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#1 2017-04-12 14:01:06

louis
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From: UK
Registered: 2008-03-24
Posts: 5,851

Analog(ue) air

Any thoughts on how to make analogue air on Mars?

Oxygen should not be too much of a problem...that's about 20% of air on Earth.

What about the 78% that is nitrogen?

The amount of nitrogen in the atmosphere on Mars is at 1/85000th the density of nitrogen on Earth.

Is it practical to concentrate that 1/85000th into the colonists' living spaces?

Could we also add argon in the mix? (it is more prevalent than nitrogen in the Mars atmosphere).


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#2 2017-04-12 14:53:44

Terraformer
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Re: Analog(ue) air

Sure. Argon works just as well as a diluent gas, though since it's heavier people will sound somewhat deeper.

If you're processing vast amounts of atmosphere for Carbon anyway, you should be able to pick up enough Argon and Nitrogen to handle any atmospheric needs.

Shouldn't this be in Life Support Systems, though?


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#3 2017-04-12 15:22:54

RobS
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From: South Bend, IN
Registered: 2002-01-15
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Re: Analog(ue) air

There are lots of ways to extract carbon dioxide from the atmosphere. You can run Martian air over a cold zeolite bed and the zeolite will adsorb the carbon dioxide. Or, compress Martian air and cool it off; the CO2 will freeze out. The resulting left over gas will be something like 40% nitrogen and 60% argon, I think. I'd just pump that into the life support system; it's a fine neutral gas combination to add to a breathable atmosphere. I'd also use a different Martian standard atmosphere for enclosures. The Earth's atmosphere is 3 pounds per square inch oxygen and 12 psi nitrogen. I'd use 2 or 2.5 psi oxygen, which is the typical pressure in a lot of Colorado, which people adjust to fine, and maybe 4 or 5 psi of neutral gas (nitrogen and argon). The big issues are cooking and the transmission of sound. Martians may need to use pressure cookers, and they may have reputations for speaking too loudly if they visit Earth. One advantage of argon: it doesn't give you the bends like nitrogen does if you are changing your air pressure, as you might when you put on a space suit.

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#4 2017-04-12 15:47:35

louis
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From: UK
Registered: 2008-03-24
Posts: 5,851

Re: Analog(ue) air

Thanks.  Good point about carbon extraction.

You might be right about the index filing - sorry!

Terraformer wrote:

Sure. Argon works just as well as a diluent gas, though since it's heavier people will sound somewhat deeper.

If you're processing vast amounts of atmosphere for Carbon anyway, you should be able to pick up enough Argon and Nitrogen to handle any atmospheric needs.

Shouldn't this be in Life Support Systems, though?


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#5 2017-04-12 15:54:24

louis
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From: UK
Registered: 2008-03-24
Posts: 5,851

Re: Analog(ue) air

Thanks. That's v. helpful. I see that Mars is thought to have plenty of zeolite - so creating the zeolite bed with ISRU materials is not liekly to be a problem.

So it's beginning to look like we could really just use the Mars atmosphere to make Earth analogue air using these various processes (including breaking down CO2 to oxygen and CO).

RobS wrote:

There are lots of ways to extract carbon dioxide from the atmosphere. You can run Martian air over a cold zeolite bed and the zeolite will adsorb the carbon dioxide. Or, compress Martian air and cool it off; the CO2 will freeze out. The resulting left over gas will be something like 40% nitrogen and 60% argon, I think. I'd just pump that into the life support system; it's a fine neutral gas combination to add to a breathable atmosphere. I'd also use a different Martian standard atmosphere for enclosures. The Earth's atmosphere is 3 pounds per square inch oxygen and 12 psi nitrogen. I'd use 2 or 2.5 psi oxygen, which is the typical pressure in a lot of Colorado, which people adjust to fine, and maybe 4 or 5 psi of neutral gas (nitrogen and argon). The big issues are cooking and the transmission of sound. Martians may need to use pressure cookers, and they may have reputations for speaking too loudly if they visit Earth. One advantage of argon: it doesn't give you the bends like nitrogen does if you are changing your air pressure, as you might when you put on a space suit.

Last edited by louis (2017-04-12 15:54:47)


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#6 2017-04-12 16:20:17

RobertDyck
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From: Winnipeg, Canada
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Re: Analog(ue) air

I have posted about this several times. I gave a presentation at a Mars Society Convention.

First, Dr. Zubrin's method to extract CO2 from Mars atmosphere starts by freezing out dry ice. Mars at night is just a few degrees above the freezing temperature for dry ice, so the idea is to run a freezer only at night. At dawn seal the canister, then heat to sublimate the dry ice. That phase change will self-pressurize. Dry ice freezes at -79°C at 1 Earth atmosphere pressure, a touch colder at Mars pressures. However, nitrogen and other gases require much much colder temperatures. So this will separate just dry ice. Sublimating that dry ice will produce pure CO2. There will be a trace amount of Mars atmosphere from the container with the dry ice, but it will be swamped in CO2 from the block of dry ice.

That's very efficient and effective. However, it only produces CO2. To produce other gasses you need something else. My idea was to use a pump to pressurize Mars atmosphere to 10 bars. Yes, going from 0.007 bars to 10 bars pressure means dramatic compression. This pump will consume significant power. Then freezer coils in the bottom of the canister will chill to -100°C. That will freeze out most CO2, but there will still be a bit left. The idea is to remove CO2, keep everything else. The remainder will be used as diluent gas. That is, mix this gas with O2, use that to fill a habitat for air to breathe. Since 95.32% of Mars atmosphere is CO2, this will dramatically increase everything else. Mars has a little carbon monoxide and ozone; not much but when concentrated this way the CO will be lethal. So the top of the same canister will have a rhodium based catalyst, warmed to +24°C. Yes, the bottom of the canister will be chilled to -100°C while a small patch of metal at the top of the same canister will be warmed to +24°C at the same time. Yes, this will consume power. Yes, you have to just do it. Mars atmosphere also has oxygen; not much but there's more O2 than CO. This catalyst will combine CO with O2 to form CO2. One reason for doing it in the same canister is the CO2 produced will be frozen out. The rhodium catalyst will also decompose ozone: 2 O3 -> 3 O2. This produces even more O2, so plenty of O2 to react with CO.

The remaining diluent gas will be primarily N2 and Ar. It will have a little CO2 left, but the best way to remove that is with a sorbent bed. The life support system of the habitat can remove that. Air will smell stuffy until that CO2 is removed, but will be safe to breathe.

The freezer will also remove all water. That's not intended, but can't be helped. Trace amount of water will be about 10^-13, so such a low trace it's practically zero. So very dry. There will also be trace amounts of neon, xenon, and krypton, but these are trace gasses in Earth's atmosphere anyway. You're breathing them right now.

Operation: run the compressor until it reaches 10 bar. The freezer will turn CO2 into dry ice, dropping pressure in the canister. When pressure drops below 10 bar, an automatic switch will turn the compressor back on to draw more Mars atmosphere in. Continue drawing in compressed Mars atmosphere until it reaches 10 bar, then turn off the compressor. The catalyst will convert CO and O3 into CO2 and O2. Continue to run this until the compressor doesn't turn on any more. Continue to run until a CO sensor detects the CO level has fallen below detection threshold; so effectively zero. With zero CO and the pressure stable at 10 bar, then turn off the compressor (already off but turn off the automatic switch), and turn off the heater to catalyst. Removing this source of heat will cause the canister temperature to drop a little. That will drop pressure a bit, but just let it, don't draw in any more Mars atmosphere. When pressure becomes stable, then open a valve to a tank with complete vacuum. This will flash draw the gas into this second tank. Once pressure between the tanks equalizes, close the valve between them. Then heat the dry ice to sublimated it, draw the CO2 into a separate tank for that. Once all dry ice is gone, and all the CO2 you can get is stored, then vent the rest to Mars atmosphere. Then start another cycle.

This will leave you with 2 storage tanks. One with CO2, the other with diluent gas. My estimate of diluent gas:
CO2 - 0.74935%
N2 - 61.0%
Ar - 36.1%
O2 - 2.1%
Ne - 0.0056%
Kr - 0.00068%
Xe - 0.00018%

After adding pure O2 but before scrubbing CO2, habitat air should be:
CO2 - 0.52%
N2 - 42.4%
Ar - 25.1%
O2 - 32.0%
Ne - 0.0039%
Kr - 0.00047%
Xe - 0.00013%

This is based on total habitat pressure of 8.43333 psi, with partial pressure O2 = 2.7 psi.
Note: Boulder, Colorado has partial pressure O2 = 2.54 psi.

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#7 2017-04-12 16:33:14

GW Johnson
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From: McGregor, Texas USA
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Re: Analog(ue) air

You have a fire danger problem if you exceed Earth's 21% (by volume) oxygen.  This is already known to get extreme at 40% oxygen by volume.  The identity of the diluent gas does not matter to the fire danger,  but it may (or may not) matter to human reproductive biology.  NASA's figure-of-merit for unacceptable fire danger is 30% oxygen by volume.  We already know from long hospital oxygen experience that 40% oxygen really is an extreme fire danger. 

Note that % by volume is the same thing as % by partial pressure.  If you run NASA's max at 30% oxygen,  and you run 3 psi partial pressure oxygen (similar to Earth air),  the total pressure must not be less than 10 psi,  for which the diluent gas must then be at least 7 psi.  It does not matter so much what the diluent gas is;  both nitrogen and argon (even helium) have served. 

2-2.5 psi oxygen with 4-to-5 psi diluent gas is 29% oxygen at 2 psi oxygen with 5 psi diluent,  and 38% oxygen at 2.5 psi oxygen and 4 psi diluent gas.  You only overlap with what's considered "safe enough" by NASA relative to fire danger if you run closer to 2 psi oxygen with closer to 5 psi diluent gas.  Your total atmospheric pressure is then 7 psia.  This is OK for temporary exposures,  but may possibly be a real problem for pregnancy,  since it's somewhere near 18,000 feet altitude equivalent,  if oxygen-nitrogen. 

These two issues are both something very,  very,  very serious to worry about. The fire issue is the proximate cause for the Apollo 1 fire deaths.  Reproduction biology in any conditions not Earthlike (cities as high as 15,000 feet) is completely unknown. 

GW

Last edited by GW Johnson (2017-04-12 16:45:30)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#8 2017-04-12 17:03:05

RobertDyck
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Re: Analog(ue) air

Apollo and Skylab both used 3.0 psi partial pressure oxygen, and 2.0 psi partial pressure nitrogen. That's 60% O2, with total pressure 5.0 psi. It worked.

The figures you quoted are for 1 atmosphere pressure. Human metabolism is dependent on partial pressure of oxygen. Mostly. Humans become less tolerant to extreme low oxygen when pressure is also extremely low. Fire isn't as dependent on partial pressure, but it is affected by pressure. Earth has 20.9% oxygen at sea level, but flammability of something in 32% O2 at 1 atmosphere pressure is not the same as flammability in 32% O2 at 0.573854 atmospheres = 8.43333 psi = 581.4573 mbar = 58.14573 kPa.

::Edit:: Because you mention reproductive health, I should also mention Earth's atmosphere is 0.9% argon. And Ar, Ne, Kr, and Xe are all noble gasses. They don't chemically react with anything. And they're all in Earth's atmosphere, so you're breathing them right now.

::Edit again:: The Apollo 1 fire used 17.7 psi pure oxygen. The reason was before the fire they intended to use 3.0 psi pure O2 in space. To test the capsule, they increased pressure so the stress on the hull was the same. Since they tested at a location close to sea level, where pressure is 14.7 psi, they increased the inside to 17.7 psi. But they didn't add nitrogen or air, they made it 17.7 psi pure oxygen. That's incredibly dangerous. After that they decided to dilute the oxygen with some nitrogen. But they still used 60% O2 at 5.0 psi total pressure.

Last edited by RobertDyck (2017-04-12 17:20:37)

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#9 2017-04-12 17:15:38

SpaceNut
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Posts: 18,933

Re: Analog(ue) air

All things equal what we do not have in the topic is the volume to which the crew needs this air within.
Or was this a planet wide level of air that the topic was exploring?

The starting point if it is an enclosed fixed volume the ISS is a good starting point to help solve the equation of not only energy but also for the systems needed to be able to retain and recycle what we start with plus also for what we need to replace due to loss from normal useage.

All links are quoted information....

https://www.nasa.gov/centers/marshall/p … _eclss.pdf

Earth to support six crewmembers by 15,000 pounds (6800 kg) per year

The Oxygen Generation System is designed to generate oxygen at a selectable rate and is capable of operating both continuously and cyclically. It provides from 5 to 20 pounds (2.3 to 9 kg) of oxygen per day during continuous operation and a normal rate of 12 pounds (5.4 kg) of oxygen per day during cyclic operation.

https://en.wikipedia.org/wiki/Oxygen_storage

Air is the most common source and reservoir of oxygen, containing 20.8% This concentration is sufficient for many purposes, such as combustion of many fuels, corrosion of many metals, and breathing of animals. Most humans can function at rest with an oxygen level of 15% at one atmosphere pressure; a fuel such as methane is combustable down to 12% oxygen in nitrogen.

A small room of 10 meter3 has 2.08 meter3 (2080 liters) or 2.99 kg of oxygen which would occupy 2.62 liters if it was liquid.

http://science.howstuffworks.com/oxygen … craft1.htm

The SFOG, which is also called oxygen candles or chlorate candles, has canisters that contain a mixture of powdered sodium chlorate (NaClO3) and iron (Fe) powder. When the SFOG is ignited, the iron "burns" at 1112 degrees F (600 degrees C), which supplies the heat energy required for the reaction. The sodium chlorate breaks down into sodium chloride (table salt- NaCl) and oxygen gas (O2). Some of the oxygen combines with iron to form iron oxide (FeO):

600°C

NaClO3 (s) + Fe (s) -> 3O2 (g) + NaCl (s) + FeO (s)

The SFOG supplies 6.5 man-hours of oxygen per kilogram of the mixture. Russian spacesuits also make oxygen using SFOGs.

https://www.cnet.com/news/breathe-deep- … uts-alive/

In the case of the ISS, the hydrogen generated from the electrolysis process is fed back into the space station's Sabatier System. A catalyst is used to combine the waste hydrogen with the waste carbon dioxide exhaled by the astronauts at high temperatures to create water (H2O) and methane (CH4) -- the process is described by the exothermic reaction CO2 + 4H2 → CH4 + 2H2O + energy.

The water produced is then fed back into the water reclamation system, while the methane is vented into space.

In all, this process produces around 2 kilograms of oxygen per day. According to NASA, the average person needs around 0.84 kilograms of oxygen per day to survive and the International Space Station typically has three astronauts aboard at any given time.

http://www.jamesoberg.com/elektron2_tec.html

This ‘Elektron-V’ system could produce up to 1900 liters per day, with an average power load of 860 watts. Its mass was 150 kg. The design lifetime was 3 years and the First unit operated for three and a half years.

https://en.wikipedia.org/wiki/Internati … ce_Station

Pressurised volume 931.57 m3 (32,898 cu ft)

It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.

http://www.space.com/8876-international … mbers.html

The number of pounds of crew-expelled air that the ISS systems recycle each day (6.4 kg). Of this, 6 pounds (2.7 kg) comes from the U.S. members of the ISS crew. The water produced by this recycling is used for technical or drinking purposes.

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#10 2017-04-12 19:14:21

Dook
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Re: Analog(ue) air

If the idea is to terraform Mars atmosphere and give it an Earthlike atmosphere with 78% nitrogen.

You can't.

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#11 2017-04-13 03:55:29

Terraformer
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Re: Analog(ue) air

Dook, it's generally considered basic etiquette to at least read the first post in a thread before commenting.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#12 2017-04-13 08:06:14

Tom Kalbfus
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Re: Analog(ue) air

We aren't talking about terraforming the planet, there is a separate section for that, and its not here.

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#13 2017-04-13 08:54:53

Dook
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Re: Analog(ue) air

Terraformer wrote:

Dook, it's generally considered basic etiquette to at least read the first post in a thread before commenting.

In another post Louis talked about terraforming the Martian atmosphere and making it like the Earth's, so I asked him "Where are you going to get the nitrogen from?"  That's why he started this topic.

Also, SpaceNut in his post, #9, asks "Or was this a planet wide level of air that the topic was exploring?"

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#14 2017-04-13 11:06:55

Tom Kalbfus
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Re: Analog(ue) air

I always thought terraforming would be a touch nut to crack, but Titan has lots of nitrogen, and a low gravity as well, despite its size, the surface gravity on Titan is less than out Moon. By the time we're ready to terraform Mars, the tech should be available to obtain nitrogen from Titan. Titan has more than enough. Probably th easiest way to transport it is to collect the nitrogen at the Saturn-Sun L1 Point, and then give the big ball of nitrogen a shove when the planets are light up just right for a gravity assist trajectory to impact Mars. Well need some insulation to get the stuff closer to the Sun while keeping it frozen, and then we unpack it prior to impact. The native atmosphere on Mars will intercept it and we'll end up with an atmosphere that is 50% carbon-dioxide and 50% nitrogen, we then send another package to Mars upping the atmosphere to 25% carbon-dioxide and 75% nitrogen and we keep on sending more and more nitrogen until we can get the carbon-dioxide percentage to under 1% of the atmosphere. Along wit the nitrogen de also deliver enough water to fill the ancient Ocean basin on Mars.

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#15 2017-04-14 09:14:15

elderflower
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Registered: 2016-06-19
Posts: 1,255

Re: Analog(ue) air

You might consider supplying Ammonia as it is easier to keep it liquid or solid. Break it down when it gets to the destination and recycle the hydrogen as fuel to launch another batch. There is ammonia on Triton.

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#16 2017-04-14 17:29:24

SpaceNut
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#17 2017-04-14 18:04:46

Dook
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Posts: 1,409

Re: Analog(ue) air

I could not open the first two links you provided.  I downloaded the PDF, will read it later.  I remember the "Mars Needs Nitrogen" topic, I started it. 

As for nitrates, how would you get them to release the nitrogen as a gas, heat them?  To what temperature?

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#19 2017-04-16 18:12:58

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,933

Re: Analog(ue) air

The moxie unit might be a good demostrator for its size to also prove out what we need for a volume correcting device for atmospheric loss from the recycling process.

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#20 2017-04-17 16:09:40

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Analog(ue) air

Ar-60/N2-40 is an inferior buffer gas compared to N2 alone, because argon has a substantially lower volumetric heat capacity compared to N2.  That means a higher flame temperature and a more rapid rate of flame spread on solid or liquid surfaces.  You could get around that by increasing total pressure whilst keeping oxygen partial pressure the same.  But that means more expensive habitat pressure shells.

Other options: (1) Use alternative fire engineering methods to offset the additional fire risk; (2) Add an additional buffer gas to the atmosphere; (3) Remove the Argon from the air mix; (4) Live with the additional risk.  The first would be difficult and adds to the complexity of designing the habitat.  The third involves cryogenic fractionation or boil-off, or centrifuge separation, which may be capital intensive on early Mars, but is not technically difficult.  The second option could be fulfilled by a dense freon type gas, such as a flourocarbon.  This might only need to be added as a few percent by volume to bump up heat capacity to the equivalent of normal air.  On the plus side, any freon leaking would assist terraforming efforts.  But freon is something that would need to be manufactured.

Another option would be to fit all habitat modules with water mist, which could be activated by infrared detectors.  But again, that is expensive.  The option that wins will be the one that achieves the best balance between safety and total cost.

Last edited by Antius (2017-04-17 16:20:17)

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