Kethane Usage and Proper Fuel Routing

[DMagic]

Kethane is a popular mod and one that generates a lot of confusion. To alleviate some of this I'll go over how to setup a kethane refinery that can generate fuel, LOX, and monopropellant.

First off, kethane itself is routed the same way as RCS fuel. That is, kethane can move between any two points on a vessel regardless of what is between them. Stack separators, structural hard points or docking ports don't affect the ability to automatically transfer kethane. A drill anywhere on a vessel can fill a kethane tank anywhere else on the vessel. And a kethane tank anywhere on a vessel can be used by a converter anywhere else on the vessel. Generating monopropellant follows the same rule, any kethane convertor will fill every monopropellant tank on the vessel, no fuel lines or manual transfers are necessary. Monopropellant will also flow through KAS pipes.

Fuel Lines:

Fuel and LOX generation are more complicated though. My understanding, and someone correct me if I'm wrong, is that kethane convertors work by consuming a negative amount of fuel/LOX. That is, a kethane convertor works much like an engine does, but instead of removing a positive amount of fuel/LOX from the fuel tanks, it "removes" a negative amount from the fuel tanks.

Because of this, fuel flow has to be setup in the same way that you would route fuel to an engine. To ensure that a convertor can make fuel/LOX, fuel lines must run from a fuel tank, to the kethane convertor, not the other way around. As long as at least one fuel tank is connected to a kethane convertor in this way you should be able to generate fuel/LOX, you may have to manually transfer it from this point though.

Ideal setup:

Of course this is not the only way to generate fuel/LOX, any setup where fuel would normally flow from a tank to an engine without fuel lines or manual transfer should also work with a kethane convertor. Fuel can flow through docking ports (as long as you don't disable fuel crossflow), trusses, kethane tanks, or any other part that allows fuel crossflow. The safest way to setup a refinery though, is just to directly connect a fuel tank to the kethane convertor. You may have to manually transfer fuel to some other tanks, but it will always work with this setup. Fuel/LOX won't flow through KAS pipes regardless of how or where they are connected.

Examples:

Below you can see a somewhat complex setup. The kethane convertor at the top can fill up all of the highlighted fuel tanks despite all of the docking ports, structural parts, and radial attachment points between them. Even if there were an issue or bug that prevented me from filling up the other tanks, I still have the small tank attached directly to the converter. I could manually transfer from there to anywhere else on the craft.

Of course, it is possible that some bugs could crop up on a more complicated designs. Lots of docking ports and other parts between a tank and convertor could cause issues and prevent you from generating fuel/LOX. This is most likely a problem on the core KSP end though, and not an issue with the kethane mod itself.

And if someone wants to add something about kethane detectors that would be helpful, too. I haven't played around with those much, I usually just identify a few sites and land at the first suitable one.

Edit:

Using engines to test fuel flow:

One way to test your design is by assembling everything in the VAB, launching, filling up the kethane tanks on the launch pad, and checking if it works. You can use a kethane debugger part, or just edit your persistence file to fill up the tanks. You can see in the picture that the kethane converter in the top right can fill up the tanks shown with the green arrows through all of the docking ports and structural parts between them. It cannot, however, fill up the tank shown with the red arrow. The decoupler shown in yellow prevents automatic filling of this tank.

If you don't want to mess around with editing your savefile, or resetting your kethane deposit data you can also use engines to check fuel flow. If you have a fuel tank on one part of vessel that you want to check, just add an engine to it (or to a part that should be connected to it). Disable all but the fuel tank attached to the kethane converter by right-clicking each tank and clicking the little green arrows on the right side, circled in red below. Then ignite the engines. If the engines can pull fuel from a tank attached to the kethane converter, then, in most cases, the converter should be able to fill up and fuel tanks attached to the engines. Below you can see the same fuel flow story. The green arrows indicate fuel flowing from the tank in the upper right to the two tanks on the left, but not the one shown by the red arrow, which is separated by the decoupler.

It should also be noted that some complex docking setups can screw with fuel flow. Using bi- or tri-couplers to make 2 or 3 point docking attachments can cause issues and might prevent fuel flow through those ports. Radially mounted docking ports can also cause issues in some circumstances. That's why it can be a good idea to test out your crafts on the launch pad before launching and assembling everything. And generally, a few struts and launch clamps can hold up even very large and complex structures without collapsing.

Radial Docking Port Issues:

Below is an example of how radial docking clamps complicate things. On the left you can see that fuel does not flow from the tanks on top to any of the engines on the bottom, only the activated tank (far left) can supply its engine. However, kethane, for some reason does not match up exactly to fuel flow. Converted fuel can flow from the converter to the central tank on the bottom, but not the two tanks on the side. I don't know what causes this disparity, but it is something to keep in mind. And even more confusing, the side mounted engines can run on fuel from the central tank, but not the other way around.

Obviously there are issues related to how fuel flow works through complicated connections. In most cases though, these are probably due to issues on the KSP side of things, not the kethane mod. If you run into these issues you might consider using 6-way nodes instead of radial attachments. The nodes don't work the same way as radial connections and shouldn't have this kind of problem.

This is all assuming, of course, that you want to be able to automatically fill up all of your fuel tanks. In all of these cases you can manually transfer fuel from the tank attached directly to the converter to any other tank.

This thread has some examples of what does and does not (and what might not) work as far as fuel flow goes:

http://forum.kerbalspaceprogram.com/showthread.php/26660-Interplanetary-ship-design-problems?p=329049&viewfull=1#post329049

Edited December 20, 2013 by DMagic
Typos

[Majiir]

Thanks for posting this.

Just to clarify, it is not always necessary to use fuel lines; most designs will work fine without them. In particular, any setup where the fuel tanks are connected on the same stack as the converter will work fine, because fuel can transfer between parts in a stack (as long as they're crossfeed-enabled). You might need fuel lines if you have tanks attached radially, but most often you'll need fuel lines in that case anyway because you're feeding fuel into a center engine.

In other words, don't worry about it too much! Try building a ship without lines, and you can test the converter on the pad by blending up a Kerbal.

[elfindreams]

Great stuff, but can you link to the image, right now it is just showing a "thumbnail" (512x320 I think) which doesn't give enough detail to understand it at all.

[elfindreams]

That is... awesome.

I am not even going to ask how you can do orbital stationkeeping if you need to nor why there seems to be an ASAS randomly welded to the side... that has to be the most... Kerbal station I have seen.

[DMagic]

That is... awesome.

I am not even going to ask how you can do orbital stationkeeping if you need to nor why there seems to be an ASAS randomly welded to the side... that has to be the most... Kerbal station I have seen.

Ha, those would be pretty useless ASAS units, but they are quantum strut cores, they do look pretty much identical though. The station doesn't have any RCS thrusters, but those 3 cupolas give it a ton of torque, so I use quantum struts to keep things stable when turning it around, especially when I have big things docked to the central ring on top.

And yeah, it can't really change it's orbit. Though I guess I could dock to landers to those ports on the bottom (one lander is visible behind the orange tank) and use those to move it. There are a few posts on this stations construction in my Moho thread if you want to know more about it. It's small and simple (just 88 parts without anything docked to it), but I really like how this station turned out.

[HoY]

Question. I've been trying various configurations but can't seem to get this to work

I'm trying to get converted fuel to flow on its own from the mining rig Through a KAS winch to the tanker ship. What I'm going for is a 1 click fill all tanks solution so that the processors on the mining rig will fill all the tanks on the tanker landed beside it.

I'm sure it would work if I physically docked the two ships together on the surface, but that's not what I want to do.. I want to EVA and connect them in docked mode with KAS, but I can't for the life of me get it to work!

Anyone have any hints?

[DMagic]

I've never used KAS. Do the connections have directionality? If they do you would have to connect it from the receiving vessel to the kethane rig. But my understanding is that a KAS winch connector acts like a dock, so maybe something else is going on.

If the rig itself has fuel lines on it you could run into some weird fuel loop issues. Can you make the connection directly to the kethane convertor?

[HoY]

They don't have directionality but don't work Exactly like docking ports. I've tried using the stack mount connections, radial mount connections, and I've tried connecting the winches directly to the converter, a fuel tank, both of those with fuel lines from OR to the winch.. It jus doesn't want to work. One thing I have not tried is firing an actual engine across the connection, I'll try that now but my hopes aren't high.

[DMagic]

That's a good way to test fuel flow. If an engine can pull fuel in one direction then a kethane convertor should be able to fill it up in the other direction.

Later today I think I'll add a section about this to the first post, as a way to test fuel flow.

Edited June 18, 2013 by DMagic

[HoY]

I have a feeling the two will be out of sync in this case. Hopefully it will just be a cfg edit to fix but that's why I posted here

[CaptainKipard]

It jus doesn't want to work.

I have successfully used KAS with kethane. I have a drill/converter on one rocket and an empty tank on another. I can drill, convert and fill the tanker all at the same time. Here's my setup:

Tanker has: LFO/Xenon/Monopropellant tank --> Radial attachment point --> KAS Vertical Winch --> KAS Connector

Drill/converter has: Converter --> Radial atachment point --> 3 KAS radial connector ports

I just attach the connector from the tanker to one of the ports on the converter craft in docked mode and when i click "convert" it fills my tanker.

[HoY]

I have been trying to get it to work by stack mounting the winch rather than using it radially, hoping that that would eliminate a variable. But if its working properly for you like that ill give it a try. On your mining rig where is the radial attachment point hooked on? On the fuel tank, kethane tank, or the processor?

Also the radial attachment point on your tanker,, you have 3 surface mountable KAS ports installed on a single stock radial attachment point? Or did I take that wrong? A screenshot of the two crafts would clear it up perfectly

[Konraden]

Ha, those would be pretty useless ASAS units, but they are quantum strut cores, they do look pretty much identical though. The station doesn't have any RCS thrusters, but those 3 cupolas give it a ton of torque, so I use quantum struts to keep things stable when turning it around, especially when I have big things docked to the central ring on top.

And yeah, it can't really change it's orbit. Though I guess I could dock to landers to those ports on the bottom (one lander is visible behind the orange tank) and use those to move it. There are a few posts on this stations construction in my Moho thread if you want to know more about it. It's small and simple (just 88 parts without anything docked to it), but I really like how this station turned out.

There is a mod for that. This guy made some nice models for the Quantum pack (they are _only_ the models, the mod isn't included).

http://kerbalspaceprogram.com/quantum-parts-pack/

[CaptainKipard]

A screenshot of the two crafts would clear it up perfectly

Ok. This is the tanker. The attachment point sits on the LFO tank. Only the winch is connected to the radial attachment point node. The port sits on the attachment point surface and is unused but it's there anyway just in case.

This is the drill/converter. The radial attachment point sits on the converter unit. The converter is sticking out through the winch there. When i built the rocket I didn't know it would extend like that when converting. Anyway there's also a winch under there connected to the radial attachment point node. It's also unused at the moment. The three ports are visible below. They sit on the surface like you said (you have to fiddle with orientation) with the hose from tanker plugged in.

Here's the whole thing. In this image it's drilling, converting and filling the tanker RCS tank. I think it only does one resource at a time.

Basically i noted 3 things when coming up with this.

1. The radial attachment point is fuel crossfeed capable just like everything

2. I assumed KAS works like a fuel line so I connected from the tanker to the drill/converter, and not the other way around in order to get the negative fuel usage.

3. Docked ships can exchange resources so I used the docked attachment mode.

I might try other ways of doing it some other time. For now this works just fine. One thing I did notice however was that the drill/converter fills it's own tanks first and only then fills the tanker.

Edited June 19, 2013 by Cpt. Kipard

[HoY]

Ok perfect. My problem seems to be that those KAS surface mount hardpoints don't cross feed the way you'd expect when mounted radially. Nor do the stack mount hardpoints. But with that radial attachment point under them they seem to work

I've been trying it without those parts and wit an identical setup it wasn't working. This morning I had a few minutes and tested firing engines through the cables and they worked. Except::::

With the fuel tank connected to a stack winch, with NO radial attachment mode the engine will fire in Launch a unpack mode, but as soon as you extend the winch moving the tank away from the engine it no longer feeds the fuel. If the winch has the radial attachment point under it, it will cross feed while extended.

There seems to be a glitch in how HAS parts connect to stock parts hampering full fuel crossfeed

[DMagic]

I updated the initial post and put a section about radial attachments. This doesn't seem to be limited to KAS. I tried this on a stock installation with only kethane added.

Using radially attached docking ports (and maybe other connections) can cause weird fuel flow issues. And they don't always match up with how the kethane converter's flow works, either. Using fuel lines across these connections can solve the issue, but that's not always an option when you are docking multiple vessels together.

Launchpad testing of more complicated designs is a good idea if you can manage it (subassembly loader helps a lot here with multi-part vessels).

[HoY]

I'll have a few hours tomorrow for testing, I'll document and screenshot what works and what doesn't. Had my daughter today to give her babysitter the day off, so no chance except for her 10 min nap at noon to play today lol.

[HoY]

Unable to replicate this, even going by those pictures. have the winches and ports installed similarly on both crafts but it simply does not want to send fuel across the line

filled the kethane tank on the pad with hyper edit, have a large empty spherical tank on the craft the winch is on that I want filled. I've tried attaching to every one of the hard points you see in the picture plus some other ones that arent mounted on radial attachment points, but none of them crossfeed properly.

Just to be clear, yes I am using docked mode, and yes I can manually move fuel across the cable by alt+clicking the tanks. Thats not what im going for tho, im attempting to get this setup so that it works the same as if the two ships were docked and fuel flowed freely between them to and from the converter.

I have a converter on the tanker with the spherical tank on it, and it draws kethane through the line just fine to convert it. but that doesnt need actual fuel crossfeed at all

[CaptainKipard]

Let's see.

1. I'm using KSP v. 0.2.02, KAS v. 0.3.1 and Kethane v. 0.6 although my setup worked with 0.4.4.

2. My tanker is using a KW rocketry SC-2 LFT. I don't see why that would change anything but it's the only significant difference I can see from your screenshots.

3. Does your converter (is it a rover?) have any partially empty LFO/RCS/Xenon tanks? It might be filling those first like I said.

I can't think of anything else, but if you upload your craft files somewhere I can see if it works on my computer and whatnot. If you do then remove all the extraneous mod parts first.

[DMagic]

Have you tried replacing the KAS connections with docking ports? I know this would probably be tricky to put together as your craft looks fairly complex, but it would at least confirm if this is a stock fuel flow issue, or a KAS issue.

[HoY]

do you mean docking ports on the ends of the winches? or using docking ports built right onto the hulls?

cant put them on winches because you cant "grab" them and plug them in where you need them,,

The rover, which is barebones minimum needed for testing has the smallest stock tank, you can see it right on the kethane converter mostly coverd by the radial attachment point,, it comes filled, I tried it with it filled then again with it empty and had the same effect. The converter filled the tank, then it wouldnt fill anything on the other craft.

On a reversal of your request for a craft file, would you be willing to replicate your results with two nearly stock rovers? one with just the kethane tank and converter, the other with a fuel tank and engine to empty it? with KAS and your working port configuration obviously

the tanker pictures is just another Vall tanker but its like 99% mod parts so if I were to strip it down all you would get is a couple of t8 tanks and some docking ports in a pile on the launch pad... Large spherical tank starting empty, LOTS of kspx parts, B9 landing gear and lights, quantum struts,, and the FtMn 240KN LNV's

[CaptainKipard]

Well something's definitely wrong here. I just loaded my game and I realised that the LFO tank isn't actually filling up, which is weird because the RCS tank fills up just fine and I've also used the same setup to fill a xenon tank on a different test craft.

[HoY]

Yeah Monoprop and Xenon dont follow fuel flow rules, they can jump anywhere they are needed or called from on a craft even across non cross feed capable parts like the flat steel plates and any type of decoupler

[DMagic]

I mean replace the winches with docking ports. You would need some way to connect the 2 crafts together after this, like a bunch of trusses or structural elements stuck on the ends of those docking ports (and I assume that since at least one of the vessels is a rover you could just drive into place for docking). But if you could find a way to actually dock the vessels together instead of use the KAS connections you could eliminate that as a variable.

Fuel flow is weird about radial, or otherwise complex connections. So this would help to figure out if you have a KAS problem or a fuel flow problem.

[HoY]

Oh, I already know this setup would work if I were to dock the things together, but thats not how I am trying to do it The rover you see is just what I was using for testing on the launch pad. the actual drill and convert rigs are vtol with no wheels currently. I may change them to use some cat tracks in a while, but not until I get back home and start streaming and posting videos on youtube again in a couple weeks.

The whole point of my question was to try to find a way to cross feed fuel Solely using KAS winches and cables. What I'm going to end up doing is what ive been doing all along and just moving the fuel over by hand while its being converted...