Mun or Minmus (For orbital fuel refinery)

[jackellice]

12 hours ago, 5thHorseman said:

You can leave Mun backwards 180 degrees from where you'd eject from LKO, put your periapsis where you'd eject to your destination planet, and then burn at that periapsis to eject. Costs about 310 from Mun and 160 from Minmus and is like burning 860 or 930 from LKO back up there.

You still have to spend twice the deltaV

1. to get your interplanetary craft to Low Mun(860 m/s)
2. and rendezvous(310 m/s) with the OPD there
3. before returning for the Kerbin periapsis burn (310 m/s).

By then you've already have spent 1480 m/s to get to the mun and then back for the ejection burn... and another 90m/s (950m/s escape velocity - 860m/s Mun intercept) to escape Kerbin's SOI.

This is assuming your LKO's periapsis that you've made matches up with your ejection angle burn point so corrections have to be made along the way.

Instead of spending 1570 m/s to escape from Kerbin's SOI, why not just refuel your ship at Kerbin and save yourself 620 m/s? 
It could go to other things as well as the complexity of having to conduct 6 different orbital maneuvres with just 2 like so:

Spoiler

 

LKO > Munar Injection > Capture/Circularization > LMO OPD Rendezvous(include docking) > LKO Return > refine periapsis > Interplanetary Injection

LKO > LKO OPD Rendezvous(include docking) > Interplanetary Injection

 

Let the refueling tankers move between the surface of LMO to the LKO OPD.

Edited January 1, 2017 by jackellice

[Superfluous J]

1 hour ago, jackellice said:

You still have to spend twice the deltaV

1. to get your interplanetary craft to Low Mun(860 m/s)
2. and rendezvous(310 m/s) with the OPD there
3. before returning for the Kerbin periapsis burn (310 m/s).

Not to sound curt, but who cares?

Fuel at Mun, once you've set up a mining operation there, is free. If you can get a ship there on fumes, fill up with totally free fuel, and eject to Duna for about 600m/s less than it would take from LKO, then you've got a lot more options on how you build the ship you sent up from Kerbin.

And the savings is better from Minmus.

1 hour ago, jackellice said:

Instead of spending 1570 m/s to escape from Kerbin's SOI, why not just refuel your ship at Kerbin and save yourself 620 m/s?

Because the ship you "saved 620m/s" with will either have partially empty tanks or tanks you brought up from Kerbin's gravity well that you could have avoided ever sending. And the bigger lifter. And the slower game speed due to all those extra parts on the launch pad.

If Kerbin was reality and Kerbals were working in space, there would likely be both of what we're talking about. You'd launch a ship to LKO with empty tanks, fill up just enough there to get to Mun (or more likely Minmus), fill up there, and then burn down to swing by Kerbin to eject to your destination. The LKO fuel would come from Minmus, too.

[jackellice]

6 hours ago, 5thHorseman said:

Not to sound curt, but who cares?

Fuel at Mun, once you've set up a mining operation there, is free. If you can get a ship there on fumes, fill up with totally free fuel, and eject to Duna for about 600m/s less than it would take from LKO, then you've got a lot more options on how you build the ship you sent up from Kerbin.

And the savings is better from Minmus.

Spoiler

 

Following the orbital maneuvers I detailed in the spoiler, A craft that refuels from LKO saves 620m/s to reach Kerbin Escape Velocity, refueling at LKO than they do refueling at LMO. After the final burn to escape Kerbin's SOI,

1. The ship that refuelled at LKO would have spent 950 m/s of its reserve.
2. The ship that refuelled at LMO would have spent 400 m/s of its reserve.

Which makes sense to what you're saying. the LKO ship would have 550 m/s less deltaV on board leaving Kerbin's SOI.

 

The point you made about counting deltaV spent from the point of refueling as opposed to from LKO is a good one I didn't consider and you're right on that.

That said, I noticed you hadn't touched on the second part of my post with was about complexity.

From LKO it would still require you to do 6 different orbital maneuvers over 2, with the LMO ship. One of those maneuvers includes adjusting your craft's periapsis along its orbit, whilst returning from the mun, to be at the right ejection angle for your interplanetary injection burn. 

Now I know we're all about doing orbital maneuvers, that's what we love. But if we want to get to duna (in this scenario) easily we should go for the two maneuver approach with the LKO OPD over the six maneuver one with the LMO OPD. It's much easier to do and unless you have a ginormous show stopping ship, adding a tank that could hold 550m/s isn't too heavy on your ship's systems.

It doesn't even need to be filled for the launch if you're worried about complexity of the craft at launch.

6 hours ago, 5thHorseman said:

If Kerbin was reality and Kerbals were working in space, there would likely be both of what we're talking about. You'd launch a ship to LKO with empty tanks, fill up just enough there to get to Mun (or more likely Minmus), fill up there, and then burn down to swing by Kerbin to eject to your destination. The LKO fuel would come from Minmus, too.

Towards this: If Kerbin were reality, If we were to go interplanetary, I do not believe that an interplanetary ship would have bothered going to the Mun or Minmus to do it. they would just refuel at LKO and burn once.

Yes there would be OPDs in LKO, LMO and LmO But unless there was a interplanetary spacecraft built near Mun or Minmus, I would see the LMO and LmO refueling points strictly for kerbin orbital operations.

 

 

Edited January 1, 2017 by jackellice

[storm6436]

Because complexity is largely not a limiting factor to space programs.   Where you can go with the fuel you have is.   A ship dropping from Minmusorbit to abuse the oberth effect has much more effective dV than an identical one burning from LKO. 

Edited January 1, 2017 by storm6436

[Birdco_Space]

The argument of which mode is more efficient really boils down to how you play.  From a purely stock perspective, Mining fuel from the Mun is more time efficient, Mining fuel from Minmus gets a larger usable fuel fraction to orbit.  If the goal is a large amount of usable fuel in LKO in as short of time as possible, Mining the Mun requires a smaller investment in infrastructure for a given fuel rate delivered to LKO.  If you just need an occasional fuel stop at one of the moons, Minmus is generally a better option.

 

If you are playing a modded game where there are several different fuel types refineable from ore (like Near Future), there is a greater benefit of hauling ore into orbit, which pushes Minmus higher up the value chart. My kerballed interplanetary missions using near future and Nertea's Nuclear engine mod, I use detachable LH fuel Nuclear rockets to eject from Kerbin's SOI (which then retro burn and stop at a fueling depot for refuel and re-use), and Lithium fueled plasma thrusters for capture at the destination and return.  In this case, I tend to have a fuel depot in LMO (easier to get an cheap intercept with from a highly elliptic orbit) which I keep stocked with fuel either generated on Mun (for LH and Lqfuel/OX), or brought in from Minmus (Lithium)

[DrunkenKerbalnaut]

7 hours ago, Birdco_Space said:

...detachable LH fuel Nuclear rockets to eject from Kerbin's SOI (which then retro burn and stop at a fueling depot for refuel and re-use)...

That's very Von Braun of you. How are they attached to your vessel?

[Blaarkies]

On 1/1/2017 at 7:37 PM, jackellice said:

  Reveal hidden contents

 

Following the orbital maneuvers I detailed in the spoiler, A craft that refuels from LKO saves 620m/s to reach Kerbin Escape Velocity, refueling at LKO than they do refueling at LMO. After the final burn to escape Kerbin's SOI,

1. The ship that refuelled at LKO would have spent 950 m/s of its reserve.
2. The ship that refuelled at LMO would have spent 400 m/s of its reserve.

Which makes sense to what you're saying. the LKO ship would have 550 m/s less deltaV on board leaving Kerbin's SOI.

 

But if we want to get to duna (in this scenario) easily we should go for the two maneuver approach...

As long as you are only aiming for Duna/Eve, you might as well just launch straight from Minmus low orbit. You save like 50m/s by going back to an eliptical Kerbin orbit before ejection(for Duna/Eve destinations)...but going to Moho/Dress/Beyond really benefits from the Oberth effect.

Minmus' slow orbit means you will likely catch the optimal launch window by +-15 days though  but it's not nearly as complicated as everyone here says. It is definately not a 6 different orbital maneuvers...it's more like 5 

[Birdco_Space]

15 hours ago, DrunkenKerbalnaut said:

That's very Von Braun of you. How are they attached to your vessel?

Radially using Nertea's Near future Structure square docking ports.  These ensure that thrust is aligned downed the axis of the space ship because the docking ports only couple at exactly 0, 90 , 180, or 270 degrees relative rotation. 

 

Edited January 3, 2017 by Birdco_Space
clarity

[lodger]

I started running my own mining operation and decided to use Mun for ore mining and fuel refining "not because they're easy but because they're hard" (to quote a great visionary of his time). 

Edited January 3, 2017 by lodger
spelling

[jhousen]

I prefer mun, with lmo and lko fuel depots, and a couple tankers.