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Dummy question.

A launch vehicle is restrained during ignition by hold-down clamps.

But exactly what part of the rocket do the clamps grab onto? The engine nozzles seem too fragile... but maybe some part of the thrust structure just above the nozzles?

Can someone illuminate :D

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  • $\begingroup$ Isn't this very similar to space.stackexchange.com/questions/28008/…? $\endgroup$
    – Duck
    Commented May 31, 2021 at 6:51
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    $\begingroup$ @Duck Close, but not a duplicate - I'd say "mirror part" of this one, asking about the ground infrastructure (clamps and similar) while this one asks about support points on the rocket. In case of SpaceX Falcon 9 it's a bit more simple, "tapping into" a part of the landing legs attachment infrastructure (meant to sustain the rocket mass anyway). In case of non-reusable rockets the engineering is less intuitive. I could provide a "bikeshed level" answer, but I hope someone else knows more and could say something that will teach me something new too. $\endgroup$
    – SF.
    Commented May 31, 2021 at 7:41
  • $\begingroup$ Visitng the above links, Comments to this answer mention two examples pertaining to the rocket side. For falcon, it is mentioned to be the octaweb. A shuttle SRB example also provided. $\endgroup$
    – AJN
    Commented May 31, 2021 at 9:16
  • $\begingroup$ related: Saturn V and STS holding to launch pad mechanism and What holds the Space Shuttle orbiter itself stable on the launch pad? $\endgroup$
    – uhoh
    Commented May 31, 2021 at 12:48

1 Answer 1

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On the rocket, it's going to be a sufficiently reinforced piece of the vehicle structure. I've attached a photo I took of the Saturn V in Houston with the relevant hard point on the first stage circled. Note in particular how thick the block of metal that gets clamped down is, and note its structural connection as it goes up the length of the rocket.

View of the Saturn V first stage, with an annotation added around a structural hard point

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  • $\begingroup$ How does that hole interface with the holddown arm, which looked like this i.sstatic.net/JLqYY.png $\endgroup$
    – Organic Marble
    Commented Jun 1, 2021 at 13:50
  • $\begingroup$ @OrganicMarble Having trouble finding anything showing what it interfaces to, but here's a photo of the hold-down arm grabbing onto it: i.imgur.com/0yMb6p7.jpg $\endgroup$
    – Tristan
    Commented Jun 1, 2021 at 14:08
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    $\begingroup$ The hole looks more like a place an alignment pin would go. IIRC, the hole is only a couple inches deep (would have to go back and look to be sure). It doesn't go all the way through. $\endgroup$
    – Tristan
    Commented Jun 1, 2021 at 14:25
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    $\begingroup$ @OrganicMarble The pins that pull out were apparently off to the side: 3.bp.blogspot.com/-hsuIr4uPBYA/W3OLHDfIBRI/AAAAAAAADrI/… $\endgroup$
    – Tristan
    Commented Jun 1, 2021 at 14:27
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    $\begingroup$ All the drawings show a "shelf" with conical protrusions above and below, with the larger cone on the bottom. The 9th Aerospace Mechanisms Symposium (which I don't see on NTRS any more) has a good writeup on the mechanism but not much on the vehicle side. i.imgur.com/q3444NG.png $\endgroup$
    – Organic Marble
    Commented Jun 1, 2021 at 14:51

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