Launch Question

[jeffglau]

I've been wondering this ever since I saw the first shuttle go up, and I thought someone might know the answer.  When the main engine ignite at T - 6 seconds, what keeps the shuttle still attached to the pad until the SRB's light?  It seems once the SRB's light, the shuttle jumps off the pad.

[Spacewalker]

The SRBs are attached to the pad by frangible bolts (that's the engineering term for "explosive bolts" ). These bolts are fired at almost the same time as the SRBs are ignited (well, actually about 1/1000 s earlier).
Of course the Shuttle stack would not be able to lift off anyway, as long as the SRBs are not ignited, because the SSMEs alone are not powerful enough to lift the whole stack off the ground, but the bolts keep it from tipping over after SSME ignition. You can actually see the whole stack swaying after SSME ignition! (which is also beautifully simulated in SSM )

[Chris Bergin]

And they've changed the design, starting with STS-125 in October:
http://www.nasaspaceflight.com/content/?cid=5469

[shanes80]

thanks, I have all so wanted to know about this. 

[STS78MEMBER]

That article was interesting as I did not know they changed the design. Thanks for sharing.