It Is Rocket Science

[RBG]

How is it that, what appears to be, a mere couple of rods can hold the shuttle together to the fuel tank with all that explosive thrust, acceleration and atmospheric drag going on?

I would have to guess that when all the parts are moving at the exact same rate, the shear stresses must be relatively low. You have to tip your hat to the people who have the confidence in their understanding of material physics to be able to do these kinds of things.

RBG

[Nicolas]

the short answer is that those rods are really really strong

The ET has been designed for minimal air resistance adnd orbiter acceleration is rather modest, so in total the shear forces aren't extreme. The SRB and orbiter connecting rods form some good pairs of hands that lift the ET up as they rise .

Indeed they must trust their understanding of material science and mechanics in order to do that safely. On top of that, the connections are detachable; you can't just weld them to the orbiter .

Of course, the shear forces can be tested on the ground, so it can be checked in a safe environment.

[gwiz]

The Shuttle thrust is transferred to the tank mainly through the two fittings at the rear, which are oriented to be loaded in compression, not shear.

[Nicolas]

45° forward orientation (|\ as seen from the side) indeed will give a nice amount of compression. As long as buckling does not occur, this is a nice way of transferring loads. Don't ask me why they did not do it in tension ( /| ) though. Those are the details known in the design option tree, but not so easy to extract as an outsider. If it were only for the ^ under the nose, the orbiter would leave without ET .

[gwiz]

Putting the rear fittings the other way round to give a tension load would mean two attachment points at the orbiter end, one on the tank, rather than the one on the orbiter, two on the tank of the compression arrangement. This doubles the number of hatches in the tiled lower surface.

There is also the possibility that you would need to lower the position of the tank relative to the orbiter, putting it closer to the main engines. If you left it where it was you would need extra compression structure in the orbiter to reach the attachment point.

[Nicolas]

erm, you can just turn them around with 2 attachment points on the ET and one on the orbiter as well

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But this would indeed put the ET lower compared to the current situation.

[gwiz]

OK, I'll just go with the lower tank point.

[Nicolas]

And that point can be solved by attaching the struts higher on the orbiter.

So I don't know what the problem/disadvantage would have been .

[gwiz]

No, if you put the attachments higher on the orbiter, you need more compression structure on the orbiter between the engines and the attachments.

[Nicolas]

True. I overlooked it the first time you said it, my bad.

Somewhere in the pro/con these factors must have made the tension layout unfavorable. I'm sure there are (many) more points. This one might be aerodynamically better.