"J. Random American" has a bit of fascinating deja vu from Aviation Week about Shuttle tile repair, and some good questions to which I don't know the answers off the top of my head:

The similarity of the rest of the system to the original tps repair kit makes me curious about the circumstances under which the original tps repair system development was abandoned. Do we have some new 21st century technology that is essential to making it work which just wasn’t available then? Or did early luck with re-entering the shuttle on damaged tiles convince NASA that tps inspection and repair was unnecessary, until the Columbia accident forced them to reconsider that decision? Were they right then to not risk in-orbit repairs, and now they are developing it anyway just to look like they are Doing Something?

His blogsite requires me to register in order to comment, and I'm pretty sick of filling out internet registrations. So I'll comment here instead.

During the CAIB investigation, I worked on a section for the final report that was going to address "roads not taken" in the shuttle program. This was to answer some persistent questions (in the press) about why certain choices were made in the program, primarily policy, budget and technological--such as the decision to use external foam on an ET versus a reusable first stage. Ultimately, I didn't get much traction on this and did not have enough time, so it never made it into the drafts of the report.

One of the issues that I started to look at was the early effort to develop tile inspection and repair. In particular, I wanted to find out how much money had been spent on the TPS repair program in the 1980s before it was abandoned, and why it was abandoned. I discussed this at length with Sally Ride (a CAIB Board member) who suggested that I discuss it with STS-1 pilot Robert Crippen. Ride explained that it was the STS-1 crew that ultimately put the brakes on the tile repair effort. As she remembered, there were several reasons for this. One of these reasons was that they thought it was totally unreasonable to expect a two-man crew to conduct an EVA, particularly underneath the vehicle. This would have been using the untested MMU as well. I believe that another reason was that they already had too much to do for their test flight and did not want more things added to their training schedule.

So TPS repair got dropped early, with STS-1, and apparently was considered impractical for those early two-man test flights.

I did ask why it was never picked up again after the shuttle was declared "operational," but I cannot remember Ride's answer. I think she may have said that the astronauts thought tile repair was impractical. Plus, by that time they had an idea of the fragility of the TPS system and believed that damage (some damage, anyway) was survivable. Another issue that I wanted to look into was why on-orbit TPS inspection was abandoned, but that issue was highly classified (because of the systems used to image spacecraft in orbit) and there was no way to look into that subject and get it into our report. (We did have someone with the requisite clearances who was briefed about earlier inspection efforts, but he could only use that information in framing his part of the report, and could not actually write about it in the report.)

I think that getting a good answer as to why NASA abandoned TPS repair (and inspection) in the 1980s would require a lot of research--digging through old NASA files and interviewing astronauts and program officials. There is probably no easy answer.

Thanks for the information, Dr Day.

Also, due to your complaint I am changing the comments stetting to permit comments without registration.

Dwayne - the person to ask is Bonnie Dunbar. She was a TPS engineer before becoming an astronaut. NASA developed a repair material and some of the tools. One major problem was that the repair material had a very short working time after it was mixed if not kept heated - it was an epoxy of sorts. The applicator tools were power hungry, bulky, and there was concern about stabilizing the crew doing the repair without damaging the tiles further. The whole problem ballooned into needing more and more equipment.

The new repair goo has better characteristics and EVA is simpler since the station arm can get the crew to the underside of the shuttle.