NASA managers are midway through their two day Flight Readiness Review (FRR), with all elements of flight rationale being evaluated for Atlantis’ launch. NASA is working towards announcing June 8 as the official launch date for STS-117.
The only issue that is gaining some level of discussion relates to the aluminum housing/inserts for flange bolts that hold the Low Pressure Oxidizer Turbo Pump (LPOTP) in place inside the main engines. However, this has received a waiver and flight rationale.
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At present, the main threats to the June 8 launch remain the weather, possible complications arises from the two EVAs being undertaken by Expedition 15 on the International Space Station (ISS), or a future problem ahead of lift-off.
All concerns with ET-124 were addressed ahead of rollout from the Vehicle Assembly Building (VAB) and no further issues have been noted since. The same can also be said about evaluations surrounding Atlantis’ Composite Overwrap Pressure Vessels (COPVs).
One issue that is being discussed at the FRR relates to the LPOTP. This gained attention at last week’s Program Control Requirements Board (PRCB) meeting, which ultimately approved a waiver, allowing STS-117 to proceed, with future waivers expected for the next two flights.
‘The aluminum housing of the Low Pressure Oxidizer Turbo Pump (LPOTP) utilizes silver plated A-286 inserts for the flange-bolt female threads,’ noted NASA information. ‘One of the O5 joint inserts on LPOTP 4606 pulled out during joint installation stretch (preload) operations at SSC (Stennis Space Center).
‘Since this was the third occurrence of insert pullout in five years (and the eighth overall), folks began thinking this was more than just a random failure type happening. There has been however, no evidence of joint leakage in program history.’
The cause is believed to be related to corrosion, and the observed issue poses no issue to flight safety. However, evaluations proceeded to work on the instance of two adjacent blots show the same problem.
‘Analysis shows that one bolt out poses no problems and 1.2 Factor of Safety is maintained even with 10 of 14 uniformly spaced bolts remaining. What is not known is the capability remaining if two or more adjacent bolts lose preload.
‘In the problem history, most ‘seem’ to be associated with age life of >16 yrs, although there have also been occurrences at 5-10 yrs. Corrosion was noted on only one of the problem inserts, and that was on a 28-yr LPOTP housing.’
Most importantly, the PRCB meeting emphasized that Atlantis doesn’t even have one of the raised inserts. Endeavour was also checked, and found to have no raised inserts either.
‘On OV-104 (STS-117) visual inspections have confirmed no raised inserts, and the preload has been reconfirmed on all. The LPOTP housings are also ‘low time’ relative to fleet experience. Also, haz gas monitoring is in place in the aft compartment during launch count.
‘Based on the Acceptance Rationale, the PRCB accepted the waiver for STS-117 only and will entertain a waiver for STS-118 and STS-120 when those inserts have been inspected and preload verified. Oversized inserts have been ordered and will replace the standard insert as they become available.’
Given the above, the FRR wouldn’t normally have this subject discussed further. However, due to a dissenting opinion from a MSFC (Marshall Space Flight Center) manager – which is very much encouraged in the new openness of NASA evaluations – NASA managers have decided to give his opinion an airing.
‘A dissenting opinion was presented by MSFC/(name removed),’ added PRCB information, which summarized his opinion, which appears to be based on the ‘possibility’ of corrosion being present.
‘Since the capability and margin are unknown for two or more adjacent bolts losing preload, the consequence of occurrence is catastrophic, and we know how to fix the problem (oversized inserts, use corrosion inhibiting primer), the Program should not risk a catastrophe when the ‘fix’ is merely a fairly short schedule delay.’
If NASA decided to remove the waiver and take the above action – which is deemed very unlikely due to the lack of evidence of raised inserts – repairs would push STS-117 into August at the earliest.
‘The PRCB accepted the flight rationale and waiver, but will further discuss at FRR and Mr. (removed) was invited to present his concerns there also,’ noted NASA information.
The latest news from sources claims that NASA will proceed with the waiver and STS-117 remains on target for an opening launch attempt on June 8.
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