Moonwards

MolbOrg

04:23

interesting outline, project explanation, also maybe it would be interesting to hear other engines suggestions(actually catching for some specific engine, which I do not recall now)

>yes, there is, and a target that large is probably going to get hit with something worth worrying about within a century.
things are not that good in that regard, it is a distribution in size and frequency and proportional to the surface.
>about 30000 impacts per year per square meter of surface, which produce 0.1um craters, 300 impacts produce craters 10um and more, 0.1mm and more about 0.6 impacts, 1mm and m…

Feeds

06:52

0

Q: Why were the "perfectly functioning" seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977?

The Wikipedia subsection Moonquake says: Information about moonquakes comes from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15 and 16 functioned perfectly until they were switched off in 1977. According to NAS...

uhoh

08:30

1

A: Constant lunar sub-surface temperature

tl;dr: The number is often given as 252 +/- 3 K (or about -21°C or -6°F), so @BowlOfRed pretty much nailed it using first principles! Without atmosphere, equilibrium temperature at 1AU is about -17C. I would expect that to be the temp "near" the surface around the equator. Colder as the latit...

kim holder

15:04

@MolbOrg well, i caught myself after that, and said probable enough that it should be engineered for. and later i mention another relevant thing, that really you should engineer for it to last a millenium if you are going to build something that big.

MolbOrg

still in process of reading, so to say

kim holder

i have a graph somewhere, i won't go looking for it right now, though it should be posted whenever i get into documenting the city.

ah.

MolbOrg

>for it to last a millenium
disagree on that btw, maintenance and repair still a thing

kim holder

well, of course, but one still speaks of the structure lasting that amount of time. it is to say, it shouldn't need anything more than regular maintenance and repair during that time.

kim holder

15:30

@uhoh that is quite useful, it adds good data to what i'd found in the Lunar Sourcebook. thanks.

uhoh

15:56

@kimholder I was thinking that this could be a source of backup or supplemental or emergency cooling. It is not long-term sustainable (the rock will eventually just get hot), but if the radiator breaks...

kim holder

the subsurface? yes, that is what i want to do, use it essentially as thermal mass

Feeds

0

Q: Were there any policies or technical reasons beyond "common sense" behind powering down all Apollo ALSEPs in 1977?

I first tried to include this in the question Why were the “perfectly functioning” seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977? but after three comments from three different users stressed some aspect of it being "common sense" to shut it down since NASA would ...

the-moon apollo-program data-transmission scientific-data

kim holder

however the volumes are so large, it doesn't seem to me that it would work unless very long and deep channels, or boreholes, or tunnels are dug through the rock.

and the transmission of heat is so slow through regolith, it also seemed to me that the thing to use was the bedrock that would be available near the surface in the lower part of the crater.

uhoh

the math is pretty easy (at least it was 20 years ago) so I'll do a quickie tomorrow.

kim holder

that would be great, because i've tried to approximate before, and i didn't have much confidence in my result.

that was a basic stab at it, for one of the structures i showed you yesterday, the 'chalets' on the crater wall.

i'm pretty sure i don't have the calculations any more, i think i just did them on paper somewhere, just using heat flow in rock and an approximation of the incoming heat from sunlight piped in.

that's this model:

moonwards.com/colonies.html#GalleryCutaway

of course, the city has that giant transparent roof...

uhoh

16:26

Is the sunlight just for natural lighting, and the heat is undesirable, or is the heat produced by the visible light also used to warm the space also?

In other words, is the heat produced by the light "friend" or "foe"? (I'm assuming heat from the near IR is removed with a filter).

kim holder

the sun is lighting. the heat is enough for it to build up, i think. the radiation shield of regolith won't let much heat back out through its roof.

uhoh

okay I got it. With a good filter, Sunlight is all light, compared to electric lights which for ever Watt of light add roughly a 2nd Watt of heat independent of it.

Even if you use electric lights, it would be better to put the light bulbs outside the room and use the same light pipes.

But other stuff like computers, TV, appliances, etc. will all probably make more heat than a few hundred watts of visible light.

I guess what's needed is a total energy budget.

kim holder

that has always been something i've shied away from doing. MolbOrg has mentioned the same thing.

i mean, for regular appliances i guess we could come up with a figure per person, but other activities, related to work?

i don't know how to tackle that. i'm inclined to ignore it for this, as i want to make manufacturing independent of the habs, in other buildings that would have no thermal impact on them.

uhoh

16:42

I'll write up a little thing then, with some blank spaces. Do you have a common area for documents, or should I e-mail? It's nothing fancy.

kim holder

or maybe fudge in something that seems like a reasonable guess

ah documents - there is a wiki on the repo, and there were some google docs...

let me check for a moment, it might be better to do it a different way.

MolbOrg

>Even if you use electric lights, it would be better to put the light bulbs outside the room and use the same light pipes.

I would not advocate for that, LED light are good
I would not ay that heat buildup on the moon would be a significant issue to solve. There is plenty of ways available to deal with it

it is not pure space problem

kim holder

actually, wait, are we talking about the earlier habs, or are we talking about the city? or both?

uhoh

@MolbOrg for the same amount of light, artificial light makes twice as much heat as sunlight. IF the heat generated by visible sunlight is a problem, then LEDs would be twice the problem. I'm still trying to understand why heat from Sunlight is a problem to begin with.

MolbOrg

>for the same amount of light, artificial light makes twice as much heat as sunlight.
I'll give you a time to think about that

chance to reconsider

or convince me

uhoh

16:48

LEDs are roughly 50% efficient. 1 Watt of light needs 2W of electrical power. Both of those Watts end up as heat.

Unless you move the LED out of the room, and re-use the same light pipes that bring in sunlight.

kim holder

@uhoh do you use google docs?

uhoh

ya

MolbOrg

okay, let's go easy - why light bulbs are not a thing anymore, and luminescent light and LED's are now a thing?

kim holder

docs.google.com/spreadsheets/d/…

uhoh

I'm just conserving energy, there's no ambiguity here.

kim holder

16:55

so i just made a google spreadsheet called Heat Budgets, and set it so anyone can edit.

it's blank right now.

uhoh

@kimholder okay I will type some stuff on a tab. Do I save this link in order to find it later?

kim holder

one thing about artificial lighting, is that at night most of it is for the plants, and so even with matters of heat, they have to be close enough to the plants that all of their light goes to them.

@uhoh could you star it so it gets pinned to the sidebar? i can't because i posted it.

or wait, yes i can, because i'm room owner...

Luminous efficacy

Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on context, the power can be either the radiant flux of the source's output, or it can be the total power (electric power, chemical energy, or others) consumed by the source. Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation, and the latter luminous efficacy of a source or...

uhoh

@kimholder I've only used google docs between me and someone else when we log in to gmail. I've never used it in a public way before. I added a 2nd tab and typed "this is a test" on it.

kim holder

sure, go nuts.

yeah... the lights needed for the plants at night become a significant heat source, it looks like.

there are figures on it for some kinds of plants, i haven't looked at it in some time.

am i understanding the wikipedia chart right, that luminous efficiency means that the remainder after the percentage that is light is removed, is all heat?

uhoh

okay great. As usual it's late here, gotta start winding down the lumens so I can make more melatonin and sleep ;-)

kim holder

17:06

cheers. i'll reflect on this while i model regolith.

uhoh

17:17

2

Q: How can I estimate the optical power that a single-color LED generates?

This excellent answer addresses the Luminous efficiency and Luminous efficacy of LED lighting, but these are based on human vision and it's variability with wavelength. It's a good idea to read it. I'd like to be able to convert these to absolute efficiency, which would be the ratio of optical p...

power led efficiency

...and links therein. okay good night!

9

Q: Are LEDs in modern streetlights usually pulsed? If so, roughly what frequency?

I can think of some reasons why modern LED streetlights would likely be pulsed; Efficient voltage conversion starting from line voltage would likely include an AC or switching step higher than 60 Hz. Highest efficiency operation of LEDs often occurs at a current greater than can be sustained c...

led light led-driver lighting

answers here are particularly helpful.

kim holder

good night, uhoh. i'll read that.

uhoh

Now I must power down my light sources :)

Those are my questions. I modified my icon because I kept getting abused by users there. Somehow this one makes people take me more seriously, even though it's from Dr. Strangelove :)

3

Q: How to make a green LED as visually bright as a 0 magnitude star?

I'm trying to estimate the distance and power I'd need for a green LED to appear visually roughy as bright as a relatively bright star - say a visual magnitude of zero. Here is what I have so far. Be warned I am just ballparking it here. The sun is visual magnitude -27, and five visual astronom...

optics visible-light vision light-emitting-diodes

0

Q: What is "unseen blue light" from LED lighting?

In the Washington Post story Some cities are taking another look at LED lighting after AMA warning I noticed the phrase "unseen blue light" in the first full paragraph: The American Medical Association issued a warning in June that high-intensity LED streetlights — such as those in Seattle, L...

visible-light perception light-emitting-diodes

0

Q: Do III-V based photovoltaics "glow" (photo-luminesce) when illuminated but not loaded?

In this nice answer I started to learn about how the silicon photovoltaics cells on the International Space Station are managed. In that case, the cells are generally either delivering useful power to the station, or shunted to a dummy load. However, some satellites may leave some fraction of the...

electronic-band-theory optical-materials photovoltaics

The last one is just creepy/cool

MolbOrg

17:50

the difference between led and light bulb(and the sun in that matter) is that led produce different light spectrum, we and plants do not need all the spectrum and all the spectrum will be converted in heat.
so if you use sun light it does not mean this solution will be less heat generation solution.

kim holder

18:20

yes, there is lots of good work on the spectrum for plants, i have one or two papers, and i should check again, because its been a couple of years.

heh, in fact, i recall it was awkward for uhoh because i posted a link to a grow light on a marijuana home-grow website, and it didn't occur to me that for him that is kind of a problem.

or at least, not for him, he made me aware that i should think before posting a link to a place that could get some people in trouble, in places where web activity is tracked.

which is a little alien to me.

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