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Imagine an ICBM with a nuclear warhead is launched from the US to reach Moscow.

How long does it take to reach its target? I've read numbers of about 30 minutes (if the missile is launched from America) or even 15 minutes (if the missile is launched from Europe). Is this realistic?

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    $\begingroup$ Well, for the last part of your question, large part of Russia is in Europe (the continent, not the European Union), so that would be 0 minutes then :) Yes, your numbers seem reasonable, less for EU to Russia tho, 15 minutes seems more like UK to, say, Moscow (at average speed of a bit over 3 km/s). $\endgroup$ – TildalWave Sep 17 '15 at 19:22
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    $\begingroup$ Why do you ask? $\endgroup$ – Russell Borogove Sep 17 '15 at 19:40
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    $\begingroup$ princeton.edu/sgs/publications/sgs/pdf/3_1-2gronlund.pdf as a good start. Yes. Depends on where the sub patrols. Please note that the accepted answer is approx. correct for your stated question (Minot to Moscow). $\endgroup$ – Deer Hunter Sep 18 '15 at 5:47
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    $\begingroup$ Please also have a look at nrdc.org/nuclear/warplan/index.asp $\endgroup$ – Deer Hunter Sep 18 '15 at 7:21
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    $\begingroup$ For the scenario you describe in the comments, I think the major difficulty would be early launch detection and target estimation, then getting the information to people (ideally without causing a countrywide panic). If you have to spend the first, say, 1/3 of the ICBM flight regimen just to figure out where it might be headed, that is 5-10 minutes that you just lost. Then at the very least, someone or something has to push the proverbial button to get the message out to people to take cover, and you have to consider that not everyone will be monitoring whatever channel you use. It adds up. $\endgroup$ – a CVn Sep 18 '15 at 11:40
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Those numbers are realistic, yes. Peak speed for an ICBM is in the ballpark of 6-7km/s (any faster and the payload would go orbital), and it takes about 10 minutes to accelerate to that speed.

New York to Moscow is 7500km, at 6.5km/s is ~20 minutes. Add in the acceleration time and you're looking at about 30 minutes total.

London to Moscow is 2500km; most of the flight time there would be accelerating on ascent and decelerating in re-entry rather than coasting; as TildalWave indicates, 15 minutes is about right for that.

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  • $\begingroup$ Well, the ICBM would make some distance as it accelerates too, but the target moves ~ 552.8 km East in the mean time, so roughly 30 minutes is still about right. ;) $\endgroup$ – TildalWave Sep 17 '15 at 20:04
  • $\begingroup$ ICBM starts with Eastward velocity also, though. (But those aren't actually the same "East"!) It does cover distance during the acceleration, yes, but it also loses a lot to going vertical. It also decelerates a bit on re-entry. But 30 minutes is a good round figure. $\endgroup$ – Russell Borogove Sep 17 '15 at 20:34
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    $\begingroup$ I know, I used cosine of the latitude twice!! :)) $\endgroup$ – TildalWave Sep 17 '15 at 20:36
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    $\begingroup$ You win this round. $\endgroup$ – Russell Borogove Sep 17 '15 at 20:42
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    $\begingroup$ Shall we play a game? $\endgroup$ – a CVn Sep 20 '15 at 14:01
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This response addresses the practical warning time for ordinary citizens. It isn't quite the scenario asked in the original question and is a response to the various comments that clarify that citizen perspective is of interest and also that the flight path Russia -> Western Europe is of interest.

In the 70's and 80's in the UK there was an awareness of the "four minute warning". The wiki article is quite chilling. Some salient points:

  • "the four-minute warning was a public alert system conceived by the British Government during the Cold War and operated between 1953 and 1992"
  • "From the early 1960s, initial detection of attack would be provided primarily by the RAF BMEWS station at Fylingdales in North Yorkshire."
  • The British government was not the main beneficiary of BMEWS, given that it would only receive ... ... "no more than 5 minutes warning time" of an attack. The United States ... ..., however, and its Strategic Air Command would have thirty minutes warning from the Fylingdales station.

As a peripheral point there may also be some inspiration for the novel in the book and film "On the beach".

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    $\begingroup$ The big difference here is that it takes time to detect, identify the target and confirm that the threat is real. A rocket is a rocket, the only way it can be identified as hostile is where it came from (space launch complex = low threat, ICBM field = high threat) and where it's heading--and you can't solve the latter until the booster burns out. $\endgroup$ – Loren Pechtel Jan 25 '16 at 20:54

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