Is my Minmus fuel station useless?

[TheDog]

How can I make good/better use of my Minmus fuel station?

Setup in low Minmus orbit (80km), completely self-sustaining due to refueling by a Karbonite lander, which ships fuel back up to the station.

Was great fun to set it up and practice operating with it.

I had anticipated it to be useful as "the" gateway for interplenetary missions.

Now, my first Duna mission in en route. And what had happened?

-> We started actually from low Kerbin orbit, without going to Minmus first. Why?

1. Using Mechjeb to plan the trip, both Hohmann and porkchop selection does not work in Minmus SOI (transfer calculation needs both bodies having the same "parent" body). Bummer.

2. Flying to Minmus, topping off fuel, then dropping to highly elliptical Kerbin orbit for interplanetary burn takes a long time (2days from Minmus back to PE at Kerbin) -> does not seem practical

3. Flying to Minmus, topping off fuel, then burn to get Kerbin escape trajectory, then calculate transfer via porkchop or Hohmann -> possible, but sounds risky (would you board a craft when the mission plan says "just burn to Sun orbit, then we'll see what we can do..." ???)

So,how can I make my beloved Minmus fuel stop useful?

Thanks for all suggestions!

Edited March 30, 2015 by TheDog
answered

[Red Iron Crown]

I would use tankers to bring the fuel for refueling your interplanetary stuff down to LKO from the station. Almost always easier to bring the fuel to the ship rather than vice-versa.

[Taki117]

I agree with Red Iron Crown. Pack some LV-Ns on a tug and run a space train to bring fuel to your interplanetary ship in LKO from your Minmus Refueler. You're going to have a heck of a time rendezvouding, but Mechjebs Rendezvous autopilot helps there.

[Kerbart]

Top off at Minmus, a light burn to get out of the minmus SOI into a large circular orbit around Kerbin, burn from there? Has the advantage that you don't need 1000m/s dV to escape Kerbin. Given the long period of the orbit transferring to other planets may be tricky though.

But as Red Iron Crown mentioned, returning full tanks to Kerbin (with some aerobraking to save even more fuel) is probably the more practical approach.

[TheDog]

I see... so the consensus seems to be towards shipping fuel down to LKO.

My only grip with that is, that it takes about 2 kerbin days for the tanker to arrive there and rendezvous...

[Red Iron Crown]

You have to do that transfer one way or the other. If you go the other way it will take two days to get your ship out to Minmus to refuel.

[LethalDose]

Soooo, question. Why is this impractical:

2. Flying to Minmus, topping off fuel, then dropping to highly elliptical Kerbin orbit for interplanetary burn takes a long time (2days from Minmus back to PE at Kerbin) -> does not seem practical

The only trick is that you need to time your exit burn from Minmus so that your Kerbin Pe is in the right location for your exit burn. This strategy can save you ~ 750 m/s dV for escape burns. Not all that necessary for Trans-Duna or Trans-Eve injections, but for destinations more distant it can be useful.

Also, lower orbits for refueling stations may be more useful. 80 km is pretty high.

[Taki117]

I see... so the consensus seems to be towards shipping fuel down to LKO.

My only grip with that is, that it takes about 2 kerbin days for the tanker to arrive there and rendezvous...

You shouldn't be doing this less than about two weeks prior to transfer. That way you have plenty of time to make multiple trips to and from Minmus.

[TheDog]

OK, thanks guys, I'll try both suggestions (shipping fuel down in advance, dropping down with PE)...

Btw, how can I set the thread marker to "[answered]" ??

edit: found it

[FlyingPete]

Bringing fuel down to LKO is going to be much cheaper to do- it doesn't take much dV to escape Minmus, and you can aerobrake at Kerbin to save fuel. Have a couple of tankers running back and forth, returning the empties to the fuel station.