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Whilst watching yesterday's Starliner launch I've noticed how skinny that Centaur (3.1m) looks compared to the CST-100 (4.5m).

Looking up the Atlas V I was amazed to find out that it has even larger (5m) fairing as part of its design (although protruding all the way down to the thicker first stage).

Apparently, apart from Atlas V and Falcon 9/heavy, there are quite a few of launcher designs utilizing this feature (fairing larger in diameter than the booster it is attached to), whilst others (like Delta IV, Proton-M, etc.) are designed with booster and fairing diameters matching.

Tyler Skrabek's The World’s Rockets to Scale

The picture, Tyler Skrabek's The World’s Rockets to Scale is borrowed from here and originally from The Universe Today.

This answer and also this answer explain what disadvantages dropping down the (larger) fairing diameter to the (smaller) booster diameter cause: additional drag and stability issues.

There must be reasons as to why they don't design those launchers with booster diameter to match the fairing.

What would those reasons be?

Update: found this tightly related question about Falcon 9 specifically. The answer mentions that the booster diameter was limited in order to conveniently (and less expensively) move the hardware by road.

But there are many more examples of launch vehicles with boosters smaller than fairing. I am wondering are there any more reasons (structural, choice of propellant-wise, lifting capacity to LEO etc.) other than those related to transportation to launch pad.

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  • $\begingroup$ for one of them: If not constrained by underpasses, etc., would Falcon 9 have been less of a flying noodle? $\endgroup$ – uhoh Dec 21 '19 at 7:10
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    $\begingroup$ If your design starts with a fairing the same diameter as the launcher, then evolves to support larger payloads, it’s much easier to enlarge the fairing than to enlarge the rest of it. $\endgroup$ – Russell Borogove Dec 21 '19 at 7:19
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    $\begingroup$ These are artist-compiled images for visual appeal as much as for documentation, it is possible that some or many of these flew with smaller diameter fairings some fraction of the time, and that the largest fairings of multiple options were chosen for visual impact. I don't know though. $\endgroup$ – uhoh Dec 21 '19 at 7:31
  • $\begingroup$ @RussellBorogove yes, this is an obvious reason. But there are so many of those cases. Would it (along with logistical constraints as in case of Falcon 9) be the only reasonable explanaitions? Ariane series, for example grew in length from -1 to -4 keeping same diameters, but the first one, Ariane 1, had 2nd stage diameter smaller than 1st, then it grew again on the fairing. The other interesting observation: out of whole Japanese rockets family only the latest one, H-IIB has this "hourglass" diameter variation case $\endgroup$ – Sergiy Lenzion Dec 21 '19 at 9:36
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    $\begingroup$ Picture doesn't show how staggeringly huge some Titan fairings were: upload.wikimedia.org/wikipedia/commons/5/5c/… $\endgroup$ – Organic Marble Dec 21 '19 at 13:40

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