuddered from the impact of a meteoroid or orbital debris.
They found nothing out of the ordinary.
Only one place had a chance of deciphering the faint radar signal — the Hog Works, a windowless laboratory behind two sets of locked security doors at Wright-Patterson Air Force Base near Dayton, Ohio.
Inside, signs warned against classified discussions in the hallways. A red security light flashed in warning when the janitor came by to mop the floors.
When a visitor entered the building, a researcher made a timeout gesture with his hands like a football referee, indicating that conversations should stop.
Technically, the radar range was called an occult chamber.
The sealed room was the size of a strip mall cinema. Its walls, floor and high ceiling were covered with thick layers of blue sculpted baffles that resembled the sound-scattering acoustic clouds in a concert hall.
In the center was a 40-foot-high pylon. Researchers secured targets at the top and bombarded them with radar waves.