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Answers to Why do many Mars missions launch now, if the Hohmann transfer orbit is the most propellant-saving one? and discussions below them made me wonder what makes Earth-Mars transfers more non-Hohmann; inclination or eccentricity?

So I've asked.

The answer might be different between Earth-to-Mars and Mars-to-Earth, then again, it might not!

Maybe it depends on the year? If so, I think which is more often the reason or "on average" might be good enough, but someone may be able to dig up a table somewhere, I can't be the first person to wonder this, and it can be addressed quantitatively with a fairly simple analysis provided a definition for "non-Hohmannness" can be established.

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    $\begingroup$ What’s the metric for non-Hohmannism? $\endgroup$ – Russell Borogove Jul 27 '20 at 5:35
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    $\begingroup$ @RussellBorogove MNU's (Mars Non-hominy Units) is my preference, but I think there's some inclination to allow for more eccentric mectrics. $\endgroup$ – uhoh Jul 27 '20 at 5:37
  • $\begingroup$ Every-Hohmann-Transfer is eccentric? So what do you mean with: eccentricity reduces the value of MNUs? $\endgroup$ – CallMeTom Jul 27 '20 at 8:28
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    $\begingroup$ Ahh, okey, I understand.... $\endgroup$ – CallMeTom Jul 27 '20 at 9:00
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    $\begingroup$ Actually the definition of dV_h is not as important (just kind of an offset for the MNUs) you just need to keep always the same definition.... most important is the composition of dV_r .... "dV_r = dV_e + dV_i", your qestion is basically: which is bigger dV_i or dV_e .... and I am sure it is for most cases or nearly always dV_i $\endgroup$ – CallMeTom Jul 27 '20 at 9:21

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