No gaps in NASA’s inspection ability

by Chris Bergin

NASA have managed to clear Shuttle Atlantis’ Thermal Protection System (TPS) in just 60 hours – half the time Shuttle manager John Shannon had budgeted for.

The crew of Atlantis were given the news that they have a clear bird during Tuesday’s EVA-1, although analysis did find some interesting conclusions to some previous concerns.

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‘Yesterday there was a question on focused inspection, when we have to add a day to the flight plan between EVA-1 and EVA-2, but we do not need to have that day,’ noted Shannon.

‘We were able to clear the leading edge and nose cap, plus all the tile areas, and the engineering/orbiter team found no issues to want to go back and take a second look at any areas.

‘However, we did have two questions for the team. One was on the gap filler on the Port ET door, and the other was on a blanket, where a small piece of it was puffed out on the right OMS pod. The team didn’t need additional data, but they went off to work those two problems – and I’m happy to say they are both resolved.

Originally tagged as ‘critical’ – the Gap Filler, protruding out of the Port ET umbilical door isn’t actually a Gap Filler at all, instead it’s a Shim Stop, a piece of plastic used to protect tiles, when new ones are being installed inside the OPFs (Orbiter Processing Facility).

‘For the Gap Filler work, the team went down two parallel paths,’ Shannon added. ‘The first was to look at all the installation records, the other was to do the thermal analysis required to clear it. It was a kind of curious thing to look at the installation records, as there were no Gap Fillers in that location, as well as on the baseline imagery.

‘From that, they took a closer look at the colour of the Gap Filler, noticed it was a strange colour – and looked like it was a little bit melted – and they then came to the conclusion that this was not a Gap Filler, it’s what’s called a Shim Stop.

The Shim Stop should have been removed before Atlantis launched last weekend, but given its position on the ET Door, it would have been likely impossible to spot after she had been mated with the External Tank.

‘It is just a piece of high visibility plastic, which are installed when we put a new tile, to ensure you have the right clearance – that you’re not pushing against other tiles up against one another, which are not glued in – they are just placed in there by orbiter technicians.

‘That is what we’re seeing on the ET door.’

The concern was dropped after it was confirmed the Shim Stop will simply burn away before re-entry. However, after due diligence, it was evaluated that even if this had been a Gap Filler, it would not have required removing by a special EVA, as seen on STS-114.

‘This is not an issue at all. It’s sticking out just a little bit. Since it is plastic, it will melt really easily, after tests were run, which show it will soften at 250 degrees Fahrenheit and melt at 450 degrees Fahrenheit,’ said Shannon. ‘It will see that melting environment about seven minutes before we hit mach 25 – before we hit entry interface, by which time it will be long gone, so we’re not worried about it.

‘We took the thermal analysis to conclusion anyway – and good news to report on that side as well, because even if this was a Gap Filler we would have been able to come in.’

‘It was just a miss by the team. We had a Shim Stop fall out in-between the Main Engines on STS-121 (with Discovery), so we sent the team to ensure we had pulled them all out of Atlantis, but the ET doors were already up and latched and we did not drop those doors to take a look for Shim Stops – so we learnt something there, and when we fly Endeavour, we will check that.’

Rounding up what is another clean ascent, post-Columbia, Shannon noted the other area of interest, a puffing of a thermal blanket on the right OMS (Orbital Manoeuvring System) pod. Although no new MMT (Management Mission Team) updates have been posted on the previous notes of concern relating to the two engines, showing what appears to be stains from hydraulic fluid – they both appear to be working without any problems.

‘The other piece was the blanket on the right OMS pod, and we zoomed in on pictures taken from the International Space Station (ISS) – and it’s no issue at all.’

‘We were able to clear the whole of the Thermal Protection System (TPS) in 60 hours. My best estimate was five days – which is 120 hours – so we did it in half the time,’ Shannon said in praise of the team responsible.

‘That just shows how better the processes are at being able to support the program.’

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