Optimal air pressures.. - Which is best? More O2 or more pressure?

SpaceNut · 2020-02-15 18:30:55

We know these things from scuba diving and from space walking that man can tweak the psi and gas content and we can survive just fine so we need to do the same for mars in the beginning rather than trying to duplicate earth on mars....

kbd512 · 2020-02-15 19:00:06

tahanson43206,

What you're noting is that there are limits to every technological solution. If you drink too much water, you can die. However, most people have the opposite problem that often does produce the same undesirable result. There are narrow operating limits for everything and the human body is no different in that regard. Argon is a viable substitute buffer gas if the limits of its usage are respected.

tahanson43206 · 2020-02-15 19:38:46

For kbd512 re #52

Thanks for your note on my attempt to collect data on the gas mix question which is (sort of) the theme of this topic.

I am hoping the forum can (collectively) assemble a concise guideline for persons who will be planning their habitats at Mars. Those people are (probably) alive today, and probably not yet out of college. While the members of this forum may not be going with them, we ** can ** do our best to assemble concise, accurate guidelines for various activities they will be undertaking.

Assuming (for example) the decision is made to work entirely with Mars native materials to create comfortable habitats, it seems reasonable (at this point of my understanding) to compress Mars' atmosphere, extract the components and put together a gas mixture with 20-21% Oxygen and the balance Nitrogen and Argon as those molecules present themselves.

Asking Mr. Google for "mixture of gases in Mars Atmosphere" we have:

It is primarily composed of carbon dioxide (95.32%), molecular nitrogen (2.6%) and argon (1.9%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen and other noble gases. The atmosphere of Mars is much thinner than Earth's.
Nitrogen: 2.6%
Carbon dioxide: 94.9%
Argon: 1.9%
Carbon monoxide: 0.0747%

The Oxygen component can be obtained from the CO2, and the Carbon can be saved for manufacture of methane or other Carbon compounds.

The inert gas component would then contain a bit more Nitrogen than Argon.

I see no reason at all to create an atmosphere with any Carbon components at all, since we will be busy creating CO2 which will then have to be removed when the level exceeds the threshold you've warned us about.

Manufacture of atmosphere for habitats would be a specialization which should have a place in the community.

Manufacture of atmosphere for greenhouses might require a separate specialization, since it would appear that there are differing mixtures needed depending upon the pressure at which the greenhouses will be operated.

(th)

RobertDyck · 2020-02-16 14:06:29

One concern is getting into a spacesuit. Shuttle and ISS use Earth sea level pressure, which is absolutely not necessary. That creates major problems when an astronaut has to go outside in a spacesuit. Shuttle astronauts had to pre-breathe pure oxygen for 17 hours to flush nitrogen out of their blood. If they don't, decompression would result in nitrogen dissolved in blood coming out of solution, creating bubbles. Those bubbles will block blood flow, starving tissues that are supposed to be fed by those blood vessels. Starving tissues of blood will cause tissues to die. Tissue can withstand blood flow blockage about as long as you can hold your breath; a little more, but not much. After that the tissue starts to die. This is a medical condition called "The Bends".

There is a maximum partial pressure of nitrogen for zero pre-breathe time. Take total pressure of the lower pressure environment (spacesuit), multiply by 1.2, that's the maximum partial pressure of nitrogen in the higher pressure environment (habitat, spacecraft, space station, etc).

Apollo used 3.7 psi pure oxygen for spacesuits. Apollo Command module used 5.0 psi pure oxygen. After the Apollo 1 fire there was much discussion about using a mix for fire safety, but the additional weight of carrying nitrogen bottles and pressure regulators needed to balance gas pressures were considered too much. So Apollo used natural air from the launch site for launch, then "bled out" that air as the Saturn V ascended. Apollo continued to bleed out air, reducing pressure and flushing out air to replace with pure oxygen. When finished Apollo had 5.0 psi pure oxygen. This was done slowly enough that astronauts did not risk "The Bends". It was important that Apollo not use 14.7 psi (Earth atmosphere at sea level) pure oxygen, because pure oxygen at that pressure is dangerous. Velcro will smoulder in Earth air, but will not sustain a flame. That means Velcro will stop burning once you take a flame way; it will not burn on its own. I believe Velcro will smoulder but not burn in 3.0 psi pure oxygen, not sure if it'll burn in 5.0 psi pure oxygen. But the test that was posthumously called "Apollo 1" used 16.7 psi pure oxygen; in that much oxygen Velcro will ignite like the head of a match. In 14.7 psi pure oxygen, Velcro will not burn quite as vigorously, but still quite vigorous.

Skylab also used 5.0 psi total pressure, but used 60% oxygen / 40% nitrogen. That works out to 3.0 psi partial pressure oxygen + 2.0 psi partial pressure nitrogen. Apollo spacesuits used 3.7 psi pure oxygen, so maximum partial pressure nitrogen would be 3.7 * 1.2 = 4.44 psi. Skylab used 2.0 psi nitrogen, so well below the maximum. This allowed astronauts to don a spacesuit and go through the airlock at any time, no oxygen pre-breathe.

The EMU suit was designed for Shuttle, and currently used on ISS. It uses 4.3 psi pure oxygen. Maximum partial pressure nitrogen for a habitat to allow using that suit without oxygen pre-breathe: 4.3 * 1.2 = 5.16 psi. Earth at sea level has 3.0 psi partial pressure oxygen, so if a habitat uses that then 3.0 psi O2 + 5.16 psi N2 = 5.16 psi total. That's the absolute maximum, it would be a good idea to reduce nitrogen a bit for safety.

Do I have to mention that EMU uses higher pressure to reduce oxygen pre-breathe time? So EMU uses higher pressure because Shuttle and ISS use higher pressure.

Original design work for Apollo spacesuits intended to use 3.3 psi pure oxygen. Since Earth at sea level has 3.0 psi partial pressure O2, astronauts can breathe that just fine. This allowed for a 10% pressure leak in the suit without jeopardizing astronaut health. In the end they chose to increase pressure a bit because extreme low pressure causes lung tissue to dry out. If lung tissue gets too dry, it will crack and bleed. This can be managed with high humidity in breathing air (suit oxygen), but high humidity can cause the visor to fog.

Dr. Paul Webb did the initial work on mechanical counterpressure (MCP) spacesuits. He used 170 mm mercury (3.287 psi) pure oxygen. His papers describe problems at 130 mm mercury (2.51 psi): mild tachycardia and small collection of edema fluid in the hands. Of course the solution is stick to 170 mm mercury (round off to 3.3 psi). Recently Dr. Dava Newman of MIT said designing an MCP suit to work with 20 kPa (2.90 psi) pressure is easy, designing for 30 kPa (4.53 psi) is hard. Of course the solution is don't. By that I mean don't use the higher pressure of an EMU suit, instead use the original pressure MCP was design to work with.

Dr. Paul Webb designed a second generation suit, described in his contractor report to NASA, filed November 1971. That report describes. A then-new high-tech material that would work much better. Dr. Webb worked with cotton threads dipped in rubber for his elastic fabric, because that was state-of-the-art at the time. In fact he hired a company that manufactures women's girdles to manufacture his elastic spacesuit garment: Playtex. But his contractor report describes a new material that would work better: Spandex. Yup, the same material as 1980s exercize/gym wear. In 1971 it was new. Today we have even newer materials, but my point is we don't need anything radical, just tight Spandex. Dr. Webb's second generation suit used a neoprene rubber air bladder vest over the thorax (chest) and upper abdomen. This vest had a non-elastic outer fabric; as the subject inhales that squishes air out of the bladder, but volume in the lungs increase by exactly the same volume. Exhale does the reverse. Connecting the air bladder to breathing air (helmet or breathing mask) ensures constant volume. This is done with Navy diver rebreathers; it's called a "counter lung". Ensuring constant volume prevents restrictions to breathing. I would further recommend a breathing mask over nose and mouth, similar to a fighter pilot breathing mask. This allows breathing air to have higher humidity than air inside the visor. Yes, EMU suits today use an anti-fog spray on the inside of the visor, but a breathing mask is an easy way to reduce this problem.

Furthermore, MDRS found safety concerns wearing a shoulder-worn helmet when driving a 4-wheel ATV. Some crews take off their helmet, breaking sim, when driving an ATV. I would argue for a spacesuit helmet that is head-worn, like a motorcycle helmet. That would allow the helmet to be a crash helmet; literally providing the same protection as a motorcycle helmet. An MCP suit can do this. Mercury and Gemini spacesuits did this, but found a gas bag suit made turning the head difficult. Apollo suits went to shoulder-worn to resolve that. However, an MCP suit uses a neoprene air dam over the neck, to hold air pressure in the helmet. The suit is an elastic fabric. So an MCP suit doesn't have the same problem turning the head. So this solves the "crash helmet" problem. And a head-worn helmet can easily include a breathing mask.

Dr. Paul Webb worked with 170 mm mercury because that's what NASA was working with at the time. I would recommend dropping pressure even further to 3.0 psi pure oxygen. That makes moving easier. And using the original Apollo rule of suit pressure being 10% higher than oxygen partial pressure the astronauts are used to, in case of pressure loss, then I would drop habitat oxygen to 2.7 psi partial pressure. Note: oxygen on Earth at sea level is 3.0 psi partial pressure, but at Boulder Colorado it's 2.54 psi.

Spacesuit design is critical, because you don't want to require multiple hours of oxygen pre-breathe just to put on a suit and go outside. Dropping suit pressure to 3.0 psi, means optimal habitat oxygen will be 2.7 psi, and maximum habitat nitrogen will be 3.0 * 1.2 = 3.6 psi. If that's all you have then that totals 2.7 + 3.6 = 6.3 psi. But Earth's atmosphere is 0.9340% argon, you're breathing a tri-gas mix right now: oxygen, nitrogen, argon. I recommended making the nitrogen:argon ratio exactly the same as Mars atmosphere, simply because that means we don't have to separate them. Just harvest Mars atmosphere, filter out dust, use a freezer to convert CO2 to dry ice, and keep the rest. Turns out that's not quite enough: there's carbon monoxide and ozone, but a rhodium based catalyst can combine CO with O2 to form CO2. Turns out there's more oxygen in Mars atmosphere than carbon monoxide, so this works. Furthermore, that same catalyst breaks down ozone: 2 O3 → 3 O2. This provides slightly more oxygen while CO is being converted. The result will still have a bit of CO2, a freezer is good at removing the bulk but can't remove the last big. However, a habitat life support system can remove the rest. I call this gas "diluent gas" because it's used to "dilute" oxygen. A habitat filled with oxygen / diluent gas can support humans right away, it'll just smell stuffy until the life support system reduces CO2. Assuming Mars atmosphere has the same gas mix measured by Viking lander in 1977, and assuming 3.6 psi partial pressure nitrogen, that works out to 2.133 psi partial pressure argon. However, modern Mars rovers have measured a slightly different N2:Ar ratio. I wouldn't think it would vary, but looks like it does. Samples taken decades apart, and different locations on the planet. But using the data from Viking 2, that adds up to: 2.7 psi O2 + 3.6 psi N2 + 2.133 psi Ar = 8.433 psi total.

A small operation would use the same air for greenhouse and habitat. This allows the plants to recycle oxygen, so no power is necessary for oxygen generation. As a safety factor, this allows life support with completely power failure. It also means you can just walk from habitat to greenhouse, extending total living space. Yes, artificial lights would be needed in case of dust storms, and artificial life support would be needed as a backup. But using plants in an ambient light greenhouse as primary life support reduces power demands under normal operation. And means power failure only becomes life threatening if it occurs the same time as a major dust storm.

A large commercial greenhouse would most probably elevate CO2. That increases plant growth. And pressure could be reduced. Guelph University did an experiment with spinach grown in a hypobaric chamber. They found plants grow just fine, but water transpiration through leaves increases as pressure drops. As long as there's enough water, plant growth continues at the same pace. In a sealed greenhouse, water transpired through leaves will condense on walls/windows, dripping down through to collection trough that routes the water back to plant roots. So the water goes in a big circle, it's not consumed. Below 10 kpa pressure (1.45 psi) the plants wilt, stop growing. The university did an experiment where they dropped pressure to Mars ambient for one hour, then restored pressure. The plant wilted, but perked back up and continued to grow as soon as pressure was restored. So plants can withstand lower pressure than humans.

RobertDyck · 2020-02-16 15:25:35

I said the test was called "posthumously" called Apollo 1. The proposed name of that test was Apollo 1, but the name was not approved. I ran into someone older than me who claimed it had some technical name, but the name "Apollo 1" was proposed months before the test. After the fire, the name "Apollo 1" was posthumously approved. To respect the deceased astronauts. The crew received approval in June 1966 for a patch that said "Apollo 1". That approval was withdrawn pending final approval, but was approved after the fire. The the capsule was delivered to KSC in August 1966, with a cover that read "Apollo One". The accident happened January 27, 1967.

SpaceNut · 2020-02-16 15:29:28

For mars anything that is much lower than the earth air pressure that we enjoy means less energy and construction materials for forces is that we will be just as comfortable in that new environment even in a new levels of composition.
So what have we tried and where is some of how we get to that answer for mars.
https://en.wikipedia.org/wiki/ISS_ECLSS

The Urine Processor Assembly is designed to handle a load of 9 kg/day, corresponding to the needs of a 6-person crew Although the design called for recovery of 85% of the water content due to bone density loss has led to a revised operational level of recovering 70% of the water content. Normal air pressure on the ISS is 101.3 kPa (14.7 psi); the same as at sea level on Earth.

http://tornado.sfsu.edu/geosciences/cla … ition.html

While we are scrubbing and cleaning we are not 100% closed loop and must replentish what ever we are low on from the resupply vessels from earth but for mars we will draw it in from many insitu sources with energy and equipment mass for launch plus landing being the only limiting factors.

http://web.mit.edu/16.00/www/aec/lif_sup.html

With higher pressures for a cabin and a lessor one for the space suit you must take time in a reduced pressure chamber breathing in pure oxygen before being able to get acustomed to the new mix and pressure so as to not get the bends like symptoms caused by nitrogen.

http://www.collectspace.com/ubb/Forum29 … 01309.html
skylab information

http://lsda.jsc.nasa.gov/books/skylab/ch37.htm

oxygen partial pressure equal to 22.6 kPa < 3.27785 psi> ( 225.99980 mb)
nitrogen partial pressure equal to 10 kPa < 1.45038 psi> ( 100.00018 mb)
water partial pressure equal to 1.3 kPa < 0.18855 psi> ( 13.00006 mb)
carbon dioxide partial pressure equal to 6.7 kPa < 0.971753 psi> ( 67.00001 mb)

values in <> () I have computed

kbd512 · 2020-02-16 16:31:43

RobertDyck,

If you vomited into your oxygen mask, you could die in an otherwise perfectly good suit. A heating element in the helmet visor could take care of the fogging issue caused by respiration. Other than that, I think woven CNT and elastic fabric could supply sufficient mechanical counter-pressure while not significantly impeding the mobility of the wearer nor weighing more than conventional cotton polyester clothing. The additional weight of the life support equipment should not significantly impede movement on Mars. It would be like carrying a 45 pound pack here on Earth, which is routinely done on extended hikes.

RobertDyck · 2020-02-16 17:25:11

Vomiting in a spacesuit is a problem for any spacesuit. Heating element is a good idea. I wouldn't use carbon nanotube, because that's expensive and very stiff; non-elastic. You could use fancy new fabric; for example a fabric over the knee that provides strong elastic radially around the leg, but weak elastic longitudinally along the length of the leg. So it acts like a convolute joint of a gas-bag suit. Along the side of the knee the fabric could be completely non-elastic longitudinally while providing the same elastic counter-force radially. So again, it works the same as the knee joint of a gas bag suit, but instead of neoprene rubber and metal rings it's done entirely with fabric.

As for the backpack, the cooling system is greatly simplified. A gas-bag suit uses an undergarment with plastic tubes carrying cool water. An aluminum heat exchanger in the backpack actively cools the water. A bottle of water sprays water on the outside of the aluminum heat exchanger, which immediately freezes in the vacuum of space. That sublimates into space, carrying away heat. It consumes water, requires a water pump and battery to power the pump. An MCP suit is fabric, so the human body sweats into space. Temperature regulator is the human body itself. The fabric is not sealed; Dr. Paul Webb found human skin is air tight, only requires counter-pressure to ensure fluids inside the body remain pressurized. He found skin can withstand a gap in fabric 1mm square with no damage what so ever. "Insensible perspiration" means the vacuum of space will "suck" water out of pours, causing the subject to cool when he doesn't need to. Dr. Webb measured this, found heat loss due to that is less than heat produced by an astronaut just standing at rest. This means the astronaut will get warm, and will sweat to get rid of that heat. If the astronaut works at 300 kcal/hour for 4 hours, he will lose just over 2100 grams water over the whole period. Note 1 gram water = 1 cubic centimetre (cc) = 1 millilitre (ml), so 2000 grams water = 2 litres. So the entire cooling system is a bottle of drinking water. This would be a 2 litre plastic bottle, made exactly the same way as a 2 litre pop bottle. Pressure in a pop bottle is less than pressure differential between spacesuit pressure and space. You may want to make it of something that could withstand the cold of space, even though it has to remain warm enough that the water won't freeze. So you could get fancy and make it of PCTFE, which is the most impermeable to water of any known polymer, and becomes brittle at -240°C. Place that bottle in the backpack, positioned so astronaut body heat will keep the water warm. Inside the plastic bottle will go a plastic bag, a "bladder" liner. Water would go inside the bladder, air would go between the bladder and bottle. A drinking hose would go from the bladder to helmet, and a second hose from bottle to breathing air. So as you suck water out of the bladder, the bottle back-fills with air to ensure no pressure problem. But you want the water in a bladder so the drinking hose get water, not air. Especially important in zero-gravity.

Would you make the bottle smaller? One litre? That could result in dehydration if you work hard, especially if you work for a full 8 hour shift. But no pump, no heat exchanger, no mechanism. Simple, reliable, light.

I would also design the breathing mask with one-way valves. Exhaled breath would go through one hose to the vest, with a one-way valve to ensure air can't come back. The vest would have a direct connection through the back to the CO2 sorbent cartridge; again with one-way valve so air can only pass from vest to cartridge, not back. Another hose would go from CO2 sorbent cartridge to breathing mask; and again one-way valve ensures not back. This means action of breathing alone would circulate air. No need for any fan.

Apollo used lithium hydroxide because it's light, but that isn't reusable. EMU suits for ISS have been modified to use silver oxide, which is heavier but CO2 can be baked out. In any case the CO2 sorbent would have activated charcoal to absorb bad smells, like bad breath. That can also be baked out.

With 100% oxygen for spacesuit air, plus exhaled CO2 and humidity, that means the human body will convert O2 to CO2, then the sorbent will remove CO2. This will reduce pressure in the breathing system. As pressure drops, a pressure regulator will top-up pressure from an oxygen tank. Again, no valves or pump or actuator or motor, nothing electrical. This means the breathing system works in case the spacesuit battery completely fails. The suit would most likely have fancy electronics, monitoring equipment for pressure and airflow rate, sensors for CO2 and O2 content in breathing air, temperature, etc. All available via space-hardened smartphone installed in a suit forearm. With touch screen designed to work with gloved hands. But if the electronics and completely electrical system fails, the suit continues to provide breathing air using nothing but one-way valves, a pressure regulator, and breathing action of the astronaut's own lungs.

How does that reduce the backpack?

RobertDyck · 2020-02-16 17:39:18

The suit could connect the vest to the backpack with only one air connection. A "T" connection in the backpack to the back of the vest, with a one-way valve from the "T" to the sorbent canister. The other side of the "T" would be a one-way valve to a hose to the helmet. So both hoses from the helmet go to the top of the backpack. Furthermore, the helmet could have the breathing mask integrated with ducts to connections in the back. So both hoses go from the back of the helmet to the top of the backpack. That keeps them out of the way.

SpaceNut · 2020-02-16 17:57:21

We would not what any vomiting in any area that we would occupy, a suction tube in the helmet that can be moved to swipe in the area to remove would work to vacumn it out of the visor area. For inside one would want to do about the same with cleaning of both areas after we can get out of the suit in the habitat area as well.

RobertDyck · 2020-02-16 19:00:09

Another advantage of a MCP is that it's machine washable. A gas-bag spacesuit certainly isn't. Apollo had a problem with contamination with Moon dust. An MCP suit consists of several layers: the MCP layer is Spandex or equivalent. The vest is neoprene rubber with a non-elastic outer cover fabric. There could be a hard shell to squish the air bladder close to the body. The shell would be light-weight, not the hard fibreglass shell of an EMU suit. Just a chest piece of vacu-formed plastic, with ridges for added strength, but the ridges would have to be rounded to ensure they don't dig-into/cut the bladder. The point of the shell is so it isn't a barrel, it's close to the body. The ridge pattern could be made aesthetically pleasing: muscle plate for men, or breast plate for women. With an air-filled bladder over breasts and a thin plastic shell formed over each breast, the result would "augment" the woman's "natural assets", making her look "well endowed". Robert Zubrin argued against MCP suits claiming that middle-age astronauts (40s or 50s) would suffer middle-age spread so a skin-tight suit wouldn't look good. So one reason for this muscle plate is to counter that. Besides, the whole thing will be covered by the thermal and micrometeor protection garment. For an MCP suit that's a parka and ski pants.

On the surface of Mars, there's no micrometeorites. Micrometeorites are the size of a grain of sand, or smaller. Some the size of a grain of dust. But in LEO they travel 10 to 20 times the speed of a bullet. On Earth they burn up in the atmosphere 100km above the surface. On Mars they burn up 30km above the surface. A Mars surface suit doesn't need micrometeoroid protection, but will need scuff protection from sharp rocks and spacecraft parts. EMU uses Orthofabric, which is a double-layer fabric. Surface is Goretex with thread weight 400 denier. Every 3/8" two threads are replaced with Kevlar, also 400 denier. The back is Nomex; the same fabric as a firefighter's jacket and pants. On Mars you don't need a fire proof suit, the atmosphere is 95+% CO2. And this suit is not intended to wear inside the spacecraft. So a Mars suit doesn't need Nomex. It doesn't need Kevlar either. Goretex of Orthofabric is fibres of PCTFE polymer, the same polymer as Teflon. Tenara architectural fabric is the same material, from the same factory. You could use 400 denier thread weight Tenara, or even 80 denier. Arctic parkas have an 80 denier Tenara fabric shell.

Multi-layer insulation is aluminized mylar separated by "fish net". In the vacuum of space, this works very well. The aluminum layers reflect radiant heat (infrared light). In vacuum there is no heat loss from conduction or convection. That works in LEO, interplanetary space, and the surface of the Moon. It won't work on Mars. Mars has an atmosphere; it's thin, but enough that multi-layer insulation won't work. You need something else. Thinsulate is light-weight insulation used for ski jackets and ski pants. Simply use Thinsulate for the surface of Mars. So two different sets of outer garments: thermal and micrometeoroid for space, and thermal and scuff for Mars. Both a parka and ski pants.

Hmm... the backpack would require thermal insulation integrated. The water bottle pressed against the back of the air bladder vest, with just a thin "slip" layer to avoid abrasion. With insulation around the water bottle, where it doesn't press against the vest. Electronics in the backpack would also require warmth from body heat, so also pressed against the air bladder vest, also with a "slip" layer, also insulated where it doesn't press against the vest.

Electronics could use a cold weather lithium-ion battery. Even though the electronics would be pressed gainst the back of the astronauts air bladder vest, with insulation outside the electronics, still. A for over heating, pressing against the air bladder of breathing air, would also ensure it doesn't get too hot. The astronaut's body would ensure the small electronic package doesn't get too hot.

The electronic package in the back would probably be smaller than a smartphone. The touch display on the forearm would not have the battery, just touch screen and user interface. A cable sewn into the sleeve to the electronics box in the backpack would provide power and data connection to the processor there.

SpaceNut · 2020-02-16 19:20:23

Posts copied to New idea for Mechanical CounterPressure suit

edit new content 5-30-22

tahanson43206 wrote:

For SpaceNut ...
This post is to hold information about human settlement on Earth at altitude ...
As the altitude increases, the barometric pressure decreases. The availability of oxygen decreases as the altitude increases. The increase in oxygen content through the increase in the number of red blood cells is one of the most important mechanisms of adaptation to high altitude. As of May 2003, National Geographic Magazine reports that La Rinconada, Peru, is currently the highest permanent human habitation. La Rinconada, a mining village of over 7,000 people in Southern Peru at an altitude of up to 5100 meters, has been in existence for over 40 years.
Monique Anthony -- 2005
https://hypertextbook.com/facts/2005/Mo … hony.shtml
www.mide.com
Air Pressure at Altitude Calculator
Calculate Altitude from Air Pressure
Pressure at Sea Level
101325 Pa
Default
Temperature
15 °C
Default
Air Pressure at Altitude
50000 Pa
Altitude =
5574.44 m
Calculate Air Pressure at Altitude
Pressure at Sea Level
101325 Pa
Default
Temperature
15 °C
Default
Altitude
5100 m
Air Pressure at Altitude =
53301.9 Pa
Humans live continuously at 5100 meters without oxygen boosting.
RobertDyck's atmosphere prescription for Mars is 3-5-8 3 psi O 5 psi N 8 psi net.
The discussion on Zoom was whether people would be comfortable at 1/2 sea level atmosphere.
The answer appears to be that when oxygen is maintained at equivalent partial pressure to sea level, people ** are ** comfortable.
However, it would be helpful to know who humans experience RobertDyck's prescription for extended periods.
The Peruvian miners appear to show that humans can adapt to 1/2 BAR without oxygen enrichment.
A Real Universe test could be carried out on Earth on the side of a mountain where the atmospheric pressure is 1/2 BAR.
The test would be to fill the human habitat to the Mars prescription of 3-5-8 and measure human experience for an extended period.
(th)

SpaceNut · 2022-05-30 08:44:44

kbd512 wrote:

tahanson43206,
If you read these articles, then you should be able to determine that I am not "speculating" about how higher partial pressures of Oxygen in a higher or lower total pressure environment will eventually become "toxic" in various ways to the human body:
Wikipedia - Oxygen Toxicity
NIH - National Library of Medicine - Pulmonary challenges of prolonged journeys to space: taking your lungs to the moon
From the article:
The earliest measurements of pulmonary function in space flight date back to the early 1970s during the Skylab series of flights. The principal measurement was that of vital capacity. Data from an 84-day period in zero gravity on Skylab 4 showed about 10% reduction in vital capacity compared with before and after flight in the three crew members.11 However, because of the physical structure of the Skylab space station (it was built in the fuel tank of a rocket upper stage), the absolute cabin pressure was only 258 mmHg, and in order to avoid severe hypoxia, the fraction of inspired oxygen (Fio2) was 0.70 (70%). Ground chamber tests with a comparable atmosphere also showed a similar reduction in vital capacity, likely through the development of some atelectasis.
Just because some people never did the required reading, or were never curious enough to know to begin with, doesn't mean that's applicable to everyone.
Atelectasis
Nobody has used the exact atmospheric composition that RobertDyck has proposed using, but that doesn't mean we can't draw useful inferences from our Skylab missions and NASA's ground hyperbaric chamber testing that preceded the Skylab missions.
Here's what I think will happen, and what most likely will happen over time:
Over a significantly longer period of time, those living at 8psi with a 40% ppO2 will also develop atelectasis. The onset and severity of the symptoms (reduction in pulmonary capacity) will not be as fast or severe, but it will still happen.
Why do I think that?
1. Prior testing done for the Skylab missions, on the ground and at 1g
2. The actual mission data which mirrored ground testing, completed in micro-gravity
3. What we know about the human body's tolerance for abnormal life support conditions (there's no hard line between what's tolerable and what's intolerable, similar to poisoning and radiation doses- all we really know is that "more" of certain things is not equal to "better", much less equal to "desirable")
I'm willing to take that risk, because the risk of aerobullosis is even greater for people doing frequent EVA activities, and aerobullosis (aka, "the bends") can be immediately fatal.
Everything is a trade-off in engineering. Lower pressure environments are another form of trade-off. In return, we gain zero pre-breathe EVA capabilities that present little to no risk of "the bends" (which is an exceptionally serious and possibly immediately fatal medical condition). Gradual onset of atelectasis is a less serious medical condition, but over time it will become a problem.
I will repeat myself one final time here:
Human beings are best adapted to operate at 1g (9.81m/s^2) and 14.7psi of atmospheric pressure, with about 21% O2 and about 78% N2.

SpaceNut · 2022-05-30 08:45:05

tahanson43206 wrote:

For kbd512 re RobertDyck's Atmosphere prescription...
Thank you for your detailed follow up on your (quite surprising to me) revelation that you have serious doubts about the long term sufficiency of the atmosphere prescription recommended by RobertDyck.
Your example of experience on Skylab is instructive, to show what NOT to do.
In a quick search of the internet (with the assistance of Google) I confirmed that people have lived on Earth for extended periods at 500 Mg. And ** that ** is at normal oxygen for that altitude. One citation gave forty years as the time period for a mining village in Peru.
The experience of that set of people would surely be instructive, just as the experience of Skylab was instructive on what NOT to do.
In any case, your NOW PUBLIC caution is available for everyone to study.
It is clearly indicated for someone to set up a Mars Simulation at the Peru mining village, and to supply the RobertDyck atmosphere prescription for an extended period. The cost would be modest, compared to flights to Mars, and the scientific study should be valuable.
Your concession that the atmosphere prescription offered by RobertDyck might be useful for preventing bends after EVA is encouraging but not conclusive.
The gentleman you spoke to might not be aware the atmosphere he is publishing for his space station is too high.
It is entirely possible that if the reasons for the RobertDyck atmosphere prescription are offered to him, he might appreciate the savings that will result by the reduced pressure on the interior walls of his space station, and the distinct advantage that his customer/guests can go for space walks conveniently and safely.
What is more, if the budget available is sufficient, this gent might be willing to secure funding for an experimental scientific station in Peru (or a comparable site in the US if there is one). Having searched previously, I am pretty sure the US has no mountains tall enough to deliver 500 Mb as the base pressure.
Your concern about possible negative impact of 500 Mb pressure on human beings over long periods deserves to be given the attention it deserves.
Thanks again for taking the time to explain your concern in the first place, and then to follow up with a detailed explanation of recorded experience of what NOT to do.
(th)

SpaceNut · 2022-05-30 08:45:27

kbd512 wrote:

tahanson43206,
The danger of "the bends" occurs DURING the EVA (when it's very difficult for anyone else to help you if you're totally disabled)!
We don't need a research station in Peru. We can simulate any artificial atmosphere environment we choose in a NASA or US Navy hyperbaric chamber. NASA did that prior to their Skylab missions, because until their biomedical research was conducted nobody actually knew what the results would be. Now we know. We already know that humans can adapt to lower levels of O2 over significant periods of time. We also know that humans can survive much greater ppO2 at greatly reduced total atmospheric pressure (74% ppO2 at 5psi, the Skylab station's atmosphere). We also know that such atmospheric compositions are NOT ideal from a human physiology standpoint, so we're accepting an engineering and biomedical trade-off in return for something else that we want (zero pre-breathe EVA). If you suffer a serious bout of "the bends" during an EVA, then there's a better than average probability that you will die before we can get you into a hyperbaric chamber.
I would like to plainly state that I AGREE with RobertDyck about what the atmospheric composition should be, if we need a bunch of people to perform a bunch of EVAs to construct the Mars base. However... Long term, as in "the rest of your natural life", the human body is best adapted for 14.7psi, period. Millions of years of evolution have "made that so", and it should come as no surprise to anyone that "it is so".

SpaceNut · 2022-05-30 13:16:51

GW Johnson wrote:

There is a switchover in the body when breathing Earthly air below and above 2500 m = 8200 ft. It switches from holding blood CO2 concentration constant at variable O2 concentration below that point, to maximizing blood O2 concentration with a rapidly-reducing blood CO2 concentration, as you go higher and higher. That 2500 m = 8200 ft altitude is the critical point for developing chronic mountain sickness in a significant portion of the population if you live at altitude.
Presumably the "collapsed lung" risks would go along with all the other risks of chronic mountain sickness. It's all ultimately driven by biochemistry, which is not my specialty, so don't ask. I've told you all I know.
I posted an article on "exrocketman" that uses data published in AAAS's "Science" journal about this chronic mountain sickness/long-term hypoxia problem. It was more of a news article than a research report, but it cited data derived from studying populations living at high altitudes in the Andes and elsewhere. I used the data associated with that critical elevation, as a long-term hypoxia criterion to recommend some habitat and suit atmospheres, such that EVA's with no pre-breathe were possible, while also avoiding risk of long-term hypoxia/chronic mountain sickness in the habitat. I also looked at fire danger.
Childbirth problems do seem to correlate as part of the multiple health risks associated with chronic mountain sickness. The “Science” article mentioned that, in the context of the Spanish colonial experiences 4 and 5 centuries ago, and continuing ever since. That's really why I chose to use the "Science" elevation data for developing my long term hypoxia criterion. It's not a sharp thing, the risk of chronic mountain sickness seems to be zero below 2500 m, and increases rapidly with altitude above it, to something like at least 25% at 5100 m. That was a mining town in Peru.
According to the standard atmosphere table, the pressure at 2500 m = 8200 ft is 0.7373 that of sea level. In other words, you can safely breathe 20.94% O2 diluted with N2 (or N2 plus a dash of Ar) down to a total habit pressure of 10.835 psia. Below that pressure, you must increase the oxygen percentage to avoid the risks of long-term hypoxia/chronic mountain sickness (and presumably elevated childbirth risks).
In a two-gas mix of O2 and N2 at 10.835 psia and 20.94% O2, the N2 partial pressure is 8.5662 psia. The no pre-breathe ratio of 1.2 then says the pure O2 suit pressure must be at least 7.138 psia to avoid the bends risk. Which neatly explains the trend toward higher suit pressures proposed by the traditional vendors, both here and in Russia.
But this ignores the long history we have of using 40% O2 in hospitals at elevations as low as sea level. That is an O2 partial pressure of 0.40 atm at sea level, lower at elevation. The risk is oxygen toxicity, for which the rule of thumb from diving has been 1 atm pure O2 kills half the people breathing it, and 2 atm pure O2 kills all the people breathing it. The hospital oxygen mask at 0.4 atm seems to provide much benefit without killing anybody. So, even without considering vented oxygen masks at high altitudes for air crews, with which we also have over half a century of experience, I think a rough limit for avoiding oxygen toxicity might be the hospital max 0.4 atm partial pressure.
I think the proposed hab atmospheres that Rob and I bandied back-and-forth all meet the long-term hypoxia/chronic mountain sickness criterion, the oxygen toxicity criterion, my wet-in-lung hypoxia criteria (both long and short-term), and the factor 1.2 for no pre-breathe, for suit pressures near 3 psia. And these atmospheres present no more fire danger than warm sea level Earthly air (based on oxygen mass concentrations in kg/cu.m), as would be used in a 1-step, 2-component Arrhenius reaction rate equation model. They are all near 40-45% O2 in 0.40-0.45 atm total pressure.
For the record, the article in which I addressed a long term hypoxia criterion based on risks of chronic mountain sickness (related to childbirth difficulties) was "Habitat Atmospheres And Long-Term Health", posted 1-11-2022 on "exrocketman". The update for 2-2-2022 addresses CO2 displacement effects for the alveolar gas equation. I don't use it because nobody knows or agrees on what the correct blood CO2 concentration is, above 2500 m.
So, they don't know what the "right" value is, to use in the alveolar gas equation, when total pressures are under 10.835 psia. Using the below-2500 m values leads to too much displacement, too low an alveoloar O2 concentration estimate, and thus too high a recommended suit pressure (surprise, surprise!). It is already known to produce incorrect estimates for mountain climbers above 2500 m.
I just use the "wet" oxygen concentration in the freshly-inhaled air for my criteria and analysis. Those data for water vapor displacement are very well known.
GW
PS -- I had meant to sign in and participate yesterday evening, but had received some very disturbing news that afternoon, and was in no condition or fit state to do so. Maybe next time.

SpaceNut · 2022-05-30 13:17:13

tahanson43206 wrote:

For GW Johnson re #327
Thank you for once again posting on this important subject, in the NewMars forum.
Clearly it is helpful to keep repeating these posts, because (obviously) not everyone has read them, or is aware of them.
I hope that whatever came up on Sunday is something that can be dealt with in time. Not everything can.
***
Had you ** BEEN ** able to attend, and assuming the conversation was similar (which is unlikely with a third party present), you would have heard the question posed: Why does the space station proposal at the Gateway web site show default Earth sea level atmosphere?
The snap reaction was that humans evolved with that atmosphere, so there is no reason not to go with it.
In fairness, there ** was ** acknowledgement of the value of the Atmosphere proposal from RobertDyck, which comes pretty close to yours ...
By choosing partial pressures carefully, a Mars resident or space craft traveler can go EVA with no (or greatly reduced) risk of the bends.
I would like to think that the designers of the Gateway space station are simply unaware of the work done by Mars Society members and others, to arrive at the Atmosphere Prescription published here multiple times, and in multiple topics.
If the designers ** were ** aware of the Mars Habitat atmosphere prescription, as published here, they might well embrace the recommendation for many reasons.
***
All that being said, it ** is ** possible to test the Mars Prescription on Earth, by building a Mars Habitat Simulation facility at that mining site in Peru, if the government of Peru is willing to support such a venture.
The participants in such a venture would be using ** real ** EVA suits when they step out of the habitat, instead of pretend ones such as (I understand) are in use at the Utah facility.
Ideally, the experiments would be set up, supervised and reported upon by ** real ** scientists, supported by eager volunteers I am sure.
(th)

SpaceNut · 2022-05-30 13:17:41

kbd512 wrote:

GW,
Nobody in a hospital is breathing 40% ppO2, except after a serious injury or during the terminal phase of their life. We don't have many people breathing 40% O2 for months to years on end, and virtually all of those people would otherwise be dead much sooner without increased O2 concentration. I never stated that it wasn't feasible to use higher ppO2 at reduced total pressure, either, merely that it wasn't ideal from a human physiology standpoint.
We're making concessions here to eliminate EVA pre-breathes, and we should be honest with everyone about why we're really doing this, rather than coming up with false justifications for why this shouldn't affect people, especially when we know that it will affect people over time.
NASA's own fire research aboard ISS shows that O2 concentration as a total percentage of the atmosphere is what increases the flammability of various materials:
Oxygen Partial Pressure and Oxygen Concentration Flammability: Can They Be Correlated?

SpaceNut · 2022-05-30 13:27:59

https://www.ncbi.nlm.nih.gov/books/NBK493219/

https://www.ndafp.org/image/cache/12H.pdf

https://www.ncbi.nlm.nih.gov/books/NBK482268/

SpaceNut · 2022-05-30 18:13:49

GW Johnson wrote:

What the cited report calls "oxygen concentration" is really the volume percent oxygen.
What I used is the oxygen concentration expressed as mass of oxygen per unit volume of total gas. That has the units of density, being kg/cu.m, not volume per unit volume. That sort of thing worked very, very well for me decades ago, when I tried to model fuel-air reactions in the flameholding zones of ramjet engines. My models actually did successfully predict combustor blowout and ignition limits as functions of air delivery conditions, mixture ratio, and physical size.
I was using an Arrhenius reaction rate expression r = C Cfuel^r Coxy^(n-r) exponential T factor, to model 1-step 2-component overall reactions that were of order 2 (n = 2) with a near-unity exponent on the fuel concentration (r = 1). It worked just fine. So why would it not work for a flammable immersed in some sort of habitat air? I don't think anyone could say "no, it won't work".
As for 40% oxygen masks in hospitals, there are those who are supplied this way for weeks at a time. For any of a variety of reasons. Ignoring the breathe-back breath displacement in the vented mask, that is oxygen at 0.4 atm partial pressure at sea level, lower at elevation. Deaths are not attributed to oxygen toxicity, near as I can tell.
As for pilot oxygen masks, the Navy says go on 100% oxygen at 5000 feet, the Air Force at 10,000 feet. These are vented, so the pressure inside the mask is the same as the ambient atmospheric pressure. The Navy criterion corresponds 0.83 atm partial pressure of oxygen, ignoring any displacement by exhalation or water vapor. The Air Force criterion corresponds to 0.68 atm partial pressure of oxygen. Both have been used, with ZERO oxygen toxicity reported, for over half a century now.
What I was taught decades ago in scuba diving class was that 1 atm partial pressure of oxygen was lethal to about 50% of the people breathing it (exclusive of any exhalation or water vapor displacement effects), and that 2 atm partial pressure was lethal to 100% of those breathing it. Which is why pure oxygen breathing rigs are restricted to a maximum depth of 33 feet, and then only for military use.
0.4, 0.68, 0.83 atm, makes little difference. It's a fraction of an atmosphere. Choose the lowest: 0.4 atm is the most restrictive oxygen toxicity limit that has any roots in real human experience. And NONE of the proposed atmospheres by either Rob or me come anywhere close to that limit.
Volume fraction x total pressure = partial pressure. That's straight from the gas laws.
In my last posting on exrocketman about this topic, I didn't try to force a low oxygen suit pressure and from it derive a hab atmosphere. I worked the other way around from my wet in-lung inhalation oxygen partial pressure allowing for water vapor displacement, but ignoring the carbon dioxide displacement effect.
Both my analysis and my criteria are based on this inhaled wet oxygen pressure, so they are consistent. All I did was add a long-term hypoxia/chronic mountain sickness criterion based on the data I found in the "Science" journal.
Using that long-term hypoxia criterion to set hab atmosphere, I fell in the very same ranges that I fell into before, around 0.4 to 0.45 atm at around 40 to 45% oxygen by volume. The corresponding zero-pre-breathe suit pressures still fell nearer 3 psi, than anything I see out of NASA (or the Russians).
That being the case, why would I continue to worry? Especially since the fire danger concentrations all fell below (or well below) the 0.275 kg/cu.m oxygen concentration of 70 F sea level air?
Go look at my article on "exrocketman". I think you will find most enlightening. And far more sophisticated than the usual papers I see coming out of NASA.
GW

Mars_B4_Moon · 2024-03-02 08:08:30

GW Johnson has a configuration of gases he remembers by the Rule of 431, RobertDyck's formula 3-5-8

"Ground Space Station" built jointly by Harbin Institute of Technology and CASC is now online. This landmark facility can simulate nine space environmental factors, including low temperature, vacuum, and electromagnetic radiation

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#51 2020-02-15 18:30:55

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#52 2020-02-15 19:00:06

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#53 2020-02-15 19:38:46

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#54 2020-02-16 14:06:29

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#55 2020-02-16 15:25:35

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#56 2020-02-16 15:29:28

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#57 2020-02-16 16:31:43

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#58 2020-02-16 17:25:11

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#59 2020-02-16 17:39:18

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#60 2020-02-16 17:57:21

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#61 2020-02-16 19:00:09

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#62 2020-02-16 19:20:23

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#63 2022-05-30 08:44:44

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#64 2022-05-30 08:45:05

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#65 2022-05-30 08:45:27

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#66 2022-05-30 13:16:51

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#67 2022-05-30 13:17:13

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#68 2022-05-30 13:17:41

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#69 2022-05-30 13:27:59

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#70 2022-05-30 18:13:49

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

#71 2024-03-02 08:08:30

Re: Optimal air pressures.. - Which is best? More O2 or more pressure?

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