Does Rocketry Work beyond Earth's atmosphere?

[simonshack]

The numbers are right.

Oh well, I guess that their numbers are 'right' and that, most likely, this part of the ongoing Space Scam would be well covered from a strictly technical perspective. I should probably (and ideally, all of us non-rocket scientists) stick to exposing the ridiculous imagery of these rocket launches which, technically speaking, are way below any acceptable / believable standard. The imagery seems to be the weakest point of the Grand Space Hoax - so let us (mere observers) keep pointing out this utterly laughable visual data.

I'm sorry but, at this point, NO technical 'evidence' of the feasibility of launching rockets in space - as advertised by NASA and ESA - can possibly convince me that their proposed rocket launches - and subsequent space explorations - are in any manner real / truthful / legit / authentic. Any number of people is of course free to believe that NASA and ESA do what they say they do - but just count me out of that number.

[brianv]

Hypothetical question!

Consider a handgun that is somehow floating in mid-air. Now imagine that same gun can be fired by remote control. The gun isn't being held, the trigger is not pulled, the ignition happens electronically. The gun has been cocked before being set adrift then fired remotely. Will the gun reload? Remember nobody is holding it!

Challenge:

If one of the vacuum rocket guys can build a working model of the rocket that pushes against itself

I will build one of the other type that uses propellant and gases that pushes against the earth and atmosphere

[simonshack]

Does a seagull fly without air?

Does a rocket fly without air?

Can a dolphin propel itself in the air?

Same question.

[rusty]

I'm not sure if this has been mentioned here or not - but there are actually toy "water rockets" out there which work quite well.

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

Everyone can build one...and I suppose they'd actually work in a vacuum as well, because they rely on repulsion. Go figure.

The thing I haven't figured out yet: Is this design generally working better than a pure "pressurized air rocket", and if so, why? I mean, the energy put into pressurizing the air in the bottle should be the same regardless of the added water. Does this tell us something about the efficacy of "gas rockets" in general?

[brianv]

and I suppose they'd actually work in a vacuum as well, because they rely on repulsion

?
the old solid fool argument

That Professor Goddard[...] does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react -- to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools.

—New York Times, 13 January 1920

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

[hoi.polloi]

Everyone can build one...and I suppose they'd actually work in a vacuum as well, because they rely on repulsion. Go figure.

Do you mean "go figure" as in you imply that the supposition you make must be true and no figuring is actually necessary? Or do you mean to say that we should actually all go figure it out using proper maths and figures? If the latter is true and you are not using the colloquial, I would encourage you to actually do the figuring yourself. I am satisfied that shooting water out of a rocket would not actually work as adequate propulsion for the activities said to be going on "in space" (i.e.; maintaining orientation, orbital corrections, launching satellites, etc.) until it is proven that:

1. a liquid as such could be adequately pressurized to carry plenty of days' worth of fuel without the rocket exploding in the vacuum of space
and
2. the entire system including the entire weight of all this fuel could actually reach the vacuum in the first place based on Earthly propulsion such as engines, jets and shooting flaming fuel out the butt

Sometimes we seem to forget that vacuum means total absence, the same rules may not apply, and said rules are extremely difficult and expensive to test for.

[rusty]

Are you suggesting that not only exhaust gases can interact with the surrounding atmosphere, but also ejected liquids and solids? Do you entirely question the existence of the repulsion principle? That would be a new twist I'd need to go and figure out indeed.

Seriously, no one is suggesting that water/liquid/solid rockets could ever reach or surpass the boundaries of our atmosphere (if there is such a thing). Their design is too obviously limited to smaller applications (toys), at least in my understanding. Nevertheless, those toys do work and I can see no reason why this should not be based on repulsion. If it works in a vacuum (if there is such a thing) or not is, of course, purely speculative, but I currently can't think of a solid reason why it should not.

The thing that puzzles me is: Is this water rocket design really more effective than using a pure pressurized air rocket design and why? I mean, the contained energy is the same and the mass is by far greater.

[Flabbergasted]

The thing that puzzles me is: Is this water rocket design really more effective than using a pure pressurized air rocket design and why? I mean, the contained energy is the same and the mass is by far greater.

Honestly, I don´t see the mystery here. A water rocket (or ANY rocket for that matter) pushes against a fixed surface (the ground) in order to lift off. If it were possible to launch a water rocket at an altitude of 100 m, it would push against the air alone (instead of primarily pushing against the ground), but since the air is less dense than the water expelled by the rocket, little or no forward movement would be produced (we have been through this with the discussion on flyboards further back in this thread).
In a vacuum, the environment is "infinitely" less dense than whatever type of mass a rocket ejects, therefore the forward movement is "infinitely" small. NASA therefore insists on the notion that the mere ejection of mass into the atmosphere or into the void produces enough "recoil energy" to make a rocket attain and sustain staggeringly high speeds.

[rusty]

A water rocket (or ANY rocket for that matter) pushes against a fixed surface (the ground) in order to lift off. If it were possible to launch a water rocket at an altitude of 100 m, ...

There's no doubt this is possible. It's impossible that a water rocket reaches an altitude of several 100 meters (as some of them do) just by pushing against the ground.

NASA therefore insists on the notion that the mere ejection of mass into the atmosphere or into the void produces enough "recoil energy" to make a rocket attain and sustain staggeringly high speeds.

And I agree with them, as long as we're talking about ejecting solids or fluids. With gases, it's a different story, at least in the vacuum, because gases can't be "ejected" there.

[Flabbergasted]

Water Rocket Altitude World Record with Onboard Camera (615 m)
http://www.youtube.com/watch?v=ZBV-kphMfSY

The rocket design appears to be similar to this:

http://www.uswaterrockets.com/

The "power" of the rocket is simply compressed air. The water is ejected not as a "liquid" but as a fine spray, making it more efficient when pushing against the ground and air.

Chicken Little also had a go at it:
http://www.youtube.com/watch?feature=pl ... M_Gpw#t=57

A feat which has inspired younger generations:
http://www.youtube.com/watch?feature=pl ... lYlj0#t=98

[simonshack]

Do you entirely question the existence of the repulsion principle? That would be a new twist I'd need to go and figure out indeed.

Rusty,

I don't think Hoi nor anyone here is questioning the existence of what you call the 'repulsion principle' ( I call it 'recoil force' / or 'recoil effect' - but please correct me if this is not what you mean by 'repulsion principle').

See, my feeling is that it's precisely the other way round: it is the NASA 'apollogists' (who defend the strange idea that rockets "actually move BETTER in a vacuum") who seem to be the ones who - absurdly enough - 'deny the existence' of the surrounding air and its predominant role in making a rocket move. Predominant? Well - if you at least agree that rockets are ALSO propelled by pushing on the surrounding air (and not ONLY by 'recoil effect') - should we not start calculating the relative action-reaction RATIO of these two forces? Has anyone done this before?

Also, may I call "friction" (for the purpose of this discussion) the force that the compressed air in a water rocket applies on the surrounding air? Surely, if you just suspend (upside-down, with a string) an uncompressed soda bottle in a vacuum chamber - and remove the tap - the bottle won't be propelled upwards by the "recoil effect" alone of the soda exiting the bottle? The question is: would a compressed soda bottle do so? But let us talk a little about "friction":

From Wickedpedia's "NEWTON'S LAWS" page:

"In swimming, a person interacts with the water, pushing the water backward, while the water simultaneously pushes the person forward—both the person and the water push against each other. The reaction forces account for the motion in these examples. These forces depend on friction; a person or car on ice, for example, may be unable to exert the action force to produce the needed reaction force"
http://en.wikipedia.org/wiki/Newton%27s ... _third_law

.

So I think what we all are debating here really breaks down to this (deceptively) simple - yet evasive - question: would not a car spinning its wheels on ice (and thus NOT moving forward) be equivalent to a rocket's frictionless thrust upon an empty (air-less) environment? The "recoil force" in this case would be the energy transmitted by the explosions inside the car's engine > to the car's wheels - yet the car would remain motionless. To be sure, NASA claims that the surrounding air has little (or NO?) role in propelling their rockets upwards. Is this not akin to saying that "the water surrounding a dolphin has little (or NO) role in propelling the dolphin forward"? Would a wiggling dolphin suspended from a ceiling-rail in a vacuum chamber move forward with the same, tremendous speed it can attain in water? Will it move at all?

[rusty]

Thanks Simon and Flabbergasted, I think I'm starting to get it. Still it's vital to point out that this "recoil effect" (let's stick with this term, sorry for the confusion) actually does exist and also plays an important role in the water rocket physics.

Maybe it's helpful to get back to a very basic experiment - a bullet fired from a simple toy gun with a spring (not explosives). Air pressure should not play a big role here, and I think it's quite obvious that the spring force would act in both directions, so it's pushing both the gun and the bullet (with the same force but different outcome due to different mass). And this works the same in a vacuum.

So can we suspect that what's generally considered as "recoil force" is nothing else than a simple "separation" force caused by two (or more) objects pushing on each other?

And if you (somehow) remove the bullet from the spring gun and simply charge and discharge the spring...nothing would happen. There's no force on the gun, of course.

In a water rocket the compressed air is acting like the spring, pushing the water and the bottle from each other. Furthermore, yes, the water is mixed with air and expelled and thus pushing against the surrounding air. So, yes, a water rocket would probably work less efficiently in a vacuum, too.

Back from here to the original question of the thread, leaving the law of free expansion aside for now: If gases are expelled from an exhaust based rocket, are those gases really pushed (separated) from the rocket? By means of their own force? Does that make sense? Seems more likely that force is separating the rocket from the surrounding air.

I think we can agree: At least rocket propulsion should work much less efficiently in a vacuum. This could, however, be countered with the argument, that no friction is applied to the rocket nose.

[simonshack]

So can we suspect that what's generally considered as "recoil force" is nothing else than a simple "separation" force caused by two (or more) objects pushing on each other?

And if you (somehow) remove the bullet from the spring gun and simply charge and discharge the spring...nothing would happen. There's no force on the gun, of course.

Rusty, I like your spring gun example - as a figurative action/reaction to help us wrap our heads around this.

Indeed, we may think of our "recoil effect" as the force acted by a spring pushing two objects away from each other.

So let's see - what does ESA (the European Space Agency) say about the amount of fuel being shot out of their 760.000kg ARIANE 5 rocket? Well, they say that their rocket releases a fuel mass of 2000kg every second. The "recoil force" of that mass being ejected every second is, they say, what makes their big rocket take off and shoot up into the sky (NOTE: no figures are given as to how much force - if any - is generated by the atmospheric pressure of the rocket's thrust against the surrounding air - nor whether this obviously existing action/reaction force contributes in any way towards lifting these 760.000kg off the ground). In fact, both ESA and NASA tell us that their rockets are NOT propelled by pushing against air - but only and exclusively by virtue of Newton's Third Law (our "recoil effect").

So let us put this into a simpler perspective. Let us place a compressed spring between a tennis ball - weighing 57g - and a huge medicine ball weighing 21,6kg . You see, this is approximately the same mass-to-mass ratio (1/380) as that between the above-mentioned 2000kg of ejected-fuel-per-second / and the big 760.000kg ARIANE 5 rocket :




We now release the spring - and see that the tennis ball shoots away at great speed - while the medicine ball hardly moves. Now, let us imagine that we can somehow feed a continuous flow of tennis balls to that spring - in such way that the mass of one (57g) tennis ball gets ejected every second. Will the medicine ball move much more / any faster? Would the "recoil force" generated by this constant flow of tennis balls propel the medicine ball at any significant speed? And could this continuous amount of force (joules-per-second) produced by the ejected flow of tennis balls - if applied underneath the medicine ball - possibly make it lift off from the ground and shoot up in the sky?

[CitronBleu]

Yes, if the speed of the spring releasing it's energy is the same as the exhaust velocity of Ariane's fuel, 2,400 m/s, the medicine ball will begin to move up, as long as the force of spring velocity x weight of ejected tennis balls per second is superior to the force of gravity pushing down (9.8m s).

If that force is equal to 10.0 m s, the medicine ball will theoretically move up, at a speed of 0.2 m s (or would "travel" 20cm) just like a rifle recoil would push back against one's shoulder with a certain force (equal to a certain, unconstrained, "distance").

In addition, if there is a continuous flow of tennis ball weight being pushed out of the medicine ball, the medicine ball velocity will increase incrementally since, with the same force pushing up, it will become lighter and lighter.

The key words here are exhaust velocity.

[lux]

When a dog pisses on a tree does the tree exert a force on the dog?