Mun to Minmus

[Red Shirt]

Had a fully operational Mun base for resource mining. The problem is the high dv requirements to lift a tank of fuel, transfer to LKO rendezvous, then return to Mun base afterwards. Today I set up a mining platform on Minmus to see if it brings much in the way of fuel savings. It will have to wait until tomorrow to find out as the transfer tanker with Jeb and Bill left Mun then tumbled into Minmus and exploded because I ran out of fuel. Too many course corrections and unevenly loaded tanks (yeah, I'm an idiot).

Long explanation to ask - how do you efficiently transfer to Minmus from Mun orbit?

Edited October 5, 2015 by Red Shirt

[Alshain]

Mining in the Kerbin area really isn't a great idea anywhere, it's just not worth the effort compared to just launching fuel from KSC.

To answer the question though, you just need to exetend it out until you find an encounter. Play with the maneuver nodes till you find one. It's actually a bit easier in the opposite direction unfortunately because ejection from Minmus often puts you at the right inclination for the Mun. Whenever I do a tour contract, I got to Minmus first. Nevertheless, you should be able to find one. Worst case scenario, try to get close to it and then treat it like a rendezvous in LKO. Really there is no difference between catching a craft orbiting Kerbin and catching the Mun or Minmus, except the latter two have their own gravity.

[Red Shirt]

Mining in the Kerbin area really isn't a great idea anywhere, it's just not worth the effort compared to just launching fuel from KSC.

I don't disagree. I've done single launch and fuel from KSC several times. Now I want to try out reuseable tankers and resource mining. Strictly a personal challenge.

As for the Mun/Minmus transfer, I just (wrongly) assumed it would be easy. Since I destroyed my tanker, I don't need to repeat this as my new launch will go straight from KSC to Minmus, but if I can't do it here, I won't be able to get it right at Jool and beyond. Should I escape Mun SOI first or shoot straight from orbit?

[mattssheep4]

Kerbal Alarm Clock will let you know when to make transfer burns from one moon/planet to another, if that's what you're looking for. I've used it enough that I can guesstimate pretty well now, so that's my suggestion.

[FancyMouse]

For dumb person like myself, I use transfer window planner. When I need to know when I arrive, I just cannot eyeball a transfer at all.

[Kerbart]

Just set up an intercept for an outer planet. Moons have a mysterious ability to interfere with that.

[Red Shirt]

Just set up an intercept for an outer planet. Moons have a mysterious ability to interfere with that.

Exactly what happened! My transfer crossed back over Mun's SOI (d'oh) and messed up my trajectory. A couple correction burns later I was low on fuel.

[Birdco_Space]

Transfer window planner is the best way to find the most fuel efficient transfers. The capture dV required at the Mun for one of these transfers is generally pretty low (the orbit in the Mun SOI is only barely parabolic)

For my Minmus mining operations, I actually go back to LKO via a Mun Encounter, as the gravity assist braking from swinging around the prograde side of the Mun (with a modest burn at Mun Perapsis) cuts down the amount of aerobraking required (or dV for rigs that cant aerobrake)

[Red Shirt]

Transfer window planner looks like a tiny download. I'll repeat my Mun/Minmus transfer and see how TWP handles it.

[Streetwind]

Long explanation to ask - how do you efficiently transfer to Minmus from Mun orbit?

To actually address this question:

A Mun -> Minmus transfer is simply a miniature version of an interplanetary transfer, like from Kerbin to Duna. All rules that apply to interplanetary transfers also appy to going from Mun to Minmus, and it in fact makes a great practice mission for newcomers before really committing to sending your poor Kerbals scary far away from home.

The first thing to learn is the ejection vector. To go outwards (Mun to Minmus), you need to burn so that you leave the body's sphere of influence in its direction of travel. You will perform your burn on the "night side" or "far side" with respect to Kerbin, and eject "forwards". This raises your apoapsis on the other side of Kerbin. To go inwards (Minmus to Mun), you need to burn so that you leave the body's sphere of influence in the direction opposite to its travel. You will perform your burn on the "day side" or "near side" with respect to Kerbin, and eject "backwards". This lowers your apoapsis on the other side of Kerbin.

Next, to make an efficient transfer, you need to wait until the two moons are aligned correctly with respect to each other (your "transfer window"). Where is that alignment? Well, when you make your ejection burn from the Mun as described above, and raise your apoapsis just far enough for it to touch Minmus' orbit, you want Minmus to be in that exact spot at the time you reach that apoapsis. You can technically figure this out with math, or even let a mod or website tell you where it is... But you can also approximate it quick and dirty via the close approach markers. Target your destination, make a maneuver node to simulate your transfer, and check look for the "target position at closest approach" marker. If it is in front of where your orbits touch, you must wait longer for the window to approach; if it is behind, you just missed the window (but you may still be able to get an encounter by expending a bunch of extra dV to fly faster than normal and "make up lost time"). if you don't get any markers at all, you're nowhere near a window.

Except... you need to pay attention to inclination. Just like going from equatorial low Kerbin orbit to Minmus often makes it difficult to get an intercept, going from Mun to Minmus (and back) poses similar problems. To get close approach markers, you need to actually get your apoapsis close enough to the target orbit, and that may require a normal/antinormal component in your maneuver node or a midcourse correction.