Where to put a Jool refueling base

[Ultimate Steve]

Hello, everyone. Awhile back, I did a very large Jool mission, and I am planning on doing a second one. On the first mission, I barely got home (and actually had to cheat a little bit) due to the lack of fuel. For my second mission, one of my goals is to set up a refueling system for my ships. I have endlessly been debating with myself where to do it, and didn't come up with a solution, so I thought I'd come here for help. The way I see it, I have seven options, each with its own pros and cons:

Option	Pros	Cons
Laythe	Aerobraking possible	Lots of ocean I most likely will need an airplane.
Vall	I already have a space station there (in a retrograde orbit) Central location, easiest of the three big moons	My station is in a high, retrograde orbit I have a bad track record with Vall
Tylo	???	High Delta-V requirements Hard to make an SSTO ore ferry
Bop	Low Gravity	Hard to encounter Highly inclined Long travel times
Pol	Low Gravity	Harder to encounter Longer travel times THE KRAKEN!!!
Bring all of the fuel	No need for ISRU equipment	May run out of fuel like last time, need bigger rockets.
Bring an asteroid	No need to land to refuel	Where to put it? They are heavy and cumbersome They run out eventually.

What do you think?

[Superfluous J]

Just now, Ultimate Steve said:

What do you think?

I don't actually know, but in my upcoming Grand Tour, the current plan is to park the Mothership in high Tylo orbit and go out from there to the other moons. While time-intensive, it is very cheap to get to any other moon from high Tylo orbit, and very easy to get into Tylo orbit both from other moons and from interplanetary journeys.

So, I'm thinking the best place is Tylo, getting shipments of ore or fuel from Pol or Bop, or both.

[Plusck]

I'd say Pol, with Vall coming a very close second.

Laythe would be madness, as would Tylo, because you'e heaviest going up and you don't want to use 3/4 or more of your fuel just getting up to orbit; aerobraking is no great advantage for this purpose. Bop would be good, but its inclination is a huge handicap, making planning a pain since you only have two very short windows to arrive or depart per orbit.

So that leaves Pol and Vall.

Pros for Vall: much more manageable and convenient for your station, and for visiting the system generally; nice views.
Cons for Vall: you need to stick to high orbit, otherwise the refuelled ships will start emptying their tanks just getting out of the SOI; your mining lander and fuel/ore lifter have to be built heavier, using larger engines; and you can't just drift over the landscape in search of a slightly better ore percentage without using a ton of fuel: you choose your spot and aim for it.

Pros for Pol: very cheap to mine from and very easy to navigate in search of ore.
Cons for Pol: takes a bit longer to get to; have to avoid the invisible cliffs.

[Streetwind]

On 24.4.2016 at 11:10 PM, Ultimate Steve said:

The way I see it, I have seven options, each with its own pros and cons:

I have an eighth option for you: the rarely used "flotilla" option.

If you struggle to launch spacecraft large enough to carry enough fuel and carry the crew and equipment you need on one rocket... you could launch two rockets instead. One with the crew and equipment and the fuel to get to Jool... and one with the fuel to get you home. You will have two spacecraft: one is your primary mission craft, the other is a fuel tanker. They both take the same transfer window to Jool as two separate spacecraft (hence "flotilla"). You park the tanker somewhere easily accessible (i.e. Tylo) and then go do your stuff with your main craft. When it's time to go home, you rendezvous with the tanker and fill up before you leave.

Since upper stages tend to be small, and your existing craft seems to make it most of the way home already without refueling, even a small tanker should help you. Like, just find a way to get a single FL-T800 to Tylo orbit, with a probe core, a docking port and some RCS (and don't forget that probe cores need power). That should already do it, and require only a small second launch.

Edited April 26, 2016 by Streetwind

[cicatrix]

In terms of ore mining I would suggest Vall. The benefits of using Bop or Pol with their low gravity are mitigated by their remoteness (of course if you plan your activities there then use Bop or Pol). Vall, from the other hand has relatively low gravity and it's 'in the middle of things'. 

Depending of the mods you might or not have I would also suggest Jool atmosphere scooping (using KSPI).

Regarding aerobraking on Laythe - this coin has two sides. It may indeed be convenient for aerobraking, but the cost of ascent would be higher due to the same reason. In the past I had limited success with gravity assists from Tylo. Actually, if you master the art of gravity assisting you can greatly reduce your dV budget. But of course it's easier said than done.

[Ultimate Steve]

@Streetwind I am doing a flotilla. A MASSIVE flotilla. Most of this stuff (bases, etc.) is going to be dedicated to making Jool easier to access later, so I should bring a miner.

@cicatrix I am playing mostly stock, with KAC and HyperEdit (And CameraTools, but that is irrelevant).

 

So now, I am mostly down to two options (at least ones I am strongly considering).

1) Vall. Easiest of the big 3 moons, I just need to move my failed mothership station, and get a miner.

2) Pol/Bop. Proposition: A massive ship that mines ore and takes it to the Vall Station to be processed.

 

Now that I think about it, I might do both, but I am trying to keep my flotilla under 15 launches to minimize the "orbital juggling" phase where I have to keep switching from ship to ship to do maneuvers. Without KAC, I would have never made it this far.

[Hodari]

I'd say you already have a Val station, so might as well use it.  And if you're going to be sending ISRU equipment out there anyway, just use the first load of fuel to move it into better orbit.

[Geschosskopf]

Pol is cursed with invisible colliders 1500m above the visible ground in many places.  Landing there is risky at best.  And dV required to get all they way there and back to Laythe where the action is, plus the plane changes en route, largely negate the fuel saved by landing in its lower gravity.  Not to mention the travel time.

So, let's say your major focus is on Laythe.  You of course need ISRU on the surface there to refuel your Laythe-only planes and the crew-rotation SSTO, but humping that into orbit to refuel your mothership and inter-moon shuttles is a waste.  So the spacecraft side of your Jool expedition needs its own fuel source.  Vall is the only viable alternative.  It's next door to Laythe, the gravity isn't that bad, it's not bugged, and it usually has good ore in the relatively flat areas.

Using Vall still makes for a relatively complex fuel system, however.  Say you have a station at Laythe to which your return mothership and the inter-moon shuttles dock.  That's where fuel from Vall has to end up.  So you need a mining/refining base on Vall and a tanker-lander that goes from it to a Vall station.  At the Vall station, fuel is transferred to a Vall-Laythe, non-landing tanker.  This will deliver the most fuel to Laythe from Vall for a given amount of Ore mined on Vall.  You can do without the Vall station and just have the 2 tankers dock in Vall orbit, but that limits delivery rate.  You can deliver fuel faster if you have 2 Vall-Laythe tankers and the Vall tanker-lander can make multiple trips to an orbital storage facility while they're en route.

[Plusck]

16 hours ago, Geschosskopf said:

Pol is cursed with invisible colliders 1500m above the visible ground in many places.  Landing there is risky at best.  And dV required to get all they way there and back to Laythe where the action is, plus the plane changes en route, largely negate the fuel saved by landing in its lower gravity.  Not to mention the travel time.

So, let's say your major focus is on Laythe.  You of course need ISRU on the surface there to refuel your Laythe-only planes and the crew-rotation SSTO, but humping that into orbit to refuel your mothership and inter-moon shuttles is a waste.  So the spacecraft side of your Jool expedition needs its own fuel source.  Vall is the only viable alternative.  It's next door to Laythe, the gravity isn't that bad, it's not bugged, and it usually has good ore in the relatively flat areas.

The invisible colliders on Pol are quite predictable - they are where the land "creases" inwards like a fold, or like a subduction boundary. As long as you avoid those areas - which are plainly visible from orbit - you should have no problem.

However, it's true that going to and from Pol is not without some cost. But I'm not sure that it is greater than the cost of rising out of Vall's gravity well. And the plane change is minimal. All things considered, I think they even out with the exception of travel time.

On the other hand, if the focus is on Laythe (but then again, why on earth would that be? Personally, I dislike Laythe intensely : D) then yes, Vall is the obvious candidate for sheer convenience.

[Geschosskopf]

1 minute ago, Plusck said:

The invisible colliders on Pol are quite predictable - they are where the land "creases" inwards like a fold, or like a subduction boundary. As long as you avoid those areas - which are plainly visible from orbit - you should have no problem.

Keeping with your analogy, Pol's invisible colliders are also quite common near the "mid-ocean ridges".  So yeah, they're predictable, but about 75% of Pol is near one or the other.  And even if they don't kill you on the way down, it's likely that if you leave the ship and return, it'll be way up in the air when you next see it, from whence it will fall to its bloody, screaming death.  And besides, if you're mining, you don't have total freedom in your choice of landing sites--you have to go where the Ore is.

 

1 minute ago, Plusck said:

However, it's true that going to and from Pol is not without some cost. But I'm not sure that it is greater than the cost of rising out of Vall's gravity well. And the plane change is minimal. All things considered, I think they even out with the exception of travel time.

On the other hand, if the focus is on Laythe (but then again, why on earth would that be? Personally, I dislike Laythe intensely : D) then yes, Vall is the obvious candidate for sheer convenience.

I've done it both ways.  The dV is about the same, but with Pol, the travel time pretty much forces you into using a 1-trip tanker.  If you have to do multiple refueling runs, you could well miss the window back home.  And a 1-trip tanker is going to be the biggest ship in the fleet because it needs to carry the full tankage of the return ship as payload, plus the engines and tankage needed to move that amount of fuel Laythe and then get back to Pol without needing to refuel.  OTOH, if you use Vall to refuel spaceships at Laythe, then you can get by with 2- or 3-trip tankers and not worry about the time.  Vall's gravity is only about twice Mun's, not really a big deal.