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I need to calculate the delta-v for descent from 5-sol orbit to the surface of Mars and then ascent back to 5-sol orbit from the surface of Mars. What is a "5-sol orbit?"

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    $\begingroup$ Hint: Sol = Mars day $\endgroup$ Commented Mar 24, 2023 at 21:37
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    $\begingroup$ By "5 sol orbit" do you mean "A circular orbit over Mars with a period 5 sols long?" $\endgroup$
    – notovny
    Commented Mar 24, 2023 at 21:38
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    $\begingroup$ @notovny This seems like already an answer – the OP obviously doesn't know what is meant, they just got this task from someone else. $\endgroup$ Commented Mar 25, 2023 at 22:32
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    $\begingroup$ "What is a '5-sol orbit'?" is pretty darn clear, and the prompt, clear and comprehensive answer makes that pretty obvious. The question does not ask anything that requires the eccentricity. Yes they may need that information. but but notovny's question does not need to be addressed. The OP means simply a "5-sol oribt", no more. The close votes for "needs clarity" are therefore inappropriate. voting to leave open! $\endgroup$
    – uhoh
    Commented Mar 25, 2023 at 22:33
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    $\begingroup$ I don’t think this is an inherently bad question, though it’s kind of asking two questions in one, especially in light of the new question the OP asked. As-is they’re now asking about the deta-v calculations in two places, it might be clearer to disambiguate the two questions $\endgroup$ Commented Mar 29, 2023 at 4:08

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tl;dr it's an orbit around Mars with a period 5-sols long, but in the literature they're typically parking orbits so don't assume they're circular. Check the last two paragraphs for a potential trap.

I googled around a bit to check if this was being used in a way differently than all of us have leapt to (i.e. "5-sol is a direct statement of the period of the orbit"), but A Polar Orbit for the Mars Global Network Mission gives a 1/5 sol orbit with a 275km periapsis altitude. A bit of Kepler's law shows that this is a reasonable periapsis altitude for a 0.2-sol orbital period (and it's stated to be "the most-elliptical site-synchronous orbit with the required characteristics", so the slightly higher semimajor axis value I found just means the apoapsis can be higher).

I've seen 5-sol orbits referenced as parking orbits in e.g. Optimizing Parking Orbits for Roundtrip Mars Missions; in that paper the periapsis is 250km (page 6). So it seems at least circularity is not guaranteed.

A subtlety that might be present here: a Mars sol is supposed to be a solar day, but if these orbits are intended to be site-synchronous I think the Mars sidereal day would be the period you'd want to multiply. Solar and sidereal day lengths are slightly different.

Because of that timing subtlety, but also just as a good rule of thumb, maybe check with whoever you have to work those delta-Vs out for that you've defined the "5-sol orbit" the same way.

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    $\begingroup$ Especially because parking orbits shouldn't really be that high. $\endgroup$
    – Joshua
    Commented Mar 26, 2023 at 0:37
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    $\begingroup$ Sorry, the question was closed by someone. I have updated this question and looking forward to re-opening. $\endgroup$ Commented Mar 28, 2023 at 17:41
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    $\begingroup$ @PrashantModak what update did you make? Edit 3 seems to be empty, which I didn't even know was possible. $\endgroup$
    – Erin Anne
    Commented Mar 29, 2023 at 4:36

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