Tile damage less of a concern ahead of Focused Inspection

by Chris Bergin

Deputy Shuttle manager John Shannon and the Mission Management Team (MMT) have gained more data – mostly encouraging – in regards to the tile damage on Endeavour’s Thermal Protection System (TPS), which has lowered the chances it will require on orbit repair.

Shannon – speaking ahead of Flight Day 5’s Focused Inspection on the tile – noted that the damage was caused by a piece of foam that liberated from a bracket on the 17 inch LOX feedline which runs down the side of the External Tank (ET), 58 seconds after launch, rather than a “denser” chunk of ice.

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Endeavour’s STS-118 mission has been proceeding without any other issues, confirmed by a very short ‘funny’ list, which notes even the smallest problem with the complex vehicle.

Flight Day 4 marked another successful day for the STS-118 crew, after Rick Mastracchio and Dave Williams completed the installation of the S5 space truss onto the S4 truss, along with conducting the S5 PVRGF relocation, added to S5 preps and get ahead tasks for P6 forward radiator retract.

**UPDATED: Ride home through the fire, sparks and plasma of re-entry with Atlantis, Discovery and Endeavour. FOUR Stunning high quality 2hr, 355-400mb Camcorder and HUD videos – from payload bay closure to post landing – several more videos showing landing from 90,000 ft also available**

The EVA was the first of what is expected to be four spacewalks, due to the SSPTS (Station-to-Shuttle Power Transfer System) continuing to operate nominally, allowing for the planned mission duration to be extended.

The extension to two weeks will be discussed – possibly as soon as Sunday – by the MMT, before confirming their confidence in the new modification which is debuting with Endeavour on this mission.

The MMT spent the bulk of their meeting discussing the latest data on the debris strike which caused damage, mainly to one tile, on the underside of Endeavour’s TPS. Newly gained SRB (Solid Rocket Booster) video gave managers a new insight into exactly what hit the orbiter during the ride uphill, along with the causes.

‘We’ve received the video from the SRBs, and we have significantly more data, specifically on the cause, the location of the damage and previous flight history,’ Shannon noted.

Previously thought to be ice from the ET, it now appears that a piece of foam was pushed loose by ice, which had formed in the gap between the bracket and the foam on the feedline – designed to allow the feedline to flex and vibrate during tanking and ascent.

Unluckily, the liberated foam managed to bounce off the ET strut at the bottom of the tank, which caused it to ricochet on to Endeavour’s TPS.

‘Along this feedline, there are several brackets that hold it in place, and on one of those brackets a piece of foam came off, came down and shot straight up on to the orbiter,’ added Shannon. ‘It was a bad bounce off that ET strut.

‘So we feel like we have the culprit and that is what we were hoping for when we left Friday’s MMT.’

Flight history shows that similar liberations have been noted on previous flights, with a large piece of foam from the bracket coming loose during STS-115 as one example. However, that piece of foam did not hit the strut, thus missing the orbiter.

The location of the damaged tile is under a ‘stringer’ in the shell of the orbiter’s wing structure, which Shannon noted was ‘lucky,’ because there is more structure in that specific area of Endeavour’s shell.

‘If we did have any elevated temperatures (during re-entry) then this location is extremely good, as it provide much better heat sink,’ referencing how heat would not concentrate in that direct area of the orbiter’s structure, but would spread out over a wider space, lessening the focal point of the increased temperatures.

Following Flight Day 5’s Focused Inspection – which will use the OBSS (Orbiter Boom Sensor System) suite of sensors and lasers to create a 3D model of the damaged tile – managers will be able to utilize flight history to a greater extent.

STS-26 – Discovery’s Return To Flight mission in 1988 – received tile damage in a very similar location as seen on Endeavour, which ultimately will aid NASA’s evaluation of whether to repair the tile, along with their arsenal of updated thermal models.

Ultimately, the decision that will follow the Focused Inspection will be risk trade-off, with managers evaluating if a repair is needed, if a repair could end up adding to the risk, or if to utilise EVA time to send a spacewalker out on the end of the OBSS to use one of three tile repair methods.

The chances of a repair being called appear to be getting smaller, given Shannon’s comment that – if there was an emergency scenario on orbit – evaluations have shown that they would have confidence in bringing Endeavour home, without the need to repair the tile. Models showed that this would be the case, even if the damage is found to be to the depth of the entire tile.

The Focused Inspection is set to last between two and three hours.

L2 members: Vast amounts of unreleased NASA documentation for STS-118 available to download in the L2 STS-118 Special Section, updated live.


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