Better Design for a Mun Kethane Miner

[Pope_Gregory_IX]

Hi,

I'm currently enjoying playing in sandbox with Kethane mining. The aim is to build space stations around planets and moons, top them up with kethane and so have refuelling stations scattered around the system.

So far, I just have stations around Kerbin and Mun, and have a mining vehicle which also transports the kethane up to the munstation. An ion-powered transport vessel is waiting at my Kerbin station to move the kethane around. Here's the Mk I lander/miner (with radial and ion engines) docked to the station:

The problem is currently the weight / efficiency of my Munlander. I've made some changes since the screenshot (a single Monopropellant tank, for example - docking has been much easier than I thought!) and am also working out a good way to mount nuclear engines without smashing them on landing.

Is anyone else playing in this style and I'm just wondering what efficient vehicles people have come up with for the munlanders, so that you don't spend half your mined kethane on renewing your fuel supply?

Cheers,

Adam

[cantab]

LV-N's may not be the most efficient choice. Their extra weight can drag them down more than their Isp helps them, especially on landing when the engines will be a much bigger chunk of your mass. For alternatives consider the LV-909, Aerospike, or for a huge ship even the KR-2L.

Besides that, the best thing is probably to cut off excess weight. You can refine on the ground or in orbit, it makes little difference if you're making LFO (but if you're making monoprop or xenon it's more efficient to do it on the ground), but either way don't be hoiking your converter up and down every time. Or your drills for that matter. Of course, this means you'll need to master on-the-ground fuel transfer.

Personally I don't see the point of kethane in Kerbin's SOI, beyond demonstration missions. It's quick and easy to launch fuel directly. Now if you're operating on other planets or moons, then kethane becomes more helpful.

[Pope_Gregory_IX]

Thanks for your thoughts. I did think about leaving the miner on the surface of the Mun, but it was the ideas of transfers that put me off. I agree about the lack of need for kethane this close to kerbin, but this is the first stage (and a sort of test run) of something that I hope to extend across the system.

There's a big converter at the Munstation, but I do also have conversion on the lander - perhaps with a lighter, more efficient vehicle I can ditch that - at the moment, I have been converting on the surface of the Mun in order to get me back up to orbit. Something that should not be necessary if I go back to the drawing board with the weight of the thing!

Next step: reduce weight and improve engine efficiency. After that, we'll look at on-ground transfers and leaving a permanent drilling rig on the surface.

Thanks again,

Adam

[cantab]

If you are set on avoiding surface fuel transfers, then it will be more efficient to bring a converter down than to land with all the fuel you'll need to takeoff.

[Rabada]

It is hard for me to tell in that pic but it looks to me like you have a converter on top of each radial fuel tank. My design philosophy behind Kethane is this; "More and bigger converters and drills will make your ship mine Kethane faster, but then again, so does time warp." You really only need one medium converter and one drill, but I go with one medium converter and 4 drills because 4 drills will mine Kethane at just about the same rate that a medium converter will convert Kethane into liquid fuel, oxidizer, and mono-propellant.

I just finished setting up my Kethane mining system for a tour of the Jool system. I am playing with custom biomes, so I plan on doing multiple landings on all the moons of Jool. I have a standard Kethane miner which is fairly simple. I use a 3.75m KW tank as the base of the lander with 6 landing legs. I put 3 small fuel tanks with a nuclear engine radially attached to the main tank. I also put on the medium converter, 4 drills, and a .625m fission reactor from Interstellar to power it. In Kerbin's SOI, I have a Kethane mining operation set up on Minmus. My lander never leaves Minmus's SOI, I built a giant and very efficient fuel tanker to ferry fuel from Minmus to LKO. I would suggest considering mining on Minmus. It takes ~640 dV to take of from the Mun, while Minmus only requires ~240. Also, the flatlands of Minmus are much more pleasant to land on. In Jool's SOI, I mine from Bop, then I have a tanker take the fuel to a fuel Depot between Tylo and Vall's orbit. My fuel tanker follow my landers to each of the moons for refueling.

Edited June 3, 2014 by Rabada

[michaelhester07]

You can try using the Rocomax Poodle. Those don't spend too much fuel.

The reality is that you'll spend kethane to refuel your tanks to get back to orbit. If you get 2k deltaV off the KR-2Ls to get to orbit you'll end up using kethane to refuel it after the next landing.

Kethane within Kerbin's SOI is useful if you're doing Extraplanetary Launchpads. It's the best way to fuel the ships you build in orbit.

[KerbMav]

What is heavier? A certain amount of Kethane or the LF/OX that can be generated with it?

[Blind Dead McJones]

I'm doing something similar, also in sandbox. First off, the mun is not going to be very efficient for this kind of thing because of the relatively high gravity, but it's still possible to get a net gain of fuel to your station.

I actually have three ships in my system. The first is a station orbiting the mun and acting essentially as an orbital fueling station (and also living room for a few Kerbals just in case). The second is a stationary base which has the kethane mining and converting station and a few other things. Kethane is mined and converted on site. The third is a lander that holds lots of fuel and can go between them. I transfer fuel into it from the base using Kerbal Attachment System.

The separate lander makes it more efficient because then I don't have to move the conversion equipment which increases the amount of fuel needed to reach the station.

There is one flaw: you have to land super close to the base to get all the pipes set up. This requires precision landing that uses up a significant amount of fuel, which is a problem when kethane is a limited resource. Sometime soon I plan to send up some sort of tanker truck that can go between the base and the lander, which will be easier and more efficient because wheels are electric.

Edited June 3, 2014 by Blind Dead McJones

[cantab]

What is heavier? A certain amount of Kethane or the LF/OX that can be generated with it?

It's virtually the same. Mass conversion rates for kethane to liquid fuel or oxidizer range from a few percent below to a few percent above 1:1.

[Jouni]

If the kethane miner is large enough, it's better to haul around raw kethane, refining it only when needed. The largest kethane tank has essentially the same capacity as the orange tank, but its dry mass is significantly less (3.25 tonnes vs. 4 tonnes).

My standard kethane miner had four large kethane tanks and a heavy converter. It only needed a relatively small fuel tank, because the converter was almost fast enough to feed four nuclear engines.

[Vanamonde]

This exchange of spacecraft designs has been moved to the Spacecraft Exchange sub-forum.

[Pope_Gregory_IX]

Hi,

I've now come up with a Mk II design which uses LV-909's, has less Monopropellant and does not cart around any converters. The result was much better, but I still feel I now need to look at on-surface transfers with a semi-permanent mining Munbase. I'll have a look at KAS to make this simpler. The only slight issue with MkII is that I mounted the drills too high compared to the landing legs, so have to collapse a couple of legs to be able to mine! Back to the drawing board!

Cheers,

Adam

[KerbMav]

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You might want to spawn your equipment on the launch pad first to check for things like your drills - also true for ladders, landing lights, ...