NASA Decides No Fix Needed for Endeavor's Tiles

bhmit1 writes "It looks like NASA is reporting that no repairs are needed for Endeavor. 'After meeting for five hours, mission managers opted Thursday night against any risky spacewalk repairs, after receiving the results of one final thermal test. The massive amount of data indicated Endeavor would suffer no serious structural damage during next week's re-entry. Their worry was not that Endeavor might be destroyed and its seven astronauts killed in a replay of the Columbia disaster — the gouge is too small to be catastrophic. They were concerned that the heat of re-entry could weaken the shuttle's aluminum frame at the damaged spot and result in lengthy post-flight repairs.'"

If it aint [all that] broke, don't fix it.

[reality-bytes]

They can't actually replace entire tiles on orbit. They have a 'patching' system which allows them to spread a compound into any nicks in the tiles.

Now, the compound has to be applied by an astronaut attached to a long extension arm attached to the Shuttle's robotic arm. When they tested this a few flights ago, it became readily apparent that it was at best difficult to work this way. The length of the arm caused significant 'bouncing' with every motion. At the time they only pulled a gap filler and simulated the motion of filling a tile and it wasn't easy.

The real danger is that the control issues of having a 'massive' astronaut + EVA gear swinging around on the end of that very long arm so close to the TPS could actually cause more damage to the tiles than it fixed.

Furthermore, the compound could actually cause even worse localised heating issues on re-entry depending on how well it fills the tile ie: It could cause ducting etc.

Re:To err on the side of caution...

[east coast]

but we know that spacewalks occur all the time routinely.

What's risky about this isn't the space walk itself but the concept of damaging more tiles. It's a delicate operation and one slip can make things go from bad to worse easily.

Perhaps there is a financial motivation for not carrying out the repair?

What financial motivation? The material already exist onboard. There is no investment and the amounts by which NASA would be set back in the case of a mid-air breakup or even a safe landing with an unusable shuttle far outweighs using the patch method. If you're going to say something like this I'd think that you'd need to back it up with some logic (even if it's faulty) or fall suspect to producing FUD. Not to be a dick but I find it to be a dismissive remark that borders on trollish.

What I'd like to see is an actual breakdown of the possible positive and negative consequences of each course of action and the probabilities that NASA has assigned to the outcomes. I'm really hoping that they've put some serious statistical analysis into this decision and aren't just flying by the seat of their pants.

Again, not to be a dick but I'd like to give the guys at NASA some credit here and pretty much chalk this up to random speculation of a problem that has been reviewed by NASA's best engineers for hundreds, if not thousands, of man hours. A PDF with some stats is not going to convey the experience of the teams in question. I know we joke that NASA has certain problems that are rather embarrassing but I'd like to think they went the extra mile on this one.

Certainly, the article quotes a Nobel Prize-winning physicist, Douglas Osheroff, as saying that the repairs "can only increase their chances of making it down."

Let's requote that: the [successful] repairs "can only increase their chances of making it down."

Again, I think it's a matter of potentially doing more harm then good. I think if NASA had a guarantee from the mouth of God that this repair would not cause more damage they'd go for it in a second. They'd be fools not to. This isn't a question of if the repairs will help but a question of pros and cons.

I'm not going to say that everything is going to work out but I certainly hope they do. If I were up there I'd be more willing to trust the ground engineers at this point. Not to say that Dr. Osheroff doesn't know what he's talking about, he's well versed on the subject but I don't know how much he really knows about this incident and what his take is on the chances of making the situation worse with a potentially botched repair job.

Re:I'm glad I don't have to make these calls

[vought]

IMHO if something happens during a space walk, You still can bring the astronaut back on board, and still can try an unrepaired re-entry. But even if the repairing astronaut dies (which is very unlikely), the others are still alive.

And what if the astronaut perched at the end of a 100-foot boom crashes into the tiles he's repairing, damaging them more extensively, or even beyond repair? After all, the arm is very heavy and the EVA suit is 300 pounds, along with the 200lb astronaut inside of it. That's a lot of mass to be swinging around next to all the other, undamaged tiles.

Or what if the 'goop', applied unevenly, causes a hot spot on another tile? Right now, the damaged tiles are located over a wing spar - the thickest structural part of the wing, and a section that can take more heating. Since the depth of the gouge indicates that the plasma flow over it will 'eddy' over the deepest area, keeping it from the greatest heat of reentry, models indicate that the aluminum structure of the shuttle won't fail, and that temperatures won't exceed 350f.

The problem with speculating on NASA decisions, as so many coffee urn quarterbacks are doing this morning, is that they really have no idea how complex the shuttle and its mission really are. The items I've outlined here, available in almost no major news stories about the decision, were easily obtained at NASA Tv and Aviation week - and they're a small sample of the factors in this decision.

Re:Hey, NASA, here's an idea...

[Billosaur]

But that's the difference between an aircraft and a spacecraft -- an aircraft pilot can look his plane over, read up on the maintenance, talk to his ground crew and then decide to fly or not. In NASA, it works differently. A Space Shuttle commander has command of the spacecraft, but Mission Control in Houston has command of the mission. You have to remember: the crew of the Shuttle can't just go bombing around in Earth orbit like they are flying the Millennium Falcon. Every move has to be choreographed and planned out months and even years in advance. When unexpected problems crop up, the technicians on the ground certainly know more about the workings of the machine than the crew, as they have all the data at the fingertips, they are experts in their systems, and they can draw on contractor resources to get more information. Decisions like this cannot be left to the spacecraft commander; his/her job is hard enough without having to keep in their head the compendious amount of information regarding their spacecraft.

It has been this way since Mercury; it was Chris Kraft who outlined the need for the ground to have the skills required to manage the mission and deal with problems in real time, so that the crew could concentrate on their activities in space. The system has worked extremely well over all these years, with the exception of the Columbia accident. I for one am confident that NASA knows what it is doing and will take all the precautions it can before Endeavour is allowed to land.

A bit of Tile prediction History: all bad

[Ancient_Hacker]

Ahem, I have some doubts about NASA's ability to predict tile-related events, based on their past record:

• The first calculations about the aerodynamic loads on the tiles were waay off.
• So far off, many tiles fell off when the Shuttle was carried on back of the 747!
• The calcs about the damage to tiles from loose foam were also way off.
• So I'd be rather dubious about any heat-transfer calculations from those same folks.
• We will see.

Re:A bit of Tile prediction History: all bad

[Eponymous Bastard]

Which is why they are not relying on calculations. They actually grabbed some tiles, gouged them in the exact same form from the measurements taken in orbit and then put them in a hot wind tunnel (The Arcjet facility) to check what will actually happen
see here [nasaspaceflight.com]
And:
here (with pictures). [nasaspaceflight.com]

The tests at Arc Jet used a set of tiles, with identical damage drilled on to a test article. This was then put through the heat of a simulated re-entry, to test how the damaged area performed, along with the gathering of thermal data.

'The Arc Jet test using the damaged test article was completed, initial assessment did not identify structural burn through,' noted one encouraging memo, with data showing that the heating remained 50 degrees below the baseline requirement for the underlying structure.

And those articles are from the preliminary results. They were supposed to do an additional test with the repaired tile.

Re:To err on the side of caution...

[Volante3192]

The HRSI tiles are made of a low-density, high-purity silica 99.8-percent amorphous fiber (fibers derived from common sand, 1 to 2 mils thick) insulation that is made rigid by ceramic bonding. Because 90 percent of the tile is void and the remaining 10 percent is material, the tile weighs approximately 9 pounds per cubic foot.

http://science.ksc.nasa.gov/shuttle/technology/sts -newsref/sts_sys.html [nasa.gov]

My structural physics knowledge is a bit lacking, but something made of 10% rigid fibre 1-2mm thick and 90% void doesn't sound like the sturdiest structure to be applying force to.

I'm trying to think of a similar, down to earth item that mimics that structure...but best I can come up with would be like packing peanuts. Close, but it's not rigid enough.