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Is anybody aware of a nice graphic showing for the next 20-30 years or maybe the rest of the 21st century, the time periods for Earth to Mars launches? They occur about every two years, but I'm looking for the exact best time periods to go or return that minimize fuel use (the technical term is Hohmann transfer periods or orbits - https://en.wikipedia.org/wiki/Hohmann_transfer_orbit).

I found this table (http://clowder.net/hop/railroad/EMa.htm) which seems to show the best day every two years, or so, but I think there's a wider period of a few days when the window opens for the transfer. I'm looking for a graphic that shows that, with specific dates (or second best, another table that shows more than just the best date).

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    $\begingroup$ @PcMan you can just edit the post and correct it (as some kind soul has quickly and quietly done) ; those typos don't cause any trouble with reading the post, and there are no requirements whatsoever in Stack Exchange that posts must be error-free. These days people are often typing on phones and it can be a challenge to get something posted at all, much less perfect. $\endgroup$
    – uhoh
    Aug 6, 2021 at 17:18
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    $\begingroup$ @PcMan you may be confusing me with someone else; to my knowledge I've never complained about you making a helpful edit to a post; correcting obvious typos. In Stack Exchange we don't welcome a new user to the site by complaining about typos in their first question. The overriding task at hand is to be welcoming to new users. $\endgroup$
    – uhoh
    Aug 6, 2021 at 17:25
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    $\begingroup$ The optimal transfers to Mars are not Hohmann transfers. A Hohmann transfer is from one circular orbit to another, with both circular orbits being on the same plane. Both Earth and Mars have non-circular orbits, especially Mars, and the orbital planes of the two planets are inclined with respect to one another. $\endgroup$
    – David Hammen
    Aug 7, 2021 at 15:29

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Graphics showing non-optimal but "close enough" launch opportunities, and their relative cost, are called porkchop plots.

The following example is from On the Nature of Earth-Mars Porkchop Plots

single porkchop plot

The main takeaways:

  • The eccentricities and relative inclination of Earth and Mars makes this kind of analysis far from straightforward.
  • There's significant leeway in the exact date of departure, but the cost grows faster and faster the further away form optimality one gets.

Figure 2. is exactly the kind of visualisation you are requesting:

chained porkchop plots

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