The Marshall Space Flight Center Safety Engineering Review Panel (MSERP) noted in their findings that they did not concur with information supplied by the builders of the tank, Lockheed Martin, on the risk of associated with the partially modified ice/frost ramps (IFR) – and pushed for the risk to be classed “probable/catastrophic.”
Noting they expect to see four IFR events during STS-121’s ascent next month, the “unacceptable” status of the ramps was backed by other areas of NASA Engineering and NASA Safety, leading to the call to proceed with the launch being handed to NASA administrator Mike Griffin.
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Foam loss from the ramps on ascent has already been acknowledged by NASA managers, although the evaluations from around the agency show wide-ranging opinions and dissent on just how much of a problem the partly modified ice/frost ramps will be for Discovery during her ride uphill.
Lockheed Martin – who are interlinked into the Michoud Assembly Facility (MAF) where the External Tanks are fabricated – saw their findings readdressed by MSFC in what appears to be a key to the decision to move the risk of foam liberation from the ice/frost ramps to ‘probable/catastrophic.’
‘This failure mechanism for the IFRs was found during a post STS-114 investigation on ET-120 and has not been fully understood, controlled, mitigated or bounded since the finding,’ noted the MSERP findings. ‘Lockheed Martin flight history data analysis (Super Light Weight Tanks (SLWT) only, 11 flights) has shown 12 IFR foam losses believed to be due to delamination and one of those losses meets the ‘maximum expected’ debris limit of .08 lbm.
‘This debris limit is not related to the safety of the Space Shuttle Vehicle (SSV) but is a ‘process yield’ number only. The safety requirement is believed to be more than an order of magnitude smaller than .08 lbm. (on the order of .004 lbm), but has not been fully defined and allocated down to the ET. This discrepancy is (fully documented in other presentations).
‘MSFC Engineering has performed a similar assessment and has identified a potential loss of up to .2276 lbm (3 sigma) and more variability in the flight history data. MSFC Engineering has considered other tanks (not just SLWTs) in their analysis and has not concurred with the Lockheed Martin findings/approach. This is on-going analysis by Lockheed Martin and MSFC Engineering.
‘Due to inadequate process controls for this use-as-is foam and the variability in the data, flight history data may not provide the bounding data to predict the losses for the next flight. MSFC Engineering predicts 4 foam loss events on IFRs for STS-121 (3 are due to a void with a pressure differential and 1 is due to a cryogenic event) based on: Flight history analysis and expert assessment
‘The integrated SSV (Space Shuttle Vehicle) risk assessment associated with loss of IFR foam has shown the risk to be ‘red’, probable/catastrophic.’
This decision from MSERP was not the only dissenting opinion to come forward at the Flight Readiness Review (FRR) last weekend, with NASA’s Chief Safety and Mission Assurance Officer Bryan O’Connor and Chief Engineer Chris Scolese concuring against the launch, along with JSC, KSC, and MSFC (combined) Propulsion Systems Engineering and Integration (PSE&I), who noted: ‘Catastrophic outcome could easily happen in the life of the program.
‘The risk should be classified as probable and is considered by PSE&I to be unacceptable,’ on their LH2 IFR Risk Assessment position.
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MSERP’s recommendations referred back to their problems previously noted when they recommended against the decision to fly ‘as-is’ with the ice/frost ramps partially modified. MSFC wanted to the ramps to be much smaller than they currently are on ET-119 and ET-118, to bring down the risk of foam liberation during ascent.
‘(Risk) should indicate ‘red’, probable/catastrophic, for Hazard Cause 15: TPS Design Limitation and Cause 9: Manual Poured Foam Application Process Deficiencies until a fully verified/certified redesigned IFR is implemented that reduces the likelihood of this failure mechanism occurring.
‘A waiver is required to fly STS-121 (and STS-300, LON) with an ‘open’ Hazard Report and a ‘red’ risk.
‘Prior to the next flight, the approach to documenting risk to the SSV associated with debris loss should be readdressed. (Risk) is written against ‘maximum expected’ debris allowables which do not relate to the overall safety of the SSV. Maximum expected debris allowables are derived from the process capability, not the safety associated with the debris. It is possible that the ET can meet all requirements within and still cause a catastrophic SSV loss.
‘If (Risk) only addresses the risk to the ET from ET foam loss, the risk associated with ET TPS loss will be misleadingly low and meaningless. Further investigation is needed to more clearly document the overall risk.’
Regardless of these findings, all sections of the Agency understand there is no risk to the crew of Discovery during ascent from foam loss, given that cannot cause a LOV (Loss of Vehicle) during the climb to orbit. The risk is only associated with re-entry, which would not occur if Discovery suffers a serious foam hit on ascent. The crew has the option of the safe haven on the International Space Station (ISS), before being rescued by Atlantis on STS-300.
This is where NASA administrator Mike Griffin responsibilities are key, given the disagreement between sections of NASA Engineering (against), NASA Safety (against) and NASA Management (in favour) in proceeding to launch. Thus the decision to proceed is handed to Griffin in the case of dissent.
‘Some of the senior NASA individuals responsible for particular technical areas, particular disciplines, expressed that they would rather stand down until we had fixed the ice/frost ramp the way that — something better,’ noted Griffin at the post-FRR press conference. ‘Whereas, many others said no, we should go ahead. So we did not have unanimity. Therefore, a decision had to be made.
‘Debris shed from the tank does not pose an ascent risk for the Shuttle. It poses a risk for entry, but since we have inspection methods, we are beginning to converge on some rudimentary repair methods which may be useful. Since we have Station for a safe haven, since we have the possibility of — in fact, we evaluated quite carefully.
‘We have an excellent capability for Launch on Need, and we have the Russian partners. So we have a number of mitigation strategies should the unlikely occur and we have a debris strike.’
‘I think that goes without saying, but I cannot possibly accept every recommendation which I am given by every member of my staff, especially since they don’t all agree.’