56 votes
Accepted

Why aren't spacecraft and spacesuits pressurised to 2.5 psi (17 kPa) of pure oxygen?

The sum of all partial pressures in the lungs must add up to the ambient pressure. The composition of gas inside the lungs includes the vapor pressure of H₂O at body temperature which is about 0.9 psi....
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  • 6,788
38 votes

When staying indoors, can missing gravity be replaced with blowing air?

in a building or closed vehicle on another planet, maybe air pressure could be used to imitate gravity There is no need to imitate gravity on another planet, because planets have gravity. Of course, ...
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37 votes
Accepted

How could the 2018-08-30 Soyuz MS-09 / ISS leak be so slow?

The ISS is at 1 bar, i.e. 1 kgf/cm2, or 10 gramsf/mm2. So the pressure on that 2 mm hole is 31.4 gramsf, well within the range a human finger can handle. Also, the ISS is really big compared to the ...
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  • 122k
29 votes
Accepted

If there's a hole in Zvezda module, why didn't all the air onboard immediately escape into space?

It would take around 7 hours to depressurize the ISS through a bullet hole. See http://www.spaceacademy.net.au/flight/emg/spcdp.htm Smaller holes will take longer. A tiny crack might take days to even ...
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  • 4,375
20 votes

How could the 2018-08-30 Soyuz MS-09 / ISS leak be so slow?

This is the image of the hole (news source, although the image is from NASA) The hole is 2mm in diameter. Even with a total vacuum on the other side, you're not talking a lot of volume getting ...
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  • 6,810
18 votes
Accepted

Why does the Falcon 9 use turbopumps as well as helium pressurisation system?

Pumps are great at creating positive pressure, hundreds of bars. But with tank at ~1 bar, atmospheric pressure, they can only create a grand total of 1 bar of suction - can't go more vacuum than ...
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  • 52.7k
18 votes

If there's a hole in Zvezda module, why didn't all the air onboard immediately escape into space?

The pressure difference between the inside and outside of the ISS is one atmosphere. This is the same pressure difference between the bottom of a 10 meter tank of water and the outside at sea level or ...
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16 votes

When staying indoors, can missing gravity be replaced with blowing air?

While not strong enough to produce "artificial gravity" in a microgravity environment such as an orbital space station (eg ISS), it should still be noted that air circulation, and ...
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  • 15.1k
15 votes

Why do pressure-fed systems have to be pressurized with helium or nitrogen?

Interesting and non-trivial questions. Most propellants are not self-pressurized because as soon as the engines turn on the pressure would drop precipitously as the tanks quickly emptied and the ...
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  • 3,857
15 votes

What keeps the pressure stable inside the ISS?

Wikipedia has a good overview of the ISS's ECLSS. This paper also includes some details. In particular, the Atmosphere Control and Supply (ACS) The ACS subsystem provides cabin atmosphere pressure ...
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  • 2,144
13 votes

What is the deepest place on Mars? Do humans need pressurized suits there?

Is there any particular deep areas of Mars in which a person could survive with only an oxygen supply without a pressurized suit? No. Hellas Planitia is the lowest point on Mars, the basin floor is ...
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  • 3,216
13 votes
Accepted

why do under-expanded engines have less than ideal thrust?

The hard part is that $P_e$ isn't a completely independent variable. As the gas expands past the throat, thermal energy is being converted into kinetic energy. The gas cools down and speeds up. So ...
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  • 5,812
13 votes

Why aren't spacecraft and spacesuits pressurised to 2.5 psi (17 kPa) of pure oxygen?

A mix of 79 % nitrogen and 21 % oxygen at a pressure of 1 atm, 14.7 psi or 1.01 bar is more fireproof than pure oxygen at a pressure of 0.21 atm, 3.087 psi or 0.212 bar. The partial pressure of oxygen ...
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  • 47.3k
12 votes

If there's a hole in Zvezda module, why didn't all the air onboard immediately escape into space?

It is easy to conduct simple home experiments, or even do them as thought experiments to determine the answer to this question. Think of a child's balloon. Inflate the balloon with air whilst holding ...
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9 votes
Accepted

What is the deepest place on Mars? Do humans need pressurized suits there?

To Or how deep would one have to be in Mars not to need a pressurized suit? and starting with @Rob's values and Planetery-Science.org's scale height of about 10.8 km to at least roughly ballpark ...
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  • 148k
8 votes

What effects did the different air pressure and air composition in certain spacecraft have on astronauts?

The partial pressure of oxygen (ppO2) should be higher than about 0.16 bar and lower than about 0.4 to 0.5 bar for longer exposition of some days up to a week. So breathing pure oxygen for a week is ...
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  • 47.3k
7 votes
Accepted

How to drink water on Mars?

Nobody is going to drink the water on Mars directly. It has to be filtered first. On the Apollo spacesuits, food and drink was carried internally. The port was for emergencies only. The moonwalkers ...
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  • 122k
7 votes

Why do pressure-fed systems have to be pressurized with helium or nitrogen?

Given that you are using a liquid propellant you cannot rely on its own compressibility to achieve the required pressure. Liquids do not compress very well. This is especially true as you need a high ...
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  • 71
7 votes
Accepted

Can exit pressure of nozzle be less than atmospheric pressure?

Sure! That's called "overexpansion" because the flow is expanded too much to match the ambient pressure. ME 239: Rocket Propulsion: Over- and Under-expanded Nozzles and Nozzle ...
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6 votes

Temperature and pressure of rocket exhaust

The temperature and pressure inside the engine's combustion chamber is very high -- in the ballpark of 3400º C and 100 atmospheres for the Falcon Heavy's Merlin engines. However, the bell-shaped ...
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6 votes
Accepted

Is the risk of depressurization greater in atmosphere than in orbit?

Ascent and descent are relatively dynamic. Large amounts of energy are being transformed and redistributed very rapidly and violently. On ascent in particular, there is the potential for the booster ...
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6 votes

How does the chamber pressure affect the performance of a Rocket Engine?

Yes, it is absolutely true. On this graph you can see the ISPs (aka exhaust velocity) at different mixture ration and chamber pressure. The higher the pressure the higher the velocity and thus delta/...
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  • 12.2k
6 votes

Why does the Falcon 9 use turbopumps as well as helium pressurisation system?

In a turbopump feed system it is still necessary to pressurize the tanks slightly (10 to 50 lb/in2) in order to prevent pump cavitation. Rocket Propulsion Elements, Sutton, 4th edition, p. 223 ...
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6 votes

How is the pressure within the gas generator determined?

"If the pressure in the combustion chamber has to be exceeded by the pressure provided by the pumps, is it also exceeded by the pressure in the gas generator. " Just to be clear, there's no &...
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5 votes

How could the 2018-08-30 Soyuz MS-09 / ISS leak be so slow?

It's not really that the leak was slow, more that it took some time to manifest: Another source told the news agency the worker did not report the error and instead applied a sealant of some sort. ...
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  • 264
5 votes

Ambient pressure for vaccum nozzle design

Since the pressure in space is never completely zero i will need a value for the ambient pressure for moving on with the design. Looks like you only consider the Isp to get the area, and your model ...
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  • 321
5 votes

What was pressure and temperature of LM oxygen tanks?

(Partial answer) The LEM had ... ... four oxygen supplies : two, in the descent stage, provide oxygen during the descent and lunar- stay phases of the mission: two, in the ascent stage, ...
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5 votes
Accepted

Do lower pressure pressure-fed rockets get more Delta-V?

First of all: great observation! This is indeed the reason why pressure fed rocket engines are limited in possible chamber pressure, the added weight from the tanks isn't worth it at a certain point. ...
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  • 715
5 votes

Pressure levels inside rocket liquid oxygen tanks?

According to the Flight Manual, the Saturn V upper stage LOX tanks were maintained at 38-41 psi (2.6-2.8 bar). The first-stage LOX tanks were kept at lower pressure, 20-24 psi (1.4-1.7 bar). It ...
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4 votes
Accepted

How much does pressure on Mars change with weather?

Publications with atmospheric pressure data on Mars are rather scarce. This publication about seasonal cycles at Gale Crater shows the chart below with the atmospheric pressure ranges near the ...
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  • 7,196

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