Moonwards

kim holder

00:05

hey, you know i really wondered about that

you should take that up with Hoh - he did calculations about that and i couldn't tell you how

i am at the moment struggling to produce a series of images that will explain what it is i did

it is rather more difficult to get the cameras and materials to do what i want than i thought. at least, i am having trouble figuring it out.

MolbOrg

my calculations are simple specific heat for R is about 1200J/(kgK) (average), melting stage about 3000 J/(kgK) temp range about 300 (from 13xx to 16xx) - average 2.2MJ/kg, density about 1700 kg/m^3 <- 40^2×3.14×70×1700×2200000÷15÷24÷3600 = 1'014'879'012 * 0.5 efficency -> 500MW

it is rough estimation

@kimholder it needs something like cutting tool - so it removes certain part at an intersection, IDK how to do, but would like to have

kim holder

oh, it has gotten into this tool for using objects as cameras, and now i can't turn it off, it's a blender thing

that has been what the last 7 minutes have been about, finding that one damn control

i think i may have a corrupt file

0

Q: How to stop object being used as a camera?

I accidentally turned on 'use object as camera' by pressing ctrl + numpad 0 and now I can't get it to stop doing that. I deleted all the cameras, and then created a new one, and still it keeps trying to use that object as a camera, and I can't get Blender to switch to a different camera. I'm add...

i'm switching to another version of the file, to try to fix the camera issue

ok, this starts to show what is going on. The pipes that shade from red to yellow, that is one set of the whole ring of them in the earlier picture

so those heat pipes are transferring heat to the 2nd heat exchange area, which is the big green thing. let me take a cross-section

that still looks a bit confusing to me - i cut the green thing in half, eliminated most of the red to orange heat pipes, and all the pink pipes that i'll show next.

see the green thing has thickness, and has a fluid filling of its own, so that it passes heat from the red-to-orange pipes to the pink pipes. It is 5 m from the tank walls, which are shown here in that deep blue

it has a bottom section that is a set of rings and spokes, because otherwise i'm not sure it will take the weight.

so, it is solid in the image, but actually all of it is meant to be hollow, with an inner and outer face on the vertical section and on the top, and the bottom is tubes.

kim holder

01:11

so, the pink pipes pick up the heat delivered to the green reservoir, and pass them out of the tank, into the lavender tanks

kim holder

01:22

the lavender, or light purple, boxes with the pointed end - those have the nitrogen that actually goes into the turbines, shown in dark purple

then once it has passed through the turbine blades, the nitrogen exits on either side to the cooling towers, which have not yet been connected to the radiator arrays, one of which can be seen in the upper right corner

those towers also penetrate a fair distance into the ground, to additionally tap the cold down there. but, it is hard to say how well that ground will transmit heat. it should largely be stone chunks, but those chunks are jumbled, with fines between, and they may not have good thermal contact between them.

so, without anything cut away, semi-transparent, or hidden, this is how it looks right now

it is missing the top of the tank, which has to be thought about, because it needs to be cooled as well so that volatiles collect on it, and then it needs an access system so those deposits can be scraped off before dawn. It also needs a system for adding more regolith to top up the tank.

it is a fairly complex piece - because those red-hot pipes have to descend into the middle of the lava tank while all those things also work

also missing - the pipes returning the N2 gas to the chambers where it gets heated. those will go from the cooling towers to the end of the narrow lavender boxes by the tank wall.

and the valves and pumps on the red-to-orange pipes

they are arranged the way they are in the hopes that the valves can be set up to smoothly switch circuits as the temperatures in the tank fluctuate over the course of a lunar day

and that in fact perhaps the same pump could be used for each set all month, as the distance the fluid travels through the circuit changes very little.

and i also thought about maybe putting in a grid of titanium bars just to act as heat conduits, causing the heat to diffuse from the tank center better. but that is just a thought, like the whole thing isn't huge and complex enough already.

however, if that power analysis is even close to right, i can drop the size of the tank down to a more comfortable size, and also, the tank can be filled only partly at first, and then as further sets of mirrors come on-line, it can be filled more.

one more shot, showing the pumps on the pink pipe system.

you want pipes? we got pipes.

btw - the mirrors right now are nowhere close to big enough to supply 500 MW of power

i hadn't even gotten back around to thinking about that, trying to get this part sketched

oh - also, there needs to be a way to take lava out of the tank.

so it can be sent to other stations.

tomorrow i'll make a sketchfab version

kim holder

17:33

@MolbOrg i know what the issue is. it isn't all molten lava. the pipes in the middle are the only thing melting stuff, and they have a running temperature of about 1800 K during the day. The heat diffuses outwards, the melt pool grows outwards during the day, and shrinks and freezes at night.

So, assuming i resize the mirrors to match the larger tank, and using a direct scaling based on volume from Hoh's earlier estimate, which i have to find again...

kim holder

17:57

okay, that turned into a bit of a rabbit hole. Hoh made a calculator on Wolfram Alpha but i think he was a bit optimistic (which he usually isn't, btw) so i lengthened the night to 360 h, because the mirrors are on an incline and will also block each other at dawn and dusk, and the working temp of the working fluid is about 800 C, so i decreased the number of K the heat capacity is multiplied by

wolframalpha.com/input/?i=(360MWh+%2F(+basalt+heat+capacity+*+1000K+‌))%2Fbasalt+density

hm, that link messed up...

(360MWh /( basalt heat capacity * 1000K ))/basalt density

^ put that formula in Wolfram Alpha - wolframalpha.com

but anyhow, i think it is probably better to calculate how much energy the mirrors collect, and just guesstimate an efficiency level, and base MW output on that.

30,000 m2 of mirrors, 1360 W/m2, that's 40.8 MW.

half the time

...yeah, now i see how i picked 6 MW when i first did the model. i should drop it back down to that. The mega-tank on the hill can be sized however we want.

50 MW sounds like a reasonable size

then for the city i'll do up Nuclear Lava Lake Park

MolbOrg

20:29

You have to understand energy demands for the city. Which come with the goal and what they do. Energy is an important starting point.
The second important is are you short on labor and which type of labor you have to build necessary things. How all that have to be done, and what you need to build all that.
Those things define minimums for energy, also they help to choose between designs because everything can be done in multiple ways.
It is great idea to revisit the energy thing.

Nice pictures of big tank, btw.
And in general it is not that big, 500MW isn't that much if we talk about useful activity, but it is a lot if we talking about human life support (or not a lot, depends on definition, but it should be enough for few 10's thousand people (10-50 thousand - depends on expected level of food supply)

However, if we assume that colony does not use efficient cycles for productions for different reasons like refine all wastes and byproducts to keep catalysts like hydrogen, water, carbon, helium etc it might require way much more energy than 10kW 24.7.365 per capita

Wery healthy idea to exploit cheap solar energy. It simplifies a lot of things and allows to have fewer technologies, less sophisticated technologies, and it kinda compensates for not high population.
It allows to do things which can't be done on earth with small amount of people - basicaly it multiplies what those people can do

now back to the big tank problem
Now I understand what the problem is with the tank. Yes, it starts with mirrors.
During the day it has to store heat at the rate of 1GW, best case scenario 1360W/m^2 - it is about 1km^2 of mirrors.

The problem begins with the concept of central heat storage when we think about all those tubes which are heated and have to deliver the heat carrier to the tank.
All those pipes are all over the 1km^2, at high temperature - and heat carrier flows trough them to the tank
Length of all those tubes can be 100km with ease - they loose heat

more than that - if they would just fill the tank, and not heat it as it is now it would be much better
but the heat carrier has to have the very high temperature to heat the tank to high temperature and return back to the mirror system at high-temperature to be heated there to very high temperature again.

All those losses adds-up and have to be at least calculated a bit to determine order of possible efficiency of the system

kim holder

20:53

before you go further, i want to make sure we are on the same page on a few things

MolbOrg

heating and heat loss can be solved, mirrors are rearranged in the way as done on earth with similar setups - and it is one way to solve the problem. https://img.digitaltrends.com/image/array3-970x647-c.jpg - tower and mirrors around
ok

kim holder

1 - Cernan's Promise has a total population when all the buildings shown in it are fully occupied of maybe 60,000 people.

2 - the vast majority of labor is performed by robots

3 - the power demands are so hard to accurately predict it is functionally impossible. for every aspect of life support, scale and the options created by a full colony lower power needs per person. everything that depends on heat would be heated directly by solar concentrators as much as possible. it is also fair to expect that efficiency of a lot of things will go up, and that several things now done mechanically would be taken over by bioreactors. On the other hand, industry is large scale.

4 - the full city is a million people. what we do to address that is a whole other ball of wax. that will need way more than 500 MW, but for the colony of 60,000 i think that is too much.

now just a comment or two on your approach - heating regolith directly is more efficient - until you get in the tank. after that, you can't heat it any more.

MolbOrg

*shall I speak *say when I can

kim holder

as systems get larger, what i have focused on is making the mirrors wider so that the intensity of light focused on the pipes gets much higher

yeah, i'm basically done

MolbOrg

21:10

Ok, energy budget a rough one any - is the must
With 60'000 0.5GW electric(!) is bare minimum
robots at least the same bare minimum - for them to operate, repair, produce
You not at the stage of accurately calculating the energy demands - but some bulk pack calculations can be done and should be done. Industry at large scale - which one, and add 1GW for it just to be
*can't say anything about bioreactor but is chemistry where it can help - I'll skip that part for now
Million city - the 60'000 city has enough energy to grow

wich things you plan for the bioreactor

*Million city - the 60'000 city should have enough energy to grow

Food production is one big consumer of electricity, on the earth we get the energy for free, but on the moon overnight it has to be supplied to. it probably can be optimized, etc etc, but better to be safe than to sorry, 10kW for growing crops per each human, it is a rough estimation, have seen different numbers, but I stick with that one in my estimations.

kim holder

yes, actually i would say that number is quite high

with efficient grow lights, flowering cannabis is grown drawing about 350 W/m2. ( i choose that crop because there is a wealth of accurate data.)

flowering cannabis needs fairly heavy energy input, and also we don't need to make crops actively grow overnight - they just need to get along.

based on personal experience of how much yield we get from our garden, i would say maybe 15 m2 of intensely cultivated land will feed a person.

MolbOrg

21:27

"they just need to get along." - no no no man, bad idea
plants have their live cycle, you can fake them to believe for almost infinite summer(9month at leas, with tomatoes) but they know what (thing after summer) means time to die

"i would say maybe 15 m2 of intensely cultivated land" - with infinite summer or without ?

kim holder

i live in mexico. most of our food plants just keep flowering and fruiting all year round.

i haven't read about this in a long time, but from what i recall, the studies there are show that the energy needs to get crops through the night nicely do not need to be that high

but even if we say we'd give our crops 300 W/m2 through the night, that isn't constant - give them 8 h a day of that in each 24, now you are down to 100 W/m2

and that is half the time, now you are down to 50 W/m2

and that is at pretty much 'infinite summer' levels

plus if you make good use of your plant waste, you multiply your yield.

feed it to edible bugs that like that sort of thing, then eat the bugs.

MolbOrg

22:01

@kimholder 0.750 kW 24.7.365 ?

kim holder

yeah

MolbOrg

No excess food, no safety factor, not meat but bugs instead - right?

kim holder

22:15

yes, but certainly there would be shipments of food too, so you could consider that a safety factor.

kim holder

22:52

nutritional yeast is a tasty, and like the name says, highly nutritional crop that can grow on a variety of waste plant material, without light. break the cellulose down into glucose and you can get a pretty good yield on all sorts of plant waste.

mushrooms are good for providing minerals in your diet, and also can be grown on woody plant waste without light.

blue-green algae can be grown in reactors at high efficiency. it has a strong flavor, not unpleasant but not something you'd want to eat a lot.

put all these things together and they help with the achievement of that 750 W per person figure.

MolbOrg

23:17

Ok failed to find some numbers for experiments which had the place. So far only 2 publicly known experiments which were successful in closing some loops of biomass, russian bios-3 and Chinese castle of something something one, recently.
I really do not see the reason to go big in everything else, and sticking to survival style food supply.
Another semi argument would be 0.75*24*0.1=$1.8 per day per person - some crazy dude would do that just of fun on youtube )))

I watched a lot of aquaponics setups, but most of them do not need artificial lights, but you would better stick to weed number it is more real, even with 6 times productivity of plants than usual they had in experiment setups. with 0.75 you push the limit to survivial mode. delivering some food will never be cheaper than just placing additional 10-20% of mirrors, so relying on that, there is no reason for that

Second, it makes sense to determine not a minimum of necessary, but estimate sufficient maximum. If there is excess energy, more power for regolith refinemtn etc. It is better to have more energy which is not used, than not have energy when it is needed.

but at the end, you should have some number, because energy systems depend on it, and if it is big one setup is preferable if it small enough another type can be good enough.

kim holder

23:50

the 15 m2 was an estimate, as i didn't want to go find the figures myself right now either. but it looks like you aren't adding the food that comes from the bugs, yeast, mushrooms, and algae.

it will always be necessary to bring food from Earth, because there are going to be lots of food it wouldn't make sense to grow on the Moon

and people like their favorite foods and aren't going to want to give them up. Cheese, meat, seafood, chocolate, specific brands of specific things like sauces, drinks

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