Executive Summary, NASA Foam Loss Tiger Team Report, October 2005

"As a result of foam loss on STS-114, an ET Tiger Team was chartered by the Headquarters Mission Director for Space Operations (MDSO) and NASA's Chief Officer for Safety and Mission Assurance (COSMA), to review unexpected External Tank (ET) Thermal Protection System (TPS) foam loss."

"Foam losses of significance occurred in five areas of ET foam, including the Protuberance Air Load (PAL) ramp, the left bi-pod fitting closeout, several locations on the ice/frost ramps covering the repressurization line attachment brackets, two locations on the liquid hydrogen (LH2) tank-to-intertank flange, and two locations in the LH2 tank acreage. The largest piece, approximately one pound, was from the PAL ramp.

The ET Tiger Team reviewed foam performance to determine most likely root causes, to determine whether these were unique to STS-114/ET-121, and to make both near- and long-term recommendations to minimize likelihood of recurrence.

The ET Tiger Team addressed overarching environmental, processing, and materials issues that might have contributed to the foam loss. No off-nominal ascent flight environment effects were identified. However, Inflight Anomaly (IFA) Resolution Teams should ensure ascent environmental loading and associated stress on TPS foam is fully understood. A high correlation between areas of the tank with the highest levels of processing traffic (those adjacent to work platforms, mats, etc.) and the locations from which foam was lost on STS-114 and previous missions was observed.

The ET Tiger Team also noted that ET-121 was subjected to an unusual level of rework due to modifications incorporated for return to flight (RTF). With respect to materials, this was the first flight of BX-265 liquid oxygen (LO2) and LH2 PAL ramps; all tanks prior used BX-250 ramps.

The ET Tiger Team provided a number of recommendations for near-term and long-term actions to minimize the possibility of foam loss from future external tanks. These recommendations are predicated on the assumption that on-going efforts by the Space Shuttle Program's (SSP) IFA Resolution Teams to identify root cause, including ongoing test and analysis, will be taken to fruition.

Key near-term recommendations include:

  • Remove and replace the entire length of the LO2 and LH2 PAL ramps using improved application processes.
  • Implement modifications required to prevent cryopumping through bi-pod heater wiring.
  • Investigate the possibility of venting ice/frost ramp "fingers".
  • Improve hardware protection provisions to minimize the potential for collateral hardware damage during processing.

Key long-term recommendations include:

  • Elimination of the PAL ramp at the earliest possible opportunity coincident with rigorous aerodynamic test and analysis.
  • Develop hard covers for ice/frost ramps and implement in conjunction with PAL ramp elimination.
  • Eliminate tank traffic to the extent possible in the long-term and implement a no-touch processing policy.
  • Develop and certify nondestructive evaluation (NDE) techniques for all ET TPS applications."

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This page contains a single entry by Keith Cowing published on October 24, 2005 11:00 PM.

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