some lunar water calculations

[kunkmiester]

Desiring 2 gallons a day per person, to support a lunar station of 20 people you need 40 gallons. This doesn't include fuel or oxygen extraction, or any industrial work.

40 gallons is 151.48 Kg. Using the 6% figure from another thread, you need to be able to process 2524.6 Kg of lunar regolith per day.

Number of people is debatable, but any sensible lunar mission is going to be more than two people landing, playing golf and taking off again, and that means several people, and sticking around for a while. Plus, as I said, that number doesn't indicate any other uses. If you consider some numbers that put US usage above 100 gallons per day, it starts boggling the mind.

Likely, actual occupation won't be close to 20, but you won't want to tie up enough machines to keep a processor fed with that much material all the time either. Whatever machine is going to be feeding the processor will likely also be used for any number of things, and the capacity of the system will be much larger, so that you can say, spend one day a week getting enough ice to use, and letting the machines do other things the rest of the time.

Other stuff isn't working out, for example with 2.5 g/cm3 for density, 2524 Kg is coming out to a little over a cubic meter, which doesn't quite make sense to me. I'm thinking a suitable robotic scraper for use on the moon would have a capacity of about that. Big problem with machines like that is that while they can be made somewhat light, the empty space makes them bulky regardless of weight.

[krenshala]

Its most likely higher numbers than would be needed on the moon or elsewhere in space, but at this site they discuss water needs for soldiers in the desert (and in general). About the middle of the page are some water requirements that basically boil down (pun intended ) to 6.5 gal per man per day (4 gal drinking, 2.5 gal hygiene) and 0.5 to 1.5 gal per meal (depending on cooking/cleaning requirements). So, we take the pessimistic (or happy, depending on whether you've seen military service ) value of 6.5 + 3 = 9.5 gal (call it 10 gal?) per person per day, if we assume two meals each. Now, this is probably more than will actually be needed, but gives a nice buffer for times with intensive labor (moving rocks, moving high-mass parts around in microgravity, etc), and at worst provides some extra capacity "just in case".

1 US gallon is 3.785 liters (3785 cm^3), so you would need 37,850 cm^3 per person per day if you based your storage on my numbers above. I'd round that up to 40 m^3 per day per person myself for both easier math and a more pessimistic view.

Of course, I have the feeling my being so tired today means I've just gone off in a semi-related tangent ...

[Aero]

40 000 cubic centimeter = 0.04 cubic meter

[Skipjack]

But, once you have enough water for a person, you can recycle much of it in situ. There is technology for that currently being tested on the ISS.
Of course some of the water will still go to waste and will have to be replaced but a substancial amount can be recycled.

[Skipjack]

(4 gal drinking, 2.5 gal hygiene)

Please show me one person drinking 4 gallons of water a day. I think the recommendation is 4 litres a day (slightly more than one gallon).

[Skipjack]

Here is some information about water consumption on the ISS. I am assuming that an astronaut will drink slightly less than a person on eart due to the reduce physical exercise. So you might have to take that into account.
http://esamultimedia.esa.int/images/edu ... hap3_E.pdf

The ISS lifesupport
system
on board is designed to recycle as much water as
possible – even urine and the humidity in the
cabin air. And to minimise the consumption of
water, its use has to be as efficient as possible. For
example, a shower on Earth takes about 50 litres
– an astronaut, however, would use less than four
litres for personal hygiene and not more than 10
litres of water in total per day.
Sweating astronauts
An astronaut consumes about 2.7 litres of water per day through eating and drinking.
Most of this water leaves the body again – either in liquid state (in form of urine or
sweat) or as vapour (through the pores or through breathing). If the water vapour
leaving the bodies were not removed from the air, the Station would quickly feel like
a sauna and the astronauts would have difficulties breathing.
The ISS life-support system has several tasks. It keeps the cabin air clean (filter the air for
particulates and micro-organisms), provides the right level of gases, a preferable air
pressure and the right temperature. As described in the previous paragraph, the humidity
is also controlled – if the level is too high, the ISS life-support system makes sure that
the surplus water vapour in the air is collected.

So 10 litres of water a day (for everything), that is less than 3 gallons or 0.01 m^3 of water.

[krenshala]

(4 gal drinking, 2.5 gal hygiene)

Please show me one person drinking 4 gallons of water a day. I think the recommendation is 4 litres a day (slightly more than one gallon).

As I mentioned, this was dealing with soldiers operating in desert environs. It also mentions something like persons sweating out 1.5 to 2.5 pints (iirc ... its in the link) of water per hour depending on workload (assumed manual labor) and gave examples of how to plan your water needs based on operational expectations (170 guys, various work intensities, getting 2 B-rations plus an MRE a day would need X total gallons per day, etc).

You could be right -- it might be it should read liters. However, when I was in Kuwait in '98/'99 (four months, I volunteered for winter ... it only got to the mid 80s F most of the time I was there, but was 110 F in the shade when I arrived in late October) I did, basically, office IT work (though some of it was outdoors) and ended up drinking way more than 4 liters of water per day. I guess between 6 and 10 liters per day constant sipping, and refilling the 1L bottle as I worked on computers, chased cable, etc. (I lost weight doing that, but mostly due to substituting water for my normal soda intake, i'm sure. )

[kunkmiester]

I forgot about recycling. That would reduce mining needs. You'd still need to feed mineral extractors, get water for fuel, run the building block printer, and a number of other things.

I'm still not seeing a cubic meter weighing 2500 Kg, but that's what the math says.

The biggest issue is that not all of the machines needed to do complete printing of machines exist. Even then, mostly for the construction/mining machines, you pretty much have to send them up complete anyway. On the other hand, there's only a couple of machines that can't do two jobs, except for mineral processing.

[Skipjack]

Yeah, I think your numbers could be right for a dessert environment, but I dont think they would apply to a moonbase.

[hanelyp]

Are we importing food or growing it locally? Food metabolizes to produce water. Growing food, on the other hand, uses water.

[Skipjack]

Are we importing food or growing it locally? Food metabolizes to produce water. Growing food, on the other hand, uses water.

But that water is not lost either. It is still in the closed system. You will probably urinate it out, once you have consumed the food, getting it back into the recycling system.
I think that with a very efficient recycling system, you can keep the required addition of new water at a doable level.

[D Tibbets]

.....

I'm still not seeing a cubic meter weighing 2500 Kg, but that's what the math says....

The number doesn't make sense.
One cubic meter contains 1,000 liters = 1,000 Kg.
Another approach. 1cm = 0.01 meters, 1 CC = 1 ml = 1 gram of water.
A Cubic meter = 100 cm cubed or 1,000,000 CC. There are 1,000 ml or CC per liter, thus 1000 liters in 1 cubic meter.

They may have confused Kg with pounds, but still a cubic meter of water would weigh only ~ 2,200 lbs of water.

And just to nit pick- it would be more accurate to say one cubic meter of water has a mass of 1,000 Kg. The weight on the Moon would be ~ 166 Kg.

Dan Tibbets

[kunkmiester]

Not a cubic meter of water, a cubic meter of regolith, the amount you have to process(roughly) to get the gallon of water.

[Skipjack]

Not a cubic meter of water, a cubic meter of regolith, the amount you have to process(roughly) to get the gallon of water.

Yeah, that could be about right. Not quite sure whether that is the weight on earth, or on the moon though. On the other hand, kg is the measurement of mass and not weight and mass would always be the same... Does anyone know how dense regolith is? If it was like regular rock on earth, 6 times as heavy as water per cubic meter sounds about right, but then something tells me that regolith is more like lava which is very porous and therefore rather light... Or is that for regolith that has been ground down and densely packed?
I see a whole lot of questions that need answered here...
Either way, it does not change the fact that in a closed environmental system like a moon base, you should not have to replace all the water that is being consumed. IMHO the only water you should have to replace is the water used up by rocket engines for fuel.

[kunkmiester]

I googled it, and decided to use 2.5g/cm3, in the middle of the ranges I found.

I also checked my notes, 2524 Kg regolith yields 151 Kg of water, and it was that mass that I ran. So 16Kg yields one Kg. That seems to be more like 1/8 rather than 6%, but the math is starting to spin in my head.

I did switch to metric for most of the math, to keep it consistent. No use pulling a Mars lander mistake.