Does Rocketry Work beyond Earth's atmosphere?

[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]

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]

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.

[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

[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.

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.

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?

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".

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


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.


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.

[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]

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.

[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]

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]

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



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.

[Altair]

Interesting vintage documentary about the attempts to build a nuclear powered rocket. Funnily enough, they performed just ONE test plugging the nozzle to a vacuum chamber in order to test how well it would perform in space...


full link: http://www.youtube.com/watch?v=Zm7PNlK5Aco

[patrix]

Altair wrote:

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,

I just want to clarify that the pressure inside the system/rocket has no significance. In order for a system to move it must be able to create an external force. And the only way for a rocket to do that is by creating a pressure difference outside itself. It doesn't matter if there's high pressure inside the rocket. In the atmosphere, the difference is mainly created when the rocket heats up the air behind it, causing it to expand and thus pushes the rocket forward. In a vacuum however, there is of course no way to create the needed pressure difference. A gun works (once) because it can create this pressure difference between itself and the bullet (that is external to the system since it leaves it). When the bullet is exiting, there is higher external pressure on that side of the gun.

[molodyets]

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.

Very nice illustration and description! And yes, it is simple.

Just one clarification.

Maintaining such a pressure differential depends more on the area of the escape path. As an extreme example, consider the path as a tiny pin hole. Sure, that size can maintain the pressure, like a gas cylinder. Only a small amount of gas can flow through it. But the larger the size, the more gas can escape until the hole can't maintain the pressure. It's funny though, when mainstream engineers/scientists think that showing the formula proves the rocket thrust. I don't think that enough gas can escape at a high enough speed to give the required thrust.

In space, the pressure differential is only 1 atm more than at the surface of the Earth so the vacuum of space is not that harsh of an environment for the rocket. As an example, if the pressure inside the chamber is 500 atm, the pressure differential for the combustion chamber at the surface of the Earth would be 500atm-1atm = 499atm. In space it would be 500atm - 0atm = 500atm.
499atm versus 500atm is not that big of a difference.

BTW, gas is not sucked out by the vacuum. It's just like in our atmosphere, gas always flows from higher pressure to lower pressure --> it's pushed.

[Flabbergasted]

As an example, if the pressure inside the chamber is 500 atm, the pressure differential for the combustion chamber at the surface of the Earth would be 500atm-1atm = 499atm. In space it would be 500atm - 0atm = 500atm. 499atm versus 500atm is not that big of a difference.

If we calculate the difference as a ratio, we get:
500 : 1 = 500
500 : 0 = infinite

It is not a question of a difference in absolute numbers, but of the absence of an external medium (as far as we know). In the near-absolute vacuum of space there is no medium to interact with, thus no transfer of force between the rocket and the environment, thus no propulsion (beyond a minor recoil effect).

[patrix]

thus no propulsion (beyond a minor recoil effect).

And not even that I would say. The gas expansion has to act on something for an action/reaction (recoil) to be created. I don't know if this video has been up before. I discovered it when doing a presentation about the implausibility of rocketry in space the other day. I find it rather telling that 3 minutes into the video, when the presenter explains action/reaction, he holds up a pen in one hand, representing the action, but holds nothing in the hand representing the reaction. Perhaps a subtle hint?


full link: http://www.youtube.com/watch?v=2UcQC23sZ-I

Original link: https://youtu.be/2UcQC23sZ-I