The Shuttle - How it Stood

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GregGleason

GregGleason

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The shuttle was anchored to the Mobile Launcher Platform by eight bolts attached to the base of the SRM's. The aft skirt of each SRM had four attach points where there were bolted to the platform. As the SRM's were ignited, small charges (NASA standard detonators or NSD's) would fire to break frangible nuts that held the bolt. The nuts would fragment, allowing the bolt to fall out of the aft skirt. On high-speed shuttle launch imagery, you can see puffs of smoke emit from the hold down points as the NSD's are fired, and momemts later (in high-speed time) you see flame from the SRM's and first motion. I have read were shuttle astronauts were given the remains of the nuts as souvenirs.

Each solid rocket booster has four hold- down posts that fit into corresponding support posts on the mobile launcher platform. Hold- down bolts hold the SRB and launcher platform posts together. Each bolt has a nut at each end, but only the top nut is frangible. The top nut contains two NASA standard detonators, which are ignited at solid rocket motor ignition commands.

When the two NSDs are ignited at each hold-down, the hold-down bolt travels downward because of the release of tension in the bolt (pretensioned before launch), NSD gas pressure and gravity. The bolt is stopped by the stud deceleration stand, which contains sand. The SRB bolt is 28 inches long and is 3.5 inches in diameter. The frangible nut is captured in a blast container.
Click to expand...



Frangible Nut by JetForMe, on Flickr

Greg

Ref. https://spaceflight.nasa.gov/shuttle/reference/shutref/srb/posts.html
 
I like to know who,what,and how these monster nuts are tighten to spec torque.
Thanks,interesting. What do you think one of those cost?
 
That’s the second largest Frangible Nut I’ve ever seen.

So what happens if something goes wonky and those “NSDs” don’t fire?
 
Just a guess, but the threads might be designed to strip under the force of the booster thrust. Kind of like how reloadable motor casings are designed to spit out their closures before rupturing.
 
regdoug said:
Just a guess, but the threads might be designed to strip under the force of the booster thrust. Kind of like how reloadable motor casings are designed to spit out their closures before rupturing.
Click to expand...
I would also guess that since each nut has two charges, one of them is enough to split the nut.
 
There is a display at the Cosmosphere in Hutchinson KS....we toured there during NARCON 2012. Here are pics of the display... I believe the nuts are tightened with hydraulic torque wrenches

DSC_4620MR.jpg

DSC_4621MR.jpg

DSC_4624MR.jpg

DSC_4625MR.jpg
 
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Thanks for the link, Greg.

Not only does it describe "stud hangup" but it also states that only one charge has to fire in order to fracture the nut.

-Kevin
 
Scotty Dog said:
I like to know who, what, and how these monster nuts are tighten to spec torque.
Click to expand...

Mona Lisa Vito: Because I used a Craftsman model 1019 Laboratory Edition Signature Series torque wrench. The kind used by Cal Tech high energy physicists. And NASA engineers.

Vinny Gambini: Well, in that case, how can you be sure THAT's accurate?

Lisa: Because a split second before the torque wrench was applied to the SRBs, it had been calibrated by top members of the state AND federal Department of Weights and Measures... to be dead-on balls accurate!

[She rips a page out of a magazine and hands it to him]

Lisa: Here's the certificate of validation.

Vinny Gambini: Dead-on balls accurate?

Lisa: It's an industry term.

images3.jpg
 
boomtube said:
That’s the second largest Frangible Nut I’ve ever seen.

So what happens if something goes wonky and those “NSDs” don’t fire?
Click to expand...

I read that the shuttle SRB's had enough force to shear the nuts off the post if the charges didn't go off. That may explain why the threads are so fine.
 

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