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I've seen a statement, that reducing boost phase duration by 25% of an abstract ICBM would reduce its throw weight by several times.

I don't get how is that possible. Shorter boost phase - less "fighting" with earth's 1G. We only have issues with air resistance in the very beginning, but it shouldn't have such a huge impact.

So, does it really reduce throw weight? Or engine structural stability is the only limit?

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    $\begingroup$ This report, prepared for the OTA in the '80s, says: "Studies performed for the Defense Department showed that with a 25 percent reduction in payload, a booster about the same size as MX [with a burn time of 3 minutes] could be built which would burn out in less than 1 minute[...]" $\endgroup$
    – mmc
    Commented Feb 12, 2012 at 18:16

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It is difficult to discuss the specific figure as you did not give the reference, so it is not clear if they mean boost phase reduction at the expense of the last stage of the missile or something else. You don't just need to overcome 1 g during the boost speed , but also to achieve the escape velocity. If you shorten the boost phase but still achieve the escape velocity, perhaps you need higher force, which means higher requirements to the first stages, therefore greater mass, and so on. EDIT: I should have said "velocity comparable to the orbital velocity" instead of "escape velocity".

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  • $\begingroup$ Unfortunately, original reference is in Russian. I mean 'boost phase reduction' while reaching same destination. And as it's ICBM and not space rocket, it does not need to achieve escape velocity. $\endgroup$
    – BarsMonster
    Commented Feb 12, 2012 at 15:53
  • $\begingroup$ As for escape velocity, I stand corrected. However, that does not affect the reasoning, as you need to achieve a velocity comparable to the orbital velocity. Your explanation about "boost phase reduction" is not sufficient, as this reduction can be achieved by reducing the third stage duration, or by increasing the thrust at all stages, or in many other ways. Anyway, the original reference could help (I speak Russian). $\endgroup$
    – akhmeteli
    Commented Feb 12, 2012 at 16:13
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    $\begingroup$ dancomm.ru/news/vopros_s_avantjurista/2011-02-23-38 "Так, уменьшение АУТ на четверть приводит к уменьшению забрасываемой массы в разы при сохранении той же массы ракеты." $\endgroup$
    – BarsMonster
    Commented Feb 13, 2012 at 2:38
  • $\begingroup$ Yeah, unfortunately, no extra useful information there. And this statement may be erroneous, as there is a following statement at books.google.com/… : "MX-type ICBM can be built which burns out below 90 kilometers after just 50 seconds... This would involve a reduction of about 25 per cent in payload as compared to the MX" (200 km / 3 min) $\endgroup$
    – akhmeteli
    Commented Feb 13, 2012 at 3:52

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