Do you want to build a fuel scheme ?

[Jesrad]

f you've already read the "how efficient is your mining operation" thread, you can skip this, sorry.

If you haven't read the Spudis & Lavoie paper on "how and why to develop cislunar space infrastructure ASAP", I can't blame you. But you should go and read it anyway

An excerpt:

Basically, theirs is a fully laid-out plan on which rockets (mostly Atlas) to use to send what specific crafts and modules where on the Moon and around it and at what estimated cost, in order to build a complete fuel&more extraction ISRU infrastructure on the Moon's south pole, and use it as a stepladder to Mars and the Asteroid Belt. And I wanted to simplify and adapt it to KSP, so I'd have free fuel flowing everywhere in near-Kerbin space, to leverage for future interplanetary (and interstellar ?) missions.

As I had no experience at all with KSP's ISRU and mining stuff, I set out to test it, first at the KSC, then in-situ proper:

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Then came the big work.

Echelon #1: Minmus Mining Rig

I selected Minmus rather than Mun for the infrastructure because it has a shallower gravity well and I'd rather not waste too much fuel landing and departing, but mostly because it's closer to Kerbin escape, making it more accurate to the Moon w.r.t The Plan.

Building on this fresh experience I designed a mining rig for Minmus' flats, figuring I could slap a Klaw on it and worry about what kind of ship it'd feed later:

Churn churn churn...

This went very well, the rig landed without even using up its landing stage (the two detachable engines on the sides) because I still overengineer stuff badly, for fear of lacking. I blame my college years.

Echelon #2: the Orbital Depot

The DCSN plan calls for sending the fuel extracted on the Moon to the Earth-Moon L2 point, and from there, drop it into LEO with the very cheap Farquhar route (using just 330 m/s deltaV in a couple impulses, and airbraking at the end):

Shown in its reversed form (Earth->L2) here.

But there is no such thing as Lagrange points in KSP because it uses a 2-body gravity simulation. I need a fuel depot to store fuel from and then feed it to my future interplanetary ships: putting it inside of Minmus' gravity well would put extra deltaV cost on them, and possibly some TWR constraints. And I need the depot at a near-escape energy relative to Kerbin. So I figured I'd put the depot on a Minmus-identical orbit (47 Mm from Kerbin, circular), just with a phase offset. This way it'd stay fixed relative to Kerbin-Minmus, and be just 40 m/s from interplanetary transits.

Here's the automated craft up for the task:

And once launched:

It leads Minmus by about 16000 km, so it's more of a L5 rather than L2. But I stick to the L2 name nonetheless.

Echelon #3: Minmus Tanker

I'd need to convert, store and shuttle this fuel away. So I'd need some big ship that would land on Minmus, connect to the rig somehow, have an ISRU, and with enough deltaV to bring her haul to the Depot. I hastily cobbled together this:

And launched her thus to meet the Minmus Mining Rig:

Also, Bill relieved Phoda at the commands of the Mining Rig:

The Tanker Less, as she ended up being called, then departed Minmus for the L2 Depot:

Echelon #4: Cislunar Tanker

As mentioned before, the fuel also needs to be dropped from L2 to LKO. From there it can power all manner of near-Kerbin, and possibly Munar, operations. Then the tankers would return to L2 and refill, for a new cycle. I opted for an automated, simple yet robust design. OK, I actually just recycled my Depot design, minus the side ports:

It launches easily, and even has extra fuel in the ascent stage once in LKO.

Echelon 3.5: Minmus Tanker++

I realised the Tanker Less was too small for the task of hauling massive amounts of fuel from Minmus to K-Min L2. So I made a 3x bigger one, the Tanker More:

She has crew quarters for those long transit times, too. I may be a pie-rat who press-gangs stranded Kerbals into a life of risky service, I still have to make sure they don't go crazy on me mid-mission.

She launches cheaply, using a simple booster stage then her own power:

I filled her with every loose green-horned Kerbal I could round up at the time, for the purpose of giving them a taste of what Real Space is like out there. They'd go to Minmus then K-Min L2 and back to Kerbin, as a first test of this whole infrastructure thing.

Stopover at the Cislunar Tanker for a refill, as the fuel was expended on ascent:

Hmm, this is turning out right, I think. We're already making good use of the first echelons She went to K-Min L2 first, to drop off the empty Tanker:

And was quickly joined by the Tanker Less, inbound from Minmus and heavy from her fresh load:

After a quick but intense exchange of fluids, Tanker More continues her route to the Minmus Rig:

The Rig has too small an ore capacity to make her a tankful, but that's fine, she can refill from the continuous mining in the time it'll take the other Tanker to come around from the Depot.

Echelon #5: Crew Shuttle

My bundle of rookies (a school of fishies, a herd of cows, and a bundle of Kerbals, is how I call it) is on Minmus, watching the ore get chewed. When they get back to the Depot along with the haul, they'll go their own way, back to Kerbin. But they cannot ride on the Cislunar Tankers (in hindsight, I should have slapped a few seats on those, that would have been hilarious) so I need me some crew transfer capacity to the Depot and back. Thus:

She has a smaller deltaV range, as she won't land anywhere and just switch back and forth between LKO and K-Min L2. 20-Kerbal capacity, including the mandatory pilot - she has no probe core.

Like the Tanker More, she needed a refill in LKO for the trip to K-Min L2. Fortunately I have 3 different Cislunar Tankers in my rotation:

After picking up all the, shall we say, "space-broken" crew, she dived back to Kerbin for a direct aerocapture to LKO (Periapsis 26700m):

They've been to the deepest reaches of Kerbin-space, they've seen the arid Flats of Minus, nothing can faze'm.

From there, any kind of SSTO works as a shuttle between surface and LKO

Echelon #6: LKO-SSTO

So I need me a big SSTO for large crew transfers to and from LKO. I suck at SSTOs, honestly, taking no chance I went the brute-force route and made this:

Some of it burned on reentry Fortunately, I now have the Ulysse and a few spaceplanes to replace it with. You will probably have better luck and skill than me on this echelon.

Echelon 3.999999: Yet-Bigger Minmus Tanker

I opted to make yet another, bigger-still, tanker to go between Minmus and L2, so that I could do proper rotations with decently-sized loads of fuel everytime:

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Final tallies:

Here's a recap of the infrastructure:

LKO -> K-Min L2 = 1155 m/s

K-Min L2 -> LKO = <461 m/s

Minmus -> K-Min L2 = 370 m/s

K-Min L2 -> Minmus = <450 m/s

Surface -> LKO = ~3600 m/s

Compare with:

My logical next step is to try and get a gravity assist from Minmus to get to LKO cheaply with the Cislunar Tankers. I might have to move the Depot closer. Wish me luck !

The Minmus-L2 circuit gets fuel to the Depot, in 53 or 78 ton chunks, at a ~20% expense.

From there it can feed interplanetary projects, or get transferred further to LKO in the Cislunar Tankers, in 23 ton chunk sizes, at a further ~27% expense (which is 42% expense when combined).

Lefting that much fuel from Kerbin would cost me ~90% expense, plus the refurbishing / replacement of parts and vehicles.

The whole thing costed a little under 1,150,000 to build and launch. Feel free to build your own