Vacuum of space and a balloon

[Dedjal]

What would happen to the air inside the ballon if we took it out into open space and punctured it?

Would the air be dispersed quickly, slowly or stick together?

And rocket engines used in space. Does it propel itself forward by thrusting against the exhaust emitted earlier or is there actual something to thrust against in space?

Or is that how it works on earth and in space it propels itself by simply flinging stuff out the other end?

So if someone was in a raft in space, they could throw coconuts and bananas in order to accelerate themselves?

[RenevB]

If you took a balloon up to space, chances are it will pop before you get there. If you took it up in a pressurized spacecraft, then took it outside in an airlock and it would stay together long enough for someone to puncture it, the gass will be dispersed very very quickly. This is because there is some pressure in your cloud of gas and none* in space.

Rockets indeed work by simply flinging stuff out the other end.

And yes, an astronaut throwing stuff away will accelerate in the opposite direction, following Newton's law. Though he probably won't go anywhere

[Dedjal]

So the power accumulated and then released as the coconut is thrown, is transferred through the body and into the vessel it self. The coconut is pushed against.

So a rocket engine propels itself forward then, by pushing against the exhaust emitted earlier?

But that indicates that the exhaust does not get dispersed before the aforementioned craft can benefit from it, yes?

On another note. The air released from the ballon would spread quickly. But how would it spread?

And just how powerful is the vacuum?

A glass of water would freeze and stick together, so does it all come down to density?

So a gas which is denser than water would not disperse (i guess it wouldn't be gas anymore then and no such thing exist, but hypothetically)?

[magnemoe]

First communication satellite was a balloon so they work well in space, you just keep the pressure low like 0.1 bar or less you just have to inflate it.

And yes it will probably deflate faster than a 1.1 bar balloon on ground as the escaping air don't hit other air on the outside

And yes rocket works with recoil, you want something very fast exiting the ship, burning stuff to make it hot is the easiest way.

nuclear rockets heat up hydrogen, this work even better, that is why the LV-N is so good, ion engines accelrate ions to very high speed, this work even better.

[RenevB]

So the power accumulated and then released as the coconut is thrown, is transferred through the body and into the vessel it self. The coconut is pushed against.

So a rocket engine propels itself forward then, by pushing against the exhaust emitted earlier?

But that indicates that the exhaust does not get dispersed before the aforementioned craft can benefit from it, yes?

The first paragraph makes no sense to me. I don't understand what you mean.

No, A rocket works by expelling stuff out of the back. It does not push against anything.

On another note. The air released from the ballon would spread quickly. But how would it spread?

And just how powerful is the vacuum?

A glass of water would freeze and stick together, so does it all come down to density?

So a gas which is denser than water would not disperse (i guess it wouldn't be gas anymore then and no such thing exist, but hypothetically)?

Wolfram alpha tells me the pressure at 100 km (the beginning of space) is about a million times less than the pressure at sea level.

IRRC, water in space will boil before it freezes, again, because the pressure is so low.

[andrewas]

So the power accumulated and then released as the coconut is thrown, is transferred through the body and into the vessel it self. The coconut is pushed against.

So a rocket engine propels itself forward then, by pushing against the exhaust emitted earlier?

No, the rocket pushes against the exhaust its emitting right now. The rocket forces exhaust gas out the back and the reaction to that force pushes the rocket forward. The earlier exhaust is moving away from the rocket at high speed and has no impact on it.

[Dedjal]

All right.

So O2 in this scenario would disperse, but then what? Would it orbit around the earth?

Or if released beyond the SOI of Earth, would it orbit the sun?

[peadar1987]

All right.

So O2 in this scenario would disperse, but then what? Would it orbit around the earth?

Or if released beyond the SOI of Earth, would it orbit the sun?

Well, a gas is actually a load of particles moving around very quickly. In our balloon, this means they are bouncing off each other and off the walls of the container. For Oxygen at room temperature, most particles move at below 500 m/s. For hydrogen, the average is about 1800 m/s, and many particles travel at up to 3000 m/s.

If you burst a balloon full of oxygen in earth orbit, the particles would be released at the speed they were travelling when you burst the balloon. 500 m/s isn't really enough speed to get you anywhere, so the particles would just move further apart in a diffusing cloud, all particles now on slightly different orbits. Some of the slower ones might now have a periapsis low enough for the orbit to eventually decay.

Hydrogen, on the other hand... 3000 m/s is escape velocity from low earth orbit. You pop the balloon, and the particles go charging off. Some were heading towards the back wall of the balloon when you popped it. They will be travelling retrograde so fast that they'll probably deorbit. Some will have been heading towards the front wall of the balloon. They will have escape velocity and head off into a solar orbit.

This is a simplified case, in reality, the earth's magnetic field and the solar wind will also get involved. The magnetic field tends to trap particles in certain belts around the earth, and the solar wind tends to strip away gases towards interstellar space.

[lajoswinkler]

Very low pressure gas behaves like an ideal gas - a bunch of tiny balls. Heat the sample enough and their speeds become tremendous, so they will escape Earth.

A regular balloon could exist in space if the amount of gas in it was low enough. Fully inflated one at 1 atm will burst at 0 atm, of course.

[Dedjal]

Well, a gas is actually a load of particles moving around very quickly. In our balloon, this means they are bouncing off each other and off the walls of the container. For Oxygen at room temperature, most particles move at below 500 m/s. For hydrogen, the average is about 1800 m/s, and many particles travel at up to 3000 m/s.

If you burst a balloon full of oxygen in earth orbit, the particles would be released at the speed they were travelling when you burst the balloon. 500 m/s isn't really enough speed to get you anywhere, so the particles would just move further apart in a diffusing cloud, all particles now on slightly different orbits. Some of the slower ones might now have a periapsis low enough for the orbit to eventually decay.

Hydrogen, on the other hand... 3000 m/s is escape velocity from low earth orbit. You pop the balloon, and the particles go charging off. Some were heading towards the back wall of the balloon when you popped it. They will be travelling retrograde so fast that they'll probably deorbit. Some will have been heading towards the front wall of the balloon. They will have escape velocity and head off into a solar orbit.

This is a simplified case, in reality, the earth's magnetic field and the solar wind will also get involved. The magnetic field tends to trap particles in certain belts around the earth, and the solar wind tends to strip away gases towards interstellar space.

Thank you! I have learned something new today.

So excluding solar wind (which destroyed my thought experiment), it could then be possible (excluding the enormous amount it would require) to pour enough O2 into the solar system, that there could be a large ring of breathable "air" (O2 is lethal, but bear with me)?

So in this theoretically ring of O2, how would it be like to be inside the ring?

Would the air be freezing, heated up through the sun?

Would the vacuum still bloat us humans?

[Dedjal]

Very low pressure gas behaves like an ideal gas - a bunch of tiny balls. Heat the sample enough and their speeds become tremendous, so they will escape Earth.

A regular balloon could exist in space if the amount of gas in it was low enough. Fully inflated one at 1 atm will burst at 0 atm, of course.

I was not really interested in the balloon itself. But rather what would happen to the air inside it. The balloon was just the means of containing it. Could have been a bucket with a lid aswell.

[phoenix_ca]

The only engine for use in space that actually propulses on something else is the Q-thruster, rather like a propeller on a ship or aircraft that applies force to the fluid it's immersed in, but it instead uses the virtual particles present everywhere and pushes off that.

[peadar1987]

Thank you! I have learned something new today.

So excluding solar wind (which destroyed my thought experiment), it could then be possible (excluding the enormous amount it would require) to pour enough O2 into the solar system, that there could be a large ring of breathable "air" (O2 is lethal, but bear with me)?

So in this theoretically ring of O2, how would it be like to be inside the ring?

Would the air be freezing, heated up through the sun?

Would the vacuum still bloat us humans?

Once you start getting to those scales, gravity starts to come into play. A ring is generally a pretty unstable structure in space, variations in density will cause the particles to begin to coalesce in certain places. This will be a slow process, but eventually the denser spots will attract more and more particles, making them bigger and denser, and therefore have more gravity. If you put enough oxygen out there, it would initially form a ring, but the ring would eventually collapse into several planets or moons made out of oxygen. Saturns rings are only stable on a longer time scale because of gravitational interactions with its other moons. The atmosphere of our oxygen moon would vary from tiny, imperceptible wisps of gas at the edge of space, through a standard gas we would be familiar with lower down, and then as the pressure increases deeper in the body, it would turn into a supercritical fluid. Essentially this is a strange state of matter where the lines between liquid and gas become blurred (it won't boil as such, it will transition smoothly from an almost incompressible liquid to a compressible gas). If you had enough oxygen in one place, you'd get to the stage where gravity outbalanced the solar wind, and you would stop losing mass.

It would probably be quite cold if it was out near earth's orbit, as it would lack most of our greenhouse effect.

Whether or not you would bloat would depend on the pressure. If it was a breathable pressure (which would require huge amounts of oxygen, obviously), no, it would be just like being on earth.

If it was a ring, to stop it from instantly falling into the sun, each one of the particles in it would have to be moving at orbital speed. That means that if you were a human inside the ring, you would indeed probably be able to float in it. If you started at rest, you would be blasted by a wind of particles moving at orbital speed. This would probably kill you, but it if didn't, they would eventually pull you up to their speed, and you would be dragged around the sun with them. Now you would be moving at orbital speed, so you'd essentially feel weightless.

[magnemoe]

Once you start getting to those scales, gravity starts to come into play. A ring is generally a pretty unstable structure in space, variations in density will cause the particles to begin to coalesce in certain places. This will be a slow process, but eventually the denser spots will attract more and more particles, making them bigger and denser, and therefore have more gravity. If you put enough oxygen out there, it would initially form a ring, but the ring would eventually collapse into several planets or moons made out of oxygen. Saturns rings are only stable on a longer time scale because of gravitational interactions with its other moons. The atmosphere of our oxygen moon would vary from tiny, imperceptible wisps of gas at the edge of space, through a standard gas we would be familiar with lower down, and then as the pressure increases deeper in the body, it would turn into a supercritical fluid. Essentially this is a strange state of matter where the lines between liquid and gas become blurred (it won't boil as such, it will transition smoothly from an almost incompressible liquid to a compressible gas). If you had enough oxygen in one place, you'd get to the stage where gravity outbalanced the solar wind, and you would stop losing mass.

It would probably be quite cold if it was out near earth's orbit, as it would lack most of our greenhouse effect.

Whether or not you would bloat would depend on the pressure. If it was a breathable pressure (which would require huge amounts of oxygen, obviously), no, it would be just like being on earth.

If it was a ring, to stop it from instantly falling into the sun, each one of the particles in it would have to be moving at orbital speed. That means that if you were a human inside the ring, you would indeed probably be able to float in it. If you started at rest, you would be blasted by a wind of particles moving at orbital speed. This would probably kill you, but it if didn't, they would eventually pull you up to their speed, and you would be dragged around the sun with them. Now you would be moving at orbital speed, so you'd essentially feel weightless.

Nivens Integral trees set up an setting where this would be possible.

http://en.wikipedia.org/wiki/The_Integral_Trees

You would need an pretty cold neutron star for the gravity field. You want a as dead as possible one to avoid radiation.

This however would not be enough to hold the air so you add an Uranus style planet but rather like an super earth with co2 and nitrogen atmosphere.

Put this in low orbit around the neutron star, most of the atmosphere would leak out but would be stuck in the gravity well of the neuron star, the uranus would help keep the atmosphere in place.

you then need a normal star in orbit around the neuron star at 1AU distance for light.

You could get one bar in center if this is set up right. the atmosphere pressure would go down far slower than on earth so the atmosphere would be deep.

The cool part is that you would get an natural micro gravity area with breathable air far larger than earth atmosphere.

[lajoswinkler]

Thank you! I have learned something new today.

So excluding solar wind (which destroyed my thought experiment), it could then be possible (excluding the enormous amount it would require) to pour enough O2 into the solar system, that there could be a large ring of breathable "air" (O2 is lethal, but bear with me)?

So in this theoretically ring of O2, how would it be like to be inside the ring?

Would the air be freezing, heated up through the sun?

Would the vacuum still bloat us humans?

That would be very difficult to achieve. It would require an immense source of gravity. With Solar system, no way.

I was not really interested in the balloon itself. But rather what would happen to the air inside it. The balloon was just the means of containing it. Could have been a bucket with a lid aswell.

If the container is not stretchable, then nothing happens, obviously.

[peadar1987]

If the container is not stretchable, then nothing happens, obviously.

Not quite. The bucket obviously wouldn't "pop", but the gas would still diffuse out once the bucket was opened. Rather quickly, if the contents were under pressure (which, seeing as you're in a vacuum, and there is some gas in the bucket, they will be)

[lajoswinkler]

Not quite. The bucket obviously wouldn't "pop", but the gas would still diffuse out once the bucket was opened. Rather quickly, if the contents were under pressure (which, seeing as you're in a vacuum, and there is some gas in the bucket, they will be)

Yes, and the container would melt if it was subjected to lava. What's your point?

A closed bucked is a closed bucket.

BTW here's the successful inflation of Echo II satelloon. Its folds were laced with powders of benzoic acid and anthraquinone (some derivative of it, possibly 9,10-anthraquinone) which would sublime in vacuum, gently opening the mylar skin. The gases would eventually escape, leaving a fragile sphere that was later wrinkled by solar radiation, micrometeorites and atmosphere drag.

[peadar1987]

Yes, and the container would melt if it was subjected to lava. What's your point?

A closed bucked is a closed bucket.

Just clarifying for the OP. You post could potentially have been misinterpreted as "the gas just sits there inside the bucket". Or at least, that's what I thought you had said at first reading.

[KerikBalm]

So the power accumulated and then released as the coconut is thrown, is transferred through the body and into the vessel it self. The coconut is pushed against.

The coconut has inertia, and will resist if you push against it, you can thus push against it, accelerating it (and yourself) in the process

So a rocket engine propels itself forward then, by pushing against the exhaust emitted earlier?

Not really. The rocket has a nozzle, the fuel/propellant has mass, and inertia, and a lot of energy, as it expands, it pushes against the walls of the nozzle, pushing the rocket forward. At very high pressure, ie right at the moment of combustion for a standard chemical rocket, the gas is pushing against itself, yes, but certainly not the exhaust emitted half a second earlier (which will be hundreds if not thousands of meters away by that point).

A rocket would produce thrust even with instantaneous pulses, not by continuously pushing against its earlier exhaust.

You could even have soldi fuel pellets/ explosives like a firecracker. Set of a firecracker in a cone in space, it will push the cone forward when it goes off. A rocket works the same way, just continuously. The exhaust pushes against the nozzle.

But that indicates that the exhaust does not get dispersed before the aforementioned craft can benefit from it, yes?

Nope, as the gas dispeses in all directions, some contacts the nozzle, and pushes against the nozzle, longer nozzles = better in a vacuum

On another note. The air released from the ballon would spread quickly. But how would it spread?

In all directions, according to the speed of the molecules within it.

And just how powerful is the vacuum?

Null. Nothing, no power. Having something at 1 ATM surrounded by a vacuum is exactly the same as having somethin at 2 ATM surrounded by a gas at 1 ATM.

All that matters is the pressure differential.

Its not "how powerful is the vacuum?", its "how powerful is your pressurized gas?"

A glass of water would freeze and stick together, so does it all come down to density?

A glass of water would not freeze, it would boil without the pressure to compress it into a liquid state. If you let it cool down enough to freeze first, then it may remain as ice (ignoring sublimation from solar heating when it is in the sunlight).

People speak of space as cold, a perfect vacuum is neither cold nor hot, its nothing. You will cool down due to black body radiation, but that takes time, its certainly not like dropping something in liquid nitrogen - and thats ignoring the sunlight of course (so it will get very cold on the night side of the moon, and very hot on the day side, but its not space per say that is cold, it is space that allows it to heat up or cool down as there is no other matter for it to transfer heat to/from it)

So a gas which is denser than water would not disperse (i guess it wouldn't be gas anymore then and no such thing exist, but hypothetically)?

I'd have to check, but i'm pretty sure its possible. I know its possible if you include plasmas, but non ionized gas... I need to check.

A gas will always expand, by definition, its got nothing to do with density, at least not until you get to a mass similar to the gas giants where its own gravity is sufficient to contain it (in this case its a combination of a density *and* total mass).

The only way you'd get a gas to be denser than water is by putting it under intense pressure (and cooling it down to just above its freezing point, so you'd want something with weak interaction forces to have the lowest freezing point), and that pressure means.. a pressure differential, as I mentioned above... it would produce a very powerful expansion if placed in a vacuum (or even a pressure of 1 atmosphere)

[lajoswinkler]

Not really. The rocket has a nozzle, the fuel/propellant has mass, and inertia, and a lot of energy, as it expands, it pushes against the walls of the nozzle, pushing the rocket forward. At very high pressure, ie right at the moment of combustion for a standard chemical rocket, the gas is pushing against itself, yes, but certainly not the exhaust emitted half a second earlier (which will be hundreds if not thousands of meters away by that point).

A rocket would produce thrust even with instantaneous pulses, not by continuously pushing against its earlier exhaust.

You could even have soldi fuel pellets/ explosives like a firecracker. Set of a firecracker in a cone in space, it will push the cone forward when it goes off. A rocket works the same way, just continuously. The exhaust pushes against the nozzle.

Some of the exhaust pushes against the nozzle (hence the large bell shapes especially for last stage engines), but a great deal of the thrust comes from the reactive movement. Stuff is thrown in one direction, the thrower is pushed in another. The ratio of these two things depends on several factors.

A glass of water would not freeze, it would boil without the pressure to compress it into a liquid state. If you let it cool down enough to freeze first, then it may remain as ice (ignoring sublimation from solar heating when it is in the sunlight).

People speak of space as cold, a perfect vacuum is neither cold nor hot, its nothing. You will cool down due to black body radiation, but that takes time, its certainly not like dropping something in liquid nitrogen - and thats ignoring the sunlight of course (so it will get very cold on the night side of the moon, and very hot on the day side, but its not space per say that is cold, it is space that allows it to heat up or cool down as there is no other matter for it to transfer heat to/from it)

Some of it would freeze in vacuum. Energy from the system is lost by evaporation, so when low energy particles remain, water freezes. Of course, if the radiative transmission of heat from the environment to the system is low enough or absent, water ice would cool down below appreciable sublimation temperature, where it would last indefinitively, just like in polar lunar craters.

I'd have to check, but i'm pretty sure its possible. I know its possible if you include plasmas, but non ionized gas... I need to check.

A gas will always expand, by definition, its got nothing to do with density, at least not until you get to a mass similar to the gas giants where its own gravity is sufficient to contain it (in this case its a combination of a density *and* total mass).

The only way you'd get a gas to be denser than water is by putting it under intense pressure (and cooling it down to just above its freezing point, so you'd want something with weak interaction forces to have the lowest freezing point), and that pressure means.. a pressure differential, as I mentioned above... it would produce a very powerful expansion if placed in a vacuum (or even a pressure of 1 atmosphere)

All gases would disperse, regardless of their density. From hydrogen to radon, they are all bunch of bumping balls.

[KerikBalm]

Some of the exhaust pushes against the nozzle (hence the large bell shapes especially for last stage engines), but a great deal of the thrust comes from the reactive movement. Stuff is thrown in one direction, the thrower is pushed in another.

You don't seem to understand that you are talking about the same thing. Its like saying "some of the effect is due to X, but a great deal of the effect is due to X"

All the force comes from the expanding gas pushing against the rocket nozzle. It is the rocket nozzle that shapes the exhaust and allows you to throw stuff in one direction, instead of omni-directionally (which would produce no thrust).

All gases would disperse, regardless of their density. From hydrogen to radon, they are all bunch of bumping balls.

Again missing the point. As I explicitely said "A gas will always expand"

I was referring to if it was possible to have a gas be denser than water, without turning it into a plasma.

Some of it would freeze in vacuum. Energy from the system is lost by evaporation, so when low energy particles remain, water freezes. Of course, if the radiative transmission of heat from the environment to the system is low enough or absent, water ice would cool down below appreciable sublimation temperature, where it would last indefinitively

Yes, some would freeze, but assuming the case of a glass of water at room temperature, the vast majority would boil off in seconds (if not shorter), and you'd have very little cooling and ice, I doubt you'd even get a core of ice, but rather some ice "dust"

And as far as "radiative transmission... low enough or absent" - I already addressed that "ignoring sublimation from solar heating when it is in the sunlight" - obviously that means if there is sufficient sunlight (ok, it could be another source of radiation, other than the sub), it will sublime, if not, no sublimation.

[Dedjal]

This is very interesting and enlightening for me. Thank you all for contributing.

And having a planet/moon made out of O2 sounds amazing.

English is not my native language, thus I lack the knowledge of many technical words, making me have to resort to long sentences in the hopes of getting the intended message across.

And I am prone to misspelling things alot.

But as mentioned, I am finding this thought idea fascinating.

Could it be possible to prolong a persons life in deep space (got thrown out of airlock without a suit) by sending a large "cloud" of O2 to surround the fella?

I think I read somewhere that a person could survive being exposed to space for a limited time.

Would then such an O2 cloud prolong survival?

Aunt Edit: I would not mind being told what words I misspell etc. In fact, I would like to encourage it.

[peadar1987]

This is very interesting and enlightening for me. Thank you all for contributing.

And having a planet/moon made out of O2 sounds amazing.

English is not my native language, thus I lack the knowledge of many technical words, making me have to resort to long sentences in the hopes of getting the intended message across.

And I am prone to misspelling things alot.

But as mentioned, I am finding this thought idea fascinating.

Could it be possible to prolong a persons life in deep space (got thrown out of airlock without a suit) by sending a large "cloud" of O2 to surround the fella?

I think I read somewhere that a person could survive being exposed to space for a limited time.

Would then such an O2 cloud prolong survival?

Aunt Edit: I would not mind being told what words I misspell etc. In fact, I would like to encourage it.

Disappointingly, no.

Imagine a balloon filled with oxygen at 2 bar. The atmosphere around it is at 1 bar. When you pop it, the contents of the balloon rush out and equalise the pressure almost instantaneously due to the pressure difference of 1 bar. You don't get a pocket of denser air lingering after the balloon pops. This is pretty much the same as would happen with a 1 bar balloon in a vacuum. Remember the individual molecules in your cloud are moving very, very fast, several hundred metres per second. Without any container to stop them, they're going to just fly off into space at that speed. After a few fractions of a second, all you'd be left with would be a few unbreathable wisps of oxygen that just happened to be moving at the right speed.

You can survive being exposed to a vacuum for about a minute, depending on what sort of physical state you're in. After that, you'll probably lose consciousness. There's a NASA story about an astronaut who tested a faulty space suit. Apparently the last thing he remembers before blacking out and having t be pulled out of the test chamber is feeling his saliva boiling in his mouth due to the reduced pressure!

[lajoswinkler]

You don't seem to understand that you are talking about the same thing. Its like saying "some of the effect is due to X, but a great deal of the effect is due to X"

All the force comes from the expanding gas pushing against the rocket nozzle. It is the rocket nozzle that shapes the exhaust and allows you to throw stuff in one direction, instead of omni-directionally (which would produce no thrust).

No, all of the force does not come from expanding gas pushing against the nozzle. Some of it shoots straight out and never touches it. More in first stage atmospheric engines, less in final stage vacuum engines, but some of it just shoots out and contributes to reactive movement.

Yes, some would freeze, but assuming the case of a glass of water at room temperature, the vast majority would boil off in seconds (if not shorter), and you'd have very little cooling and ice, I doubt you'd even get a core of ice, but rather some ice "dust"

And as far as "radiative transmission... low enough or absent" - I already addressed that "ignoring sublimation from solar heating when it is in the sunlight" - obviously that means if there is sufficient sunlight (ok, it could be another source of radiation, other than the sub), it will sublime, if not, no sublimation.

No, actually very little would boil off.

Number of hot particles in a room temperature water is quite low, and water molecules are highly polar, so only the topmost layer becomes kind of snowy; the rest is solid ice without appreciable inclusions.

Nonpolar liquids with low molecular mass, like liquid nitrogen, oxygen, halogens, noble gases (except helium, which is impossible to solidify without pressure), they will form slush, and then fluffy ice as the slush bumps.

You can survive being exposed to a vacuum for about a minute, depending on what sort of physical state you're in. After that, you'll probably lose consciousness. There's a NASA story about an astronaut who tested a faulty space suit. Apparently the last thing he remembers before blacking out and having t be pulled out of the test chamber is feeling his saliva boiling in his mouth due to the reduced pressure!

You'd black out in a matter of seconds. A bit more than ten seconds if you're fit.

Inevitable death in under 5 minutes or so.

[KerikBalm]

No, all of the force does not come from expanding gas pushing against the nozzle. Some of it shoots straight out and never touches it. More in first stage atmospheric engines, less in final stage vacuum engines, but some of it just shoots out and contributes to reactive movement.

"Contributes to reactive movement" is just non specific BS. It is correct, but it does not explain where the forces are acting, only what the effect of those forces are (conservation of momentum)

There is a force that accelerated that gas, there was an equal and opposite force on the rocket/spacecraft.

If you had an electromagnetic coil gun, the magnets would be pushing off of the projectile, and vice versa. In the case of a chemical rocket, there is physical contact.

Its just the same as an orion drive: sure, the nuke going off sends a lot of stuff backward, but its the stuff going forward hitting the pusher plate that pushes the rocket forward. In the case of a liquid fuel engine, where the fuel ignites at the very narrow base of the nozzle/in a combustion chamber, the gas pushes off of itself (just a bunch of balls bumping into each other) The stuff going backwards initially leaves the rocket without directly exerting any force, while the stuff going forward hits the rocket nozzle/wall of the combustion chamber, and pushes the craft forward.

I will conceed that I should have specified that the gase pushes against the walls of the combustion chamber in addition to the nozzle, and the combustion chamber can be quite large and distinct from the nozzle in a solif fuel rocket like so:

Where the expanding gas is produced far outside the nozzle, the force is not just applied to the nozzle, but also to the interior wall of the "top" or "front" of the rocket. I should have specified the nozzle+combustion chamber, which in the case of a solid fuel rocket is quite large.

In the picture above, you have a high pressure gas in a tube basically. If that tube is sealed in all directions, its exerting a force against all the walls of the tube.

The forces are equal and cancel out, no net force. When you put a hole in one of those walls, you have a force on one side, but none on the other as the gas freely escapes, and a net force is produced.

You can easily ignore this and just use equations like M1V1 = M2V2 (numbers should be subscript).

But that is skipping over where the force is actually being exerted, and just showing the net effect of that force.

Chemical Rockets are pushed by the pressure of the gas - period

The net effect is of course that the gas is reaction mass.