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“Not a concern for orbit or entry for a defect of this size.” “We run the conservative analysis that comes out with negative margin, then run mission specific with a pressure profile that shows no effect, low density cracking, high density cracking or window blows out at ~M=1.0 which still wouldn’t be an issue,” added JSC Engineer’s Steve Altemus. In response to Mr Cain asking about flight history with similar and greater strikes to the windows, the response was noted that similar size has not been an issue, though there was uncertainty in crew measurement, but that on previous missions they have not seen flaw growth for this size of frame. Can’t say if it will crack or not.”Ĭlarifying the impact is not risking safety, Mr Cain asked for confirmation that the hole would not be risking a LOV/C (Loss Of Vehicle/Crew) during re-entry, which one manager responded that it would have to be a hole through more than just the thermal plane of the window where “we might have to not come home,” which referenced calling LON (Launch On Need) rescue with Discovery. “The thermal pane can handle defects like this in peak heating, but the concern would be pressure down low,” responded Steve Stich from the Orbiter Project, “but not much you could do different for the pressure. “If you had a problem that you were concerned about what could you do? Different entry designs have different heat loads,” asked MMT chair Leroy Cain. Adding a day for the mission does not effect this window,” noted one manager at the MMT, according to MMT minutes on L2.
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Dynamic loading on the pane takes into account for the window frame thermal response. Pilot visibility should not be hindered by this location if it cracks.” “Based on analysis the window should have no issues for peak heating M=8.0, but could form cracks but remain intact during peak loading M=0.7. “MMOD Window 6 Impact – crew reported 0.5” diameter to the PLT right window to the thermal pane, 1/32” depth,” noted the Mission Evaluation Room (MER) “Funny” report. In another sign of how NASA extensivily works a problem, the Mission Management Team (MMT) immediately discussed the strike at their morning meeting. Impacts on the windows are more commonplace – or at least are observed shortly after they impact due to their visibility – with the latest strike spotted by the STS-126 crew, who sent photographs down to the ground for evaluation. More recently, a MMOD strike was found on Endeavour during the STS-118 mission, again missing a Freon-21 coolant loop. However, in a correction from the first publication of this article, the FCL1 orifice was blocked via an internal piece of debris, rather than MMOD. It was previously believed that a similar event occurred on STS-109 in Columbia’s Freon Coolant Loop (FCL1), which restricted the flow of Freon-21 in that loop. One such strike was later found to be a small slice of circuit board from an expended stage of another launch vehicle, which managed to punch a reasonably large hole through one of Atlantis’ radiators, thankfully missing a Freon-21 coolant plumbing in the panel, which would have caused an emergency to be called, and the immediate order to land. Several strikes on the orbiter’s windows have been observed throughout the shuttle program – the last on STS-123 – and at least two MMOD strikes have also been suffered on the radiator panels since Return To Flight.
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Mitigation of MMOD strikes – such as when docked to the International Space Station (ISS) – and the tracking of space debris, provides some protection for the orbiters, though small strikes are commonplace. MMOD is the third biggest threat to losing a vehicle during a mission – second only to launch and re-entry. Impacts from MMOD are a usual – if not undesirable – event during missions, with several recent flights suffering from impacts to the orbiter’s windows on the flight deck. Meanwhile, Shuttle manager John Shannon praised Kennedy Space Center (KSC) engineers for an “unbelievable” vehicle. The Mission Management Team (MMT) have initially cleared a Micrometeoroid Orbital Debris (MMOD) strike to Endeavour’s window 6 (Pilot’s window), with full re-entry rationale expected.