ISRU

[Xd the great]

So, refuelling on moon required mining for fuel.

Any more concrete ideas on this? Electrolysis? 

[Scotius]

What else? You will have hydrogen and oxygen. You can use them together. Or you can  extract aluminum from regolith, add oxygen and you'll have another fuel + oxidiser mix ready. Less efficient but easier to store and handle than liquid hydrogen. And eventually - way, way down the road maybe we will be able to use helium 3 to fuel up our torchships

[Bill Phil]

@Scotius

Helium-3 on the Moon isn't really worth it. You have to process billions of tonnes of lunar regolith to get a few tonnes of He-3, and there's not much reason to believe that He-3 will even be used, considering its rarity. 

More on-topic:

There's water ice in shaded regions, but it may be better to extract oxygen from the regolith (it makes up almost half of it by mass), using chemical processes. Then bring in some hydrogen from Earth or another source. Hydrogen makes up a very small portion of water, by mass.

[kerbiloid]

Call for Earth tanker and wait.

[YNM]

9 hours ago, Bill Phil said:

There's water ice in shaded regions

NASA is studying to use them, along with the regolith, in something called AL-ICE.

If the regolith can be easily differentiated into aluminum powder (maybe through sieve or something) and there's more ice (maybe underground), that might be more reasonable.

[kerbiloid]

How can a sieve break an alumina molecule?

[Xd the great]

5 hours ago, kerbiloid said:

How can a sieve break an alumina molecule?

You dont. You use eletrolysis. Or use Na3AlF6 to reduce its melting point. Or use displacement reaction. No sieve is strong and small enough to extract aluminium.

But after extraction, sonic, quick cooling or other stuff can be used to make nanoaluminium.

Edited July 13, 2018 by Xd the great

[kerbiloid]

4 minutes ago, Xd the great said:

You use eletrolysis. Or use Na3AlF6 to reduce its melting point.

They are together. Cryolite reduces the melting point for electrolysis.

5 minutes ago, Xd the great said:

Or use displacement reaction.

With alumina?
They use electrolysis.

And, again, 

Spoiler

1. Calculate kinetic energy corresponding to required delta-V. 
Don't forget to add several hundred kg of graphite electrodes to a tonne of aluminium, or take the result say twice if using non-electrolytic methods (beams or so on).
2. Compare to the real world 54 MJ/kg.
3. Remember that you have to keep supporting the lunar industry sending equipment from Earth.
4. Call for a tanker from Earth.

[Xd the great]

Still, producing 1 kg of fuel on the moon means saving a bunch of fuel required for transportation.

[Scotius]

Not until you have fuel industry in place, no. At least on the Moon, which is basically Earth's backyard. Mars and other planets are quite different kind of matter of course. But, when you do have industry in place on the Moon, accesing the rest of our system becomes cheaper and less problematic.

[YNM]

7 hours ago, kerbiloid said:

How can a sieve break an alumina molecule?

Ain't oxygens up there isn't it ? Wouldn't there be some pure aluminum ?

[kerbiloid]

7 minutes ago, YNM said:

Wouldn't there be some pure aluminum ?

Was it ever melted out before 1825?

As alumina is mixed with other metals oxides, so

https://en.wikipedia.org/wiki/Aluminothermic_reaction

Edited July 13, 2018 by kerbiloid

[YNM]

12 minutes ago, kerbiloid said:

 Was it ever melted out before 1825?

Ah. Yes. It was rare.

But idk on the Moon, it might be slightly more abundant.

Hall-Heroult will be pretty difficult to do on the Moon, but who knows 

[kerbiloid]

6 minutes ago, YNM said:

But idk on the Moon, it might be slightly more abundant.

Afaik, all hypotheses agree on that Moon has been totally melted.
So, probably you could find more pure iron there than pure aluminium, as the latter is a reducing agent used to reduce other metal oxides in metallurgy.

[Xd the great]

Hmm, sounds like a few companies are interested in this.

[wumpus]

4 hours ago, kerbiloid said:

1. Calculate kinetic energy corresponding to required delta-V. 

Don't forget to add several hundred kg of graphite electrodes to a tonne of aluminium, or take the result say twice if using non-electrolytic methods (beams or so on).
2. Compare to the real world 54 MJ/kg.
3. Remember that you have to keep supporting the lunar industry sending equipment from Earth.
4. Call for a tanker from Earth.

Energy shouldn't be a problem considering you have solar power that doesn't have to deal with weather or even an atmosphere, although in practice this will mean far less fuel than you would expect for a given amount of power.  That story pretty much repeats itself over and over again in lunar ISRU, the shear scale of the ISRU facility needed to provide meager amounts of fuel means you can't build the thing until it is already unneeded.

Call way, way in advance for your tanker.  You really want to use ions, solar sail, nuclear, or virtually anything but kerolox-similar fuels.  Beyond the Moon you probably want to use fancy gravity tricks to  get wherever you need to be (assuming you have the time).

[YNM]

13 minutes ago, wumpus said:

Energy shouldn't be a problem considering you have solar power that doesn't have to deal with weather or even an atmosphere...

... But you have to check what week is it. 

[kerbiloid]

27 minutes ago, wumpus said:

Energy shouldn't be a problem considering you have solar power that doesn't have to deal with weather or even an atmosphere

The problem is not "is it possible?" but "is it feasible?" 
Why spend more energy than necessary?
Why add an industry in a place where you can hardly support it and have to keep bringing everything from Earth, spending at least similar energy and efforts?

Except just splitting alumina you have to purify the raw material and product.
And if you have a look at any metallurgical or chemical process, it for 90% consists of various purifications.
So, except regolith you need a lot of materials common on Earth, but absent on Moon. At least, coke.
(Or have a supermagnetoplasmofurnace (you can, they are) which would require much more energy).
So, you anyway will spend less by delivering everything from the existing Earth plants.

Also, yes, there is no atmosphere. But how long is day night on the Moon?
You have to multiply your power several times or use nukes and forget about the solar energy.

27 minutes ago, wumpus said:

tanker.  You really want to use ions, solar sail, nuclear, or virtually anything but kerolox-similar fuels. 

If this is an emergency case, any tanker is acceptable.

If this is a long-time strategy, a low-thrust nuke with any propellant (say, hydrazine, lol. Split it into ammonia and hydrogen in your combustion chamber). Scheduled tanker voyages. Big Dumb Booster to refuel.
 

27 minutes ago, wumpus said:

Beyond the Moon you probably want to use fancy gravity tricks to  get wherever you need to be (assuming you have the time).

Fancy tricks and industry are antonyms.

Edited July 13, 2018 by kerbiloid

[wumpus]

46 minutes ago, kerbiloid said:

Fancy tricks and industry are antonyms.

Fancy gravity tricks and schedules are antonyms.  Moore's law (and most of the electronics industry) would have been dead 20 years ago without plenty of fancy tricks.  If the cost to avoid them is too high, they get used.

Ask the general public how they expect to go to Mars and they will show a torchship trajectory.  Eventually they might understand a Hohmann transfer.  While time may be money, I suspect that most beancounters will be willing to launch a year early (before the Hohmann window) to start the intricate dance that goes to Mars with 10% of the delta-v (and mostly done via ions) that the straightforward Hohmann transfer has.  In the end, engineering is all about cost and risk.  KSP mostly ignores the risk (especially for players who love the F5 key), but if the "fancy tricks" are low risk you can expect that they will be used.

[kerbiloid]

18 minutes ago, wumpus said:

Ask the general public how they expect to go to Mars and they will show a torchship trajectory.  Eventually they might understand a Hohmann transfer.  While time may be money, I suspect that most beancounters will be willing to launch a year early (before the Hohmann window) to start the intricate dance that goes to Mars with 10% of the delta-v (and mostly done via ions) that the straightforward Hohmann transfer has.

If a trick can be formalized, planned, and scheduled, it's no more a trick, it's a feature.

While a crewed flight to Mars is about duration, not about delta-V.
Human bodies decay in zero-G and under space radiation. You should deliver them as fast as possible. Especially when this is a shift rather than an expedition.
Also while floating between planet, those lazy freaks are eating but not working. The longer they fly, the more salary they get for nothing.

Edited July 13, 2018 by kerbiloid

[wumpus]

My comment for fancy gravity tricks is for fuel.

You can "beat" the rocket equation by making sure that the fuel doesn't lift fuel.  Burn ~1333 m/s from LEO, dock with fuel brought by ions (might take gravity tricks to get it into the right elliptical orbit) and burn 1333m/s, dock with last fuel depot and finally do the escape burn to Mars at 1333m/s.  Even going to Jupiter you can cut the 6000m/s to 3000m/s and one or two burns to 3000m/s.  This means far less fuel, and if you can get it in place by burning less fuel (because you are using ions an patience), you win.  Note that the orbits of the fuel depots tend to determine the trajectory of the available launches, but launch windows do that enough anyway.

Humans are doing chemical burns via Hohmann trajectories during launch windows: they are too expensive to go any other way (I'm not expecting torchships anytime soon).  Everything else gets the slowboat.