Habitat air

GW Johnson · 2014-12-15 20:20:50

Acclimatization to higher altitudes up to about 10,000 ft simply isn't an issue. Unless your beliefs make it one. But belief is not necessarily congruent to fact. And in this case, it is not congruent to fact.

Fact is, most pilots do not need supplemental oxygen until they exceed 10,000 feet. Sea level "flatlanders" go to 10,000 feet (or equivalent cabin pressure) all the time every day. They have no problems doing so. We have decade upon decade of flying experience with this, both civilian and military.

The USN sets that oxygen requirement at 5000 feet, but they are the exception, not the rule.

At 10,000 feet, pressure is 68.78% that of sea level, or just about 10.1 psia. There is absolutely no reason in the world why plain air at that pressure could not serve just fine, with zero acclimatization required. Any sea level flatlander who has ever ridden in (or flown) an airliner has already done this.

Those of us advocating MCP suits are not saying that full p-suits cannot do everything necessary in our experiences so far. What we ARE saying is that there will soon be things we need to do (like make repairs in situ on other planetary surfaces) that we have not before needed.

Most p-suit designs, especially the higher-pressure ones near 8 psia, simply cannot supply the dexterity needed to save your own butt by fixing your broken turbopump plumbing in vacuum, for example. Paul Webb's "elastic space activity suit" of 1968 did supply that kind of dexterity, way back then, right down to the gloves. Well under 100 lb, including a backpack with makeup LOX in a Dewar.

There's time to make things like MCP (and other needed stuff) fully ready by the time Musk or NASA or anybody else sends men to Mars. But it won't happen if "they" don't start now. Running into a problem on Mars that you can't fix wearing a full p-suit is a really untimely way to find out that you should have brought some MCP suits as well.

GW

RobertDyck · 2014-12-15 22:09:54

Impaler · 2014-12-16 18:01:16

Again your speaking from ignorance of current suit and glove development, high pressure dexterous gloves HAVE been made, your fixating on a myth that any glove with pressure in it is incapable of being dexterous. That is simply not true. Space suit development is not standing still and given that we are not likely going to see landing on Mars until 2030's the current pace of suit development is way ahead of all the other systems that are needed, beacause suits are actually really cheap to develop compared to everything else.

RobertDyck · 2014-12-16 19:40:05

You talk about new suit development, but ignore a major achievement in suit development. Do you see the contradiction?

GW Johnson · 2014-12-17 10:33:58

OK, if MCP gets done right (no guarantee that it will be if NASA does it), it takes the form of vacuum-protective underwear, plus an oxygen helmet and a tidal-volume bag. You wear whatever conventional (Earthly) outer clothing that suits the job at hand. The vacuum-protective underwear is not a single-piece garment. To do it that way requires a paradigm shift: your spacesuit is not a one-piece, do-everything-all-in-one-garment design. Dressing for space becomes more like dressing-for-the-job down here at home.

If you do the paradigm shift and design the vacuum-protective, multi-piece underwear, mixed and matched with whatever ordinary white coveralls, hiking boots, and insulated gloves that you need, then all those components are simple machine-washable items. That is a positive boon in dusty, dirty environments like the moon or Mars. And probably asteroids, comets, and any other destinations we might want to visit. Just try washing a rubber-lined p-suit. I dare you.

We already had severe dust contamination experiences with suits during the Apollo moon landings. We got away with it on those very brief missions, but extended missions will require cleaning. Pure and simple. The only other way to deal with dirt is to never bring the p-suit inside the airlock. Enter the suit from the rear with it docked to a port. Does anybody else see a seal-leak potential with that scheme? Airlock doors are bad enough. Does anybody else see the design complications that introduces to your vehicle and habitat designs? They reek of inert weight gain.

When there is no risk of hot or cold thermal injury, you can doff the insulating outer gloves and just wear the relatively-thin compression gloves, about like wearing surgical gloves, just tighter. Try handling AN-3 or AN-4 size nuts and bolts, sockets, and wrenches in any p-suit glove (I don't care how much they spent on it). You can do this with tight elastic MCP gloves. But not an inflated insulated glove. Mars trips are unlike moon trips. Self rescue and self-repair are mandatory. Nothing is as expensive as a dead crew, after all.

And if you need to handle smaller items still, the history of experiments plus Capt. Kittinger's experience on his first balloon jump in 1960 shows very clearly that you can doff the compression gloves and work barehanded quite safely in vacuum for up to about 20 or 30 minutes at a time, as long as there is no thermal injury risk (and that can be controlled by appropriate lighting and sunshades in vacuum). That's why the paradigm shift is required: you need a suit that is not all one piece, so you can mix-and-match, and even doff gloves.

The other unique advantage of MCP is rip/leak safety. A rip or puncture in the rubber gas bag means death in minutes in a p-suit. A rip in MCP needs no attention if small enough, a tight wrap of duct tape if too big to ignore. Then sew it up when you go inside. Both suits are vulnerable to broken helmets, and broken oxygen lines, so that's a wash. But the resistance to decompression death due to a rip or puncture makes MCP a winner hands down in environments full of sharp hard stuff. Does anyone else see the potential get a puncture or a rip while crawling around in the rocks on the moon or Mars? Or doing the things in the photos posted above?

I know a bundle has been, is being, and will be, spent on better full p-suits. Every piece of equipment will have a useful function. But, it seems foolish not to add another tool to the mix that expressly adapts to easy cleaning in dirty environments, and that offers unique rip/puncture safety. What's holding this back is attitude, not technology or expense.

GW

Last edited by GW Johnson (2014-12-17 10:37:45)

Impaler · 2014-12-17 19:56:21

RobertDyck wrote:

You talk about new suit development, but ignore a major achievement in suit development. Do you see the contradiction?

No, because I know the current state of MCP and it's history and I don't pretend that the technology is frozen and suits from the 70's are as good as they could possibly get which is the dishonest comparison constantly being made between 'dream' versions of MCP suits that don't even exist yet and EMU tech that is already the inferior of the two suits used on ISS today.

We have been over dust contamination already, MCP brings dust into an airlock do you deny that?

Suit-Port is not going to drive up mass, in the SEV it replaces an airlock and saves mass.

We have never had a puncture of a balloon suit and they are made of some damn strong materials (and getting stronger), the idea that this is some mortal danger is science-fiction.

Taking off gloves and working barehanded is a vacuum is never going to happen the contamination alone is verboten to speak nothing of the danger and MCP gloves are not remotely going to be like surgical gloves, the MIT suit would even use pressurized gloves because they haven't figured out how to make MCP gloves yet. And even if they DID make such a thing you can stick it on a balloon-suit because the body suit and the gloves are easily mixed and matched.

Thermal is a huge issue that MCP has not addressed remotely, if your relying on adding and removing layers then you've complicated the suit and cut into the supposed low mass, on Mars the problem is going to be primarily cooling not keeping warm and cooling systems are not simple layers.

GW: This is increasingly sounding like a repeat of your NTR obsession in which you latch onto some old obscure highly ambitious tech that looked promising in your youth and yet was not developed and try to beat NASA over the head claiming that if that tech had been developed all kind of Buck Rogers space development fantasies would have come to fruition. The history of the American space program shows that far from being too timid on tech we Consistently choose to develop techs that are too ambitious and end up biting off too much and creating system which are unaffordable. When you take techs that were SO ambitious that even we haven't tried them (to speak nothing of the Russians who consistently go for less ambitious and more affordable tech) and claim that THOSE undeveloped techs are what should have been developed is I simply see the old error repeated and compounded to the extreme.

If MCP suits were so great why is no one actually making them. Suit development is done by small companies like Dover that also make lots of other products, the costs of suit development are not astronomical like launch vehicles, they could do this work on their own. We have private companies developing private suits now for other private companies, but no ones going down the MCP route. We have ONE researcher at MIT who made ONE portion of a suit (the rest is a MOCKUP), and that's it. Again this technology is hardly moving at all, if your want to systematically pin hope on techs that have already lost in the competition of ideas your batting a thousand.

RobertDyck · 2014-12-17 21:30:45

We need simple technologies that allow settlers to live there. Not treat it as a hostile environment that you have to seal yourself off from. This brings back issues we went over long ago.

Dust: The hab will have an EVA prep area separate from the living area. In fact, MDRS already has an EVA prep area. This area will have air filters, with air low from the hab into the EVA prep area to ensure dust doesn't flow out. We have discussed various filters. One is a HEPA filter. But to reduce filter replacement, air can be bubbled through water before filtration through HEPA. That would add humidity, but a dehumidifier can compensate. And a washing machine in the EVA prep area. Yes, machine washable spacesuits. With a washing machine based on an RV washing machine. That is as small as an apartment washing machine, but the drum of the front loading washer acts as a dryer, so just one appliance. To reduce weight, the drum would be titanium alloy. You don't want aluminum, because that is too soft, can dent. And it would use electrical power available for the hab. ISS uses different voltage and frequency than North American household power; the Mars hab would probably be similar to ISS.

MCP developed rapidly. First full prototype suit was 1967. Second generation prototype suit 1971. Unfortunately work by Dava Newman has been very slow. She's good at titillating presentations that get attention of NASA boys, but her research is not nearly that of Paul Webb or Allen Hargens, or even Mitchell Clapp. Sorry to be harsh, but that's based on published papers.

You said "they haven't figured out how to make MCP gloves yet". Read this paper:
AIAA-84-0064
Design and Testing of an Advanced Spacesuit Glove
M. Clapp, Massachusetts Institute of Technology, Cambridge, MA
AIAA 22nd Aerospace Sciences Meeting
January 9-12, 1984/Reno, Nevada

Yup. It's dated 1984. This glove was designed for the EMU, the white spacesuit used by the Space Shuttle and ISS. It was intended for construction of ISS. Of course he had to increase pressure to match EMU.

Suit cooling is one of the advantages of MCP. Balloon suits use an undergarment with plastic tubes filled with water. Then water pumps, heat exchanger in the PLSS, and water spray system on the vacuum side of the heat exchanger. Cooling is via sublimation. With MCP, the entire cooling system is a bottle of drinking water. You cool by seat.

MCP was cancelled by Richard Nixon along with Apollo, and most space programs. The rationale was no need to develop a suit for the lunar surface considering Apollo was cancelled. Once all MCP guys were out of a job, the balloon suit guys simply justified their job. It has nothing to do with technology, it's simply job protection.

Impaler · 2014-12-18 17:31:45

Sounds like just more denial of dust contamination when doffing the MCP suit, the problem neither of you are willing to address is that the PERSON taking off the suit is being immediately and unavoidably exposed to dust. Some elaborate air filtering system is not going to address that one bit.

Newman's work is barely funded and has NOT garnered the attention of anyone but space-cadets, NASA rightly spent it's money on the balloon suits and challenge prizes to improve the existing technology and has awarded development contracts with the existing suit designers. All these groups presented working hardware and credible plans to evolve their systems to meet the mission needs, MCP suits did not even TRY to compete and to the degree it being developed now it is a high risk fringe tech.

The 1984 paper is not a glove, it's ideas for building a glove, if we don't have hardware that has had a human hand in it then we don't know how to build it yet. That's why Newman doesn't have gloves on her suit which is the specific instance I was referring too.

The accusation that balloon-suits are some how a pork barrel jobs protection program facilitated by evil Nixonian machinations is laughable, first off this suit technology is STILL the basis for high altitude military aircraft suits which are a major market that's not going away.

We obviously needed a suit for Shuttle and balloon-suits makers won the contracts based on the strength of their product and their track record of past performance, in Zero-G the main supposed benefits of MCP are largely moot so why would we expect a MCP to have been used on Shuttle. The same companies have won again to develop Mars suits, it was a open bid process and Dover had the best suit, end of story. The glove contract went to that solo guy from Maine and be beat the glove that Dover offered, if this is all an evil jobs protection program why didn't he lose?

YES, NASA is sometimes forced by Congress (read Shelby) to do terrible stupid stuff that is a naked jobs program. But their are going to be some clear line-items that tie NASA's hands and prevent a fair decision on technological merit, show me how MCP was excluded from competition by Congress. Even if you believe that bias and good-old-boy networks on the part of the NASA engineers is the problem the methods of these suit tests have consistently given objective measurements that NASA administrators have not over-ruled even when they went AGAINST their bias, the original Apollo suit manufacturer was not favored by NASA engineers but it CRUSHED the competition in testing, the meritocracy works for suits because suits are not launch vehicles which can only be made by a set of four highly consolidated aerospace companies that are fed space-pork as a means to surreptitiously fund our Military-Industrial-Complex.

This constant appeal to conspiratorial thinking and blaming politics for every disagreement between yourself and NASA as to the technology to invest in is not healthy, it smacks of self aggrandizement and snobbery and weakens your arguments profoundly.

Last edited by Impaler (2014-12-18 17:34:54)

RobertDyck · 2014-12-18 18:24:48

"Rightly"? Do you work for Hamilton-Sundstrand?

By the way, one of the members on this forum was the assistant for Mitchell Clapp who wore the glove in the glove-box. He was able to describe personally what it felt like.

And it isn't engineers who are the "good-old-boy networks". I've spoken with many engineers from Martin-Marietta (before the merger), Lockheed-Martin (after the merger), and Boeing who complained they came up with ideas to reduce work and save money. In every case their ideas were shot down. One engineer was told "you are taking bread from people's mouths".

And you're wrong, it isn't disagreement between myself and NASA. The last time I bid on a contract, one of the big old-space companies interefered. Despite the fact NASA advertised it as open to foreign companies, the project manager for United Space Alliance refused to let any foreign company bid. That company was a 50:50 joint venture between Boeing and Lockheed-Martin, and both Boeing and Lockheed-Martin were allowed to bid. Undertand what he was really doing? In fact NASA went out of their way to help me. But they let United Space Alliance manage the contract, so I was screwed.

So now you're pushing products managed by Hamlton-Sundstrand. By the way, the soft parts of the suit were made by ILC-Dover, which started as a division of International Latex Corporation, known for their brand name Playtex. They made women's girdles before going into spacesuits in the 1960s. They are ideal to make MCP suits.

So now you're talking about some sort of "meritocrasy"? What is that supposed to be? Do you think that sucking up to establishment will get you somewhere?

Last edited by RobertDyck (2014-12-21 13:24:43)

GW Johnson · 2014-12-18 20:11:12

I’m sorry, but this argument over MCP is getting quite tiresome.

The truth is, it worked in the 1940’s; it was called a partial pressure suit. The quality wasn’t very good, but that got fixed later. In the late 1960’s actually.

From Tom Billings, 3-29-14, comment RE: “On-Orbit Repair and Assembly Facility”, posted 2-11-14, on http://exrocketman.blogspot.com -----

When our team spoke with several Apollo astronauts in the 1990s about the MCP concepts, they told us the Astronaut Office, and many in it, were scared of the concept. The basic reaction was one of incredulity to exposing the skin to vacuum. ORL5 Research Team still thinks it very worthwhile, however. It will almost certainly require commercial adoption before NASA is willing to take the programmatic and institutional risk needed for greater productivity in EVAs. I'd be happy with a combination of Dava Newman's concepts and the maneuvering "pods" from "2001: a Space Odyssey", which used waldoes. This is especially so if the update suggestion about glove-free intricate work can be realized.

My reply 3-30-14 to Tom Billings, same article, same site -----

It does seem kind of silly for the astronaut office to have feared these MCP concepts, especially given (1) the success of the partial pressure suit in bailouts at unsurvivable altitudes, and (2) the experience of Capt. Kittinger with his unpressurized hand in vacuum. But you may be right: a commercial concern might be the first to fly such an MCP suit in space. – GW

That exchange simply proves the point that logic, common sense, and real data actually have little to do with how NASA funds major space suit developments. Politics and favored contractors repeating what they did before have a lot more to do with what gets funded to any significant extent. Dava Newman actually gets a pittance to do what she has done. And that really looks like the “one-piece-garment-that–does-everything” approach. Which is the wrong approach. But she does it that way to get any money at all.

One should note that the “partial pressure suits” of the 1940’s and 1950’s were the first manifestation of MCP suit technology. They were actually quite successful, for bailouts above 70,000 feet (when the “vacuum death point” is nearer 60,000 feet). Pressure breathing is required above about 45,000 feet. And pressure breathing requires in-body counterpressure beyond about 5 to 10 minutes’ exposure. That’s the half-century+ database. A 70,000 foot bailout is about a 10 minute fall, at most.

Paul Webb’s elastic garment designs of the late 1960’s and early 1970’s worked even better than the “standard” partial pressure suit. These were 6 or 7 layers of the then new panty-hose elastic material. The final 1970-ish test was 30 minutes in a vacuum tank on a bicycle ergonometer, doing heavy exercise. The pressure in that tank was equivalent to 87,000 feet, way above the “vacuum death point”. And the exposure time is beyond that needed to start showing symptoms of vacuum exposure. The subject was wearing both gloves and booties that worked just fine, unlike the old partial pressure suits that left hands and feet uncompressed entirely.

In other words, MCP worked just fine, way back then circa 1970. That’s the actual historical record, and some of that was funded by NASA itself. Yet they (NASA) persist today in scaring their astronauts about exposing skin to vacuum.

As I said, this is more about politics and corporate welfare than it is anything to do with technology and its readiness.

GW

Last edited by GW Johnson (2014-12-18 20:13:30)

Terraformer · 2014-12-19 10:22:26

You don't need full pressure on the limbs, hands and feet anyway... at least, it doesn't seem like it should be so, since people manage fine with much less than 1 bar of pressure on those parts of the body. Why pressurise them to the same level as the chest when you don't have to, since it restricts movement?

The issue of MCP vs. Balloon might be up in the air for compressing the chest, but for limbs, I can't see the case of gas pressurisation...

Antius · 2014-12-19 10:56:13

GW Johnson wrote:

As I said, this is more about politics and corporate welfare than it is anything to do with technology and its readiness.

I couldn't agree more. Aerospace is probably the only industry in existance where the design solutions adopted are not cost optimised. Basically because their scope of operations is tiny and their money comes from the public pork barrel.

If we are ever to scale-up space operations to the point where 100's or 1000's of people are living off-Earth, there needs to be a serious effort to apply a minimum cost design philosophy to all parts of the operation. We simply won't be able to afford it otherwise, in the same way that few of us can afford to get our shopping in a ferrari.

RobertDyck · 2014-12-19 22:20:13

Terraformer wrote:

You don't need full pressure on the limbs, hands and feet anyway... at least, it doesn't seem like it should be so, since people manage fine with much less than 1 bar of pressure on those parts of the body. Why pressurise them to the same level as the chest when you don't have to, since it restricts movement?
The issue of MCP vs. Balloon might be up in the air for compressing the chest, but for limbs, I can't see the case of gas pressurisation...

The problem is humans are filled with fluids. Our bodies can restrict blood flow to extremities to control heat loss; when very cold out doors in winter we can drastically reduce blood flow to maintain core body heat. You gotta keep the heart, lungs, liver, kidneys, endocrine glands, and brain warm. Blood flow to digestive organs are controlled as well, but they are kept warm but dormant. I live in Canada, I know from first hand experience what happens when you get cold. However, the body is not designed to deal with differential pressure.

Low pressure in one body part, while high pressure in others, results in blood flow from high to low pressure. This results in sequestering blood in low pressure areas. That results in extreme swelling. The lymphatic system is the most extreme; it isn't pressurized at all. When blood is forced through capillaries, nutrients and oxygen are supposed to be delivered to tissues. This results in liquids from blood (plasma) leaking into tissues. The body has arteries to deliver blood to capillaries. Arteries have muscles that can close to restrict flow, or relax to open fully to increase flow. And veins carry blood from capillaries back to the heart. Veins do not have any muscles, they cannot restrict flow, but they have one-way valves to force flow back to the heart. When veins are squeezed by skeletal muscles (running, jumping, lifting something with your arms, etc), that squeezes blood out of veins. Valves ensure blood flows only toward the heart. So skeletal muscles help the heart by pumping blood, they pump blood back to the heart. This is why massage feels so good for middle-age individuals. It forces blood out of tissues with poor circulation, which creates suction that pulls fresh arterial blood into those same tissues. This feeds tissues that are starving for oxygen and nutrients.

The third system collects leakage. The third system is lymphatic vessels. It collects leaked fluid, and directs it back to a large vein near the heart. Because it isn't pressurized, small pressure differences collect fluid. So even small pressure differential between one part of the body and the rest of the body, results in accumulation of fluid. That's swelling. To avoid that, you must pressurize the entire body to exactly the same level.

Last edited by RobertDyck (2014-12-21 13:27:47)

GW Johnson · 2014-12-21 11:04:50

Actually, you don't have to do a perfectly-even job of compression. The extremities can be compressed a tad less than the body, and the hands a feet a tad less than that. But the allowable gradients for steady-state exposure are very small. One of Paul Webb's old reports ca. 1970 has that data.

Robert Dyck is exactly correct: he points out the two problems: (1) blood pooling in undercompressed extremities is blood not carrying oxygen to other essential regions (most notably the brain), and (2) the liquid component of the blood (mostly water) will eventually leak right through the blood vessel walls into surrounding undercompressed tissues (swelling, aka edema).

You have to do a good enough job to prevent those two effects. The longer you intend to stay exposed to vacuum, the better job you have to do, until you do it "good enough" with those very modest gradients identified by Webb. The old partial pressure suits of ca. 1950 did a poor job, but it was good enough for 10 minutes' exposure. Hands and feet were entirely uncompressed, and arms and legs were very undercompressed in those suits.

That's what Paul Webb corrected in his "elastic spacesuit" prototypes of the late 1960's. And he did a very good job, with nothing available but pantyhose material.

GW

SpaceNut · 2017-08-15 17:52:57

Back to the air we will breath inside the habitat... There have been reports of headaches onboard the ISS and that the levels of Co2 are less at least in microgravity which will cause the crew to be less functional.

Why Living in Space Can be a Pain in the Head, A new study says carbon dioxide levels on board the station should be lowered. For more than a decade there has been one commonly reported ailment -- headaches -- has been linked to high carbon dioxide levels on the station.

The team was able to study more than 1,700 reported and non-reported observations of headaches since the first carbon dioxide monitors were activated on the station in February 2001. The team was able to study more than 1,700 reported and non-reported observations of headaches since the first carbon dioxide monitors were activated on the station in February 2001. Between 2001 and 2012, carbon dioxide levels on the ISS typically stayed between 2.3 and 5.3 mm Hg (a measure of concentration); those levels, however, sometimes change fairly quickly over hours or days.
On Earth, carbon dioxide is a trace molecule in our atmosphere, at a low 0.3 mm Hg. In space, exhaled CO2 builds up in the cabin, and would even linger in a cloud around the astronauts’ heads were it not for fans that circulate the onboard air. Tests on the ground have shown that healthy males have no ill effects when breathing a CO2 concentration up to 7.5 mm Hg, and can handle as much as 11 mm Hg for up to eight hours with no acute effects, like headaches.

https://www.nasa.gov/mission_pages/stat … /2101.html

It’s Taking Less CO2 Than Expected To Cause Health Risks In Astronauts

0s6K4vew6_CWgKV0a.jpg?w=638&crop=0%2C0px%2C100%2C527px&ssl=1

So gravity seems to have another effect on humans being on mars as we will need to do testing in order to be safe.

Antius · 2017-08-16 10:49:46

High CO2 also screws around with blood acidity levels in humans. After a few days exposure, bone demineralisation starts to occur - people basically pee out their bones. You need a hammer and chisel to remove the resulting limescale from the heads. Put people in a high CO2 environment for years at a time, and they will develop osteoporosis and arthritis by the time they hit their 40s.

Terraformer · 2017-08-16 15:15:44

I don't think that happened in any of the animal studies Midoshi mentioned in the Minimal Martian Terraformed Atmospheres thread. As I understand it, the body adapts to maintain the same blood acidity. They're probably need additional calcium, of course.

SpaceNut · 2017-08-16 16:46:35

Preventing Bone Loss in Space Flight with Prophylactic Use of Bisphosphonate: Health Promotion of the Elderly by Space Medicine Technologies

Bone loss and kidney stones are well known as essential problems for astronauts to overcome during extended stays in space.
Crew members engage in physical exercise for two and a half hours a day, six times a week (fifteen hours a week) while in orbit to avoid these issues.
The three key elements for promoting the health of elderly people to prevent fractures are nutrition, exercise and medicine. Meals should be nutritionally balanced with calcium-rich foods (milk, small fish, etc.) and vitamin D (fish, mushrooms, etc.). Limited sunbathing is also important for activation of vitamin D. Physical exercise to increase bone load and muscle training should also be integrated into each person's daily life.

RobertDyck · 2017-08-16 17:05:48

Antius: those effects have been obvserved. It has been attributed zero-G. I notice the NASA news announcement that SpaceNut linked does not give numbers. Exactly how high? ISS is supposed to control CO2. With two causes of bone decalcification, data on human factors has to be treated as contaminated.

louis · 2017-08-16 18:09:53

One thing about air pressure. There is an upper limit for successful reproduction (excepting those population groups that have already adapted to high altitude through natural selection and behavioural adaptation).

https://en.wikipedia.org/wiki/High-alti … _in_humans

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