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How can the Starship booster stand vertically without falling over?

In my day to day experience, similar long objects (simple objects that can be easily found in thehouse) tend to fall easily with a slight touch or wind.

Can someone explain in simple terms how such a massive object does not fall either when standing or when it is moving (even if it is very slow) on a vehicle?

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    $\begingroup$ When it's being moved on a vehicle, I very much doubt that it contains fuel, so it is not all that massive. You might ask why a strong wind doesn't blow it over. $\endgroup$
    – jamesqf
    Aug 4, 2021 at 4:43
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    $\begingroup$ Note that rockets are almost always securely attached to their launch mounts to stop them falling over. NASA is a fan of explosive bolts for this purpose. $\endgroup$ Aug 4, 2021 at 8:26
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    $\begingroup$ A version of SpaceX's Starhopper did get blown over, at least partially (reports are conflicting), on 23 January 2019. $\endgroup$ Aug 4, 2021 at 17:08

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Starships so far were simply bolted to the transport stand, I believe. Super Heavy doesn't have a skirt it could stand on (and Booster 4 in particular has 29 Raptors sticking out its bottom), so that is not really possible.

It looks like the Super Heavy transport stand has clamps to hold the booster in place: Super Heavy Transport Stand

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    $\begingroup$ I am looking for fundamental reasons something like whether center of gravity is lower, if so why it is lower, how wind does not flip this huge structures etc. $\endgroup$
    – jrp
    Aug 3, 2021 at 21:25
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    $\begingroup$ If it's clamped down, then its 'center of gravity' is roughly at the center of the Earth. $\endgroup$ Aug 3, 2021 at 22:06
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    $\begingroup$ @jrp consider the following: skyscrapers are similarly long objects, and also do not fall over easily. They are attached to foundations, attached to the Earth. Very similar to a booster, clamped to the foundation, attached to the Earth. Now, you can ask about/consider the rigidity of the object in question, but in both of these cases, they are (functionally) a part of the earth below them and therefore do not tip. $\endgroup$ Aug 4, 2021 at 4:22
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    $\begingroup$ @CamilleGoudeseune that would only be true if the entire structure were made of rigid unobtanium. Try clamping any structure that has maximum shear and bending force limits and see how the C.M. matters $\endgroup$ Aug 4, 2021 at 12:02
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    $\begingroup$ @leftaroundabout Well, it was not only wind: "As conditions worsened with 8- to 10-foot swells, the booster began to shift and ultimately was unable to remain upright." Tilting effects are scale invariant ;-). $\endgroup$ Aug 4, 2021 at 12:09
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We need to realize this is all in flux, as SpaceX is changing everything, sometimes daily.

BN3 and the other bits they built for Boosters were attached to manufacturing bases, with different attachment points.

BN3 is currently on a test stand that was designed to hold a Starship upper stage. They built an adapter for the Booster connection points.

For BN4, the one they installed all the engines on, there is a manufacturing stand that has 20 hold downs.

It has yet (as of this writing) to be rolled out to the pad. The new launch pad (as of this writing) is also not yet complete, so it is not certain exactly how that will work out.

There are a large number (20) of hold down clamps in the base to keep the booster connected. This is the current approach, if there is any constant here, it is change. So expect this to change.

(After I wrote this, they had rolled out the launch table and lifted it to the launch stand. And then they rolled out the BN4 booster to the pad. No doubt by the time I finish writing this, they will have lifted the booster. Or flown it, who knows at this pace.)

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    $\begingroup$ It was rolled out today, actually. Literally just arrived. Which just proves your point: SpaceX moves fast! $\endgroup$ Aug 3, 2021 at 19:59
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    $\begingroup$ @JörgWMittag How can you keep up? It is so much fun! $\endgroup$
    – geoffc
    Aug 3, 2021 at 20:04
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    $\begingroup$ My secret trick is to subscribe to NASASpaceflight YouTube notifications, not to watch the videos but just to read the titles :-D $\endgroup$ Aug 3, 2021 at 20:13
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    $\begingroup$ @jrp The fundamental reason is, big strong grippy things, nothing fancy like center of mass. $\endgroup$
    – geoffc
    Aug 4, 2021 at 1:24
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    $\begingroup$ I think the answer got cut off at the end. $\endgroup$ Aug 4, 2021 at 8:09
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The relationship between mass (or density, depending on how you choose to look at it) and air resistance changes with size - very small objects like specks of dust can float around with almost no regard to gravity but very much affected by airflow, while larger (hourehold) objects are more affected by gravity than by airflow even though their density may be similar. Very large objects such as rockets and buildings are influenced very little by airflow.

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  • $\begingroup$ The relation between mass and air resistance changes with shape, not size. One Lego brick has mass M and air resistance (to a wind blowing sideways) R. A vertical stack of 100 bricks has mass 100M and air resistance 100R. But it should be obvious which structure is more stable! $\endgroup$
    – alephzero
    Aug 5, 2021 at 15:00
  • $\begingroup$ Shape is significant (although in both cases we are considering a cylinder) but size most certainly does affect the importance of air resistance. I haven’t included any calculations because it’s far from straightforward. Look up Reynolds number for an insight if you’re not familiar with this. The OP is specifically comparing the same shape at different scales, not different ratios of height to width. $\endgroup$
    – Frog
    Aug 6, 2021 at 20:38
  • $\begingroup$ To a first approximation, total wind force will scale with the square of dimension while mass will scale with the cube of dimension. However turning moment is force times distance, so the ratio of mass to overturning moment should remain roughly constant as the object gets larger. $\endgroup$ Apr 1, 2022 at 18:50
  • $\begingroup$ On second thoughts though the turning moment caused by the mass will also scale with te size, so maybe larger objects are more stable after all. $\endgroup$ Apr 1, 2022 at 18:55

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