Minmus Refueling Question

[Vsimm]

Ok So I am new to KSP (only about 100 hours or so) and I’ve spent the last few building a orbital refueling base around minmus and gong back and fourth from the surface of minmus to my orbital refueler/ore processor. It has all of its fuel tank full and are ready to begin exploration of the Kerbol system. BUT HOLD UP!. I was just about to burn my first ship from an LKO to minmus and refuel there but then a thought came to my head andI paused my game and I was thinking the very thing that you are about to read:

Would it be better/more efficient to just straight up burn from and LKO to Duna (my version of an LKO being 100,000km)  or from what I think burn to minmus, refuel, and then escape Kerbin’s SOI from there because Kerbin's SOI is pretty weak all the way out at minmus, therefore taking less Delta-v to escape Kerbin’s SOI all the way out there and plus have extra fuel because you just completely refueled your tanks at the orbital minmus refueling station?

please somebody get back to me with a correct awnser and thank you for reading this

I AM CONFUSED

[James Kerman]

Welcome to the forum @Vsimm.

I've moved your question to gameplay questions.

[Vsimm]

Oh I did not know about that sry

thanks

[AHHans]

Hi @Vsimm, welcome to the forums.

[Please keep the shouting to a minimum, that's bad for my hangover. ]

If you already have a full tank in LKO, then going to Minmus, refuel there, and go from there straight to the target is usually not a good idea. Due to the Oberth effect you gain more energy (= speed after leaving Kerbin's SOI) when doing a single burn in LKO than first going to Minmus and then doing a second burn there. You gain quite a bit back from refueling on Minmus, but if that is more or less than you lost due to not using the Oberth effect depends on where you are going. Without doing the math my guess is that for going to Duna (and probably Eve) you would save a bit by refueling on Minmus. But on the other hand setting up an efficient transfer burn from Minmus' orbit to Duna is a lot more complicated than doing so from LKO. (I mean: a lot!)  --  Hmmmm... So if you want to do that as a training exercise, then go ahead!   --  Doing this for a transfer to Moho, Dres, Jool, and Eeloo will probably cost more than you gain. (I think...)

What would be the most efficient is to refuel at Minmus, burn in low Minmus orbit onto an elliptical orbit that gets close to Kerbin again, and then do your main Duna transfer burn at the PE of that elliptical orbit. But that requires that you set up this intermediate elliptical orbit in such a way, that you can burn prograde at PE and get onto the transfer orbit to Duna. Setting this up correctly requires exact timing, precise burns, and having a good transfer window from Minmus via Kerbin to Duna. Getting that right is even more complicated than setting up a good transfer burn straight from Minmus to Duna.

For myself, I decided that I don't want to bother with these triple transfer orbits, and set up a refueling station in a circular gateway orbit around Kerbin, that is refueled with a miner from Minmus and where interplanetary craft can dock to refuel and then go their merry ways.

P.S. I found the discussion about transfer orbits that I remember, here:

 

Edited November 24, 2019 by AHHans
Added P.S.

[Vsimm]

6 hours ago, AHHans said:

Hi @Vsimm, welcome to the forums.

[Please keep the shouting to a minimum, that's bad for my hangover. ]

If you already have a full tank in LKO, then going to Minmus, refuel there, and go from there straight to the target is usually not a good idea. Due to the Oberth effect you gain more energy (= speed after leaving Kerbin's SOI) when doing a single burn in LKO than first going to Minmus and then doing a second burn there. You gain quite a bit back from refueling on Minmus, but if that is more or less than you lost due to not using the Oberth effect depends on where you are going. Without doing the math my guess is that for going to Duna (and probably Eve) you would save a bit by refueling on Minmus. But on the other hand setting up an efficient transfer burn from Minmus' orbit to Duna is a lot more complicated than doing so from LKO. (I mean: a lot!)  --  Hmmmm... So if you want to do that as a training exercise, then go ahead!   --  Doing this for a transfer to Moho, Dres, Jool, and Eeloo will probably cost more than you gain. (I think...)

What would be the most efficient is to refuel at Minmus, burn in low Minmus orbit onto an elliptical orbit that gets close to Kerbin again, and then do your main Duna transfer burn at the PE of that elliptical orbit. But that requires that you set up this intermediate elliptical orbit in such a way, that you can burn prograde at PE and get onto the transfer orbit to Duna. Setting this up correctly requires exact timing, precise burns, and having a good transfer window from Minmus via Kerbin to Duna. Getting that right is even more complicated than setting up a good transfer burn straight from Minmus to Duna.

For myself, I decided that I don't want to bother with these triple transfer orbits, and set up a refueling station in a circular gateway orbit around Kerbin, that is refueled with a miner from Minmus and where interplanetary craft can dock to refuel and then go their merry ways.

P.S. I found the discussion about transfer orbits that I remember, here:

 

Thanks