Best way to get from Minmus back to the Mun??

[MadJock]

Hi all, I tried searching for a simple answer for how to get back from low Minmus orbit back to the Mun to land? None of the calculators etc have that transfer that I've found. What's the trick to it? Maybe slingshot around Kerbin?

 

Cheers, 

MadJock

[Scarecrow71]

2 hours ago, MadJock said:

Hi all, I tried searching for a simple answer for how to get back from low Minmus orbit back to the Mun to land? None of the calculators etc have that transfer that I've found. What's the trick to it? Maybe slingshot around Kerbin?

 

Cheers, 

MadJock

For starters, the best way to even get from Minmus to Mun would be at AN or DN due to the inclined planar orbit Minmus is on.  Or, at least, that should - SHOULD - save on the amount of dV needed for the trip.

With that said, gravity assist around Kerbin might be your best bet.  As far as calculators for the transfer, I'd highly suggest using MechJeb.  It should be able to plot the transfer with relative ease.

[Streetwind]

4 hours ago, MadJock said:

None of the calculators etc have that transfer that I've found.

Then you haven't looked at this one.

Generally though, you can guesstimate yourself a way to a transfer window in this case because they reoccur so frequently - once every seven Kerbin days, roughly, maybe a little quicker even. Just plot a transfer that touches the Mun's orbit, and see if any close approach markers show up. None visible? Kill the node, timewarp a bit, and try again.

You can make informed guesses as to roughly when you can expect to see something by looking at the time to periapsis of that transfer. If it takes you two days (completely made up number btw, I don't know what it is ingame), and you know that the Mun orbits Kerbin roughly every six and a half days (this is the real, proper value), that means that you should look for a transfer when the Mun is roughly one sixth of its orbit ahead of Minmus (because then it has one third of its orbit, or roughly two days, to get to the point where your transfer will meet it).

You could also just click the "orbit forward" button on your maneuver node a zillion times to move it into the future until an encounter happens, if you were less inclined to think and more inclined to click a button a lot.

 

Edited February 13, 2023 by Streetwind

[darthgently]

2 hours ago, Scarecrow71 said:

For starters, the best way to even get from Minmus to Mun would be at AN or DN due to the inclined planar orbit Minmus is on.  Or, at least, that should - SHOULD - save on the amount of dV needed for the trip.

With that said, gravity assist around Kerbin might be your best bet.  As far as calculators for the transfer, I'd highly suggest using MechJeb.  It should be able to plot the transfer with relative ease.

I agree that the Kerbin slingshot way gives you the most options.  One being more likely to cross a relative AN or DN at a high Kerbin altitude to do your plane change of leaving Minmus, or arriving b at Mun, at a Minmus/Mun relative AN/DN isn't convenient.  Syncing the AN/DN with departure or arrival can be tedious given the nested SOIs involved

[DeadJohn]

There are more "efficient" (less DV, fuel, and game calendar time) ways to do this, but here's a pretty easy way that doesn't take much of your personal time, needs no tricky calculations or mods.

1. Get into Minmus orbit.
2. When you are on the "forward" side of Minmus (relative to its orbital path  around Kerbin), burn prograde until your apoapsis will leave Minmus SOI. I suggest watching in map view so you can see as soon as your apoapsis breaks Minmus.
3. Set your target to Mun.
4. Timewarp until you are in a very high orbit around Kerbin, then timewarp more until you are at the first ascending or descending node between your current orbit and Mun.
5. Burn descending or ascending to get into the same inclination as Mun. (Changing inclination in low Kerbin orbit is expensive, but you are up near Minmus orbit and changing inclination is much easier)
6. Drop a maneuver node slightly ahead of your ship. Drag the retrograde handle of the maneuver node to lower periapsis until periapsis touches Mun's orbit. Then drag the maneuver node further ahead of your ship until you get an intercept with Mun. You might need to finetune the maneuver's pro/retro direction as you change the manuever's time (because your high Kerbin orbit is probably elliptical).

That's 3 burns in total. #1 is a rough burn to get away from Minmus, #2 is a rough burn to remove inclination, #3 is a plotted maneuver to get the right time to intercept.

There are much more elegant ways to do this, but they are IMO more complex and will take more of your real-world time trying to get a perfect maneuver in as little as one burn. It's possible to get from Minmus to Mun intercept with 1 complex burn.

Note that getting from Mun orbit to Minmus can use a similar set of steps.

 

[king of nowhere]

6 hours ago, MadJock said:

Hi all, I tried searching for a simple answer for how to get back from low Minmus orbit back to the Mun to land? None of the calculators etc have that transfer that I've found. What's the trick to it? Maybe slingshot around Kerbin?

 

Cheers, 

MadJock

a simple hohmann trasnfer is the best option, it's extremely cheap if done correctly.

a hohmann transfer is relatively easy, but complex enough that I won't take the time to explain it just in case you don't know. if you don't know a hohmann transfer, ask further

Edited February 13, 2023 by king of nowhere

[Grogs]

3 hours ago, Scarecrow71 said:

For starters, the best way to even get from Minmus to Mun would be at AN or DN due to the inclined planar orbit Minmus is on.  Or, at least, that should - SHOULD - save on the amount of dV needed for the trip.

With that said, gravity assist around Kerbin might be your best bet.  As far as calculators for the transfer, I'd highly suggest using MechJeb.  It should be able to plot the transfer with relative ease.

Yeah, MechJeb can make that transfer most of the time, maybe 80%. Sometimes it plots a maneuver it and it's a clean miss, but I can usually play with the nodes a bit and get an intercept. Personally though, I agree with the others that it's usually not worth it. For my career games, I take my new kerbonauts and tourists on a circuit from Kerbin to the Mun to Minmus to the edge of Kerbin's SOI, and then back to Kerbin orbit. I find the Mun-Minmus transfer to be relatively easy to set up, but the opposite direction seems a lot harder.

If I do need to go directly from Minmus to Mun for some reason, I would probably swing around Kerbin first as suggested by others. Ideally, I would set it up so my AN/DN with the Mun occurs just after I leave Minmus SOI and then it's super cheap to match inclinations. Then I burn retrograde at Kerbin Pe until I get an intercept with the Mun.

[MadJock]

Many thanks to everyone who responded. I'll need to clearly do more practice and I was maybe a bit unlucky with my current orbits with both the Mun and Minmus to not get an intersect.  Thank you Steetwind for the  Alex Moon Launch Window Planner which I had seen before but had yet to figure out how to make the most of all the info it can provide.

Cheers,

MadJock

[Empiro]

On 2/15/2023 at 12:37 AM, MadJock said:

Many thanks to everyone who responded. I'll need to clearly do more practice and I was maybe a bit unlucky with my current orbits with both the Mun and Minmus to not get an intersect.  Thank you Steetwind for the  Alex Moon Launch Window Planner which I had seen before but had yet to figure out how to make the most of all the info it can provide.

Cheers,

MadJock

There's different ways to do things, but the simplest (though not cheapest or fastest) way to do things is:

1. Eject from Minmus just barely so that you're orbiting around Kerbin.
2. Target the Mun and see where the AN or DN are.
3. Create a maneuver node and burn normal to reduce the relative inclination to 0. Execute the manuver so you're at 0 relative inclination with the Mun.
4. Create a maneuver node to bring down your PE so that it's barely touching the Mun's orbit.
5. Move your maneuver node so that it comes later or sooner, and get an intercept. The encounter markers can help you here -- if the Mun is behind you at the closest approach point, then burn later. If the Mun is ahead of you at the closest approach point, burn earlier. 

You can reduce the total fuel cost by basically combining the inclination change and transfer burn, and doing it all from low Minmus orbit. However, this requires waiting for just the right window and very careful maneuver tweaking. However, the Minmus - Mun transfer is cheap enough that it's not worth bothering with unless you're purposefully trying to practice timing transfer windows.

Going interplanetary is when it's really going to make a huge difference, especially to somewhere like Moho. It's the difference between a round trip needing a big ship, versus needing an absolutely massive one.