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Looking at below picture, the Delta IV Heavy is clearly much taller than the Medium. Is there any specific reason why?

enter image description here

https://www.space.com/15078-rocket-launch-delta-4-milestone.html

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The fairing is bigger (Taller) for larger payloads.

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    $\begingroup$ To elaborate a little, it's a more powerful rocket than the DIVM, capable of carrying larger payloads - so it needs a bigger fairing space to put them in. $\endgroup$ Feb 24, 2023 at 4:00
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    $\begingroup$ ...though there are exceptions, like the Parker Solar Probe which needed the Ⅳheavy not because of its payload capability but simply to get enough Δv. It actually looked a big hilarious, such a small probe sitting in that giant fairing. en.wikipedia.org/wiki/Parker_Solar_Probe#/media/… $\endgroup$ Feb 24, 2023 at 17:42
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    $\begingroup$ @leftaroundabout: next question in this series is then probably why the fairing wasn't smaller.... $\endgroup$
    – PlasmaHH
    Feb 24, 2023 at 21:36
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    $\begingroup$ @PlasmaHH there's space.stackexchange.com/questions/26725/… about a case where the fairing was similarly oversized for the payload. $\endgroup$ Feb 24, 2023 at 21:42
  • $\begingroup$ @PlasmaHH in the case of the PSP, I suspect that qualifying Delta IVH to use either the shorter 5m fairing, or the narrower DCSS and 4m fairing would have exceeded the potential cost savings from using them by a large amount. ULA produces highly reliable rockets, but they have a very expensive cost structure. $\endgroup$ Feb 26, 2023 at 1:52

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