Does Rocketry Work beyond Earth's atmosphere?

[Penelope]

Patrix, I've read the thread and also your take on the gun & bullet at March 29th, 2018, 3:06 pm.

Analyzing the gun & bullet as paired entities yields: The energy of motion (force) given to the bullet by the gun causes an equal magnitude force upon the gun in the form of a recoil 180 degrees opposite. The recoil is less in distance than the bullet travels because of the greater mass of the gun.
I have read the explanation that you refer to but wouldn't care to try to untangle it. I would welcome any objection to my own explanation.

[starfish prime]

Penelope,

How do you explain the under-expansion of a rocket nozzle? Even if the rocket has several stages, as it approaches a vacuum, seeing as how the exhaust exit pressure cannot be zero, the nozzle will become increasingly under-expanded and lose efficiency.

Either way, unless we are going to undertake rocketry experiments and test the massflow equation, it seems like kind of a moot point. If the goal is to prove that spaceflight is impossible, I personally find Proper Gander/A.A. Morris' refutation of Newtonian orbital mechanics more compelling. As elucidated on his website, an object's motion in the horizontal direction is completely irrelevant to its vertical motion. An object dropped and one projected forward from the same height will land at the same moment. There is no orbital velocity that an object can reach allowing it to simply freefall around the Earth without constantly consuming fuel. It will always be accelerating towards the center of the Earth, unless it exerts a counter-force. The only attempt I have seen at debunking this argument is that gravity is opposed by centrifugal force. However, centrifugal force is merely a perceptual illusion affecting objects within an orbiting body. Since their momentum makes them want to continue in a straight line, they seem to be pulled to the outward edge of the vessel. But this phenomenon has no bearing on the vessel itself. Spaceflight is impossible because you cannot carry enough fuel to escape Earth's "gravitational" field, whether rockets work in a vacuum or not.

[bongostaple]

Patrix, I've read the thread and also your take on the gun & bullet at March 29th, 2018, 3:06 pm.

Analyzing the gun & bullet as paired entities yields: The energy of motion (force) given to the bullet by the gun causes an equal magnitude force upon the gun in the form of a recoil 180 degrees opposite. The recoil is less in distance than the bullet travels because of the greater mass of the gun.
I have read the explanation that you refer to but wouldn't care to try to untangle it. I would welcome any objection to my own explanation.

Your explanation is about solids, and holds in any theoretical environment. The question of rocket thrust in a vacuum is not about solids, it is about fluids. And with rocket fuel burning in the combustion chamber and passing out of the chamber and into the vacuum of space is precisely the type of scenario covered by the Joule-Thompson effect. The burning rocket fuel is not going to waste its energy pushing on the inside of the chamber when in fact it can escape into space without any resistance at all. The path of least resistance. And because of this, there will be no thrust generated.

Having said that, I'm still very dubious as to whether space is a vacuum as we are told. Unfortunately I probably won't find out any time soon either.

[patrix]

Having said that, I'm still very dubious as to whether space is a vacuum as we are told. Unfortunately I probably won't find out any time soon either.

Off topic but my bet would be vacuum or aether if that term is preferred. If you remove water from a space here on Earth then it gets filled with air since we have an atmosphere. If you seal off the space and remove the air, then something non molecular but with the ability to propagate light waves remains and that something used to be called aether, but is nowadays more commonly referred to as vacuum.

[Penelope]

by bongostaple on March 29th, 2018, 3:25 pm.
Your dismissal of air or ground making a total of three forces and not a pair, is fundamentally wrong. Anything fired out the exhaust of a rocket will be met with resistance from any kind of matter that's in that location, whether it's solid or fluid. . . . whatever the rocket emits is effectively pushing against what's just outside, and all matter takes some effort to move. Therefore your three things are just two things.

Certainly air and ground possess the ability to resist other bodies. I dismiss air or ground only as participating in the paired objects of rocket & exhaust and the forces emanating from them. All forces of material bodies are paired. Material bodies are incapable of emitting an unpaired force.

The fact that forces are inevitably paired is important to rocketry as to everything else: The rocket's rise, a force vector, must be paired with the only other one available-- the exhaust's departure.

"Therefore your three things are just two things."
I'm not sure I understand you. If you mean something different, please say what. I think you are saying that the rocket's exhaust is pushing against either ground or air, and this is Newton's 3d, this is the pair of opposing forces which is lifting the rocket.

Back to my wheeled chair; this time I have 14 sandbags on my lap. I throw one, it hits the ground (downward vector) & the ground resists (upward vector). The 2 force vectors have cancelled each other (just as if you were pushing on a wall), but let's ignore that. In my understanding of what you mean there is no leftover vector representing the rocket's ascent, but ignore that.

I continue throwing sandbags and each departure from my hands causes my chair to move back by the same amount. Why aren't the earlier-thrown sandbags also causing my chair to move? Because only departures between paired objects and their forces will cause motion. Obvious in the chair-sandbag eg, of course.

You will think that it's different with exhaust because it looks continuous. Each layer of exhaust molecules/particles as it departs at great speed is paired with an opposite propulsive force on the rocket. It doesn't matter whether all the energy comes from the gas due to heating and compression, or whether it also comes from a push-piston or whatever in the rocket.

Do you still think that the continuous plume of exhaust is pushing off the ground at the far end and since it's in contact with the rocket at the near end it's pushing the rocket up? You have seen powerful exhaust come out & seen lift-off. I am asking you to ignore this perceptual conjunction, and instead apply Newton's 3d which is excrutiatingly nonintuitive.

Here, work with vectors. Represent each layer of departing exhaust with a downward pointing arrow. Say there are 10,000 layers before we have a continuous plume ground-to-rocket. So 10,000 imaginary arrows pointing towards the ground. I say that the earth is resisting the force of the exhaust and the two forces cancel to no motion, like you pushing on the wall.

You (or at least others) are saying that the exhaust force somehow rebounds from the ground, travels up the plume and pushes on the rocket. But if you are designating forces with vectors you can see that this is impossible: The plume is full of downward-pointing arrows. Each & every molecule/particle is moving downwards, and you cannot push your "rebound particles" upward to push on the rocket.

Pardon my not commenting on your evidence that rocketry is a hoax or impossible. I am making only one single point: That the following argument is invalid: Since rocketry relies on exhaust pushing on ground or air, it's impossible in the vacuum of space.

It's my intention to demonstrate only this single point, for reasons entirely friendly to the forum. I am not saying rocketry is possible or is being carried out. It can help no one's credibility to cling to an invalid argument.

[Penelope]

Bongostaple, thanks for your comments on Joules-Thompson, but I'm not addressing vacuum at this time, as carrying an invalid understanding of Newton's 3d into vacuum only makes explanations more difficult. With a correct understanding of Newton's 3d, Joules-Thompson becomes irrelevant anyway.
After I've gotten as far as I can with presenting the effects of Newton's 3d on rocketry on the earth I've promised Patrix a complete discussion of the Free Expansion experiment and the several errors regarding its applicability, and I'll address it to you as well. And present your comment.

[hoi.polloi]

You (or at least others) are saying that the exhaust force somehow rebounds from the ground, travels up the plume and pushes on the rocket. But if you are designating forces with vectors you can see that this is impossible: The plume is full of downward-pointing arrows. Each & every molecule/particle is moving downwards, and you cannot push your "rebound particles" upward to push on the rocket.

Pardon my not commenting on your evidence that rocketry is a hoax or impossible. I am making only one single point: That the following argument is invalid: Since rocketry relies on exhaust pushing on ground or air, it's impossible in the vacuum of space.

It's my intention to demonstrate only this single point, for reasons entirely friendly to the forum. I am not saying rocketry is possible or is being carried out. It can help no one's credibility to cling to an invalid argument.

I appreciate your concern, Penelope, but if you read my original argument for just such a case, you will find that the responses are quite sane and cogent; we are not discussing "building a pillar of mass" to push against. It is the fact that the useful atmosphere ends (and possibly somewhat abruptly) and that is where the pushing fails.

We are not talking about a torpedo that fires water out of itself after it surfaces into the air, but nonetheless you could apply a similar principle. Rocketry may "do something" but it won't be propelling or guiding the massive object whose main momentum was built up within the atmosphere.

Now, please — I really doubt members are largely trying to communicate what you are worrying that we are suggesting: "Since rocketry relies on exhaust pushing on ground or air, it's impossible in the vacuum of space"

Instead, an actual suggestion is twofold:

1. Rocketry relies on explosive fuel pushing on air to make the present contraptions we call rockets advance to the top of the atmosphere.

and

2. It's not possible above that atmosphere to use the same principle; instead the explosive fuel method encounters a series of problems invalidating the mode of transport, not the least of which is its inability to expand between the rocket and something else — because the "something else" is no longer there.

So, will you please stop bringing this tired "argument" to us and our thread? What you think you are clarifying has already been addressed many times in this thread. You cannot simultaneously ask us to think about a vacuum and yet ignore a place that acts like a vacuum. That's just shifting the goal posts each time someone tries to make a point to you.

Of course, fuel would hypothetically "do something" if it actually functioned in space but there are a number of problems I think we ought to ask you not to ignore:

1. Many nozzles said to bring rockets to space are not designed for (and cannot compensate) for a low enough atmosphere. The 3rd law will do a minimal amount of pushing on the nozzle in a variety of directions and start failing to "direct" the rocket in the desired direction. Maybe some claims about newly designed rockets are moot because they have advanced their fantasy scenarios to account for things they did not in the Apollo and shuttle legacies. Yet, in the end, even the new rocket designs remain of fantasy use.

2. Fuel might not react in the same manner at such extreme temperatures and altitudes, not to mention the mechanisms that inject and combine the fuel. To claim the fuel would do anything you would have to demonstrate that the functions would remain the same in a near-zero pressure environment and I doubt that's the case. But you at least would have to address this point. Again, please review the old entries in this thread which analyze the magical wordsmithing used to "explain" the functions of the jet propulsion in space. It often has to do with a similar problem to your original argument: imagining a simultaneous existence and non-existence of a mechanism (or formula) that inexplicably comes into or disappears from existence as "needed" by NASA apologist scenarios.

3. 3rd law will not likely be enough force anyway, even when you finally overcome and adapt your mechanism to more than one environment.

Spacecases are left with no choice but to ignore these important matters due to the lack of rocketry's viability beyond Earth's atmosphere, mock people and dodge when asked specific questions about the same. But deferring to an authority they have come to blindly trust, especially when that authority keeps these matters in the realm of ridicule, is not a threat to the forum.

[Penelope]

by starfish prime on March 29th, 2018, 11:15 am

An object dropped and one projected forward from the same height will land at the same moment. There is no orbital velocity that an object can reach allowing it to simply freefall around the Earth without constantly consuming fuel.

Yes, I can see that an object travelling forward wouldn't be slowed in its fall due to gravity, in our atmosphere. But if satellites exist, they supposedly stay up for years. Supposedly if you have a telescope or even a good pair of binoculars, and you watch the sky you can see a satellite pass every so many minutes. But I've never spoken to anyone who's actually done this.

No orbital velocity that an object can reach to orbit w/o consuming fuel constantly? Wouldn't mass be important too? That might be why satellites look so light-weight. Isn't it shameful-- we don't even know for sure if there are satellites.

Well the moon certainly orbits but such a distance! I suppose eventually we'll have magnetic force of some sort & won't have to carry fuel. I have to say that I regard the space program, even were it real, as a useless eater. Considering the number of people w/o modern sanitation & clean drinking water.

More later-- I have a sick chicken.

[Penelope]

Starfish prime,
I am carrying no brief for the idea that rocketry is possible. I don't know. But if you throw a discrete scientific argument at me and it's within my mathematical capabilities, I simply can't resist. In fact even if it's not within my math I'm apt to take it as far as logic unaided by the empirical can take me-- which as a faulty process, has only limited claim to approach truth. Nevertheless:

by starfish prime on March 29th, 2018, 8:15 pm
How do you explain the under-expansion of a rocket nozzle? Even if the rocket has several stages, as it approaches a vacuum, seeing as how the exhaust exit pressure cannot be zero, the nozzle will become increasingly under-expanded and lose efficiency.

I don't follow you. Do you mean how could under-expansion be remedied? And wouldn't it tend to be over-expanded?

The rocket approaches vacuum and we want to preserve (until vacuum only, I guess?) a certain speed, by maintaining force (mass of exhaust exiting x its velocity). But the rocket nozzle is under decreasing pressure from without, so that a larger mass of exhaust would exit due to the resultant higher pressure differential caused by unchanged pressure within the rocket's "exit chamber."

The exit chamber might be just the stroke of a piston plunger emptying the combustion chamber, forcing its content of exhaust towards the nozzle. I've no idea what the innards of the rocket really are and I doubt that NASA is motivated to tell us anything which might qualify as a military quasi-secret.

I probably don't understand your question, but as I've framed it there would be any number of places to modify the amount of exhaust exiting, and therefore maintain propulsion. I can enumerate a few if I'm on the right track with your question. I suspect I'm not; sorry to be dense.

[dblitz]

I have a little thought experiment about rockets and space:

lets say I am able to suspend an object, lets say a billiard ball, in a vaccuum. Next to this billiard ball I place a quantity of explosive material, suspending it one centimetre from the billiard ball.

Now lets say I detonate the explosive material. Is the billiard ball going to move? Regardless of what the resultant energy and matter happen to do on all the other sides of the explosion, the matter and energy on the side next to the billiard ball is going to reach that ball, affect it and move it.

Now lets say I am able to somehow manifest another quantity of explosive material next to the billiard ball on the same side, at the same distance and detonate it also. The ball will move a bit further. Lets say I am able to manifest these explosions continuously, one after another, each time a centimetre away from the ball, in rapid succession. The ball is going to move sideways at speed. I don't think anybody will doubt this.

A rocket is the same. Its just an object with a continuous explosion at one end, and it rides the blast wave of the energetic event occurring at its nozzle. An explosion and its blast wave will expand in all directions until it meets resistance from an object, which it will then push as far as it can. Without resistance at the nozzle end, the blast wave may dissipate quickly into space, but at the other end, the ongoing force of the contained explosion is going to push the object forward just like a series of explosions set next to it in succession would.

[patrix]

Eh, no Dblitz

If an explosion occurred near a billiard ball and the resulting gas was allowed to expand freely, then the billiard ball would indeed not move. But if this experiment is performed in a vacuum chamber it has to be a pretty large chamber. Otherwise the gas expansion will pressurize the chamber and free expansion will seize. And this is a trick used to make it appear that rockets can work in vaccum that can be seen on some YouTube videos. If you have a small chamber and a large model rocket engine, the engine will quickly pressure the chamber and then be able to act against it's own exhaust gasses.

[Penelope]

dzblitz,
Thank you for an interesting analysis, whose conclusion is

A rocket is . . . just an object with a continuous explosion at one end, and it rides the blast wave of the energetic event occurring at its nozzle. An explosion and its blast wave will expand in all directions until it meets resistance from an object, which it will then push as far as it can. Without resistance at the nozzle end, the blast wave may dissipate quickly into space, but at the other end, the ongoing force of the contained explosion is going to push the object forward just like a series of explosions set next to it in succession would.

You've substituted near-by explosions acting against a billiard ball for the explosive release of gases from a rocket, as a helpful analogy. And then described that explosive release as "a series of explosions" propelling the rocket. I understand your point.

I would ask you to pay attention to the locus of the explosive force, as you seem to vacillate just a little as to its location when you say "contained" explosion. If it's inside the rocket it can't propel the rocket. Like putting a gerbil in a matchbox; even if he tries to steer the box towards his food he can only exert traction against the floor of the box & it will go nowhere. But if we make an exit for him and he leaps out quickly, the box will go in the opposite direction. If he makes all the motions of leaping, even repeatedly, the box will not travel until if & when he exits. That's Newton's 3d.

Similarly, the superheated and compressed gas exerts traction on the nozzle just prior to exiting. If it is stopped within the nozzle the rocket will not travel. If it exits the rocket its force will be equal to its mass x velocity, and both gas and rocket will be subject to simultaneous opposite-direction forces of equal magnitude. It is possible that the rocket may add add'l velocity to the gas's exit by mechanical means.

If the explosive force is outside the rocket , having already exerted force on the rocket by separating rapidly from it, the question becomes "Does this energized, partially burned, exhaust gas have the ability to further push the rocket?

If it were actually a stream of explosions as you postulate, sure, but subject to the dissipation of much of its energy omnidirectionally as you mention. However, I think it's not really a stream of explosions, but only dramatically crackling exhaust.

The primacy and power of Newton's 3d in explaining motion everywhere is subtle to grasp while your eyes are on what is so vividly perceptual, that crackling exhaust & the moving rocket. Perception tells you they're causally connected, while the actual force of propulsion is continuously occurring one instant earlier.

[Penelope]

Hoi poloi, Thank you for your time & the long post listing some arguments for the impossibility of rocketry. I was aware of them, having read the thread. My insistence upon discussing only the one which I can readily see is invalid was not in any way to deny the existence of others.

You deny the importance of the argument which I am demonstrating is invalid:

by hoi.polloi on March 29th, 2018, 4:50 pm
Now, please — I really doubt members are largely trying to communicate what you are worrying that we are suggesting: "Since rocketry relies on exhaust pushing on ground or air, it's impossible in the vacuum of space"

You then explicitly rely on that argument in three statements:

Instead, an actual suggestion is twofold:

1. Rocketry relies on explosive fuel pushing on air to make the present contraptions we call rockets advance to the top of the atmosphere.

and

2. It's not possible above that atmosphere to use the same principle; instead the explosive fuel method encounters a series of problems invalidating the mode of transport, not the least of which is its inability to expand between the rocket and something else — because the "something else" is no longer there.

It is the fact that the useful atmosphere ends (and possibly somewhat abruptly) and that is where the pushing fails.

Perhaps the difficulty is that you don't realize that my "exhaust" equates to your "explosive fuel". You're quite right. I ought to have called the explosive fuel "exhaust" only after it had given propulsive force to the rocket, as that's when it exits & is properly "exhaust."

When a 40 lb dog leaps from my lap as I sit in my wheeled chair he propels it backward. There is no increased propulsion by his subsequently pushing on the air. Anything subsequent to his toenails separating from my jeans by a hairsbreadth will not affect the impulse he has already given my chair.

As you know, the impulse he contributes is his mass x velocity. And can be made greater by my pushing on him to increase his velocity. Note that his velocity includes all his circumstances, such as whether he is in air, pressurized gas, or vacuum; the circumstances affecting his velocity are irrelevant; only his actual achieved net velocity is a factor in the impulse he gives my wheeled chair.

What he leaps into-- even vacuum-- is irrelevant to the impulse which he has already given to the chair. Once he has separated, even if he's vaporized, it's irrelevant.

I decline to engage re your other arguments that rocketry is impossible, because I have insufficient data for an informed opinion. If my point were that rocketry is possible it would be incumbent upon me to answer all objections to my position. I reiterate that the entire purpose of my entering upon the question is to persuade CF to abandon a single invalid argument as it harms credibility.

Hoi poloi, I realize that you are the Mod and it's Simon's forum and that I have annoyed you both by insisting that "the science is not settled". It's your forum, so I'll desist after fulfilling my promise to Patrix & Bongostaple to critique the application of Joules-Thompson to rocketry, and of course to answer any comments, with your permission.

Thanks for your patience.

[patrix]

You've substituted near-by explosions acting against a billiard ball for the explosive release of gases from a rocket, as a helpful analogy. And then described that explosive release as "a series of explosions" propelling the rocket. I understand your point.

Please undertand that a "violent" gas expansion (explosion) follow the same proven physics as a slower one. As an analogy, sound does not propagate through vacuum, and it will make no difference if you scream.

[Penelope]

Patrix says--

Please undertand that a "violent" gas expansion (explosion) follow the same proven physics as a slower one. As an analogy, sound does not propagate through vacuum, and it will make no difference if you scream.

An excellent point, Patrix-- and one which I had forgotten when looking at the billiard ball subjected to explosion in Dzblitz's thought experiment. Thank you for reminding me that shock waves require a medium to travel through.

Of course he may have been thinking of an explosion so close that it didn't need to travel in order to impact the ball. I'm not certain, but I think in general. explosions supply their own omnidirectional force in a small surrounding radius, rather than atmosphere or other medium being necessary from initiation.

And in this case an explosion which hurls matter-- like shrapnel-- will function in vacuum. This might include an exhaust explosion as the gas explodes itself (i.e., is the media within which the explosion occurs) against the rocket tail, as Dblitz suggests, since the matter hurled is material. However I disagree that the superheated, compressed exhaust that exits a rocket one instant after contributing to its opposite-direction motion is a series of explosions.

In atmosphere, the high-velocity exhaust which has already separated from the rocket acts as a force vector away and confronts nose-to-nose the resistance of the air in its path, moving it until the exhaust force vector is cancelled by (has come into equilibrium with) the resistant air.

In vacuum, our usual conception is that the absence of air allows objects in motion to continue longer in motion.

Thank you for a very relevant comment, Patrix.