Indoor farming update

RobertDyck · 2014-11-16 09:08:07

Impaler wrote:

That atmosphere is wholly unsafe and isn't going to happen, it is 42% oxygen and NASA won't go above 30%. Standard 100 mBar on ISS is the future, were not going to be rolling back the clock 40 years on Atmospheres and taking fire-risks (the most horrible way to die in space or on the ground too for that matter) just to indulge in wearing skin-tight space suits.

You're obsessing about percentage again. Remember, both Apollo and Skylab used 60% oxygen, 40% nitrogen.

You tempt me to cut this off with a sarcastic remark. To ensure no fire, you have to use 0% oxygen. That's what you're saying, isn't it? Think about it.

And don't make the MAJOR mistake they made with ISS. That station uses 1 full atmosphere. Not even the same as the Baikonur Cosmodrome, it's the same as KSC. That's way too much. With that pressure, they have to go through 17 hours of oxygen prebreathe before going outside for an EVA. And the EMU suit uses to much pressure. Gloves are difficult to use because of excess pressure. The EMU is designed to reduce joint mobility problems with hard segments: hard fibreglass torso and "shorts", and rotating joints at the hips. Boots do not move at all, no ankle or ball-of-the-foot movement. You can't walk in that. New suits take this problem farther, use even higher pressure. They improved the joints and made it lighter, but it still uses too much pressure.

The Homestead Project strikes me as borderline science fiction (I read it years ago), I think your arguments consistently stem more from attachment to a romanticized vision then from practical engineering analysis and siting that project just reinforces it as it is one of the more outlandish things ever made, particularly in the raw materials processing.

No, the point is Mars is not the Moon. When the first Mariner 6 and 7 first flew past Mars, they both flew over the southern hemisphere. They saw craters, so scientists assumed it was the same as the Moon. That was an assumption. As we've seen with modern probes, Mars is not at all the Moon. Designs for the Moon just don't work on Mars.

I'm the member of Mars Homestead that kept pushing practicality. Since the objective was to design the first ever human base, I said we shouldn't waste our time designing the spacecraft to get there. So I recommended we assume Mars Direct to deliver crew. And I'm the one who pushed the idea of ambient light greenhouses. Crew on Mars will not be able to escape back to Earth, if something goes wrong they're screwed. So the design requires multiple backups, each using completely different principles. And each system must be able to mix-and-match components; we don't want another Apollo 13 problem with a lithium hydroxide canister. Mars would use reusable sorbents, but you get the point. And every life support system has a single point of failure: power. The sole exception is an ambient light greenhouse. I strongly argue for ambient light greenhouse because it's the only way to get oxygen to breathe when the power supply fails.

And there's no point with going to Mars if you're going to lock yourself indoors. If you want to stay inside, then stay inside on Earth.

Last edited by RobertDyck (2014-11-16 12:54:51)

GW Johnson · 2014-11-16 11:21:33

Two points: (1) partial pressure = volume % concentration x total pressure. I don't know myself whether flammability is more closely related to % concentration or to partial pressure, but I'd hazard the guess that is related to both, and probably more besides. That's a very complicated thing. Easy enough to experiment with in test chambers right here at home, though.

I would say that 42% oxygen is not as flammable as it sounds at low total pressure. 40% at 1 atm is something of a real fire danger with medical oxygen equipment. As for the proposed atmosphere, why include the argon? Just run a lower total pressure. Unless fire danger dictates otherwise.

POINT (2) suit pressure is fundamentally set by pressure breathing requirements, and would apply equally to full pressure suits, MCP suits, or any hybrid designs. The 1/3 atm pure O2 standard used by NASA for lo these many decades is overkill. You only need what you get on Earth: 20.9% O2 at sea level, which is 0.209 atm pure oxygen p-press, which is 3.07 psia. In point of fact, you don't really need to match sea level, in spite of the vapor pressure offset in the wet lungs. USN says pilots need O2 masks at 5000 feet, most everybody else says 10,000 ft. THAT sets what you use for breathing gases.

Say the USN is right. Total atm pressure at 5 kft is .8321 of sea level. That's 0.1739 atm partial pressure O2 in the air. At 37 C (body temperature), water vapor pressure in the (near-equilibrium) lungs is 0.0622 atm, leaving .7699 atm for the dry air, meaning you really have .1609 atm p-press O2 in the lungs. The suit has to match that, not other arbitrary criteria.

For a pure O2 suit (either or any type), you add back in the water vapor offset to see what dry O2 pressure you need in the suit. That's 0.2231 atm = 3.28 psia suit pressure. That IS the minimum. You should be as functional as any USN combat pilot at that pressure. That's not quite 23% of an atmosphere! Why do we need 33% of an atmosphere (4.85 psi), other than tradition not grounded in real science?

Even if you add a 10% kitty to cover leaks, that's still only 0.2454 atm = 3.61 psia. Use the 1.2 factor on that for habitat N2 p-press and you get .2945 atm = 4.33 psia. Your hab needs the same 3.61 psi O2 p-press and at most that 4.33 psi p-press N2, plus maybe some argon for fire risk reduction by dilution. So your hab pressure is 7.94 psi plus whatever argon you insist on using. If no argon, you are running 45% O2 at 7.94 psia (0.54 atm) total pressure. The low pressure should reduce flammability dangers some, if not enough, then by all means add some argon to the habitat atmosphere. No pre-breathe required!

The numbers are even lower if you use the 10 kft standard, even with the 10% leak criterion. USAF and airline and civilian/private pilots are all quite functional below that altitude without any supplemental oxygen.

BTW, the 1968 vintage MCP demo used 190 mmHg = 0.25 atm = 3.68 psia as its O2 breathing helmet and tidal-volume bag breathing pressure. Dava Newman's prototypes at MIT have reached or exceeded that compression. So, we CAN INDEED build suits like that right now, and they do NOT have to be as difficult to don as they were in 1968. It’s only corporate bottom-line politics that holds this back. That and inappropriate compression levels that are traditional within NASA. Tradition dies hard because people fear change, and some of them are making money on the status quo.

GW

Impaler · 2014-11-16 14:10:12

I am not obsessing, you are in denial and fail to even acknowledge your gross error in partial pressure vs oxygen % flammability, everything you've been saying about pressure is invalidated by that error but you keep insisting on your original idea without reevaluating.

I am accepting the reality of space-hardware evolution over decades. Do you really think the US abandoned it's low pressure environments and moved to basically copy what the Russians had been doing from day one for no good reason? NASA has been moving consistently towards higher pressure with each subsequent vehicle.

Russian Orlan suits conduct EVA from the ISS with only 30 minutes of pre-breathing and operate at 5.8 psi, we do not need to reinvent the wheel here. Space-suits do not drive habitat pressures down, habitat pressure drives suit pressure UP, get that through your head. The tail dose not wag the dog. Orlan suits would need to be improved in mobility and lightened but that is far simpler and safer then running high oxygen concentrations through the whole habitat which would require every single piece of equipment to be redesigned to exotic super non-flammable materials, many Life-support systems use flammable chemicals which simply can not be avoided.

In fact that seems to be exactly what NASA is doing, the new Z-1 suits being developed and tested right now are aiming for 8.3 psi which should be sufficient to eliminate pre-brething entirely (the suit can then slowly drop in pressure to improve mobility). http://ntrs.nasa.gov/archive/nasa/casi. … 011564.pdf In addition they are designed around the suit-port rear entry system which offers supreme dust containment, something a MCP suit cant offer.

GW: Their are extensive studies I posted earlier showing that Oxygen % concentration is the main determinant of flammability, please familiarize yourself with them. A 40% oxygen concentration is quite dangerous just as you note for medical oxygen concentration, this is why no one dose that in space anymore.

Once people realize this simple fact that flammability is not based on Partial pressure it is obvious WHY low pressure environments have been abandoned and are never coming back, the only low pressure used in in suits and the evolution is clearly towards raising the suit pressure not lowering it. Astronaut discomfort and exhaustion is preferable to dieing in a fire.

Last edited by Impaler (2014-11-16 15:12:26)

RobertDyck · 2014-11-16 16:50:38

You realize I'm the one who did the early work on materials processing for the Mars Homestead Project, phase 1. Work for mining and materials processing were taken over by a university professor, who had a Ph.D. and reputation for being the American lead in that field. You're just being insulting. You're the troll.

SpaceNut · 2014-11-16 17:01:55

I think the troll calling has gone on long enough, Please put an end to it and learn how to agree to disagree....
Thank You...

We truely need to be more focussed on the topic discussions as well
I do know that it is hard and maybe I am more to blame than I might know.

Last edited by SpaceNut (2014-11-16 17:04:19)

Terraformer · 2014-11-17 06:52:27

Don't forget, you can use CO2 as a dilutant gas in your habitat. They've acclimatised sheep to 120mb partial pressure, and humans to 80mbar - and it turns out you can get away with lower O2 partial pressures as a result. More information here - Minimal Martian Terraformed Atmospheres. Or at least, I think the information is there, it might have been lost in the Great Crash...

I don't know what the effects of moving from high CO2 to low CO2 would be, though...

GW Johnson · 2014-11-17 10:24:20

OK, if flammability depends most strongly on vol % oxygen, even at lower pressures, then add the argon. What would you think of 29% oxygen in nitrogen-argon, at about 12 psi total? If I use that, I can use a low-pressure less-restrictive spacesuit on pure oxygen, and do it without a pre-breathe time, assuming the factor 1.2 Pp N2 / suit P O2, and lower similar factor (0.86, ratioed by molecular weights) for Argon.

edit 11-17-14: I ran the numbers in a traceable and organized way, and got 32.68% O2 at 8.16 psia total. This assumes a pre-breathe factor of 1.2 for N2, and 0.86 for Ar. It's based on in-lung wet Pp O2 from a spacesuit designed to mimic 5000 ft altitude, then factored up 10% for leaks.

Ran it again for a 4-gas system (O2 N2 Ar and He) and got 27.03% O2 at 9.68 psia. This used a slightly larger argon factor of 1.0, and a wild guess factor of 0.5 for helium.

GW

Last edited by GW Johnson (2014-11-17 14:07:12)

Impaler · 2014-11-18 01:37:36

I don't know if mixtures of other inert gases rather then just strait nitrogen is any better or worse, I think we are all speculating now.

I seem to recall that Argon is MORE hallucinogenic then Nitrogen but all thouse hallucinogenic effects may only come into effect a high pressure as in deep sea diving so that may be totally irrelevant here. If the problem here is that the Astronaut is going to transition from high to low pressure and that if they don't expels Nitrogen from the blood then it will bubble out and give 'the bends' then it dose not seem unreasonable that a mix of gasses could do the same thing, though perhaps they do this sequentially at different pressure levels which MIGHT be less damaging. On the other hand maybe each gass can only bubble out 'alone' and can't get assistance from the others, then partial pressure of each gas is what matters. It is worthy of investigation but I am highly dubious that it will lead to a new air mix.

Based on the recent MIT Mars One feasibility study which used 30% at a Cut-off for Oxygen concentration I believe that is NASA's standard and it was expressed as a 'Loss of Crew' level violation on par with fatal loss of pressure and hypoxia conditions. This leads to to believe that 27% would be considered inadequate safety margin. It really looks like habitats are going to be running Earth-normal mixtures and the only way were going to see pressure lower then sea-level is if our crew get altitude acclimatized in Denver.

I still see no legitimate driver for this low pressure habitat or suit atmosphere, these glove-gripping issues are being addressed by redesigning the gloves alone, hard shell, constant volume gloves will work on any suit.

Terraformer · 2014-11-18 07:42:20

30% O2 at 150 mb pp would allow you to get away with a total pressure of 500 mb. People have acclimatised to that...

Impaler · 2014-11-18 19:46:12

You know if your looking for a buffer gases then maybe water is what you want. A greenhouse typically gets very very humid from transpiration and we know water is an extremely good fire quenching gases, the normal humidity shifts in our own atmosphere can turn benign slow combustion fuels into near pyrotechnics and visa verse.

It may thus be safe to use low pressure and higher oxygen IF the air is super moist, also it would be desirable if the greenhouse materials were themselves Hydroscopic as possible (the latent moisture IN a material is though to be even more important then moisture in the air) such that it becomes saturated with the moisture from the greenhouse and becomes that much harder to burn.

Now obviously this would need to be tested, to my knowledge flammability under high oxygen percentage AND high humidity hasn't been tested, each has been examined separately but we don't know which effect will dominate when combined.

This might be the extra safety margin needed to do the kind of 27.03% O2 at 9.68 psia that GW describes or something close to it in the greenhouse environment, human lungs will be able to accommodate the muggy air without any pre-breathing, though it will be slightly uncomfortable breathing the muggy air.

In addition a fire-suppression system for a greenhouse (water sprinklers) would be eminently more practical in the greenhouse, abundant water piping is already present and the plants suffer virtually no damage from an excessive watering. The main habitat though is full of computer, electrical systems and other equipment that could be significantly damaged by a drenching, the limited set of electrical equipment could and should be waterproofed too. While it would still be prudent to have a fire suppression system in the habitat a sprinkler system in a greenhouse can always be employed more liberally.

Last edited by Impaler (2014-11-19 03:23:40)

RobertDyck · 2014-11-18 20:48:24

Don't humour him. He's still on about that fire thing. The papers he linked uses the criteria of "extinguishing", not ignition or even sustaining a flame. By that criteria, wood is not extinguished in normal air on Earth. So by that criteria, Earth air is not safe. Totally invalid.

Besides, I already gave long-winded reasons why the plastic film for a greenhouse should be PCTFE, which even that chart shows is not flamable.

Impaler · 2014-11-19 03:20:37

Earth is not a closed aluminum can with a few dozen cubic meters of air per person. Fire in a building on Earth has three huge mitigating factors, 1) ability to leave the structure rapidly through numerous portals into fully breathable air 2) access to nearly unlimited quantities of water delivered through plumbing to the building allowing quenching of the fire 3) Local fire and rescue teams equipped with special tools that can be rapidly dispatched to aid in utilizing and bolstering the first two capacities.

As you know we have none of that in Space, so our level of risk acceptance is vastly lower.

PCTE is the best material I agree with that, it's just not good enough to allow 3 psi pure Oxygen (we don't have a data point at 3 psi but I'm extrapolating, also the fact that they don't even bother testing below 7 psi should kinda be a clue that 3 psi is off the table), also your desired habitat pressure would eliminate virtually all other materials now commonly used to make spacecraft interiors and you fail to consider that materials other then PCTFE are going to be need in the greenhouse as well. Space-hardware is full of electrical system, even a greenhouse is going to have them for lighting, ventilation, water-pumping etc etc. Electrical systems mean ignition sources are ever present. So NASA's methodology is to assume ignitions and small fires WILL happen and that they need to use ONLY materials that can not sustain combustion (aka self-extinguish) so that all fires die on their own and become mishaps rather then tragedies (like the Mir fire). They don't rely on crew fire-fighting to save the day, the crew could be asleep or simply unaware of the fire, and should generally be getting some kind of suit on or getting to an escape vehicle rather then fighting it (obviously on Mars they can't escape so even more reason to be hyper vigilant). NASA will simple not combine a material and an atmosphere which don't self-extinguish, the criteria and methodology in the sited paper is NASA's own method, and I quote.

The test required is NASA-STD-6001, Upward Flame Propagation (Test 1)
Test 1 is the primary method used to evaluate flammability of materials intended for use in habitable spacecraft environments. This test exposes materials to a standard ignition source in a quiescent environment at the highest-expected spacecraft oxygen-concentration to identify materials that will self-extinguish and not transfer burning debris.

If you believe NASA should be more cavalier with fire risks complain to them, but don't pretend I'm off the rails by siting NASA's standards and agreeing with them, they make a much better case then you do as to why their standard is what it is.

Void · 2014-11-19 09:18:31

Bladder Wort.

http://www.docherb.ca/BLADDERWORT.htm

It has been APPLIED TO: wounds. The plant juice has been DRANK FOR the high vitamin and mineral content. The leaves were eaten raw or cooked. The roots (up to 3' {1m} long) were also eaten.

I am really thinking about the floating types, but I suppose other types could be considered.

So, then if you had tanks in your habitat and/or greenhouses, you might then have some means to increase your fire protection, and also have a useful herb, and flowers as well.
images?q=tbn:ANd9GcQNz7TMNiubWtmg4Q4fdro3ukwMg3UvGsG2xyOlvC5QES-dRWm9

It is a carnivorous plant. While I understand the inefficiencies involved in that at face value, it may present a opportunity to grow algae or Cyanobacteria in low pressure greenhouses in water, and then to batch move it in to the hab or pipe it in (Another possible fire handling method).

So you might have a large productivity from a plant that does not depend entirely on direct photosynthesis. Little creatures like Daphnia might have to be the intermediaries.
http://en.wikipedia.org/wiki/Daphnia

Further this plant may partially and indirectly be caused to run off of chemosynthesis, if you split water and/or CO2 and grew bacteria as feedstock from chemicals.

So rather a flexible plant that might be suited to be a component of a habitat.

More:
http://en.wikipedia.org/wiki/Utricularia

Last edited by Void (2014-11-19 10:22:55)

RobertDyck · 2014-11-19 14:39:53

I'm trying to find a copy of the movie "Apollo 11". The movie produced in 1996. That movie had a re-enactment of a demonstration by North American, manufacturer of the Command Module. The demonstration had a strip of Velcro in a plastic box, a lighter held to the Velcro. There were 3 such boxes, one with air, one with 100% oxygen at 3.0 psi, and one with 100% oxygen at the pressure of the Apollo 1 test. The first box started the Velcro on fire while the lighter flame was on it, but as soon as the lighter was pulled away, the Velcro smouldered and went out. The second box did exactly the same, Velcro would not sustain a flame. But in the last box, Velcro went up in flame like the head of a match. This was demonstrated because they intended Apollo to use 100% oxygen at 3.0 psi before this accident. And it was safe. The demonstration shows it was safe, and continues to be safe.

The things: North American wrote a memo to NASA stating "DO NOT" test the capsule at 17.7 psi with 100% oxygen. It was not safe, it was a fire hazard. But NASA ignored this, the memo was not circulated to NASA managers who needed to see it. Reminds me of the Challenger accident: engineers from ATK wrote a memo to not launch, because outside temperature was "outside the database". That means it was too cold for the rubber O-rings of the booster. But apparently that was not worded strongly enough, the 1987 memo was not passed on to managers who needed to see it. History repeats.

But some Congressmen panicked. They thought percentage of oxygen is all that matters, pressure does not. So they wanted air at the same pressure as KSC. They thought that was necessary for fire safety. The final result was a compromise: Apollo used 5.0 psi, with 60% O2 and 40% N2. That means 3.0 psi partial pressure oxygen, plus 2.0 psi partial pressure nitrogen. Skylab used the same gas mix as Apollo.

So now we have a Mars Society member making the same assumptions as those 1960s Congressmen. Uh huh. He has some technical papers to cite. The papers do not support his conclusion, but add enough technical detail to confuse.

Please, someone help. Obviously we need that clip from the movie. A very simple demonstration.

::Edit:: The show I was thinking of was a TV mini-series called "From The Earth To The Moon", episode with this scene was titled "Apollo One".

::Edit:: I found video. The link below is the entire one hour episode, online, free. Skip forward to 25 minutes and 0 seconds. They don't have the test at 3 psi pure oxygen, just open air and high pressure pure oxygen.
from the earth to the moon epoisde 2

Last edited by RobertDyck (2014-11-22 22:16:35)

SpaceNut · 2014-11-19 18:18:22

Void we will definetly want some flowering plants just to help keep spirits light...

The construction techniques are important as well for using the PCTFE as panels that need assembly into some sort of framing and also is it a double pane setup that is desired since the complexity and mass of all the pieces will be important as well.

GW Johnson · 2014-11-20 16:21:21

RobertDyck and Impaler and the rest of us have been arguing about habitat atmospheres and oxygen suit pressures. I put a posting up on exrocketman a couple of days ago about this topic, and I just updated it today. In that update, I created a multi-gas habitat atmosphere at 21.3% oxygen and almost 1 full atm, with a corresponding low O2 suit pressure that would apply to full pressure suits or to mechanical counterpressure suits.

If my pre-breathe factors are anywhere near right, this can be done with zero pre-breathe time. The suit pressure is low enough to make full pressure suits more supple, more like those of about 1964. It also makes the MCP suits immediately feasible, whether you look at the old 1968 stuff, or Dava Newman's stuff at MIT.

Check it out, I think the results will startle you. As of today, the blog posting on atmospheres and suit pressures is the one at the top, first thing you see.

GW
http://exrocketman.blogspot.com

RobertDyck · 2014-11-23 02:54:31

A NASA document.
Advanced Life Support Program - Requirements Definition and Design Considerations

EVA prebreathe time
* prebreathe time decreases as the partial pressure of diluent gas (N2) in the habitat decreases
* prebreathing can be eliminated when partial pressure of diluent gas exceeds the suit pressure by a "bends" ratio, R, of 1.2 or less (Shuttle EVA suits operate at 29.6 kPa (R = 2.7 at P = 101.4 kPa; R = 1.6 at P = 70.3 kPa)

That is one of the sources from which I got that ratio. The source of that ratio is a Navy study.

Also from this same document:

* The maximum concentration of O2 in a habitat atmosphere is limited to 30 vol% by materials flammability considerations. (Extensive testing of materials at 30 vol% O2 has been conducted in conjunction with the space shuttle program.)

I already argued for suit at 3.0 psi pure oxygen. Justification was Apollo used 3.3 psi pure oxygen. And an Air Force study that showed pilots who went through high altitude training could endure 2.5 psi pure oxygen and remain conscious. At 2.0 psi pure oxygen they would remain conscious for 30 minutes, but at 2.5 indefinitely. So 3.0 psi pure oxygen is easy. They wouldn't require high altitude training.

Then using this zero prebreathe ratio to calculate N2 for the habitat results in 3.6 psi N2. Assuming diluent gas is harvested from Mars atmosphere, I assumed the N2:Ar ratio would be the same as Mars. Viking 2 measured Mars atmosphere as 2.7% N2, and 1.6% Ar. GW Johnson's article calculated zero prebreathe ratio for Ar assuming osmosis rate based on molecular weight. He came up with a ratio of 0.86, so using that then maximum partial pressure of Ar would be 3.0 * 0.86 = 2.58 psi. I calculated 3.6 psi N2 / 2.7% N2 * 1.6% Ar = 2.133 psi Ar. Ok, so that's below the osmotic maximum for zero prebreathe time. For habitat oxygen, I just used the same margin for leaks that NASA used for Apollo. That was 3.3 psi for the suit, 3.0 psi partial pressure O2 for spacecraft, so 10% margin. That margin meant 2.7 psi partial pressure O2. Adding that up: 8.433 psi total. Expressing that as percentages: 32.0% O2, 42.7% N2, 25.3% Ar.

But that is above the limit from this NASA document. Boulder, Colorado, has partial pressure of O2 at 2.53 psi, on an average day. With low barometric pressure it can be a touch lower. So we could reduce partial pressure for the habitat to 2.5 psi O2. That would reduce total habitat pressure to 8.233 psi. As percentages: 30.4 psi O2, 42.7% N2, 25.9% Ar. That would also allow 16.67% pressure loss in the suit and still have the same partial pressure O2 as astronauts would be used to. So even greater margin for leaks. Close enough?

Ps. Assuming diluent gas is harvested from Mars atmosphere, with a catalyst to decompose O3 into O2, and combine Mars atmospheric O2 with CO to produce CO2, and a freezer to remove Mars CO2. Then habitat air will also have trace gasses: 0.0039% Ne, 0.00047% Kr, 0.00013% Xe, and no He.

::Edit:: And I still argue, Apollo and Skylab used 60% O2. 32% O2 is a major improvement.

Last edited by RobertDyck (2014-11-23 10:29:46)

Impaler · 2014-11-23 19:30:41

I don't think 30% isn't going to be the TARGETED oxygen concentration of the habitat, it's the concentration at which point emergency Nitrogen injection occurs. A realistic target is more like 22% - 25% to give some margin for air handling, the hab atmosphere is after all being breathed (at a varying rate), scrubbed, pumped etc etc, it's going to fluctuate a bit on a feed-back sensor loop, it's not a mixed drink that we can just make to some exact ratio and sit on a shelf without it changing. On your Life Support link ISS is listed with a range of O2 PP ranging over 3.6 kpa, and total pressure range of 4.8 kpa so fluctuations in that range should be assumed, and in fact the longer your mission duration the more deviation you will be likely to incur.

Both GW and Robert are baselessly speculating/hoping that Argon and other nobles dose not count as a 'diluent gas' that must obey the 1.2 Bending ratio. I have seen nothing to show that this is not the case and I must point out how tenuous their speculation is. It is on yall to show that this is possible if your going to advocate for it, I'm very skeptical of it because if it worked as you wish it would presumably be a cheap and easy solution to the Bends in scuba-diving, yet no such mixes exist in scuba to my knowledge.

Good news for plant growth though, the CO2 saturation for C3 plants (everything but corn mostly) is just 150 Pa, well below adverse effects for humans at 1000 Pa (immediate) or 710 (long term), and 700 is in fact the NORMAL CO2 concentration of ISS, so the environment is already a CO2 enriched environment that is still perfectly breathable for humans.

It says that decreasing O2 PP is enhances plant growth, but I have to assume this is only a O2/CO2 ratio effect because the carbon-fixation process in plants is limited by high chemical affinity for O2 (much like CO has greater affinity for Hemoglobin in our blood), so ratios between PP should really be what matters. Still if 710 is our CO2 PP then it is already 4 times higher then the carbon saturation for a plant at normal O2 PP so it seems unlikely that that O2 could be drooped enough to break through that saturation level without creating an unbreathable atmosphere.

Last edited by Impaler (2014-11-23 19:32:26)

RobertDyck · 2014-11-23 22:32:29

The US Navy has been using oxygen/nitrogen/argon mix for decades for deep diving. They already worked out the figures for using argon. And they have numbers for quad-gas mix as well, which is O2/N2/Ar/He. There is a maximum amount of oxygen before it becomes toxic, maximum nitrogen, maximum for each gas. So very deep diving requires all four.

Impaler, you're very tiresome. And if you aren't going to be reasonable, then there's no point in pandering to you. Baseline for any space travel has to be Apollo. They used 3.3 psi pure oxygen for spacesuits, and 5.0 psi for the capsule with 60% O2 and 40% N2. Skylab used the same as the Apollo capsule.

If you demand duplicating Earth due to some irrational assumption, then just stay on Earth.

You talked about CO2 concentration. Earth has approximately 0.03% CO2, at 2.0% CO2 you get a serious headache, and 10% is lethal. We already know how much CO2 is acceptable. And yes, 1% CO2 as you reported on ISS is acceptable. We already know that.

As for plants, the enzyme RuBP fixes CO2 to the intermediate for the first step in the Calvin-Benson cycle, known in junior high and high school as the dark reaction of photosynthesis. Yes, that enzyme is highly sensative to the ratio of O2:CO2. Greenhouses already add CO2 to increase plant growth. It's all well known and documented.

Last edited by RobertDyck (2014-11-23 22:46:03)

Impaler · 2014-11-24 01:06:04

Do the O2/N2/Ar/He mixes prevent the bends (which is what is at issue here) or do they merely keep you from getting toxicity/hallucinogenic effects under the high pressure of deep diving, their is a big difference because were not talking PP of any gas being in the toxicity range were worried about bends at drops to lower suit pressure. That's why I referenced SCUBA diving which is a low pressure dive that primarily faces danger in ascending, deep diving has trouble both ascending AND descending.

If by reasonable you mean I will roll over and swallow some glaring technical error simply because it appears in "The Case for Mars" then no I'm not going to 'be reasonable', NASA is not that 'reasonable' and neither are the cold equations of physics. If all you want to do is regurgitate and reformulate Zubrin speculations (which were shoddy years ago when they were made and are now painfully outdated) without defending them while we all nod approvingly then it is you who are asking to be pandered too.

ISS and not Apollo is the baseline for any future mission, that you can even jump that far back for your justifications strikes me as desperate. Apollo tech and safety standards are respectively antiquated and unethical to employ today.

Also Apollo only used an O2/N2 mix during pad operations and vented it on assent to replace with a pure 3.3 psi O2 atmosphere during the rest of the mission. Again this and the 60/40 mix is never going to happen again because of fire hazard as I've said a dozen times, every bit of NASA material anyone including yourself here has found continues to confirm it repeatedly, that fact that your even still talking about it seems to indicate you think you are smarter then every other government agency and individual doing space development today. I doubt even Zubrin would hold to this atmosphere today once presented with the data.

Even the Chinese used an Earth normal atmosphere of 101 kPa on their first manned mission, a pure O2 atmosphere is like running your space-craft on punch-cards or using lead-acid batteries, an obsolete technology.

Last edited by Impaler (2014-11-24 01:17:32)

Void · 2014-11-24 11:19:53

I suppose I should have my head examined for trying to participate in this, but I do have a view.

Articles I have searched for indicate that the reason that the ISS has an Earth like atmosphere is because both the Russians and Americans had gone to it.

Because of this reading, I now have a better grasp of why a low pressure Oxygen fire could be dangerous. Without the Nitrogen to draw off heat, I suppose it is a hotter fire.

The article indicated that the reasons to go to a Nitrogen partial pressure were:
1) Better air circulation, would reduce the possibility of getting pockets of CO2 or CO concentrations in a large structure.
2) Higher pressures would allow for better cooling of lab and other equipment.
3) In a similar fashion, higher air pressure removed heat from an exercising persons body more effectively. Apparently, overheating in a low pressure environment while exercising can be very stressful to the human body.

So, I am going to side with the notions that where possible large enclosures should be filled with an Earth like mix if possible, and kept at shirt sleeve temperatures.

I can speculate however, that an intermediate device is needed between a stationary large habitat and a suited person doing an EVA. I would think that would be a mobile device on wheels. It should be capable of life support for extended periods. I would say that because the pressurized cabin of it could be smallish, then the hazards can be handled by extra efforts on fire prevention and perhaps emergency methods to remove the Oxygen from the cab on short notice or perhaps a fire suppressing gas. As the cab would be relatively small, build up of pockets of CO2 and CO, should not be as much of a danger. For exercising perhaps a cool down of the cab, and a fan very close might make it safer and less stressful to the body.

But fine, if they build suits with gloves that work for all things at high pressures then that is great. However, I am going to speculate that different types of tasks would be best done with different types of suits.

Void · 2014-11-24 15:03:10

I would also note, that the problem of CO2 and CO pockets would be more severe in microgravity than it would be in a gravitational field.

Similarly, natural gravitational convection in habs on the surface of Mars vs microgravity will reduce the need for forced air circulation, so that will be less of a problem.

As GW and others have suggested, evaporative cooling could be of good use when out in the ambient conditions on the surface at ~5.5 mb.

Come to think of it a low pressure high Oxygen fire in a hab on the surface of Mars would not behave the same as a low pressure high Oxygen fire in microgravity. Not that it would be good, it just would not be the same because of natural convection. I think you would want your ceiling materials to be fire resistant at least, and also to have fire brakes on the horizontal front.

Perhaps what you want is an intelligent robot on the ceiling with a squirt gun which could attempt to put out fires without directions, Drawing water from Bladderwort tanks without being directed. However it should also then have the ability to cut electrical power appropriately, and of course sound alarms. This might be the correct 1st line method no matter what gas mix and pressure you would be using. Don't know how good water is at extinguishing fires in Mars gravity at partial pressures with enriched Oxygen though. That would need to be considered. Water would definitely cool the fire, perhaps smother it.

Last edited by Void (2014-11-24 15:32:55)

RobertDyck · 2014-11-24 16:29:16

There is a maximum concentration for each diluent gas in the high pressure environment, to allow zero pre-breathe. Again, "pre-breathe" means breathing pure oxygen for a defined period of time in order to expel dissolved diluent gas from the blood. Necessary to reduce diluent gas in the blood to the level necessary for decompression without that gas "evolving" out of solution. Tiny bubbles of gas in the blood will block blood flow, causing starvation to tissues fed by that blood vessel. This can cause necrosis of the tissues affected. Said necrosis is most common in joints, causing permanent joint damage that results in movement problems. That's commonly called "the bends". And yes, there is a maximum amount of each gas to allow for decompression without causing "The Bends".

I have already quoted the ratio of partial pressure of nitrogen in the higher pressure environment to total pressure in the lower pressure environment. There is a different ratio for each gas. The US Navy has already performed experiments to determine those ratios. For nitrogen, it's 1:1.2. I don't have the figure for argon, but GW Johnson's calculation sounds reasonable to me.

And yes, the US Navy uses multi-gas mixtures to avoid toxicity at high pressure. That's used for deep diving. But they also worked out ratios necessary to work with these gasses. That includes maximum partial pressure of each gas in the higher pressure environment to permit decompression without time in a decompression chamber. The US Navy worked out all sorts of protocols for decompression; most of which are not applicable to Mars. This ratio of 1:1.2 is.

The reason ISS has the air it does, is for experiments. It is not for fire safety, or for astronaut health. It's for science experiments. During the Apollo era, NASA worked out what's required for safety. If you want a space station with appropriate air for astronauts, look at Skylab.

I suspect they also did it just to screw the Russians. Russia used 10 psi, which was very similar to the Baikonur Cosmodrome where they launched. All Salyut space stations and Mir used that pressure. But NASA decided to use pressure at the Kennedy Space Center, so Russia had to adapt. They also put ISS in an orbit so different from Mir, that no Soyuz, Apollo, or Shuttle could transfer between the stations. They just didn't have enough fuel to change orbital altitude and inclination that much. That was a concern before the first ISS module was launched. Of course I notice ISS is in exactly the same orbit as the NASA document from 1968 describing the station they wanted to build at the time. ISS is exactly where NASA always wanted to put it. That document said 400km altitude, and 50° inclination. ISS as built varies in altitude from 390km to 407km, and 51.6° inclination. That inclination causes the northern most point of the orbit to pass directly over the launch pad at the Baikonur Cosmodrome. So the only concession to Russia was to increase inclination by 1.6°. That's hardly worth mentioning.

Impaler, please, try reading the basic fundamentals first. Here are two editions, pick one.

Last edited by RobertDyck (2014-11-25 12:16:18)

Terraformer · 2014-11-24 17:00:32

Don't forget that humans can acclimatise to very high levels of CO2, so one could always include that in the atmosphere...

RobertDyck · 2014-11-24 17:02:25

Void wrote:

However, I am going to speculate that different types of tasks would be best done with different types of suits.

Actually, this point is correct. The EMU suit that NASA uses for LEO is optimized for that task. It has completely hard boots that do not move at all at the ball of the foot or the ankle. Hips and knees can move, but are very stiff. That's deliberate, because you don't have to walk in LEO. It is designed to lock feet into a restraint on the end of the CanadArm of Shuttle, or CanadArm2 of ISS. You want solid footing when working on something like the Hubble Space Telescope. But don't expect to use it on Mars. In fact, don't expect to use the EMU on the Moon.

Dr. Paul Webb developed the MCP suit specifically for the surface of the Moon. Unfortunately it wasn't ready in time. It wasn't designed for use in a spacecraft. The Sokol suit was designed for inside a Soyuz spacecraft. That was developed after a cosmonaut died when his Soyuz got a leak during re-entry and completely decompressed. The Sokol suit is very light and supple, but legs are extremely stiff when inflated, and arms are basically locked forward so hand are in front of spacecraft controls. Don't try walking on Mars or the Moon in a Sokol. In fact Russia developed the Orlan for work in LEO. NASA adapted a suit for use in the Shuttle: ACES. It was adapted from a suit developed for the SR-71 Blackbird. It's a partial pressure suit, not intended for long duration exposure to vacuum. And has a one person inflatable raft stowed around the torso. Bright orange to be easy to spot in the ocean, so a rescue helicopter crew can easily find them. But again, don't try to use ACES in LEO.

MCP is far safer in vacuum than any other suit. And more comfortable, once it's on. The catch is it's difficult and time consuming to put on. And not something you can wear with the helmet visor open, so not a safety suit for inside a spacecraft. MCP is for long duration EVA on a rough planetary surface in vacuum or near vacuum. So the Moon or Mars.

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