By NBC News space analyst
NBC News

Frustrated investigators of the Columbia tragedy are still trying to find a connection between apparently minor launch damage to the shuttle’s wing and the subsequent failure of that wing on return to Earth. They are now paying more attention to one potential gap-bridging clue, and some observers are dismayed that the clue was not recognized soon enough to do some good for the doomed shuttle and its crew.

This clue is the small “mystery object” that apparently detached itself from the shuttle after about 24 hours in space, on Jan. 17. It slowly drifted away, fell into a lower orbit, pulled ahead of the shuttle and burned up in the atmosphere over the South Pacific three days later.

“It was something that more than likely came loose,” Air Force Brig. Gen. Duane Deal speculated last month. Deal, a member of the Columbia Accident Investigation Board, is also commander of the 21st Space Wing at Peterson Air Force Base, Colo., which provides missile warning and space control for the U.S. military and allies.

Another board member is James Hallock, manager of the aviation safety division at the Department of Transportation’s Volpe Center. He recently speculated that a segment of the shuttle’s thermal protection system — perhaps the reinforced carbon-carbon bumpers along the front edge of the wing, or the tile-covered carrier panels that connect these bumpers with the regular tiled surface — was hit so hard that its attachments broke, but the segment was held in place through launch by air pressure.

“That’s one of the scenarios we’re thinking about,” Hallock told journalists Tuesday.

The mystery object “could conceivably be a carrier panel,” he noted. “It’s the right size.”

The radar blip from the foot-long fragment was so weak that Deal’s space trackers did not even notice it during the flight. Only after Columbia was lost on Feb. 1 did they manually review the 3,000 raw records from their worldwide tracking network. It took five days to find the radar signature.

Lost opportunity
Although the object may still have a tale to tell investigators about the cause of the accident on Feb. 1, it is what the object failed to tell NASA in real time — before Columbia was lost — that some observers find particularly dismaying.

For two weeks after launch on Jan. 16, NASA managers had been struggling with the question of whether to request images of Columbia’s possibly damaged left wing from Pentagon telescopes in space and on the ground. In the end they decided there was not enough evidence of potential harm to justify the effort.

But all the while, the additional evidence that might have changed their minds — radar returns from what looked like a piece broken off the shuttle — was sitting unsought and unrecognized in a military database. Nobody at NASA apparently thought to ask the Pentagon to look, and nobody on the military side realized the raw data might have contained anything important.

Board members privately have told MSNBC.com that knowledge of the existence of such evidence would clearly have prompted NASA to demand imagery from other sensors. The remote imagery would have provided the best bet for inspection: Even if Columbia astronauts had made a spacewalk, that section of the wing would have been blocked from their view by the unfolded payload bay door.

Had the mortal wound to the shuttle’s wing been recognized, other options — involving extending Columbia’s flight while rushing to launch a rescue shuttle — might have become feasible.

Even though the “mystery object” failed to trigger alarms during the mission, it may still help clear the way for resuming shuttle launches by leading to an understanding of what went wrong during Columbia’s flight. Currently, there’s a gap in that understanding, due to an apparent “disconnect” between causes and effects.

What happened when?
Accident investigators trying to understand the Columbia catastrophe have thoroughly examined launch data apparently indicating that, despite the impact of several objects on the left wing, no visible damage occurred and nothing detectable came off. Yet a careful analysis of data from the very beginning of the shuttle’s descent through the atmosphere, 16 days later, shows that under aerodynamic stresses only a fraction of the strength of those at launch, strange turbulence appeared and small pieces began coming off almost immediately.

What could have happened between ascent and entry? The mystery object may tell the story.

There are several clues helpful in identifying the nature of the object. The rate at which it slipped from orbit can determine its mass-to-area ratio, which can be compared with candidate pieces from the shuttle. Its radar “signature” — the brightness it reflected at various radio frequencies — can also help choose among possible candidates.

Soon after the tracking records were released, retired NASA space debris expert Donald Kessler told NBC News that the object’s quick descent from orbit indicated it was “a small piece of debris.” Radar returns suggested that it was about a foot across and slowly tumbling.

Ted Molczan, a highly respected Canadian amateur satellite tracker, has just completed a detailed analysis of the object’s descent from orbit. The speed with which it decayed can tell a great deal about its density, and this in turn can help indicate which part of the shuttle it could represent.

Molczan measured the density of the leading candidate materials, including different types of tiles and thermal blankets that may have come off the shuttle. He found the object’s drag characteristics were most consistent with the physical properties of the heavier components of the shuttle’s heat shielding. Tiles and blankets would have been too light and would have fallen out of orbit within hours instead of days.

During the board’s news briefing a week ago, Maj. Gen. John Barry reported that the Air Force Research Lab at Wright-Patterson Air Force Base in Ohio was “proceeding rapidly” to obtain “radar signatures on a number of items from tiles, RCC [reinforced carbon-carbon], blanket ... and carrier plates.” NASA provided the samples from its supplies of shuttle spare parts.

Hallock reported the preliminary results Tuesday: “We’ve performed tests in a radar chamber. A tile doesn’t register, a blanket doesn’t even register.” This corroborated Molczan’s analysis that the object could have been one of the heavier components of the shuttle thermal protection system.

If the object observed in space were a dense fragment of the shuttle’s thermal protection system, it may have been from the wing’s leading edge or near it. So it could have been held in place during ascent by the wind load. But the question remains why it then came loose in orbit.

The answer may be that space is “an interesting heating environment,” in Hallock’s words. “It’s very cold, then there’s sunshine every 90 minutes. These temperature extremes do things to materials.”

Retired Adm. Harold Gehman, the investigation board’s chairman, added: “And just before the object was spotted, the shuttle had just done a yaw maneuver.” Such a maneuver might have caused a loose piece to drift away from Columbia.

Radar tests continue, and the Pentagon is now searching for any satellite observations of the meteoric flash the object would have made when it hit the atmosphere. It may have left enough traces to provide sufficient information to close the gap on the mystery of the Columbia disaster. The tragedy is that the object’s message of warning was never heard in real time.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.

© 2013 NBCNews.com  Reprints

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