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.'"

Comments

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: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.