NASA: Orbital collision may be culprit
By Miles O'Brien
JOHNSON SPACE CENTER, Texas (CNN) -- Space shuttle Columbia investigators are looking into whether a piece of space junk or a tiny meteor inflicted a fatal wound on the spacecraft while in orbit.
As part of the investigation, space experts are trying to explain what appeared to break away from Columbia during its first full day in orbit.
U.S. Air Force ground-based observations along with NASA data, including sensor readings and shuttle activities that day, are being used to look into the theory.
A radar installation at Eglin Air Force Base in the Florida panhandle -- linked to U.S. Space Command headquarters in Cheyenne Mountain, Colorado -- recorded an object slowly moving away from the shuttle. One possibility is that the object struck the shuttle and then moved away from it.
The agency is checking the data against flight activities at the time to see whether the separation was something routine such as a water dump or whether the crew or onboard computers reported anything unusual at the time.
The shuttle broke apart February 1, killing the seven astronauts aboard and breaking up over Texas and Louisiana.
NASA Administrator Sean O'Keefe has asked for a report in 60 days from the independent board investigating the disaster.
Rock, ice are suspects
Tiny meteors, called, micrometeoroids, are chunks of comets or asteroids that orbit the sun, traveling faster than objects in low Earth orbit.
It is possible the object was a chunk of ice created during a routine dump of waste water from the shuttle. But no such release was planned, and the crew reported no problem with ice buildup.
If debris or a meteor hit the leading edge of Columbia's left wing, that could have led to the catastrophic end to the 16-day mission.
NASA engineers are rechecking data streamed down to the ground from several sensors that monitor motion and acceleration on Columbia to see if there was an in-orbit collision that went unnoticed by the crew.
In 1997, an independent report to NASA on the risks associated with collisions in orbit determined that a hole larger than a quarter-inch in one of the 22 so-called reinforced carbon-carbon caps that line the front of each shuttle wing could cause a disaster.
The caps are made of a heavy, dense material that protects a shuttle where it gets hottest -- nearly 3,000 degrees. The leading edge of the wings and tail and the nose cone are made of the material.
"The consequent thermal heating on re-entry could have a 'blowtorch effect' inside the wing that causes loss of flight control or failure of the primary structure resulting in the loss of the vehicle," the report said.
Speck left crater on Challenger
Rick Hauck, a former shuttle commander, led the team that compiled the report. On his first shuttle mission in 1983, a tiny speck of paint struck a forward flight deck window, creating a noticeable crater in the glass. The glass was replaced once Challenger returned to Earth.
Objects in low Earth orbit move at a speed of 17,500 mph. At that rate, a piece of junk only one-tenth of an inch in size packs the punch of a bowling ball moving at 60 mph. A shuttle and a piece of debris could collide at a relative rate of 35,000 mph.
During a shuttle mission, the U.S. Space Command notifies NASA if an object appears to be on a collision course with the orbiter -- but there was no correction in course recommended for Columbia.
U.S. Space Command uses a sophisticated network of radars to track 4,453 pieces of space junk orbiting Earth, but orbital debris experts estimate there could be as many as 100,000 untracked objects in orbit -- from one-tenth of an inch to 4 inches in size.
"We are constantly tracking space debris," O'Keefe has said, adding that no system is foolproof to avoid a collision.
In recent years, NASA has made some changes to its fleet of orbiters to defend against debris. Experts put the odds of a fatal debris or meteor strike on a shuttle at one in 200 missions.