STS-107/Columbia Ball Strut Tie Rod Assembly Issue Chronology
Over the past month NASA has been working to understand the cause of cracks found in a 2.25-inch diameter metal ball located inside the Ball Strut Tie Rod Assembly (BSTRA) of Space Shuttle Discovery’s 17-inch liquid oxygen line – and what the implications are for the rest of the Orbiter fleet. What follows is a chronology of public status reports and internal briefings that describe how this issue was examined and resolved.
“Mission managers met at the standard meeting held two days prior to launch to discuss the status of the countdown and any remaining technical issues. The Space Shuttle program reviewed the ongoing engineering analysis of a surface crack that was found on a 2.25-inch diameter metal ball associated with the Ball Strut Tie Rod Assembly (BSTRA) inside Discovery’s 17-inch liquid oxygen line. Managers feel confident with the outcome of the testing and analysis, but will meet again tomorrow for one final evaluation and decision point.”
“Meanwhile, engineers continue to analyze a crack found in a metal ball associated with the Ball Strut Tie Rod Assembly in Space Shuttle Discovery’s 43-centimeter (17-inch) liquid oxygen line. STS-107 managers met Sunday night and decided to begin the countdown. They are scheduled to receive a final STS-107 launch assessment on Tuesday.”
“Mission managers met last night to discuss the status of the ongoing engineering analysis of a surface crack that was found on a 2.25-inch diameter metal ball associated with the Ball Strut Tie Rod Assembly (BSTRA) inside Discovery’s 17-inch liquid oxygen line. No inspections were performed on Columbia. The results of the testing have given the Space Shuttle program enough confidence to begin the countdown, with the final launch rationale to be presented at the standard meeting held two days prior to launch.”
Internal NASA memo: “MP01/Alex McCool: The Shuttle Program is currently working one major safety
issue (cracked Orbiter ball strut) associated with the upcoming STS-107 Flight Readiness Review
this Thursday (1/9/03) and the subsequent launch on 1/16/03. MSFC employees put in long hours over the holiday break and worked in the spirit of One NASA with employees at other NASA Centers to test the Orbiter hardware and saw no potential issues as of this morning that would prohibit launch. The Shuttle Program team will reconvene this afternoon to assess the status of this issue.”
“No inspections are planned on Columbia related to the BSTRA ball crack evaluation.”
Download Powerpoint Briefing (240K)
ROOT CAUSE:
Root cause is under investigation. Most probable cause is attributed to the brittle properties of the BSTRA ball material combined with thermal cycling, possibly initiated by an undetected flaw in the ball.
RECOMMENDATION:
Constraint to STS-107 pending successful completion of:
- Crack arrests prior to the ball cracking in half.
- Cracking does not result in unacceptable step at crack location.
- No FOD generation beyond acceptable level (FOD criteria TBD).
100% surface inspection of cracked OV-103 ball.
- No evidence of particle liberation.
- No surprises (i.e. crack is consistent with most probable cause).
“Shuttle Processing Note: An engineering evaluation continues following the discovery late last year of a surface crack in a ball associated with a tie rod assembly inside of a 17-inch liquid oxygen line aboard Discovery. The crack was found during standard Orbiter Maintenance and Modification (OMM) inspections. The crack is located on a 2.25-inch diameter metal ball associated with the Ball Strut Tie Rod Assembly (BSTRA) inside Discovery’s 17-inch liquid oxygen line. Further inspections of similar assemblies in Discovery’s 17-inch and 12-inch lines have found no cracks. Inspections of Atlantis and Endeavour also have found no cracks. Tests using spare BSTRA ball assemblies are under way as part of the engineering evaluation and are not expected to be completed until later this week at the earliest. The ongoing evaluation has had no impact on shuttle launch preparations.”
Download Powerpoint Briefing (2.5MB)
ROOT CAUSE
- It is not known at this time, but is thought to be due to the brittle properties of the material combined with the thermal cycling, possibly initiated by a non-detectable or overlooked surface flaw on the ball.
RESOLUTION/FLIGHT RATIONALE
- No flight resolution or rationale at this time.
RECOMMENDATION:
- Constraint to the flight of STS-107.
“Shuttle Processing Note: During standard inspections that are performed on all shuttles as part of the Orbiter Maintenance and Modification (OMM) period, technicians found a crack earlier this week in a 2.25-inch diameter metal ball associated with a tie rod assembly inside Discovery’s 17-inch liquid oxygen line. The assembly, called the Ball Strut Tie Rod Assembly (BSTRA), is a type of flexible support located in the interior of the line downstream of the 17-inch disconnect. Several such assemblies are located in both the liquid oxygen and hydrogen lines of the orbiter. Further inspections of Discovery have revealed no additional cracks, although the inspections are continuing. An engineering analysis and evaluation of the situation is under way. ”
