37

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 hole. It takes a long time for hundreds of m3 to evacuate through a 2 mm hole.


20

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 through that hole. I used this calculator with a pressure gradient of 101kPa (ISS standard) and 0.1 kPa through a 2mm hole and got a water flow rate of ~0.1 cubic ...


19

As suggested by OrganicMarble in a comment, nitrogen is miscible with oxygen (you can thus make liquid air). According to NASA Technical Paper 2464, this is a major concern because using "enriched air" instead of pure oxygen as the oxidizer degrades the performance of the engine: The transfer of liquid oxygen (LOX) from a storage vessel to a ...


18

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 vacuum, can't create a negative density, can only go from original to zero - and 1 bar of pressure is a pretty meager amount, when this kind of flows is involved. ...


13

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 about 7,152 m (23,465 ft) deep and the pressure is 1.16 kPa (0.168 psi). The average surface pressure of Mars is 0.6 kPa (0.087 psi). The highest point, Olympus ...


13

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 if you shorten the nozzle (creating an underexpanded flow), there is greater pressure at the exit (good). But the exhaust speed $v_e$ is lower (bad). The $\...


8

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 possible when the total pressure is not above 0.4 bar. See also my answer to the question How long were the Apollo astronauts allowed to breathe 100% oxygen at ...


7

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 an answer: altitude (km) pressure (kPa) -7.15 1.16 0. 0.6 25. 0.03 $$P(h) = P_0 \exp\left( -\frac{h-h_0}{h_{...


6

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 nozzle of a rocket engine expands the exhaust stream, which both cools it and reduces its pressure. Ideally, for best performance, you want the exit pressure to ...


6

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 to disassemble itself in an uncontrolled manner, which could easily cause major damage to the crew capsule; descent and reentry is a little safer, but the forces ...


6

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 from Apollo 13 onwards had a drink bag installed inside the suit which allowed them to drink when wearing the pressure suit on the Moon. Shepard and Mitchell ...


6

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 Configurations It has a negative effect on the thrust shown in this equation: $$Thrust = \dot{m}V_e +(p_e-p_0)A_e$$ if exit pressure ($p_e$) is less than ambient ($p_0$) the ...


6

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 Different vehicles have used stored onboard gas (typically helium) or autogenous propellants to provide this pressurization. Further reading: Why does the Falcon 9 ...


5

(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, during the ascent and rendezvous phases of the mission. The caution and warning limit values can tell us the range of pressures expected to be nominal. An ...


5

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. After two months in orbit, the sealant apparently dried out, the source said, and was expelled by the cabin air pressure, opening up a leak. (The article is ...


5

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 always gives bigger Isp with bigger area. As soon as you're interested in something else - mass of the nozzle, for example - or the model of the nozzle is ...


4

On most of Mars, the air pressure is ~600 Pa, which means any exposed ice will sublimate. You'd have to seal the ice in with a layer of another material. Also, if you were to evaporate ice to a pressure of 1 bar, you'd have an atmosphere consisting entirely of water vapor. You'd have continuous rain inside your cavern. The next question would be if humans ...


4

Probably it will not work. The problem is that gas molecules have a wide distribution of velocities; most molecules in a gas are not really close to the rms velocity. Over the course of billions of years we should expect faster molecules to escape. At some point all the molecules have become "faster" at one time or another and make a run for it. To ...


4

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. Which is why we have pump fed rocket engines. Question 1: Some equations from Ideal Rocket Theory: Specific Impulse is the characteristic velocity divided by ...


3

From the Apollo Document NASA TN D-6724 APOLLO EXPERIENCE REPORT - LUNAR MODULE ENVIRONMENTAL CONTROL SUBSYSTEM a large descent-stage gaseous oxygen tank (approximately 48-pound capacity at 3000 psi) and two ascent-stage gaseous oxygen tanks (approximately 2.4-pound capacity each at 900 psi). A pressure regulator was used to reduce the high pressure ...


3

Sutton, 4th edition, page 288 gives: $\dot w = C_d A \sqrt {2g \rho \Delta p} $ so, trivial to arrange for $\Delta p $....but you have to get $C_d $ somehow. Sutton gives the following chart This is probably OK for estimation. Real-world it's probably first CFD and then measured experimentally.


3

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 landing site of the Mars rover Curiosity. The width of the band is an indication of how the pressure varies throughout each sol. The seasonal ups and downs ...


2

This supposed to go in comments because it's not a complete answer but I got to put it here. I'm considering rocket scales based upon LEO payload. Micro - payload to LEO in few kgs, Small - payload to LEO in few hundreds of kgs. medium - payload to LEO in few tons. heavy - payload to LEO in few tens of tons. ultra heavy - payload to LEO in few hundreds of ...


2

One thing you might want to do is be prepared for some low numbers. Even during a storm, the density of Martian dust in the air is much less than that of the gases. According to Martin[1]: During the peak of the 1977b storm, a total dust mass of approximately 4.3 × 10^(14) g was suspended, equivalent to 4.3 × 10^(−4) g/cm^2, or a layer 1.4 μm thick. ...


2

Yes, the chamber pressure in a pressure-fed engine must be lower than the propellant supply pressure. For example, the space shuttle Orbital Maneuvering System engine operated at a chamber pressure of ~130 psi and was fed from tanks pressurized to ~250 psi. Another issue that is going to limit the thrust from that demonstration engine is that it doesn't ...


2

Although it's an older question I just wanted to say that above answer uses the Young's modulus incorrectly. It is not supposed to be in the strength calculation. The sigma refers to a maximum strength (same units though force/area). One typical value you could use is the yield strength of the material but you could also use another value the designer is ...


2

The shuttle/ISS suit is protected from excessive crush loading by a negative pressure relief valve (NPRV). This valve opens when the outside pressure exceeds the inside pressure by 0.8 psi and allows gas to flow into the suit. This could come into play during repressurization of the airlock. The following image shows the NPRV and its position in the EVA ...


1

Writing an answer to summarize discussion in comments and hopefully generalize a bit. The most important takeaway is that the De Laval exit velocity equation (found on Wikipedia, also equation 3-14 in Sutton, 4th edition) requires that you use the properties of the combustion chamber as inputs into the equation. This includes the temperature rise due to ...


1

A spacesuit is designed to be strong in tension, not compression. Most parts of a space suit are soft. If you try to suck all the air out of a space suit at sea level, the suit will simply compress flat. Sea level air pressure is 14.7 pounds per square inch. So every square foot of space suit would have to hold back a force of 2000 lbs. You would need ...


1

For a pressure fed engine, the propellants entering the combustion chamber are at a significantly lower pressure than the propellant tank pressure - otherwise they wouldn't flow the right way. You'd have to do something to increase the pressure of the fluid that was headed back up to the tank ullage, otherwise your pressurization line would flow the wrong ...


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