CAPE CANAVERAL - An internal NASA review has found major flaws in the way the agency analyzes possible damage from debris strikes during space shuttle flights.
A March 26 report obtained by the Orlando Sentinel identified six disturbing trends that indicate damage assessments from three shuttle missions in 2000 and 2001 were based on uncertainty and false assumptions. Similar criticisms about a Jan. 23 study of debris damage during shuttle Columbia's launch have surfaced since the orbiter's breakup above central Texas during re-entry Feb. 1.
"The goal is to find out what went wrong," a Johnson Space Center engineer said of the new report, "so we never have to go through this again."
The Columbia assessment - put together in less than a week by 37 engineers from the National Aeronautics and Space Administration and four shuttle contractors - was prompted by launch video showing a large piece of foam insulation breaking off the shuttle's external tank 82 seconds after liftoff and striking near the leading edge of the orbiter's left wing.
Engineers performing the analysis were unable to accurately pinpoint where the impact occurred. As a result, the assessment focused on possible damage to insulating thermal tiles on Columbia's belly and gave far less attention to the leading edge of the left wing, the area where investigators believe a breach in the shuttle's protective heat armor likely occurred.
Holes in the Columbia analysis prompted the ongoing review of the assessment process by NASA and shuttle contractors. Three missions before Columbia's final flight have been looked at.
During a May 2000 launch of shuttle Atlantis, launch video showed a streak - possibly debris - leaving the right wing's lower surface or rudder. Seven months later, tracking cameras detected a streak originating from the middle of Endeavour's tail during a December 2000 liftoff. Also, film of Atlantis' February 2001 flight indicated debris struck tiles near the middle of the orbiter's fuselage and on the leading edge of the tail.
None of those cases proved dangerous. But a review of how the damage assessments were conducted and presented found several troubling similarities:
Estimates of the debris' size and shape from analyses of launch films were "consistently insufficient" to accurately determine where the orbiter was hit, the review concluded. That uncertainty also added to the unreliability of a computer program called Crater, used to calculate the extent of damage to the shuttles' heat-resistant tiles. The report noted that unspecified changes in November 2001 improved the quality of the film reports.
In Columbia's case, the lack of good images of the impact led engineers to conclude that the foam debris mainly hit tile on the orbiter's belly and not on the wing's leading edge.
The assessments routinely assumed debris damage would not pierce completely through the insulating tiles and expose the shuttle's vulnerable aluminum frame to super-hot gases during re-entry.
A similar assumption was made during Columbia's flight, although the Crater program predicted one debris strike might have penetrated more than four inches deep through the tile and into the underlying aluminum.
Little effort was made to view possible shuttle damage in orbit. On flights to the international space station, the station's crew seldom was asked to survey the shuttle for damage during docking or departure. Requests for photos by spy satellites or ground-based telescopes were rare. NASA managers turned down similar proposals for pictures of possible damage to Columbia in orbit.
"Worst case potential effects and uncertainty associated with damage assessment results" were not clearly spelled out during briefings to senior engineers. Those engineers used the briefings as the basis for short oral presentations to the shuttle's Mission Management Team. The management team then determined what, if any, action to take during the mission without fully understanding the issues.
The findings of the studies that the debris events had "no safety of flight impact" generally went too far and were "not sufficiently substantiated by facts or analysis," the review concluded.
Debris strikes consistently were not flagged as so-called in-flight anomalies (IFAs) by top-level engineers or the shuttle's Program Requirements Control Board.
IFAs are defined as any event between fueling the shuttle's external tank for launch and the end of the mission that affects critical systems or significantly impacts the flight. The IFA designation is important because it triggers a formal process for resolving such problems.
The Program Requirements Control Board has the responsibility for determining whether an issue is a barrier to future launches. NASA rules specify any IFAs that impact safety, affect the successful completion of a mission or present a flight hazard must be reviewed by the board. Nevertheless, some debris strikes meeting those requirements were "consistently not flagged" by the board.
The review of past damage assessments is likely to continue through mid-April. A final report is expected by month's end.
Michael Cabbage is space editor for the Orlando Sentinel, a Tribune Publishing newspaper.