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Discovery Launch
Source: Discovery Launch Captured by Multiple Cameras, NASA, YouTube; edited

A more clickbaity but accurate description of my question would be:

  • How did the Space Shuttle / External Tank not shear off?

The view above always fascinated me. Note how once the ET is jettisoned, where it connects is revealed, and it is a small connector.

During lift-off I always thought of the SRBs carrying the ET, and the Shuttle carrying itself, but once the SRBs are jettisoned, and the acceleration is coming only from the Shuttle (thrust-line is now parallel more or less to the ET's vertical axis), I can only wonder how is that small connector possible; how is it designed to withstand such a shear force, yet remain with minimal footprint on the Shuttle underside / heat shield?

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  • $\begingroup$ Note that the much of the ET volume is liquid hydrogen, with a density about 1/14 that of water, and once the SRBs separate, it's burned about 1/4 of its contents, so it is somewhat less massive than it appears at a glance. A good question, though! $\endgroup$ – Russell Borogove Sep 11 at 22:46
  • $\begingroup$ The other connections are at least somewhat more substantial $\endgroup$ – CourageousPotato Sep 12 at 1:21
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    $\begingroup$ different but related: Shear forces between Shuttle, tank, and boosters - what pushes what? $\endgroup$ – uhoh Sep 12 at 2:30
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There were three attach points. The forward bipod that you show in your answer, and two aft attach points. At each attach point a large explosive bolt held the tank and Orbiter together. Large umbilical door openings in the aft of the Orbiter let the aft bolts pass through and also had all the fluid and electrical connections. After separation tile-covered doors closed over these openings.

Read all about it here: https://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/sep/sepsystem.html

The 1982 Press Manual has some detailed drawings of the bolts and associated fittings.

enter image description here

Here is a picture of some of the bolts being prepped for flight.

enter image description here

(Personal photo)

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    $\begingroup$ That helped me find this paper. If I'm reading it right, the Orbiter/ET forward attachment experienced ~500 kN in two directions. That's equivalent to the thrust of a Boeing 777's engine, which is also bolt mounted to the wing. So while it's a big number, I suppose indeed a bolt can do it. (I think I have overestimated the thrust of the SSMEs.) $\endgroup$ – ymb1 Sep 12 at 2:54
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    $\begingroup$ They were big bolts. $\endgroup$ – Organic Marble Sep 12 at 3:44
  • $\begingroup$ SSME's produced ~400,000 lbf of thrust for a combined 1.2M lbf will all 3 firing at 104%. The thrust of each individual SSME varied slightly based on the number of cores (basically picture a collection of ~ 100 straws through which the propellant mixture flowed) that were operative for each engine. $\endgroup$ – David Rankin - ReinstateMonica Sep 13 at 5:39
  • $\begingroup$ A reasonably SSME Diagram shows the main injector cores feeding the main combustion chamber. $\endgroup$ – David Rankin - ReinstateMonica Sep 13 at 5:50
  • $\begingroup$ "Cores" is not a term I've ever heard associated with the SSME. $\endgroup$ – Organic Marble Sep 13 at 12:39

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