Creating a (small) Lunar atmosphere

Terraformer · 2011-11-26 08:35:50

I'm talking about an atmosphere of ~5mb - Areoforming, if you like, rather than Terraforming. This would result in cloud cover over the moon, hopefully an Ozone layer forming, a smoothing out of temperature, and allow small craft to aerocapture. Predominantly, though, it would be a vanity project, so that one can look up from the surface of Terra and see clouds across the surface of Luna - mainly because I don't want to get into a discussion about cost-benefit.

Luna has a surface gravitational acceleration of 1.62m/s^2, so to provide a 0.5kPa pressure on the surface would require ~310kg per square meter. Overall, we're looking at 2.42e16kg of atmosphere. If we can get ~1km body comets with a density of 1g/cm^3 and which are 50% by mass of Ammonia and CO2, each impact would deliver ~2.62e11 kg of atmosphere, so we'd need about 100,000 such impacts. Eeek. Depending on how the water behaves, though, we may "only" need 50,000 (if the water disocciates under the influence of the UV). Still, it's a great deal many impactors needed. Are there any other ways of getting a small Lunar atmosphere going?

JoshNH4H · 2011-11-26 09:35:25

Well, if you're willing to wait... how about an orbiting mirror, to photodissociate the regolith. Unless you have a really freaking huge mirror, it'll be slow; it will also be relatively difficult to do and would totally change the surface of the Moon (Imagine what it takes to boil ~300 kg of oxygen out of every square meter of lunar surface!).

Terraformer · 2011-11-27 08:51:45

Hmmm. I seem to recall that turned out to be unfeasible (unfortunately, it was a post-2008 thread...)? Though perhaps as a way of driving out trapped water...

If we lower the atmosphere to 1mb, and manage to get all the mass of the comet to be turned into atmosphere, we only need 10,000 of the ~1km impactors, or 10 impactors of ~10km size. The main problem with that is that people might be funny about sending such objects near Terra... if we can use ~5km objects, we're talking 800 of them. Hmmm. Perhaps we need Dysons mass streams to make this work...

Say, 1mb means 62kg/m^2. Whether we could get that much is a decade or so out of the regolith... certainly, we don't want a fully oxygen atmosphere. Ideally it would be one full of CO2 and N2 if it's going to be that small, so that it's neither an oxidising or reducing atmosphere, though if Ammonia and Methane somehow react with the rocks to produce water, then I'd say import them.

I think the only way, barring unexpected discoveries of massive quantities of Lunar Nitrogen, CO2, Ammonia, Methane etc, we'll get an atmosphere there, is by using comets. 1000 impacts in the ~5km diameter range should give us decent enough atmosphere...

JoshNH4H · 2011-11-27 14:18:27

Well, the real problem with that idea was that I was incredibly overoptimistic (Read, I accidentally dropped ~6 zeroes) in terms of how much energy it would take to get 1 kg of oxy out of soil. Assuming 50 MJ/kg O2, if you have a soletta the size of the Moon, you could generate 2.5e8 kg O2 per second. To get the 2.42e16 kg required for a 5 mb atmosphere would take about a hundred million seconds (calculations show 93.4 million seconds, but 50 MJ/kg is relatively optimistic in terms of O2 yield). A hundred million seconds is 3.17 years. This is for the 5 mb atmosphere. The 1 mb atmosphere could be done in about 8 months, or alternatively you could have a much, much smaller mirror.

Of course, this requires a parabolic mirror the size of the moon...

Though that is perhaps less unreasonable a proposition than it would appear if you make it out of solar sail material.

Terraformer · 2011-11-27 15:32:51

Getting a 2.5e8kg atmosphere in a year, assuming you are correct, would only require a mirror of about 310m radius. It wouldn't be much, but what it would be is somewhat permanent - at that point, effects come into play which make thermal loss the dominant atmospheric escape mechanism. What it would do is provide a limited amount of sheilding against the solar wind. Could be interesting if it results in more water being produced due to there being more oxygen available for protons to react with.

If your calculations are close enough for government work, we're looking at 6-20 years for a 1mb atmosphere if we have a mirror of radius 580km. Probably close to 20, if they're close enough for government work Probably best to work the methods in synergy - use mirrors to produce oxygen, and import volatiles, using the oxygen to mop up excess hydrogen and carbon. Importing, for example, Methane, would result in a net decrease in pressure of approx. 1/4, as the Hydrogen would result in water and the carbon would result in CO2. Might be worth it, though.

Hop · 2011-11-27 15:41:24

Terraformer wrote:

I'm talking about an atmosphere of ~5mb - Areoforming, if you like, rather than Terraforming. This would result in cloud cover over the moon, hopefully an Ozone layer forming, a smoothing out of temperature, and allow small craft to aerocapture.

Since the lunar surface is vacuum, you can launch via rail. Not only does this eliminate gravity loss, but also allows you to cut some km/s from your delta V budget when figuring reaction mass. An atmosphere could take that away. An atmosphere would be a net loss in terms of delta V, in my opinion.

The best place to settle is near the volatile deposits in the lunar cold traps. Plateaus neighboring some of these cold traps enjoy nearly perpetual sunlight. The temperature swings for these is plus or minus 10 degrees.

The habs would still need radiation shielding, even with a 5 milli bar atmosphere

Midoshi · 2011-11-27 18:06:56

I think I agree with Hop here. Unlike some solar system bodies, Luna is not screaming for an atmosphere, no matter how romantic it would be. Considering the difficulty and trade-offs involved, I think it is best to leave our Moon as it is.

Don't let that discourage wild speculation though!

SpaceNut · 2011-11-27 18:49:51

Current level of atmosphere is thought to have come from impacts kicking up dust to form this weak vail....

JoshNH4H · 2011-11-27 22:56:09

Hop and Midoshi-

Given that Terraformer specifically stated that this was more assuming that we had already decided that we wanted to aeroform the moon, I figured I would leave those details out. In reality, terraforming would probably rid the moon of its meager concentrations of volatiles and minimize the benefit of aeroforming the the first place; this would of course be negated if you use comets.

Anyway, back to the topic: I'm not sure which is more practical between asteroids and soil burning. I have a feeling that asteroids are better. However, there is perhaps something important to keep in mind when the atmosphere you're looking for is that small: Water's vapor pressure at room temperature is 23 mb. Sending just hydrogen and allowing it to react with the lunar rocks upon impact is a lot cheaper in terms of mass sent to the Moon; Since water is quite a good greenhouse gas, perhaps in combination with a few other GHGs (methane, ammonia, perhaps?), the planet could remain at some equilibrium with a significant amount of atmosphere in the form of water vapor.

Hop · 2011-11-28 10:24:40

JoshNH4H wrote:

Hop and Midoshi-
Given that Terraformer specifically stated that this was more assuming that we had already decided that we wanted to aeroform the moon, I figured I would leave those details out. In reality, terraforming would probably rid the moon of its meager concentrations of volatiles and minimize the benefit of aeroforming the the first place; this would of course be negated if you use comets.
Anyway, back to the topic: I'm not sure which is more practical between asteroids and soil burning. I have a feeling that asteroids are better. However, there is perhaps something important to keep in mind when the atmosphere you're looking for is that small: Water's vapor pressure at room temperature is 23 mb. Sending just hydrogen and allowing it to react with the lunar rocks upon impact is a lot cheaper in terms of mass sent to the Moon; Since water is quite a good greenhouse gas, perhaps in combination with a few other GHGs (methane, ammonia, perhaps?), the planet could remain at some equilibrium with a significant amount of atmosphere in the form of water vapor.

Here Chris McKay suggests strapping "a quartet of 5000 MW nuclear thermal rocket engines" to a comet for Mars terraforming. That's 20 giga watts. The very large Palo Verde Nuclear Power Plant in Arizona is about 3 gigawatts. McKay's NTR rockets would take the power 6 Palo Verde plants.

If you're using the comet substance for reaction mass, you need a way to get the comet's substance to the NTR's rocket chamber. This entails setting up a mining infrastructure on the comet as well as transportation infrastructure to deliver the mined volatiles to the NTR's rocket chamber.

A mammoth engineering project on an object in the outer solar system.

Real estate on a planet is measured in area. Temperature and pressure prohibit burrowing too deep into a planet, so accessible resources are also confined to a planet's surface.

The surface area of the small bodies is many, many times that of the rocky planets and large moons. Not only that, but the entire volume of a small body is reachable.

If we terraformed the moon and Mars, that might double our living area. If we developed the asteroids, humanity's living space could be increased millions of times.

The time and effort crashing small bodies into a planet or large moon would be better spent developing the small bodies.

Terraformer · 2011-11-28 10:54:49

Hop-

I wrote:

Predominantly, though, it would be a vanity project, so that one can look up from the surface of Terra and see clouds across the surface of Luna - mainly because I don't want to get into a discussion about cost-benefit.

I'm just thinking about what we could do if cost-benefit wasn't an issue. Certainly, actually getting a Lunar atmosphere which is somewhat permanent wouldn't be too difficult, but it's nowhere near the thickness I want it. Getting a few microbars in a decade by simply baking the regolith from orbit won't be difficult; getting millibars, however, would be. We're talking about maybe 100 comets in the ~5km range, which will be quite... difficult to move. I don't suppose we can lower them to the Lunar surface using the interplanetary highway?

JoshNH4H · 2011-11-28 11:32:32

Looking at it, I would think that the Hydrogen bombardment strategy is probably best for this, given that you could get a large majority (89%!) of the mass of the atmosphere from the regolith, while you can get the hydrogen from a gas giant. Uranus would seem to be ideal given the delta-V requirements. Just particle accelerator it over to the Moon.

Terraformer · 2011-11-28 13:14:34

Use Hydrogen to produce water for the atmosphere? Hmmm.

I'm still holding out for the discovery of Carbonate deposits on Luna... it would seem unlikely, but stranger things have been found. How does CO2 behave when Magma crystallises, exactly? Plenty of unknowns in the Lunar formation period which could offer us leverage. Otherwise, I don't see it likely that well be terraforming (or even Protero- or Areo-forming) any time soon (though the idea of an atmosphere of waste volatiles, mainly oxygen, forming as a consequence of large scale settlement is interesting...).

SpaceNut · 2011-11-28 19:16:51

Forgotten that the LCROSS spacecraft had significant finds....NASA finds reservoir of water ice on the Moon

Plus the moon is bombarded by lots of others (He3)....a product of tritium decay, and tritium can be produced through neutron bombardment of deuterium, lithium, boron, or nitrogen targets.

Terraformer · 2011-11-29 06:31:25

I don't think the reserves are going to be sufficient for making an atmosphere, even a small one...

What about the possibility of gas pockets being formed by volcanic activity early on in Luna's existence?

Hop · 2011-11-29 07:43:53

Terraformer wrote:

I don't think the reserves are going to be sufficient for making an atmosphere, even a small one...
What about the possibility of gas pockets being formed by volcanic activity early on in Luna's existence?

http://blogs.airspacemag.com/moon/2011/ … a-gas-man/

Terraformer · 2011-11-29 10:01:13

Hmmm, even a small (<1mb) oxygen atmosphere on Luna would have benefits in term of blocking UV:

Martyn Fogg wrote:

Thus, we might assume that complete protection from ultraviolet radiation requires a column mass of oxygen equivalent to ~20mb on the Earth (0.1PAL); satisfactory protection from most wavelengths is possible down to a terrestrial column mass of oxygen equivalent to ~2mb (0.01PAL).

That corresponds to a pressure of ~0.35mb on Luna for the minimum protection, and ideally about 3.5mb to get full protection from UV. Coupled with the charged particles that will be deflected by the atmosphere, it will at least offer some benefit... we could bake the minimal atmosphere out of the rocks in ~2 years with a 580km radius mirror, or ~10 years for a 260km radius mirror. An interesting side effect of this might be that volatiles would be baked out of the Lunar surface and precipitate out at the poles, vastly increasing availability.

Managing say 30 100km diameter mirrors would be a significant undertaking, though... I'd still prefer to use comets.

As far as outgassing goes... perhaps creating a stable atmosphere, on the order of 1e8, would enable any gas released by deliberate outgassing events to stay around rather than being immediately lost.

Certainly, using multiple methods for terraforming always seems to be the best idea. Once we get a 1mb atmosphere or thereabouts, we could perhaps direct comets to burn up in the atmosphere and release their volatiles...?

Spaniard · 2011-12-14 10:16:35

Midoshi wrote:

I think I agree with Hop here. Unlike some solar system bodies, Luna is not screaming for an atmosphere, no matter how romantic it would be. Considering the difficulty and trade-offs involved, I think it is best to leave our Moon as it is.
Don't let that discourage wild speculation though!

I'm not so sure.

Have an atmosphere allow you to aerobrake, so you have a gain on descending.

On another point, escape velocity is only 8.5 km/h aprox. It sounds like a manageable speed with a thin atmosphere for a heat shield.

Of course is more easy without atmosphere, but only from Moon to space.
So, in short term, Moon is best as is.

But once you have a colony in L4-L5, and a growing colony on the Moon with bidirectional trading from-to the Moon, a minimal atmosphere could be an advantage for protection and mitigate the extreme temperatures.
Moon will have a space elevator and rail launcher for "short" distances (Earth, L4/L5 colonies, ...).

Terraformer · 2012-07-17 05:29:44

Hmmm. I like the mirror idea to try to get a 0.5mb atmosphere on Luna, which will provide slight protection against radiation (the solar wind) and allow very small (50kg?) packages to land using the atmosphere, without being much of a hinderence to launching things. I'd prefer, of course, that the atmosphere was one of CO2 rather than oxygen, so that it doesn't oxidise anything. Perhaps we can source some carbon dust to inject into the atmosphere and burn up? We'd need something on the order of 1e15kg of carbon, though? That's a single body made of carbon approx 10km diameter, but you have to make it react. Still, 1000 1km impactors is a much easier goal than 100,000 of them... ish...

Damnit, I want to be able to look up and see Lunar clouds and greenhouses.

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#1 2011-11-26 08:35:50

Creating a (small) Lunar atmosphere

#2 2011-11-26 09:35:25

Re: Creating a (small) Lunar atmosphere

#3 2011-11-27 08:51:45

Re: Creating a (small) Lunar atmosphere

#4 2011-11-27 14:18:27

Re: Creating a (small) Lunar atmosphere

#5 2011-11-27 15:32:51

Re: Creating a (small) Lunar atmosphere

#6 2011-11-27 15:41:24

Re: Creating a (small) Lunar atmosphere

#7 2011-11-27 18:06:56

Re: Creating a (small) Lunar atmosphere

#8 2011-11-27 18:49:51

Re: Creating a (small) Lunar atmosphere

#9 2011-11-27 22:56:09

Re: Creating a (small) Lunar atmosphere

#10 2011-11-28 10:24:40

Re: Creating a (small) Lunar atmosphere

#11 2011-11-28 10:54:49

Re: Creating a (small) Lunar atmosphere

#12 2011-11-28 11:32:32

Re: Creating a (small) Lunar atmosphere

#13 2011-11-28 13:14:34

Re: Creating a (small) Lunar atmosphere

#14 2011-11-28 19:16:51

Re: Creating a (small) Lunar atmosphere

#15 2011-11-29 06:31:25

Re: Creating a (small) Lunar atmosphere

#16 2011-11-29 07:43:53

Re: Creating a (small) Lunar atmosphere

#17 2011-11-29 10:01:13

Re: Creating a (small) Lunar atmosphere

#18 2011-12-14 10:16:35

Re: Creating a (small) Lunar atmosphere

#19 2012-07-17 05:29:44

Re: Creating a (small) Lunar atmosphere

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