Moonwards - 2017-05-02

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12:42 AM

that is reasonable. Still, doubt the lava variant. Molten aluminum seems to be a better choice for two reasons - metal more heat conductive thus better heat exchange system than lava, lower temperature, iron pipes, ceramic pipes(or coatings) may work at those temperatures.
IDK why you worry about weight in the case, the tank should be built in place or something like that and buried so it will be insulation and wall reinforcement

1 hour later…

2:07 AM

3

Q: What color is earthshine?

What color is earthshine (e.g the average color of earth that shines on the moon)? I am making a solar system exploration game, and would like to know this for the lighting of my moon level at night, with a "full earth".

the-moon earth light

@kimholder I seem to remember reading something you've written about the moon and color but can't find it now

13 hours later…

2:59 PM

i'm thinking...
> If the resulting glass is more than about 2% iron, it will have a green tone visible enough to be distracting. Not nearly as distracting as living with tiny windows, but not ideal. Of course, the lunar landscape is not exactly brimming with color, so that may be a pretty minor point.

that is the only thing that crosses my mind, from the most recent blog post. i wouldn't be surprised if i have wondered about it before, but i don't recall.

@MolbOrg molten aluminum where? in the heat exchange pipes?

i don't really worry about weight, it's just that when you state that you are going to build a tank 70 m high and fill it with lava, it tends to cross people's minds.

and actually, i have put in a network of pipes going through the bottom of it to minimize the contact area between it and the ground underneath. so, to the extent possible it is an elevated tank of lava 70 m high...

3:18 PM

> In my answer to Color of planets I estimated the colour of the Earth as #2f6a69

@uhoh that made me laugh out loud.

3:51 PM

@MolbOrg when i talk about the lava, i'm talking about the medium for the whole thing - the tank is filled with regolith, which largely melts from the heat brought by pipes that go through the parabolic mirrors, and other pipes maybe full of molten aluminum also go through the regolith to carry that heat to an exchanger.

or do you think molten aluminum should go in the pipes through the mirrors too?

(no, that doesn't make sense - it would freeze at night.)

4:08 PM

@kimholder I thought it was 'interesting' too.

About the color, I somehow remember the term "wavelength dependent albedo" connected to a question or an answer by you. I don't know why I remember it like that, but I'll keep looking.

your memory seems to be considerably better than mine

wait - something is occurring to me

5

A: How dark is the side of the Moon in shadow as compared to the side facing the Sun?

When the sun goes down on the Moon, Earth is waxing and at half full as seen from its surface on the near side. At lunar dawn Earth is a waning 'half-Earth', if you will. This is noticeable to us in the way you can see the full disc of a young waxing crescent Moon in the early evening, because Ea...

Found using "site:space.stackexchange.com color of the moon"

yep, you beat me by about 30 seconds :D

i found it by going to my user page and searching for earthshine

i remember TildalWave awarded me the 100 bounty points on that question, and did so before the answer was even finished, which made me so anxious i edited it about 30 times.

It's a memorable answer!

It gave me a lot to think about.

But I don't see anything about color. I must have started from this answer and then did more reading. This was a while ago.

well, one could use the chart to assign a color to the different albedos...

4:27 PM

yep, there are a lot of approximate plots of that around, but still looking for high quality data on wavelength-dependent albedo. Anyway, I'll chat later, it's lat.

late

ok. good night, uhoh.

4:53 PM

no, the medium in the tank.
Watched this video about thorium recently, about its properties and potential applications(a bit) https://www.youtube.com/watch?v=q3-jvKW75G0
Now I wish to put thorium everywhere ))))

thorium as a metal, as a construction metal

say you wish to build it 10m height size of 4 Olympic pools
hm why you need an elevated tank, any way you need insulation at those temperatures, any way you insulate it with regolith stuff, use it for free, dig a hole.

that's so much aluminum i don't think it's practical. besides, if you think the tank doesn't have enough heat capacity, why not just make it bigger?

vacuum still insulates better than regolith, by quite a bit. anyways, the pipes only form about 2/3 of the floor, maybe 3/4

@MolbOrg it is an awful lot bigger than that

what was the figure i put before? 50 x 50?

that was a shorthand between Hoh and me

what we mean is, 25 m radius cylinder by 50 m high

and now it's bigger...

Hoh did calculations showing the heat that reaches the outer wall, after 5 m of regolith, is still significant enough that it is beneficial to try to reduce heat leakage through the floor

5:22 PM

it's 1.57m high 4 olympic pools (one Olympic pool is 25x50 meters)
heat loss in vacuum at 1500K is 287kW/m^2 of the surface.
Regolith and rock conductivity at 1200K is about 1 W/(m*K) - so one meter of such insulation loses about 1.5kW/m^2, so it is not important which regolith it will be in a hole or in a layer of a cylinder, unless you use better inculating material, then there will be a difference

no, its about 3 such pools, stacked 30 deep

@kimholder you mean 70m variant? which dimensions it have

it is a cylinder, which at the moment is 70 m high. the circle part of the cylinder has a radius of 40 m

so it has a volume of 112,000 m3

let me find where Hoh discusses the heat loss

the thing is, when you are losing heat to a vacuum, you can reflect it back. that can cut down heat loss a lot.

Apr 19 at 21:56, by kim holder

how hot can we let the walls get and still control heat loss well?

Apr 19 at 22:07, by Hohmannfan

I get a loss of 220 W/m² on the cylinder wall on the 5m radius setup.

actually the second one is better - click the date to go to the page of dialogue

Apr 19 at 22:53, by Hohmannfan

Combining the diminishing return with the square-cube law to get the loss per volume of stored lava: (wall component only)

ok - that's the one i really wanted. again, it is much better to see it in context.

5:37 PM

yea that's 70m heigh 4 OLP, ok then let it be 7m heigh 40 OLP )) difference in surface area is 3.8 times.
With 3.8 times thicker walls, which is automatically achieved for bottom and sides of the 40 OLP reservoir
but all that is not so much important, what really is interesting is melting point of regolith is pretty high, there is no problem to heat it up such temperatures without heat carrier, but what is heat carrier and most imprtantly what are the pipes

wait... it has a volume of 350,000 m3. sorry. sloppy.

for the pipes going through the mirrors, i was thinking titanium carbide

@kimholder hm, "titanium carbide", hm, anything about making tubes from it, from pure material not with cobalt or any other matrix.

it's not something i have looked into at all. basically what i did is confirm there is a material that could handle it

i suppose the thing would be to build them up with a 3d printer that laser sinters a powder feed

if it's good enough for rocket parts, it must be good enough for that

5:58 PM

hm, probably the way to go, interesting, really curious now how to make tubes from such materials. but yes, something like that probably should work if it sticks well enough

3 hours later…

8:46 PM

you know, i have spent about 4x as much time staring at my lava tank model, deciding the right way to do things, than i have actually doing anything.

I'm doing the same since my last comment

I would say it is not so important technology wise, it is just a system to store the heat

and it has multiple variants to do so

well, i'm creating the systems that go with it too

and even though i'm just sketching it, there are a lot of things to consider, when i think about each bit

what are you working on?

but visually those variants would be different, but none is superior, there are some aspects which favorites one or another variant, but they are different visually for sure

oh, i'm thinking about practical stuff, actually

it'll be done soon, you'll see what i mean

practicality is also different, very different.

at the moment I'm reading this denning.atmos.colostate.edu/readings/… , listening daily wire, and thinking about details of moon colony episode with other people from Isaac Arthur group

8:56 PM

oh, you are moving on that huh? i didn't want to get into that contact for now, i have just way too much to do as it is.

I helped with few last episodes, more like proofreader and a few corrections there and there
now it moved to a new level, trying to convert 5k people group into ca 20 group of people for teamwork on topics - pretty interesting experiment as for me.

as contacting, no problem, you do what is best for you, as you find that convenient.

however, team work have some exciting cons, and some pros too, nothing is perfect ))

i do need a team, i just need a better set up for them to work with

so, i need a small team i can work closely with, not a large team. the project isn't at that point yet.

one of the problems in terms of numbers - about 50k subs on youtube, some people are interested in topic, about 5k people in FB group, about 20 people in production group (was created 24h ago), and I would say about 5 people worth the time spend to talk.

I'm generous, but at least 3 are very interesting

1/10000 to select for a team for such topic - yeah, IDK

my recruitment has been through Space.SE, and The Space Show. so i tend to get good people. :)

9:14 PM

@kimholder all people are good ), not all are skilled and knowledgeable.

you know what i mean. the people who are right for the job. :P

true. Just find interesting to have some numbers about the situation.

everybody watches youtube. it doesn't require the same level of background knowledge and commitment to join a group there, as it does to join a group here.

true. numbers like that from the source allows to project it on the general public. It still totally warped s statistics but at least it can get some feeling about 1 million mars colony - is that many is that not many. Based on that I would say it is a lot, even when it will be reinforced by financial interest (which is opposite it is expected they will pay for a ticket)

if we expect them to be knowledgeable to achieve self-sufficiency of the colony etc etc.

it is a lot in terms that there is not that many people for it

10:02 PM

hm have language question, is there something racistic about using word "impossibur" instead "impossible" ? is off topic but just got such edit on WB, try to figure out, is that joke or not

oh - first, it's 'racist', not 'racistic'

and as for the rest, my guess is that they thought you were imitating an Asian accent

tnx, lol, oh my god ))))

11:00 PM

user image

here we have an excellent example of how hard it is to usefully mock up something that is 30 storeys tall.

even more so when it involves a whoooole lot of pipes

11:51 PM

looks great
btw radius 40 height 70 molten lava should be enough for 500MW over 15 days

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May '172

Moonwards

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