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What holds stacks down or up?


Kokoro

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Is it true that a shuttle stack was held down by just eight bolts at the bottom of the SRBs?  The whole thing?  Orbiter and payload.  By these bolts that sheer (spelling of that?) when the SRBs are lit?

Soyuz stacks are held up by those four towers.  How are other rocket stacks held to the ground/launch-platform?

 

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The SSSRBs provide most of the thrust in normal flight conditions, so the thing sitting on its boosters is basically the same as the thing lifting off, save the aerodynamic loads. Also the entire thing sitting on 8 bolts seems reasonable: when you start looking at the components of a rocket engine when firing, you'll find that these bolts have it easy.

Most rockets are attached by clamps/bolts/glue themselves attached to the thrust structure of the rocket first stage. Since it's made to handle the thrust of the engines lifting the whole thing up, it can handle the rocket sitting on it at rest.

Edited by Gaarst
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1 hour ago, LordFerret said:

You might appreciate a peek at this ->

That's such an awesome video.

So it doesn't matter that the orbiter attached to the tank is not perfectly centred over the SRBs, the bolts still hold.  The weight of fuel in the tank probably helps.

Just looking at pictures the blot lugs are not evenly spaced.  Two are on the farside of the orbiter and two are next to it under each srb.

100604main_image_feature_233_jw4.jpg

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I'm not sure of the reason for the 'where and why' of the bolts being placed, but I'm sure there's an engineering answer in there somewhere though... maybe distribution of stresses?... maybe because of the design of the mobile launcher platform (accommodates more than just the shuttle)?

More on the posts / bolts.

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The Soyuz tower arms use a lever and counterweight balance system. The rocket weighs down on 4 pads, which push the 4 strongback arms against the rocket. As the rocket lifts itself, it no longer weighs on the pads and the arms are pulled back by their counterweights. Clever.

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10 minutes ago, Nibb31 said:

The Soyuz tower arms use a lever and counterweight balance system. The rocket weighs down on 4 pads, which push the 4 strongback arms against the rocket. As the rocket lifts itself, it no longer weighs on the pads and the arms are pulled back by their counterweights. Clever.

4 strongback arms are much better than just several more pyrobolts...

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15 hours ago, Kokoro said:

By these bolts that sheer (spelling of that?) when the SRBs are lit?

The upper ends of the bolts were held by frangible nuts.  On launch, two detonators were set off in each nut, the pieces of which were caught by devices on the boosters.  The bolts were under enough tension that they were pulled down into the pad when the nuts released.  At launch, the stack generated enough force that the bolts would fail if the detonators failed to operate.

On his retirement, my father received a plaque with half of one of the nuts from some folks he worked with at KSC.

You can see pictures of the nuts here.

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I'm no rocket scientist but a few bolts doesn't sound unreasonable. The strap-on boosters are not the only ones fireing so the bolts are not carrying the full weight of the center core/payload, more like they are strapped on to keep them on a leash, stopping them from running around like lunatics. That would, I imagine, demand less in terms of strength.

Edited by LN400
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I've actually held those bolts. There used to be a geodesic dome at KSC visitor's center where folks would talk about their part of the Shuttle program. They would bring "visual aids" such as the bolts, or pieces of tile.

They were huge. They weighed about 70lbs and Wikipedia says they were 28" long and 5.5" in diameter. You had to be careful, as the threads were kind of sharp and in combination with the weight of the bolt, could give you nasty cuts.

I can easily imagine 8 of those holding down a Shuttle stack.

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On Tuesday September 13, 2016 at 7:27 AM, kerbiloid said:

4 strongback arms are much better than just several more pyrobolts...

Boris Chertok in his memoirs mentioned that they had lots of trouble with those arms at first. They have to be moved in perfect unison to prevent uneven forces to tip a whole stack, which turned to be somewhat difficult with structures weighing many tons. They did it this way because it allowed them to save on structural weight of a rocket, not because its easy.
 

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