Fuel farming efficiency

[Shmauck]

I wonder what is the most efficient way to provide my interplanetary missions out of Kerbin with farmed liquid fuel. I would launch empty transfer stages from KSC and fuel them on orbit. I can think of a number of ways:

• Mine ore on Minmus (probably not Mun due to its higher dV requirements) and bring ore to LKO to process it there
• Mine ore on Minmus, process it in Minmus orbit and transport the fuel back to LKO
• Mine ore and process fuel on the surface of Minmus, then transport the fuel back to LKO

I assume all three options to be more efficient than launching the (paid) fuel from Kerbins surface due to Kerbins gravity and atmosphere. Is this assumption correct?

Which of the three is the best way to do it? Are there numbers to calculate this kind of efficiency? If someone can point me to a posting or a video to explain this, I‘d be happy. 

Thank you in advance.

[HebaruSan]

A fourth option to consider:

• Mine on Minmus, process in Minmus orbit, launch interplanetary ships to refuel in Minmus orbit, launch Minmus -> LKO -> interplanetary

Minmus's orbital period is about 50 days, which means it will be properly aligned within 25 days of a given transfer window. You pay the cost of a Minmus transfer up front, but once you're refueled you have a ~930 m/s head start on your interplanetary burn (net benefit 770 m/s if you assume 160 m/s to leave). In theory this could allow a smaller stage for that part of the journey.

[Shmauck]

Interesting, but I am not sure if I understand you well. When you say launch Minmus > LKO > interplanetary, what would that mean for LKO? Would you fully circularize a low Kerbin orbit and then do the escape burn? Or would you try to slingshot around Kerbin to find the right escape trajectory?

[Superfluous J]

20 minutes ago, Shmauck said:

Interesting, but I am not sure if I understand you well. When you say launch Minmus > LKO > interplanetary, what would that mean for LKO? Would you fully circularize a low Kerbin orbit and then do the escape burn? Or would you try to slingshot around Kerbin to find the right escape trajectory?

The latter. You can also without much loss eject straight from Minmus, so now you're always within 12 days of a transfer window.

And you have to define efficiency. It's actually (and slightly) less FUEL efficient, as you use more fuel. It's more COST efficient because any fuel you don't lift off of Kerbin is not only free, but it doesn't need any fuel to get it off Kerbin. It's (far) less TIME efficient, though. You can do a full trip to Duna and back in the time it takes you (the player) to do all these fuel runs, rendezvous and dockings, and ejections at the exact correct time and in the exact correct direction to take full advantage of the Oberth effect at Kerbin.

However it can be extremely FUN efficient, which really is all that matters when playing.

[bewing]

After trying all the above methods a number of times, I have decided that I like to use method 3. The deltaV needed to get a tanker ship from the surface of Minmus to a 45km Pe at Kerbin is pretty tiny. So trying to conserve there is not too useful.

And a large interplanetary ship may not have enough fuel remaining to get from LKO to Minmus for refueling.

But circularizing a tanker at LKO takes a relatively large amount of dV. So I created a tanker with a very high heat tolerance that could aerobrake (in 3 passes) from Minmus with a huge load a fuel. And I find that to be fun.

[Shmauck]

I am totally with all of you on the fun part. I am trying to run a realistic space program and going to Duna and back in as little time as possible with lots of time warping and doing nothing in parallel isn‘t tempting me. 

I think I will try option 3 first as I am currently assembling my Duna mission in LKO and it is most likely going to be too large to take the trip to Minmus. Also, I think I need more practice to pull off option 4. Aerobraking the tanker at Kerbin is a great idea. 

Thank you guys very much for sharing your insights!