Cost, reliability factored in decision to tile shuttle / STS-107

Sac Bee ^ | 2/4/03 | Matthew Fordahl - AP

[NormsRevenge]

SAN JOSE, Calif.(AP) - As the space shuttle program took shape in the late 1960s, engineers had to find technology that could withstand the heat of re-entry without being too heavy, unreliable or costly.

They settled on the small silica tiles that brought shuttles home safely more than 100 times, but have fallen under suspicion in Saturday's loss of Columbia as it descended over Texas.

[NormsRevenge]

I met Bob at Lockheed and toured the facility he worked at. He was a good man and is missed by all who knew him.

[Wright is right!]

I would strongly recommend that the shuttle crews be equipped to inspect and repair/replace tiles in orbit. There are a few challenges to be met, all surmountable.

First, at least 2 crew on every mission should be trained to do EVAs for inspection, and this should immediately be the first order of bidness upon achieving orbit on every flight. These would be tethered EVAs.

The flight should carry several sheets of tile material and a CD ROM of the .pdf files with the exact specs for cutting a replacement tile - ANY tile - and a bonding agent that will cure in a vacuum, such as epoxy. This kit would be lightweight, fairly compact, and be capable of replacing a couple dozen key tiles.

And a simple tether system could easily be devised from stuff available at Home Depot, and employed by two people in an EVA. That would allow the crew to be able to work on the exterior.

Michael

[John Jamieson]

While tile damage may have contributed to the problem, the big issue and the root cause of the Columbia disaster may well turn out to be the fact that it was overweight.

Columbia is the heaviest of the orbiters, and it was carrying what I think was the heaviest payload ever returned from orbit: the about 30,000 pound Double Spacehab.
Total reentry weight could have been as much as 250,000 pounds vs. the normal 200,000 to 220,000 pounds. More weight means more heat to stop.

I have not been able to download the STS107 presskit to get the exact landing weight. Does anyone have a copy?

[spudsmaki]

There's a problem with epoxy. It loses all strength and turns to much at 160 F. I built a cedar canoe, can't let it get too hot in the sun.

There really isn't anything that will self cure in space. Heck, even a lot of the panels are pyrolyzed in the manufacturing process.

Pyrolyzing is heating to a high temp in the absence of oxygen to flash off the burnable stuff. A tricky process.

[John Jamieson]

You obviously have NOT studied the process of making and replacing tiles. You also have a very poor knowledge of the problems of working in space. Do some research, then talk.

The experts are NOT idiots.

[ContemptofCourt]

I posted an interesting article here http://www.freerepublic.com/focus/news/835018/posts about tile damage in 1988 on the Atlantis....it appears that it takes significant tile damage to cause a problem....

[Steven W.]

ARMCHAIR PHYSICIST ALERT!

[dennisw]

So true! Even less than optimum tiles would have helped. The key is an adhesive that will keep them stuck onto the aluminum frame.

[Howlin]

I tried to download it for you last night and couldn't get it either. It seems all the pdf pages are GONE.

[ContemptofCourt]

http://www.shuttlepresskit.com/STS-107/STS-107_SPK.pdf

I just accessed it and it is all there.

[Stefan Stackhouse]

Rather than replacing the tiles (and it appears that the adhesive might be an insurmountable problem), it might make more sense to look at some sort of silicon foam that could be applied into the void. It would not be a permanent repair of course, and probably would not last through the entire re-entry. But it might provide just enough of an extra margin of thermal protection through the worst of the re-entry to bring the shuttle through, and that would be the only necessary goal of an in-orbit repair.

[Wright is right!]

"So true! Even less than optimum tiles would have helped. The key is an adhesive that will keep them stuck onto the aluminum frame."

What you need is a sort of Space Bond-O. It needs to be able to cure in a vacuum, so you need a material and a catalyst, such as epoxy and hardener. Even if some of the replaced tiles came off during reentry, if they even lasted for PART of the trip down, that's better than no tile at all.

Michael

[Jael]

It's not really a tile problem, it changing the formula for the insulation to remove the Freon.

"NASA knew from the second day of Columbia's 16-day research mission that a piece of the insulating foam on the external fuel tank had peeled off just after liftoff and struck the left wing, possibly ripping off some of the tiles that keep the ship from burning up when it re-enters Earth's atmosphere." http://www.washtimes.com/national/20030203-87326768.htm

http://ltp.arc.nasa.gov/space/team/journals/katnik/sts87-12-23.html
"Damage numbering up to forty tiles is considered normal on each mission due to ice dropping off of the external tank (ET) and plume re-circulation causing this debris to impact with the tiles. But the extent of damage at the conclusion of this mission was not "normal."

The pattern of hits did not follow aerodynamic expectations, and the number, size and severity of hits were abnormal. Three hundred and eight hits were counted during the inspection, one-hundred and thirty two (132) were greater than one inch. Some of the hits measured fifteen (15) inches long with depths measuring up to one and one-half (1 1/2) inches. Considering that the depth of the tile is two (2) inches, a 75% penetration depth had been reached. Over one hundred (100) tiles have been removed from the Columbia because they were irreparable.

During the STS-87 mission, there was a change made on the
external tank. Because of NASA's goal to use environmentally
friendly products, a new method of "foaming" the external tank
had been used for this mission and the STS-86 mission. It is
suspected that large amounts of foam separated from the external
tank and impacted the orbiter. This caused significant damage to
the protective tiles of the orbiter."



http://www.arnold.af.mil/aedc/newsreleases/1999/99-041.htm
"According to NASA, during several previous Space Shuttle flights, including the shuttle launched Nov. 29, 1998, the shuttle external tank experienced a significant loss of foam from the intertank. The material lost caused damage to the thermal protection high-temperature tiles on the lower surface of the shuttle orbiter.

Although the AEDC Tunnel A tests did not replicate the in-flight failures, they did provide detailed measurements to better understand the flight environment and fundamental failure mode. From these tests, NASA determined the failure is caused principally by foam cell expansion due to external heating at approximately Mach 4 combined with pressure change and aerodynamic shear. Specialized miniature shear gages and other instrumentation were installed during the test to measure these forces."

[Wright is right!]

"There really isn't anything that will self cure in space. Heck, even a lot of the panels are pyrolyzed in the manufacturing process."

There isn't anything THAT YOU KNOW OF that will cure in space. I tend to shy away from absolute pronouncements - such as the one back in the 70's that the earth would only need about 5 or 6 computers worldwide. And that we'd run out of food to feed the earth by the end of the 80's.

BTW, I wasn't suggesting epoxy. What I WAS suggesting is an adhesive that would cure in a vacuum. Big diff.

And I was NOT suggesting that a crew could do perfect tile replacement in space. What I was suggesting is that even a FAIR tile replacement would be better than nothing.

Michael

[Wright is right!]

"You obviously have NOT studied the process of making and replacing tiles. You also have a very poor knowledge of the problems of working in space. Do some research, then talk."

It is unlikely that you are completely aware of my knowledge of ANY subject, so it's never adviseable to assume that you do. And I don't feel as though I should have to post a complete resume with every response.

I am aware of MANY of the problems of working in space, not the least of which are absolute cold/radiational heating from the sun, zero-g conditions, and virtual lack of atmosphere. I am also aware that our guys have dealt with these condx many times and, in an emergency, could be counted on to do it again.

No, I am not an applied physicist in tile replacement, but I DO know that one can carry tile material and one can cut it and fashion it to a degree. I further know that in space, I am not trying to do a tile replacement worthy of Bill Gates' master bathroom - but one that will, however, marginally, increase my chances of returning to MSL in a sentient condition.

Michael

[Wright is right!]

"It would not be a permanent repair of course, and probably would not last through the entire re-entry. But it might provide just enough of an extra margin of thermal protection through the worst of the re-entry to bring the shuttle through, and that would be the only necessary goal of an in-orbit repair."

The in-the-box thinkers around here are beating me up over this kind of approach. I.e., it won't be a perfect job, the tiles might come off (duh!), they might not have a perfectly-stable workstation under the wing, etc., etc. I'd like to see how quickly their ideas of Perfection-In-Repair would hold up if THEY were up there and could give themselves at least a 10-20% increased chance of making it home vs. flying on bare aluminum.

Michael

[John Jamieson]

I tried again, but can't download it. Can you find the "landing weight" in the document?

[Robe]

Don’t be too fast to discount a theory or comment from someone. I’ll tell you a little story....

Way back when I worked for NASA (Contractor), it was the waning days of Apollo, Skylab was being launched and the shuttle was only in the future for us.

When Skylab was launched aerodynamic forces stripped a large section on the thermal protection from its side and resulted in one solar wings failure to extend and the other
being ripped off completely. As a member of one of many contingency teams we were directed to an office and told the following. “ We think that the solar wing is being held
in by the binding straps ( Kinda like those nylon packing straps) Find a way to fix it”.

We spent hours trying our minds to conger up something beautifully extravagant, a perfect engineering solution. Still in thought and with out a solution, someone said “What you fellers need is a big ole tree pruner”.

The room went silent, pens and pads were put to work.
Later that afternoon with a few hundred bucks from petty cash we went to the local Ace Hardware store on NASA Road 1, we bought a tree pruner, a pole for a swimming pool net/skimmer, some pulleys and a length of nylon line. We put it together, tested it in the TANK, then gave it to the guys to make it flight certified.

It worked just fine,it saved the entire Skylab project.
Oh yes, the guy who blurted out about the tree pruner... he was the JANITOR emptying the trash cans

[Robe]

Orbiter/ Payload Landing weight = 232,788 lbs

[Jim Noble]

>>the exact specs for cutting a replacement tile - ANY tile - and a bonding agent that will cure in a vacuum<<

Or we could just install transporters in the cargo bay.