11 May 2003
11 May 2003
Tests conducted in the past week to determine the impact force of loose insulation on the space shuttle's thermal protection system have produced no visual evidence of major damage.
The tests are intended to reveal whether insulation that came loose from shuttle Columbia's fuel tank could have punctured the spacecraft's left wing and triggered its fatal Feb. 1 breakup, a leading theory that emerged soon after the disaster.
The results of the first salvos -- aimed at thermal tiles like those found on the landing gear door of the Columbia -- still are under evaluation. They don't necessarily indicate what researchers will find when they begin foam impact tests on reinforced carbon-carbon panels like those found on the leading edge of Columbia's left wing, a source close to the Columbia Accident Investigation Board said Friday.
""We didn't predict high damage to the (underside and landing gear) tile,"" a source familiar with the San Antonio testing said Friday. ""I don't think the results so far are unexpected. I don't think we expected any significant damage.""
The investigative panel, which is sponsoring the impact testing as part of its inquiry into the causes of the shuttle tragedy, believes the breakup was precipitated by a breach in the leading edge of the left wing. But the 13-member board earlier this week said is it not ready to declare the foam blow as the cause of the damage that triggered a thermal and structural failure of the shuttle.
""Even if the foam testing does break the (carbon panels), that doesn't prove that that's what happened. It just proves that it could have happened,"" board Chairman Harold Gehman said Tuesday. ""If we do major damage to the leading edge, that still doesn't prove it. That just proves it's plausible.""
The board source said the impact tests had nothing to do with the panel's assessment.
Foam impact testing on the reinforced carbon-carbon panels at the San Antonio facility is expected to start in early June, though some effort is under way to move up the evaluations.
The tests -- being conducted at the Southwest Research Institute in San Antonio using a nitrogen gas-fueled cannon -- aim to reconstruct the conditions that Columbia was subject to when it lifted off on Jan. 16.
Within 82 seconds of the launch, a chunk of foam insulation from the forward region of the fuel tank peeled away and struck the underside of the shuttle's left wing.
Initially, NASA mission managers believed the impact -- then believed to have occurred on the underside of the wing near or against the left landing gear door -- did not represent a safety hazard, though a number of engineers questioned that assessment internally.
In the weeks after the accident, the Gehman panel suspected the fatal breakup was caused by a two-to-three pound chunk of foam insulation that struck the underside of the wing, possibly damaging a vulnerable landing gear door seal.
Through subsequent analysis of film and video of the liftoff recorded by ground-based cameras, experts determined the foam hit the underside of the wing at its leading edge.
The impact zone appears to have included some of the 22 U-shaped carbon-composite panels that lined the leading edge of Columbia's left wing, specifically panels five through nine -- a region near the fuselage. Data from a recovered flight recorder and telemetry radioed directly to Mission Control at Johnson Space Center before the breakup suggest the actual wing breach occurred in panels eight or nine, the board said earlier this week.
The incomplete results of the impact tests on the underside of the wing are not considered an indication of what will happen when foam samples are fired at leading edge carbon panels, an investigative source said Friday.
At 22 years, Columbia was the oldest of NASA's four shuttles, and investigators believe deterioration of the carbon panels or other wing components over the years may have weakened the materials enough to make them susceptible to damage from the kind of hit the shuttle took Jan. 16.
One of the issues investigators have uncovered is an internal oxidation, or corrosion, of the carbon panels caused by a zinc oxide paint primer used on the shuttle's launch pads at NASA's Kennedy Space Center in Florida.
The tests slated for San Antonio next month will include older carbon panels flown on other space shuttles.