How long does Duna transfer window last?

[OscarJade]

I'd like to launch about 3 missions to Duna/Ike - outpost on Duna, Ike landing and perhaps a rover/other Duna landing. Is it possible (or feasible) to space out the transfer burns a day or so apart, and then manage the SOI changes at the other end?

[SchweinAero]

It should be very possible, I've done it myself for very little extra delta-V. However, because of the natural human variation in your transfer burns, your vessels will most likely arrive with several days between them, even if they escape Kerbin on the same hour.

[bigcalm]

> Is it possible (or feasible) to space out the transfer burns a day or so apart

Oh yes, easily. You've probably got a 30 day window in most instances -- see http://alexmoon.github.io/ksp/

For other bodies it can be less, but rarely less than a week.

[Reactordrone]

I launched my last mission three days past optimal with no real noticeable impact on the delta v requirement. A few days either side should be fine.

[Hcube]

just wondering, btw : how long does a Mars transfer window last IRL ?

[Kryxal]

Windows really aren't all that fixed ... you're not "in" the window at one instant, then "out" of the window 5 minutes later. It's just a matter of the delta-v requirements gradually rising as you get further from the optimal time and transit time. Do note that doing a non-optimal (fast/early) Duna transfer allows you to get there in time for a good return transfer with a dwell time of a few days.

[Reddeyfish]

just wondering, btw : how long does a Mars transfer window last IRL ?

there isn't a hard boundary, since it is always possible to reach mars no matter what the relative phase angle is.

(for the worst case scenario: burn continuously towards mars until the halfway point, then flip over and burn retrograde to slow down)

Therefore, the transfer window length depends on the power of the spaceship being sent. The window ends when the spaceship no longer has the delta-v to make the transition at the current phase angle.

Also, IRL it is possible to launch from earth, do an orbit around the sun, then use earth again for a gravitational assist. (e.g. the Rosetta mission). If the mission to mars chooses to do that (probably a probe), then calculating the length of the transfer window gets really complex because of the gravity assist.

rosetta mission flight path:

Edited July 9, 2015 by Reddeyfish

[Tatonf]

Yeah. But there's a kind of big difference between the perfect Hohmann transfer and having to burn straight to Mars in a case of Sun - Earth - Mars alignment. That would probably require to go near light speed if you don't want to miss it. Meaning an almost 600 000 000 m/s delta-V requirment (including the breaking, not the return).

BTW, for OP's problem, let's say that there's theorically a very precise moment where the transfer is optimal, but burning a few hours before/after will barely change anything to your delta-V cost (1 or 2 m/s probably). So don't worry that much.

Something worth considering however is the inclination change. There's a lot of tutorial saying that for a good Hohmann transfer you need to look at the phase angle between the planets. But you should really consider to wait for a window that will almost cost you nothing in terms of plane change. In the worst case, which is Moho, you can get up to a 2520 m/s burn plane change (according to delta-V map) !

[Rosco P. Coltrane]

Is it possible (or feasible) to space out the transfer burns a day or so apart, and then manage the SOI changes at the other end?

Two things here. Yes you can space your launches as other said. The best approach I think is to have them all in orbit already, so you'll be doing the burns with 20-30 minutes of difference between them.

But also, the time of arrival at Duna will NOT be spaced the same way, a little difference in the time and speed you leave Kerbin makes a huge difference down the road, so you might end up with days apart even if you launched the vessels within minutes of one another, so you'll have plenty of time to manage all SOI changes easily.

[Geschosskopf]

I'd like to launch about 3 missions to Duna/Ike - outpost on Duna, Ike landing and perhaps a rover/other Duna landing. Is it possible (or feasible) to space out the transfer burns a day or so apart, and then manage the SOI changes at the other end?

Certainly this is possible. I do flotillas all the time and it's no big deal. See the tutorial in my sig (and be sure to read to the end of the thread where things got a LOT easier thanks to a change in MJ).

Anyway, don't worry about spacing things at all on the departure end. That doesn't matter. You can put all your ships in orbit at once and burn them consecutively one after the other. Due to slight inaccuracies and differences in your transfer burns, and any mid-course tweaks you make, your ships will arrive spread out over an interval of several weeks by the time they get to Duna. And the further away you send your flotilla, the wider the spacing gets. At Jool, it might be a couple months before everything shows up.

The only place where you MIGHT run into having to juggle several ships at once is Eve. It's the shortest trip so usually a flotilla will all arrive within a day or 2 at most, with from 1 to a few hours between ships. But even that isn't really a problem because even with just 1 hour between ships, they're still far enough apart to burn one, jump to the next, burn it, etc.

But anyway, I do find it easier on me if I space my departure burns out by about an hour or 2. This is possible with the MJ "Advanced Transfer to Another Planet" thingy. Just move your mouse slightly until you see a slightly different departure time than ships youlve already made nodes for.

Of course, Kerbal Alarm Clock is an absolute must for this.

[Kryxal]

For that matter, a small burn prograde or retrograde combined with radial in/out will affect your arrival time with minimal effect (if you plan it that way!) on your arrival trajectory ... or you can adjust your arrival while you're at it (and this is VERY good for avoiding Ike!)

[OscarJade]

Thanks all! Speaking of Kerbal Alarm Clock...has anyone else had an issue with the latest KSP updates? I have downloaded the latest version of alarm clock (3.4.0.0), and can only see the clock icon in the VAB. I can set it from there to alert me to the transfer window, but I'm not sure how it will work when I'm nearing Duna's SOI

Edited July 10, 2015 by OscarJade

[Geschosskopf]

Thanks all! Speaking of Kerbal Alarm Clock...has anyone else had an issue with the latest KSP updates? I have downloaded the latest version of alarm clock (3.4.0.0), and can only see the clock icon in the VAB.

Hmm, works fine for me. Might want to check its settings and make sure you have it enabled where you need it.

[OscarJade]

Is there anyone familiar enough with Kerbal Alarm Clock to give me guidance on checking its settings to fix the above problem?

[Weywot8]

There is a settings button in the top right hand corner (wrench) when KAClock is open. Click that and an additional submenu should appear. One of the buttons in the top row is for 'visibility' - make sure it's visible for fight mode and you are all set.