Does Rocketry Work beyond Earth's atmosphere?

If NASA faked the moon landings, does the agency have any credibility at all? Was the Space Shuttle program also a hoax? Is the International Space Station another one? Do not dismiss these hypotheses offhand. Check out our wider NASA research and make up your own mind about it all.
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Penelope »

bongostaple says
April 2nd, 2018, 6:55 am NASA rocket thrust equations seem to ignore the density of whatever matter/air/etc is already sitting there when the burning fuel comes out of the nozzle. Are we expected to believe that a rocket on a launchpad and a rocket already in the air produce exactly the same thrust? That certainly appears to be the gist of the rocket thrust equations - I can't see why there wouldn't be a huge difference. But obviously if we extend that thinking from solid ground - air, and compare air - vacuum, then it starts looking rather unthrusty.
The most basic equation is Force = mass x velocity. Velocity at the relevant instant is already net of all affective factors. Those factors occurring after separation of Newton's two paired entities, the rocket and its propulsive gases, are irrelevant to the propulsive force already determined.

The results of that propulsive force will of course differ in that atmosphere exerts drag on the rocket and vacuum doesn't. Inertia of rest vs inertia of motion also is a factor.
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

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by Altair on April 2nd, 2018, 9:51 pm

There's one important difference between gas expansion and the 'pushing' of a liquid or solid body. Intermolecular forces between molecules of a gas follow a completely different set of laws, and you cannot apply Newton's Laws to them.

Newton's laws apply to material bodies, whether solid, liquid or gas as these are the forms of matter.
A very simple experiment (that seems nobody has carried on, at least I didn't found anything valid) would be to open the valve of a CO2 fire extinguisher in an appropriately sized vacuum chamber and measure the forces exerted.

The differential pressure between the tank of CO2 and 0 pressure of vacuum would determine the speed of exit of the CO2. Other factors like size of opening; temperatures of both, which are a factor in the number of molecular collisions, which would slow down exit of the CO2.
It's strange that there seems not to be any scientific literature, nor tests regarding the working of rockets in vacuum, and this would be of paramount importance before sending things up there, as a very small deviation in calculated vs. real thrust would mean that the object would not achieve the desired orbit.
Vacuum is just lack of atmosphere. Of course they're tested. Google "testing rocket nozzles in vacuum" to get 451,000 results which cover more than nozzles. Obviously not everything is truthful, but it's the most readily available data we have. If you want something more technical exert yourself to find it,
patrix
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Re: Does Rocketry Work beyond Earth's atmosphere?

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Penelope » April 2nd, 2018, 9:48 pm wrote:Patrix said, "Why all these weird analogies when it's easy to conclude the non effect of gas expansion in vacuum?"

The superheated, compressed gas is NOT within a vacuum when it has its effect; it's still inside the nozzle and its effect-- propulsion of both rocket & gas-- is manifest upon exit.
So the NASA rockets move by pushing at themselves with "superheated" compressed gas from the inside then. Same old same old. Physics says no... ( https://youtu.be/AJQ3TM-p2QI )
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

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by patrix » April 2nd, 2018, 7:31 pm
So the NASA rockets move by pushing at themselves with "superheated" compressed gas from the inside then. Same old same old. Physics says no
If the movement of the gas inside the rocket causes it to exit, that movement will propel the rocket.
If the movement of the gas inside the rocket is prevented from causing exit, the rocket will not be propelled. (provided the gas has enough mass & velocity, of course)

Try it yourself. Sit in a wheeled chair on a smooth surface with a 40 lb dog on your lap. You, the dog & chair are all considered one object now, one mass (like the gas inside the rocket is included in the rocket's mass). The dog may make all the attempts he likes to jump free, but so long as you hold onto him, you are still considered as one mass. But if you open your arms so that he actually jumps free, your chair will be propelled backward. It doesn't matter whether he jumps into air or vacuum. Only his movements and velocity while he is still on the way to exit matter. When his paws are clear of you he can no longer affect the chair's movement.

If no dog, use sand in a garbage bag.

The idea that the rocket is propelled by its exhaust pushing on the air is a misunderstanding of Newton's 3d, which deals with paired objects and the forces they exert. Rocket and gases until separation are a pair involved in the transactional force which gives both a motion which separates them.

The gases after separation are exhaust. Within atmosphere the air resists the exhaust. The exhaust being initially more energetic pushes it aside, continuing to travel away from the rocket until equlibrium is reached. This going-away exhaust does not affect the rocket, even if it goes into vacuum.



Even though when he made those exact same movements while you prevented his leap your chair did not move.
Altair
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Altair »

Sorry for the retro-quote, but here is my take on it:
Altair » October 31st, 2017, 5:32 pm wrote:I think it has been mentioned in this thread or in some one related, but it seems that free expansion of gases cannot produce any work, in physical sense. There is a pretty good discussion here: https://www.physicsforums.com/threads/w ... um.725702/

So, the idea is that work is done by pressure. In an atmosphere, the gas ejected from the rockets would build a pressure gradient, from a maximum near the exhaust, and gradually decreasing until it levels off with atmospheric pressure. So, it's the pressure buildup what pushes the rocket upwards. A nice way to model this would be to imagine a compressed air cilinder and then opening the valve.

But in a vacuum, the gradient 'endpoint' would be 0, so the gas molecules would have no opposing force when moving away from the rocket.

In fact, it's strange that I've found no literature about such a simple experiment as would be opening the valve of a compressed air cilinder in a vacuum chamber and measuring the resulting forces. And then comparing it with the same experiment in the atmosphere. My guess is that the exerted force would be almost negligible, but maybe non-zero.
As for testing in vacuum, yes, there were some results. Maybe the most reasonable one at first glance (obviously, I didn't check all of them) is this one: https://www.reddit.com/r/spacex/comment ... ve_a_large

But still this seems to me too much of a stretch: "So an engine designed to function optimally at sea level will have a diverging section that reduces the gas pressure to 1 atm at the exit; an engine that is optimal for vacuum will try to get a diverging section that will reduce the pressure to 0 atm as the exit (this is impossible, it would require an infinite nozzle, but we can get pretty close with a large enough shape). Since lower pressure at exit = larger nozzle, vacuum-optimized engines have larger nozzles than atmospheric engines."

To put it simply, we can give a hoot about the exit speed of the gas, because what "pushes" the rocket upwards is good old plain pressure against the rocket's structure. If you think that just accelerating the gas will produce such pressure against the nozzle walls, so let it be. But in fact, as the cited article states, accelerating a gas just means that you're trading pressure by speed.
Altair
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Altair »

To put another comparison: think about a hovercraft. It's suspended some inches above the ground/sea because the pressure inside the cushion pushes it upwards. But lift it just a bit more, and it will fall again, because the air exits too quickly and pressure falls.
So in that sense, a rocket's nozzles are just like the hovercraft cushion: you must create enough gas pressure in the inside in order to generate a force that lifts the rocket.
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

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Altair at 8:16 AM said
To put it simply, we can give a hoot about the exit speed of the gas, because what "pushes" the rocket upwards is good old plain pressure against the rocket's structure. If you think that just accelerating the gas will produce such pressure against the nozzle walls, so let it be. But in fact, as the cited article states, accelerating a gas just means that you're trading pressure by speed.
Sorry, the de Laval nozzle is far too technical to get into here. The reddit comment you referred to was speaking of extreme cases-- sea level vs vacuum. But the rocket would be operating at a variety of altitudes. Also, he simplified considerably.

Since you suggest looking at a compressed gas cylinder, here is probably my last effort to explain Newton's 3d.

We have lying on a smooth surface a compressed gas cylinder, modified by the addition of a nozzle which is mostly internal to the tank. The gas is under 50 lb/sq in pressure, which means it exerts a force of 50 lbs on each inch of the tank & nozzle. The nozzle's interior is a total of 20 sq inches. So the total force on the nozzle by the gas is 1,000 lbs, plus the nozzle is resisting this pressure with a matching 1,000 lbs. So we have two objects pushing on each other with no means of separation because the exit is closed.

We know that when we open the exit, cylinder and gas will fling away from each other. Just as my palms and the sandbag pressed together until a hairsbreadth of space opened between them. That separation permitted the two to fling themselves in opposite directions by availing themselves of the force built up while they were pressing together.
patrix
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Re: Does Rocketry Work beyond Earth's atmosphere?

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Very interesting Penelope. So with the special "de Laval nozzle" (too complex for us mere mortals to understand) and really really high pressure gas we will achieve the "real" Newtons 3d as you referred to it before, that apart from the old boring one is not dependant on Newtons 1st.

May I suggest another name as to avoid confusion with old plain Newtons 3d. Let's call it the Munchausen effect, since that old Baron was known to be able to lift himself by pulling his own hair.

I understand and sympathize with you Penelope that these new exciting discoveries in physics are hard to explain.

May I therefore suggest that you instead describe an experiment we can perform that will demonstrate this new Munchausen effect. And I take it you understand I prefer to use gas and not wheelchairs or water hoses since gas expansion is the subject matter.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Flabbergasted »

Penelope, I may have missed something during my absence, but did you answer Simon´s two questions from his post on 28 March 2018, 9:39 pm?
http://cluesforum.info/viewtopic.php?p=2405496#p2405496
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by SacredCowSlayer »

I do appreciate the thoughtful discussion on this topic. It seems to generate a lot of attention, and one gets the feeling that there are some members (perhaps, and from time to time) that wish to imply the following (in italics):

Since rocketry in the vacuum is feasible and possible (a conclusion I am NOT convinced of), NASA must be legitimate. Those words are never stated, but the implication lies just under the surface.

So, in an effort to keep things in perspective, I will simply note that if the NASA claims and their abundance of released imagery were authentic and convincing, then this thread would never have achieved lift-off in the first place. :lol:

Here (below) is a previous post of mine that can be found in the Elon Musk thread for a classic example of just how un-serious I consider these propaganda artists.
SacredCowSlayer » July 2nd, 2016, 8:50 pm wrote:Here is the laughable and oddly named Mercury blastoff that has been posted above. But I have to wonder, which one of the released "videos" is the real one? :rolleyes:

I count at least three different versions so far, all collected from a variety of NASA documentaries depicting this glorious moment in history.

Moreover, I'd like to add that the first living thing put in space by the U.S. was a chimp named Ham. You really can't spell sham without "ham". :lol:

The following clip can be seen in the NASA documentary at https://youtu.be/v5ZFT7TpYqM at the 23:33 mark.
Image

And this one with the wooden shack (prop) flipping backwards (unlike the previous one above) can be seen here https://youtu.be/KkG1WMzoikY at roughly the 8:14 mark.
Image

Then of course there is this little bit of magic. Just one minor problem that should be readily observed. Yes, the entire scene is mirrored. :wacko:
Image
Last edited by SacredCowSlayer on Thu Jul 04, 2019 5:22 am, edited 2 times in total.
Reason: Deleted a redundancy.
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Penelope »

Flabbergasted, if my purpose were to prove that rocketry is possible I would have to answer all challenges to it. My purpose is merely to show that CF misinterprets Newton's 3d as it applies to lift-off, flight in atmosphere, or vacuum. And therefore impairs its credibility.
Penelope
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Re: Does Rocketry Work beyond Earth's atmosphere?

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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.
You know, starfish, I originally thought this was correct. But upon reflection I have doubts: Imagine we have two pickup trucks drop off over a cliff's edge at the same instant. But one is going 5 mph & the other 85 mph. Surely the one going 85 would make a considerable inertial path pretty close to horizontal before he began his gravity-pulled descent. His path would actually be longer than that of the slow truck. Also his time to hit bottom.

We've all seen this "temporary defiance of gravity" by skiiers and skateboarders. It's actually just that their paths are the result of the gravity force vector at right angles to the horizontal inertia of motion vector-- with the resultant path being an hypotenuse whose dimension is largely determined by their initial velocity.

As for a velocity which would allow an object to orbit, defying a reduced gravity long-term, I wouldn't know how to compute that. Wikipedia says
Near the surface of the Earth (sea level), gravity decreases with height such that linear extrapolation would give zero gravity at a height of one half of the earth's radius

So at 2,000 mi above Earth we'd have 0 gravity. We don't want that. Is there a distance where satellites would neither fly off at 0 gravity, nor fall to earth? Since we do have natural satellites, it appears so. And it's logical that speed of orbit would help to offset gravity, allowing a lower orbit.

Do we have the fuel-carrying and other technology to get there? I haven't a clue. Obviously they've told us a lot of lies about nonexistent programs. It's possible that the lies dovetail with the constant refreshing of the "alien visitation" hoax. Another major psy-op that could be pulled out of the hat if it suits some scenario.
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Kham »

Penelope,

Why don’t you do your own research and THEN present your findings here at Clues Forum instead of presenting half finished thoughts expecting members to resolve your issues. I think we would all appreciate that.

You are engaging in tactics that are sucking time from members over tired old issues. How things fall is a pretty basic idea, a straight drop or the parabolic motion of projectiles. Perhaps you can start your research there and then make an awesome post of your findings of which you will be proud.

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

Unread post by patrix »

I agree Scacredcowslayer and Kham. And if this is deliberate "noise making", (which I have no way of knowing) it's about seeding doubt. To accept that there's no way for rockets and satellites to work "because physics" is a hell of a leap. At least it was for me. Cognitive dissonance kicks in and looks for the slightest reason to be able to dismiss it.

But as it turns out, much of science, including physics have been turned upside down during the entire 20th century. Einstein, the "rocket equation" and so much more is utter propaganda BS.

I encourage everyone interested in physics to go back about hundred years, to unlearn and relearn. Look at the works of Joule, Thomson, Michelson and Morley for example. And this is possible from your armchair because of the wonders of internet :-)

A suggested starting point:
https://archive.org/details/baltimorelecture00kelviala

Edit:
Penelope made a comment that was derailed and rightfully so. This is supposed to be a thread about Rocketry and I've slided away from that subject as well. But forgive me for commenting on it in an edit. I will also keep non rocketry issues elsewhere from now on.
Patrix, I guess Isaac Newton would be even safer then, since he lived in the 17th century.
Penelope, it's not about the age of the science, it's about if it follows the scientific method that stipulates that if you have an hypothesis, you should try to find observations and experiments that falsify your hypothesis. And if you and others fail to do this, then you have something more than a hypothesis - a theory and if it stands the test of time, a law. But this principle has eroded. It started as far as I know with Kepler who made elliptical orbits to seemingly make the Copernican model work. A hypothesis that's been falsified through observations as Simon shows in his book. Then we have Newton and his "laws" of gravity. Another hypothesis disproven by observations, if we are not willing to accept binary stars have absurdly high masses. Something I'm not willing to do because there are no evidence what so ever that could be the case.

So the entire field of science needs a renaissance, and hopefully this forum and its discussions is the first steps towards that. And at the bottom lies in my view a media that for a very long time has been about selling lies and hiding the truth. Einstein, Kepler and Newton has been raised to the skies by media, even though their hypotheses have been falsified. And the ones who have not like Joule-Thomson expansion, are ignored. So I'd definitely say this falls into the realm of media fakery.
Altair
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Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Altair »

Image

Ok, here we go again... Sorry for the crude graphics, but it's much fasterthis way than fiddling with graphing applications.
To illustrate my, point, the one and only thing that can move a rocket (or any other thing) upwards is a FORCE exerted in the same direction as the desired movement. That's physics 101.

As we're dealing with gases, the one and only way a gas can exert a force upon a solid body is by means of PRESSURE. We're not absolutely concerned about action-reaction and such niceties, because we don't need to know how much and how fast the gas is ejected. That is just a nice-to-know datum, but what we want is just to have the maximum possible force applied to our dear rocket. Right?

So, as we see in the graphic, the most important thing is to build a huge pressure in the combustion chamber. Being it a closed recipient except for one end (where the gases exit), assuming a more or less homogeneous pressure, the horizontal components of the force neutralize themselves leaving only the vertical component, that would be dependent upon the throat's surface, as only in this part of the chamber pressure is zero or near zero.

The same would happen also for the nozzle, but forces there would be much less, as it is the pressure.

Now, the problem is whether it's possible to maintain such pressure in the combustion chamber in a vacuum, or the gases would be effectively 'sucked' out of it as soon as they're generated. And no pressure, no thrust! It's that simple.

I've looked at the purported parameters of a 'real' rocket engine as the Merlin 1C: https://en.wikipedia.org/wiki/Merlin_(r ... #Merlin_1C

Image

This thing is supposedly capable of generating 480 kN of thrust, roughly 48 tons of weight. To make an idea of it, that's enough to lift three 15 ton fully loaded articulated trucks. Yet, I cannot see any massive attachment fixtures capable of sustaining such a force and transmit it to the rocket's structure. Another issue is that most of the force is applied to the combustion chamber, which de facto would be 'pulling' from the inside.

Also, the purported pressure inside the combustion chamber is 6.7 MPa. So if we want to have a forward thrust of 480 kN, we need a 'zero pressure' area in the bottom of the chamber of 0.07 sq. meters, what tells us that the throat should have a radius of 0,011m, or 11 cm, which more or less could match the photo.

Now, all what rests is to find out whether such pressure in the chamber can be maintained in vacuum conditions. In fact, that would be a near-perfect implementation of the Joule-Thompson box experiment!

As a corollary, it's quite funny that all discussions verse about the 3rd law, the gas exit speed and so on, which are absolutely irrelevant points.
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