# Tag Info

136

We can breathe pure oxygen for unlimited time if the pressure is not too high; about 0.4 bar is okay. Breathing pure oxygen at 1 bar is possible for some hours, but a longer time may damage the lungs. A mix of oxygen and helium is also breathable and is used for deep diving. Xenon cannot be used due to its narcotic effect on the body. Argon is less ...

112

(*) Jupiter, for all intents and purposes, doesn't have a solid surface to stand on. Not any more than you could say that Earth's atmosphere has it, before you hit Terra Firma. It's an enormous ball composed of mostly Hydrogen and Helium, but also other heavier elements in smaller parts, and it's so massive that its own gravity compresses these gases into ...

69

Am I not considering something? Yes. You are not considering Mir, Soyuz, and the Space Shuttle. The International Space Station is a multinational program, jointly led by the US and Russia. While the US and Russia had to compromise on many design decisions, the makeup of the breathing atmosphere was not one of them. The decision to pressurize the ISS to ...

64

Although the temperature at altitude can be several thousands of degrees, the atmosphere is so thin it does not transfer heat efficiently. Wikipedia explains it very well - The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is ...

62

I've done a lot of work on this subject with researchers and engineers at JPL, NASA Langley, and NASA Ames. There are some interesting things that come out of high-fidelity CFM (Computational Fluid Mechanics) modeling of entries or re-entries, and also from flight experience. This FAA tutorial segment is a good general reference for the principles involved. ...

53

“Bouncing off the atmosphere” is a misleading turn of phrase. When returning to the Earth from the Moon, a spacecraft is on an elliptical orbit with the high end somewhere around the moon’s altitude and the low end just grazing the top of Earth’s atmosphere. The concern around a too-shallow reentry angle is that it won’t slow the spacecraft enough for a ...

36

It can keep an atmosphere, and in fact does. The atmosphere is something akin to a high grade Earth-based vacuum. But that's probably not what you are looking for. Okay, so what would happen with, say, an Earth sized atmosphere on the Moon? A lot of really interesting things would happen actually. First of all, in longest days of the night, the atmosphere ...

32

It's not the temperature that matters, it's the heat transfer. The density of the atmosphere up in the thermosphere is very very thin. There simply isn't nearly enough mass to transfer any significant amount of heat from the thermosphere to a spacecraft travelling through it. Spacecraft do need heat protection to survive re-entry, but that is because they'...

31

Rockets are much faster than airplanes for most of their flight. Here's a graph of a Space Shuttle launch: The red line is speed. It's in ft/s, 1000 ft/s is 1097 km/h. So At about 45 seconds, the Shuttle flies 1000 km/h which is faster than an airliner. At about 1:40 it crosses 3000 ft/s which is about Mach 3 (the speed of the fastest aircraft). ...

30

The short answer is no -- an internal combustion engine needs to pull oxygen from the air to operate, and no solid bodies in the solar system have that kind of atmosphere. Venus' atmosphere is mostly carbon dioxide with a small amount of nitrogen; neither of those is combustible. Mars, similarly, has a mostly inert atmosphere; there's a trace of oxygen ...

28

I'll give you the numbers. I'm breaking this up into 3 different terms. There's atmospheric drag, what I'll call the "hover" term, and the gravitational potential climb. I will more or less assume a flight directly up. You're welcome to use whatever term for velocity you want, as none of them will be representative. I'll take the Shuttle's speed at ...

27

The Chelyabinsk meteor was travelling at over 65,000 km/h when it hit the brunt of the atmosphere 23 km high in the air. This is 60 times the speed on sound! NASA estimates that the meteor's mass at this point was 10,000 tonnes, and it had a diameter of 20 meters. At these incredible speeds, the body is placed under immense stress. Colossal pressure is ...

26

In order for a combustion process to happen, you do not only need fuel, you also need an oxidizer. On Earth, that is usually the oxygen in the air. In Titan's atmosphere, there is no oxygen. This applies to other atmospheres too, like the hydrogen dominated atmospheres of Jupiter and Saturn. Hydrogen, just like the methane in Titan's atmosphere, is flammable ...

25

Buoyancy is a big problem. To stay aloft, the average density of the balloon envelope, lifting gas and gondola must be <= the density of the surrounding atmosphere. The pressure inside a balloon must be equal to or slightly greater than the surrounding atmosphere, otherwise the balloon will collapse. If you look at the ideal gas law you'll see that see ...

25

Short answer: Yes. Mars is not windy enough to properly wave most flags. Long answer: In storm conditions, a flag constructed out of a very light material would be able to properly wave. If we take a standard flag, say 3'x5' that's made of 200g Nylon $\ell= 1.5$ meters $h_f = 0.9$ meters $W = A * 0.2 * g_{Mars}$, $W = 1$ Newton Going off the calculations ...

25

No, unless your structure is located directly on the equator and your satellite follows a perfectly circular orbit, atmospheric "orbits" aren't possible, even in a vacuum tunnel. Because the Earth is on an axis of ~23 degrees and rotates every day, it is not possible to create an orbit which has no ground track precession except for equatorial ...

23

Based on saturation diving operations, it looks like the limits are as follows: Compressed air: Nitrogen narcosis limits you to around four times Earth's atmospheric pressure. Any gas mix: Hydreliox was used for the current depth record; insomnia and fatigue issues appear to limit you to around 65 times Earth's pressure regardless of gas mix. Neither Titan ...

23

Yes, a capsule cannot literally bounce off the atmosphere and its kinetic energy must be reduced by an encounter with the atmosphere, rather it would just pass through the atmosphere and back into space, having failed to lose enough velocity to stay in the atmosphere. After going partially around the planet it will reenter the atmosphere, that is actually ...

22

I was actually just reading a great What If? article on this found here. Flight on other planets is possible. I think the included comic strip summarizes it wonderfully: As for each valid body in our solar system (barring Earth of course), I'm going to paraphrase a bit: The Sun: Attempting flight on the sun is more or less useless as any vessel close ...

22

I would argue that no specific level of molecular or atomic oxygen in atmosphere is indicative of carbon-based life (i.e. life as we know it on Earth). A planet could have oxygen rich atmosphere which could be due to naturally occurring thermo-chemical reactions (e.g. Sabatier/Bosch reaction), loss of hydrogen in water vapor through atmospheric escape and ...

22

The mass of Titan is 1,345 · 1023 kg, but the mass of the Moon is 7,349 · 1022 kg. The gravity at the surface is 1,35 m/s² for Titan and 1,62 m/s² for the the Moon. But the surface temperatures are very different, 94 K for Titan but the mean surface temperature of the Moon is 218 K and the peak about 300 K. Due to the high surface temperature of the Moon,...

21

I think it's fairly safe to assume that Mars has plenty of nitrogen locked in its mineral deposits, since it's one of the most abundant elements of the Solar system and the planet formed out of the same protoplanetary disk as Earth has. Some nitrogen rich minerals are a safe bet, especially the ones of magmatic origins that might be easily accessible in top ...

21

Yes, humans definitely have been to outer space. The easiest proof I can think of immediately is this video of commander Chris Hadfield demonstrating wringing of a wet towel on the ISS. Or this one — it contains more than 200 seconds long uncut shot of a̶b̶s̶e̶n̶t̶ micro-gravity. It also shows vast interiors of the ISS, which are technically challenging to ...

21

Rory mentions oxygenation rate which is an excellent point but there's additional reasons why not keep ISS atmosphere at a lower pressure - thermal convection and air cycling. Pressure at roughly one atmosphere means that the ventilation system on the station works better and no pockets of carbon dioxide or even carbon monoxide build up, which would be ...

21

A rocket isn't automatically fast - a small firework rocket may be no faster than a car. The important point is that rockets carry their own oxidiser and aren't limited by the need to interact with the air. Most aircraft engines need to develop lots of thrust at low speed for take off, and they have propellers or large fans that cause drag at high speeds, ...

20

No, not really. The atmosphere of Mars is very thin. It has below 1% of the pressure on Earth. That means it has less than 1% of the force of wind on Earth with the same speed. Wind only occures at dawn or dusk. Wind happens when there is a pressure gradient between two areas of an atmosphere. Pressure gradients are caused by temparature- and humidity ...

20

Several approaches are taken. Cargo vehicles bring up Oxygen and other atmospheric components (Nitrogen, etc). The Russian segments life support system works different and independant of the US side, which is a nice redundancy model. The Russian side has a system that recycles water from urine and moisture that needs to be removed to electrolyze to oxygen ...

19

The key concept is that for a satellite at a fixed altitude, when the atmospheric temperatures below its altitude increase, atmospheric expansion pushes more atmosphere up above the satellite! At the satellite's altitude the pressure must increase to support the weight of that additional atmospheric mass above, and the increase in pressure outweighs the ...

19

As discussed here, very few satellites have ever orbited at a higher altitude than the moon, making images from lunar orbiters our highest imagers of eclipses from orbit. In fact, in order to get a 1:1 ratio of the apparent sizes of the Sun and the Earth you would have to be at ~4x the altitude of the moon - right near the edge of Earth's Hill Sphere. This ...

18

The problem here is that your standard of proof is ridiculous. By the same token, you'd have to doubt the existence of Moscow because you've never met anyone from that city. the only face to face eyewitness event that I can remember where humans actually observed an attempt to fly into outer space... Then your memory must not be very good. There have ...

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