Does Rocketry Work beyond Earth's atmosphere?

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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby patrix on March 29th, 2018, 6:39 am

Patrix, your belief that Newton's 3d doesn't come into play in vacuum

That no work occurs during free expansion is not a "belief". It is a proven physical fact.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby pov603 on March 29th, 2018, 8:57 am

Without wishing to trivialise matters can someone consider the following?
A "closed tube" is managed to be placed into "space" in an area relatively free of gravity but, nevertheless, supposedly in a vacuum.
We then insert a human within the "tube" and ask that he spend time walking to one end of the "tube" and running as fast and hard as he could towards the other end of the "tube" smashing into the wall/closed end, then calmly walking back to the other end to repeat the exercise over and over again.
Would we achieve forward momentum in this friction-less abyss?
Would a "transactional" force between the "tube" & man have already taken place, an instant prior to the impact?
Would it be safe to assume that the "tube" would not only move forward but also go faster and faster, after each repeat of the above, as there would be an absence of friction/air-resistance to slow it down?
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby patrix on March 29th, 2018, 12:16 pm

pov603 » March 29th, 2018, 8:57 am wrote:Without wishing to trivialise matters can someone consider the following?
A "closed tube" is managed to be placed into "space" in an area relatively free of gravity but, nevertheless, supposedly in a vacuum.
We then insert a human within the "tube" and ask that he spend time walking to one end of the "tube" and running as fast and hard as he could towards the other end of the "tube" smashing into the wall/closed end, then calmly walking back to the other end to repeat the exercise over and over again.
Would we achieve forward momentum in this friction-less abyss?
Would a "transactional" force between the "tube" & man have already taken place, an instant prior to the impact?
Would it be safe to assume that the "tube" would not only move forward but also go faster and faster, after each repeat of the above, as there would be an absence of friction/air-resistance to slow it down?


Of course it would not move. I mean it could bounce back an forth but this would never cause it to travel in any different direction than it did in the first place. If it did it would be a violation of Newtons laws of inertia, that rocket believers hold so dearly to their chest.

If the body is not affected by an outside force it will keep its current direction and momentum. The human inside is not an outside force.

Take it from the horses mouth: https://www.grc.nasa.gov/www/k-12/WindT ... otion.html
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby pov603 on March 29th, 2018, 1:07 pm

Believe me, I would not have expected it to move either (almost like trying to pull oneself up by ones own laces...it ain’t gonna happen...), nevertheless we are told that satellites use Reaction Wheels to rotate etc.
Anyway, back to the tube, consider that when running at the wall of the tube it miraculously opened for a nano-second and allows the human to pass through.
What happens to him and what happens to the “tube”?
They both move in opposite directions?
He moves in one direction and the tube remains stationary?
Neither of them move?
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby patrix on March 29th, 2018, 3:06 pm

pov603 » March 29th, 2018, 1:07 pm wrote:Believe me, I would not have expected it to move either (almost like trying to pull oneself up by ones own laces...it ain’t gonna happen...), nevertheless we are told that satellites use Reaction Wheels to rotate etc.
Anyway, back to the tube, consider that when running at the wall of the tube it miraculously opened for a nano-second and allows the human to pass through.
What happens to him and what happens to the “tube”?
They both move in opposite directions?
He moves in one direction and the tube remains stationary?
Neither of them move?


An action/reaction can only occur when a force outside the system/body acts on it. This is why the gun/bullet scenario would work in the assumed frictionless and gravity free space. The bullet becomes something outside the system that the gas expansion from the gunpowder can react against. So if the tube is open in one end and that human jumps, pushing the tube one way and itself the other way, the tube would change direction. But that can never occur as long as that human remains inside the system.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby bongostaple on March 29th, 2018, 3:25 pm

Penelope » March 29th, 2018, 5:07 am wrote:
by patrix » March 28th, 2018, 1:02 pm
I have no problem with Newton's laws of motion. . . perfectly fine and valid. they never come into play in the rockets in vacuum scenario

Patrix, your belief that Newton's 3d doesn't come into play in vacuum is because you interpret Newton's 3d to mean that rockets travel by pushing against either air or ground. This is expressly denied by Newton's 3d because it deals only with relationships between pairs. Air or ground makes 3.

You may avow Newton's 3d or that third entities like air or ground determine the outcome of paired forces transacted by paired material objects-- namely the rocket and its exhaust one instant before it separates from the rocket. You can't have both; you have to choose. Please review my discussion last post concerning force vectors. Just as numbers are necessary for math, force vectors are necessary to analyze forces.

Further, regardless of the misinterpretation & misapplication of the Free Expansion experiment, I'm sure that you are aware that vacuum is not a force, and therefore cannot stop or slow speeding bits of exhaust. However this is actually irrelevant because the transactional force between the exhaust & rocket will have already taken place, an instant prior to separation. This means that the force (resulting in motion) will already have been apportioned between them, so that nothing which happens to one can now affect the other.


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. The amount of resistance will be much higher in the case of solid concrete, for instance, than water, or air. But regardless of that, 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. The opposing force is highest for solids, and decreases for fluids.

This makes sense when you light a firework rocket, which accelerates from the ground very strongly, but then slows down. But for some reason, every 'space' launch I've ever seen on TV has the rocket lifting incredibly slowly from the launchpad, before apparently getting to tens of thousands of mph once out of sight. The only logical explanation I have for this slowness is that we are not watching a real thing.

Rocket thrust decreasing as the density of the outside medium decreases makes complete sense to me, and a natural extrapolation of the concept makes no surprise of tending toward zero thrust if the local material is a vacuum.

As regards the 'vacuum of space' though, I'm by no means wed to the idea that a vacuum is what 'space' consists of - as I'm certain man has never been there to find out.

By all means stick to theoretical arguments, but much of the history of space travel suggests that about 100km is pretty much the limit for any man-made technology to date. The US Air Force nudged up to that height with the experimental rocket planes , and encountered great difficulty staying there. If it was possible to go further, I very much doubt that the military, who were owning the effort then, would suddenly lose all interest and hand it over to a newly created civilian body, i.e. NASA. As a rule, when military are in posession of some technology that would allow military use, they get right on and use it, they don't give it away to a bunch of civilians.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby Penelope on March 29th, 2018, 6:10 pm

by patrix on March 28th, 2018, 9:39 pm
That no work occurs during free expansion is not a "belief". It is a proven physical fact.

You are sticking to your preference that we discuss the rocket in space first. And I am sticking to mine that we shall resolve the applicability of Newton's 3d to rocketry outside space first. In order not to annoy others with our endless repititions, I propose a compromise:

I promise on my honor to give a full and complete critique of Free Expansion of gases and its relationship to rocketry in vacuum after we have the resolution of the matter in atmosphere and on the ground. You know I didn't want to discuss Free Expansion at all until the earthly questions were resolved. Yet I have bent quite a bit on the topic and given you some indications. No more. Please discuss rocketry on lift-off and in atmosphere. Please, pretty please?
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby Penelope on March 29th, 2018, 6:19 pm

pov603,

Thankyou for entering the fray. Until now Patrix, with a little help from Simon, has been holding down the fort. You question the effect of a man within a tube upon the velocity of the tube if he repeatedly crashes into one wall of it. It isn't a trivializing question, but one which requires an understanding of Newton's 3d. Will you permit me to transfer the situation out of space and into atmosphere or on the ground? I am quite insistent that we should resolve Newton's 3d with rocketry flight here before we transfer the problem to space/vacuum.

Newton's 3d refers to the paired forces of paired objects and how they affect each other. They may be flung apart, as my chair and the thrown sandbag, or the forces may cancel each other as when rocket exhaust pushes on the pad or you push on a wall which resists your push.

As I'm sure you realize, in order for the paired objects to be pairs whose behavior is described by Newton's 3d in the "flung apart" example they must be separate in mass. One may not be within the other. The sand bag acts as a part of the me+chair mass and has no effect on the chair's velocity if I make all the motions of throwing it but still maintain contact with my hands.

pov 603 said, Would a "transactional" force between the "tube" & man have already taken place, an instant prior to the impact?
Would it be safe to assume that the "tube" would not only move forward but also go faster and faster, after each repeat of the above. . . .


Yes, I knew someone would get me on this. For me, it is a grammatical conundrum. You may interpret it as something else, and I would like your thoughts on the matter. I explain it this way: If I describe the moment at which the two separating bodies (chair & sandbag) apportion the forces incumbent on their separation as occurring just prior to separation then I am stuck with your little man making his tube accelerate.

But if I describe that moment as occurring just after separation-- well, obviously the two masses aren't in contact and can't influence each other. So if I compromise and say "at separation" the picture in my mind's eye is somehow always of 2 things no longer touching. So should I say during separation? Perhaps I should. But then, at what point during separation? Surely not that last instant when only the fingernail of my right index finger is in contact.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby hoi.polloi on March 29th, 2018, 6:21 pm

Although we have had this same seemingly endless discussion about ten times in this thread already (with Penelope representing my excuses for rocketry that never actually add up to a feasible way to move beyond the atmosphere since moving beyond Earth's atmosphere is the discussion), it seems it's still a "mental hurdle" for people to understand that rocketry encounters serious issues once the momentum ends and gravity takes over.

However NASA seems to be hedging their bets as usual, since the latest in exciting space technology news includes phasing out rocketry. Yes, the latest from NASA and private spacecases is the following:

Rockets, people and satellites will "now" (as if it hasn't been done the same way for the last half-century) be brought up by balloon. In fact, a private company is considering a sort of "space ride" (with tickets in the several thousands of dollars per ride) as a means of bringing people up nearly to the Karman line (though I wouldn't put it past the rich industry moguls to build all their instruments specifically to lie to the pilots and all the passengers that it's going higher than it actually goes, by a smidgen) via balloon — and then descending through the release of flotation and finally parachuting back to Earth.

In addition, satellite launches are now speculated to be cheaper, safer and more ecologically sound by bringing a rocket up as far as a balloon will take it, and then launching from there. You might even hear spokespersons for NASA, Space X and other enthusiasts contradict themselves once more and say "the balloon brings you so high that gravity is significantly reduced and therefore launching from higher conserves resources".

This is what I've heard from one of my favorite astronomer friends and I couldn't come up with the words to query him before we were on to the next subject. Now it may conserve rocket fuel to bring us up by non-incendiary buoyancy, but to say there is less gravity at the Karman line is weird when contrasted with the notion that Earth's full gravity is almost fully present hundreds of kilometers from the surface, or so it's said. I guess we ought to bring that to the "What is Gravity?" topic so ... moving on ...

Erdgvarp.png


The point is it seems NASA is already smelling the end of their rocket fables. All it will take to cement the change in the public's imagination is some fluffed up "disaster" or "pseudo-disaster" or "narrowly averted catastrophe" that never took place; and we'll all be primed for the change to new, exciting balloon technology.

:lol:

It's been balloons the whole time, with rockets for show and expensive (and maybe even somewhat wasteful) experiments, no doubt. And personally, I am coming to the appreciation that high speed lightweight military balloons and aircraft may be the best explanation for artificial so-called satellites. But in any case it seems "the age of rocketry" as we know it is presently little more than a marketing gimmick of the most expensive corporations to run: namely, imperial governments.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby Penelope on March 29th, 2018, 7:15 pm

by pov603 on March 29th, 2018, 1:07 pm
consider that when running at the wall of the tube it miraculously opened for a nano-second and allows the human to pass through. What happens to him and what happens to the “tube”?


How inventive you are. Back to me on the wheeled chair with a sandbag on my lap. Whether the chair (tube for you) moves backward away from the departing sandbag depends on at least three things. Obviously the velocity & mass of the departing item. If it's only a feather, regardless how fast (within reason) I make it depart by blowing on it, its departure won't move the chair. (too little mass)

Sufficient velocity of departure is also necessary if we are to move the chair: If I bend over and drop the sandbag 2 inches to the floor, the chair will not move backward.

But here is the factor you may not expect. If the action of departure by one of the paired entities is accomplished by a third entity, that action will not cause the remaining one of the pair to move. If a giant sucking vacuum (no pun) removes the sandbag from my lap at astronomical speed, my chair will not move backward.

If your man in the tube jumps to his death, and if his mass and velocity are sufficient, then your tube will move synchronously, in equal magnitude and 180 degrees in opposite direction. But before your little man contemplates suicide for the sake of our experiment I want to remind him that any velocity which he acquires from the passing wind (or any entity other than himself or the tube) will not contribute to the "reactive" movement of the tube.

Any energy internal to the man which adds to his velocity at? separation counts-- like getting a running headstart & leaping with all his might. Any energy from the tube which adds to his velocity also counts-- the use of pistons, compressed gases, etc.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby Penelope on March 29th, 2018, 7:33 pm

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.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby starfish prime on March 29th, 2018, 8:15 pm

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.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby bongostaple on March 29th, 2018, 10:09 pm

Penelope » March 29th, 2018, 6:33 pm wrote: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.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby patrix on March 30th, 2018, 1:09 am

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.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Postby Penelope on March 30th, 2018, 1:36 am

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.
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