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Russia uses the R-7 ICBM-derived Soyuz launch vehicle for most of its space launches. The advantage of it is that there's no concern on what the weather is like on launch day and Soyuz launches almost never get postponed due to weather. The only ICBMs the USA used for crewed flights were the Atlas for several Mercury missions and the Titan II for the Gemini program. The Saturn V must have been quite strong too obviously, they even launched Apollo 12 during very bad weather.

Many present-day rockets of NASA are quite weak and launches get postponed due to not very strong winds. Why don't the USA use ICBMs for crewed and other more important flights? They aimed to launch the planned Dream Chaser on the Atlas V but the plans for the crewed Dream Chaser went on hold for some reason.

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    $\begingroup$ Atlas V was never an ICBM (it's a completely different rocket from the original Atlas), and it's dubious of ICBM-versus-non-ICBM has bearing on the weather issue. $\endgroup$ – Russell Borogove Apr 30 at 5:16
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    $\begingroup$ Making an all-weather launch vehicle is pretty expensive, so why the rush? There are hardly any instances that your launch window is so short that you can not wait it out, except the actual ICBM missions? Most important missions are important in a sense that failures are expensive, not delays. $\endgroup$ – user3528438 Apr 30 at 5:18
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    $\begingroup$ The climate in the continental desert is fundamentally different from the coast of the Atlantic Ocean near the tropics. $\endgroup$ – A. Rumlin Apr 30 at 5:40
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    $\begingroup$ Increasing structural strength for bad weather increases the rocket weight and decreases payload weight. You get nothing for free. $\endgroup$ – Uwe Apr 30 at 10:19
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    $\begingroup$ "they even launched Apollo 12 during very bad weather". And never did so again, because having lightning strike your rocket turns out to be not good. $\endgroup$ – Polygnome Apr 30 at 10:57
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I think you got it wrong: R-7 launches sometimes are also postponed due to weather. Just to name few examples: 18 December 2018, 9 March 2018, 22 April 2016 - Kouru; March 22, 2016 - Baikonur, 2 october 2011 - Plesetsk. These are just few examples of Soyuz launches delayed to weather conditions. R-7 is actually not especially structurally strong, it's a bad ICBM in nearly every aspect, including this one. Besides the raw strength is not the only one concern; Apollo-12 was nearly lost when it was struck by a lighting during liftoff.

Going back to your question, it all boils down to economic reasoning. Making a rocket that can ride harsh weather costs significant amount of additional money and in exchange you get essentially no practical gain. Nearly every launch (except for some deep space missions) can be postponed by few days without losing pretty much anything and there are many more possible reasons for delays that are not related to weather.

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  • $\begingroup$ I changed my statement to "almost never". $\endgroup$ – user35272 Apr 30 at 12:23
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    $\begingroup$ Yes, they are postponed there due to bad weather. spacedaily.com/reports/… $\endgroup$ – Organic Marble Apr 30 at 12:24
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    $\begingroup$ @user30007 "less frequently" - maybe. "Almost never" - a gross overstatement, especially when you look at spaceports located in comparable climate (Kouru vs Florida). $\endgroup$ – Sergei Ozerov Apr 30 at 12:51
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    $\begingroup$ @user30007 Judging by the number of argumentative responses you have made to every answer and commenter, simply becuae they have "challenged the frame" and have not told you what you want to hear, it appears that nothing less than saying "why yes, you are right, America has always done it wrong," will suffice. America has done it different, not wrong. $\endgroup$ – CGCampbell May 1 at 0:08
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    $\begingroup$ You can always trade few days to some delta-v loss. In Voyager case the window opened on August 20 and closed on September 20. Two spacecraft were launched during that window, with Voyager-2 on the very first date possible and Voyager-1 close to the optimal date 16 days later. Thanks to the launch on a better date, Voyager-1 quickly overtook Voyager-2, but both fit the window of opportunity. This seems typical for planetary missions, but I guess that visiting some comets and asteroids might require tighter launch windows. $\endgroup$ – Sergei Ozerov May 2 at 21:53
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This question is based on several serious misconceptions.

  • R-7 launches never get postponed due to weather.

Actually, they do. "The launch of the Soyuz 2-1A modernized carrier rocket, scheduled for Wednesday evening, has been put off again, this time due to bad weather conditions at an altitude of more than 11 kilometers," the source said.

  • The only ICBMs the USA used for crewed flights were the Atlas for several Mercury missions and the Titan II for the Gemini program.

Actually, there was one other. The Redstone was an ICBM (well, an IRBM).

  • The only ICBM-derived rocket NASA is currently using for (uncrewed) spaceflight is the Atlas V, afaik.

Actually, the Atlas V is not an ICBM but a purpose-built space launcher.

  • To address "Why don't (sic) the USA use ICBMs for crewed and other more important flights?":

The US stopped using liquid-fueled ICBMs in 1987. All current US ICBMs are solid-fueled. Attempts have been made to use derivatives of these ICBMs as space launchers but they were not notably successful.

A general statement on winds and launching is

You choose the wind conditions to design your system for based on a statistical study of the wind conditions at the launch site, your tolerance for scrubbing based on winds, and your budget. Then on the day of launch you measure the winds of the day to ensure that the design criteria are not exceeded.

Source

No economical system could be designed to launch in all weather conditions.

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    $\begingroup$ You could add that "structural strength" is insufficient to guarantee safe launch in windy conditions. You'd probably need massive "side-thrusters" to offset wind shear $\endgroup$ – Carl Witthoft Apr 30 at 12:16
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    $\begingroup$ @OrganicMarble: wind shear appears to be a control issue rather than one of vehicle strength. At least in the case of Atlas V and it seems likely for other vehicles to be similar. nasa.gov/pdf/605813main_Atlas-V_MSL_Weather_Criteria.pdf $\endgroup$ – Christopher James Huff Apr 30 at 23:48
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    $\begingroup$ @ChristopherJamesHuff you could be right, not familiar with those. I worked on shuttle and it was an issue there for the wings and vertical tail, so not applicable to most vehicles. "Structural dynamic/flexible body effect is included as an increment based on a flat-top discrete gust with wind shear that is added (RSS with other dispersions) to the deterministic load" - personal notes $\endgroup$ – Organic Marble Apr 30 at 23:58
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    $\begingroup$ @OrganicMarble: That might be relevant to the crewed Dream Chaser variant as well (which can't be enclosed in a fairing, to allow for escape if things go wrong). $\endgroup$ – Christopher James Huff May 1 at 2:10
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    $\begingroup$ @user30007 I think solid-fueled rockets are "not good for a crew" because they rattle quite a bit and are also hard to scale up to human+support system (see: Shuttle). Once your ICBMs have gone solid fuel, you won't be even thinking about "Use ICBM to get astronaut aloft" anymore. $\endgroup$ – David Tonhofer May 1 at 9:07
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Structural strength is not the only factor in rockets dealing with weather, they are already designed to withstand many Gs of acceleration carrying tons of explosive fuel. Flying through a cloud isn't going to hurt them. Although there delays due to winds launches are postponed because of weather for several other reasons, including:

  • Wind: High winds could potentially blow a spacecraft into its launch tower
  • Sea State: an abort of a manned spacecraft from Florida shortly after liftoff means a spacecraft splashdown, heavy seas will complicate rescue and endanger lives
  • Visibility: Most launch authorities want to be able to visually track their spacecraft using cameras, clouds prevent that kind of tracking
  • Lightning potential: lightning can disrupt spacecraft electronics and potentially cause an abort. This almost happened on Apollo 12, it was only the quick thinking of one controller who saved the mission

Increasing structural strength will solve none of these.

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  • $\begingroup$ A heavier rocket wouldn't be blown that easy into its launch tower and as for the 3rd point Visibility there are onboard cameras on many rockets (and even their separate stages) today. $\endgroup$ – user35272 Apr 30 at 18:13
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    $\begingroup$ How much extra weight are you envisioning @user30007? An Atlas V is 730,000lbs typical launch weight with a maximum of 40,000lbs payload to LEO. You can't just add weight to it, the maximum it can be is 730k lbs. Make it twice as heavy and 10 times as expensive so it can be launched on a windy day? Why in the world would you do that when you can just wait? $\endgroup$ – GdD Apr 30 at 19:19
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    $\begingroup$ Also, your premise that a heavier rocket wouldn't get blown into the tower as easily isn't correct @user30007. A denser object would have more inertia and move less in the wind, but a heavier rocket would have pretty much the same density as a lighter one, and would get moved similarly. $\endgroup$ – GdD Apr 30 at 20:19
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    $\begingroup$ How will you achieve said denser rocket @user30007? Heavier materials? You do that and you reduce the payload to orbit, which defeats the purpose. They are already a compact mass of fuel, oxidizer, pumps and structure to hold it together, it's hard to see how you could make them more dense. $\endgroup$ – GdD May 1 at 7:20
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    $\begingroup$ @user30007: your initial proposal for strong rockets isn't obviously insane. (Although making something stronger usually costs mass). But then people pointed out that getting blown off course is a different problem from strength, and I think you lost sight of the all-important en.wikipedia.org/wiki/Propellant_mass_fraction being in the 80 to 90% range when you proposed making rockets denser to avoid this problem, too. Rockets don't have much empty space to compact. To be fair, a larger rocket of the same density would have less area to volume ratio and be somewhat less affected by wind $\endgroup$ – Peter Cordes May 2 at 4:39

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