Shuttle Launch Pad Damaged During Discovery's Launch

pumpkinpuss writes "Launch pad 39A at the Kennedy Space Center suffered unusual damage during the shuttle Discovery's blastoff Saturday. Pictures from a NASA source show buckled concrete and numerous concrete blocks or bricks, presumably from the flame trench, littering a road behind the pad."

Comments

Kinda old

[felipekk]

LC39A was used the first time almost 41 years ago by Apollo 4. It was used for more than 80 launches since then. Maybe it's time to replace it?

http://en.wikipedia.org/wiki/Kennedy_Space_Center_Launch_Complex_39

Re:anyone know?

[MLCT]

Many. It was built for the Apollo program, first used in 1967 - and handled almost all of the Saturn V Apollo launches bar one (so ~ 16). After that it has, along with 39B been handling Shuttle launches - and so presumably taken close to, if not more than 50% of them (so around 60+). Hence we could be looking at around 70-80 launches - launches of the heaviest kind.

39B has already started to be refurbished for Project Constellation, launching the Ares Saturn like rockets. The plan is that 39A will follow suit after the last of the space shuttle missions are finished.

Thermal Cycling

[Thelasko]

Making things hot and cold in rapid succession can cause fatigue due to the materials expanding and contracting. Things exposed to the elements, such as this, also have to deal with moisture.

I don't know what these bricks are made of (CNN says they are special bricks but TFA says they are concrete), but I bet water was trapped in between the cracks and crevices of these bricks and then suddenly boiled when it was heated by rocket exhaust. The steam rapidly escapes from the bricks and makes the cracks a little bigger. This occurs over and over again, each time the cracks get a little bigger. Finally, the cracks become big enough that the bricks can't stand the stress anymore. They get heated one more time and explode. It only takes one brick to explode to cause a chain reaction, and wipe out a bunch of them.

This is of course, the simplest explanation. I would hope NASA would have thought of this before. It happens all of the time with the freeze and thaw cycles in highways and bridges. However, sometimes the simplest explanation is the best.

Re:Thermal Cycling

[rahvin112]

Newsflash: Concrete is batched in high capacity batch plants with rapid speed distribution and mixing systems. It's also comprised of materials that vary dramatically per load. No cubic yard of excavated rock is identical to the last just as no cubic yard of sand is identical to the last. Measuring everything with a computer matters little if the ingredients that comprise the concrete vary so consistently across the spectrum and are measured and mixed so rapidly. Combine in different moisture contents in the aggregates, different chemical compositions of the aggregates and one of load of concrete can vary dramatically from the last in the properties that matter for construction. Having spent 12 years working in the transportation sector and having hand tested more loads of concrete than I care to even estimate I like to think I say this with a fair amount of expertise.

But go on believing that every batch is identical, the testers on the ground will tell you otherwise. Hell, if what you said was true we wouldn't need testers, the very existence of testings refutes your assertion that there are only minor differences. I've also got a newsflash for you, concrete is a highly forgiving material, even with wide disparity in the mix the design of mixes is done with minimum characteristics in mind. Even today 4000psi concrete is the design norm with 98% of all breaks exceeding that number, most by a very large margin. Recent tests of sac-crete (small, poor aggregates) on a project I worked on yielded 6500psi, far in excess of the minimum strength required of 3500psi. You obviously know nothing about the design and use of concrete in the construction industry. Because concrete is so different per lot random statistical sampling is done to ensure the concrete falls within specific minimum parameters. But keep on believing that fancy computer at the batch plant does anything more than speed up the delivery and mixing rather than ensure consistent batching which has and will always be a human task. A simple pound of rock with 15% more sulfer than the rest can change the mix significantly and 0.5% more moisture in the sand can alter the cement/water mixture significantly.

Re:anyone know?

[SGDarkKnight]

according to the all-knowing wiki, http://en.wikipedia.org/wiki/Launch_pad_39A/ there have been 82 launches.

Re:how?

[Cecil]

It depends on your definition of "nearby".

With nearly 10 million pounds of thrust, I imagine there are still significant blast pressures on that pad even when the shuttle is a kilometer or more above it. For comparison, the blast danger area for other aircraft behind a 747 at full takeoff thrust is more than half a kilometer. If you don't believe that, there's a Top Gear episode that amply demonstrates the fact.

Re:anyone know?

[WindBourne]

Hmmmm. this will work better.

Also: it's a heavy mission

[kaptain80]

STS-124 is carrying Kibo, making it a rather heavy liftoff. It would have taken Discovery a little longer than usual to get away from the pad, subjecting it to a longer duration acoustic/vibration environment.

Also, it wasn't that far off the pad when the bricks were flying off according to this image. (Same photo as TFA, but a little farther out)

Re:how?

[idontgno]

the rockets are causing the damage, so the damage occurs while the rockets are nearby, right?

Well, the rocket exhaust isn't the only high-pressure fluid rushing out through the flame trench in the launch process.

The Sound Suppression Water System dumps about 300,000 gallons of water into the launchpad base and exhaust flame ports in the first 20 seconds after engine ignition, so that flow can't be good for the stability of the flame trench insulating blocks as they start to work loose.

Re:how?

[Thelasko]

Thermal cycling. Cracks can occur in many structural materials while *cooling*, not while heating. Next time try heating a piece of glassware to an unholy temperature, and then dropping it into an ice water bath. Not true, the cracks can occur while either heating or cooling. The cracking occurs due to high temperature gradients (very hot next to very cold).

In your glassware example, you heated the piece of glassware slowly, so the thermal gradient was low. In other words the entire piece of glassware was roughly the same temperature while it was heated. When you dropped it into ice water the outside became much colder than the inside because the change in temperature was sudden. I recommend you read this article.

Remember, heat transfer is not instantaneous.

Re:how?

[ChrisA90278]

No, the safety zone that that keep in back of an airliner like the 747 is not due to the engines. It is due to what they call wing tip votices. This is caused by the high presure air rolling around the ends of the wing into the low pressure zon on the top of the wing. The plane leaves a 'wake" that is like two horizonal toranados.

The 747 would have this same kind os wake evn if all four engines were shut down.

We dont know what happended to the pad yet. my guess is something to do with the combination of heat and old age.

Some Hi=Res Closeups of the Aftermath

[ausoleil]

here are some closeup photos of the pad damage.

The photos show the debris field, holes blown through the security fence by flying debris and the bricks on the walls of the flame trench ripped away. Interesting stuff.