## Does Rocketry Work beyond Earth's atmosphere?

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### Re: Why Rocketry Doesn't Work in the Vacuum

Boethius wrote:
A rocket is not like a ship in the water. Don't you see? A ship is in contact with the water while a rocket isn't in contact with anything.

The rocket in space/vaccum is in contact with other objects in space/vaccuum by gravity, i.e. with plenty things that you can see by light. If the rocket is close to Earth, Earth may attract it back by gravity and it will crash. If it is close to the Moon, the Moon will attract it by gravity and it will crash on the Moon. Same with Mars. And as it is always close to the Sun, the Sun will attract it by gravity. Gravity is a force as explained by Newton. It evidently works in Vacuum. Like Rocketry. Prove me wrong and earn €1M at http://www.heiwaco.com/chall.htm .
Heiwa
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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote:
Boethius wrote:
A rocket is not like a ship in the water. Don't you see? A ship is in contact with the water while a rocket isn't in contact with anything.

The rocket in space/vaccum is in contact with other objects in space/vaccuum by gravity, i.e. with plenty things that you can see by light. If the rocket is close to Earth, Earth may attract it back by gravity and it will crash. If it is close to the Moon, the Moon will attract it by gravity and it will crash on the Moon. Same with Mars. And as it is always close to the Sun, the Sun will attract it by gravity. Gravity is a force as explained by Newton. It evidently works in Vacuum. Like Rocketry. Prove me wrong and earn €1M at http://www.heiwaco.com/chall.htm .

I can see how a rocket is pulled towards a planet/star via gravitational attraction. But I don't see what this has to do with rocket propulsion.

Are you saying that a rocket can accelerate by pushing against a gravitational field?

If I jump in the air gravity pulls me back to earth. Is it not possible for me to jump up and push so hard enough that I will defeat gravity's pull.
Boethius
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### Re: Why Rocketry Doesn't Work in the Vacuum

Boethius wrote:
I can see how a rocket is pulled towards a planet/star via gravitational attraction. But I don't see what this has to do with rocket propulsion.

Gravity is just a force applied to the rocket by masses in space/vacuum. Same with a rocket engine attached to the rocket. It can also apply a force on the rocket = propulse the rocket in space/vacuum. Most rocket engines use liquid fuel/oxygene that, when burnt in the engine combustion chamber, ejects gases through a nozzle into space/vacuum that in turn provide the propulsion force.
Problem is just not to run out of fuel, as you cannot top up in space/vacuum. Evidently no rocket or space ship cannot carry enough fuel to brake into Moon orbit, land on Moon, start again from Moon and accelerate out of Moon orbit and try to get back to Earth (and brake there) as explained at http://www.heiwaco.tripod.com/moontravel.htm . But apart from that rocketry actually works in vacuum.
Heiwa
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### Re: Why Rocketry Doesn't Work in the Vacuum

So Boethius,

If you were somehow floating in space with a rifle in your hand, and fired that rifle, do you think you would feel any recoil?
CitronBleu
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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote: But apart from that rocketry actually works in vacuum.

Dear Heiwa,

Apart from that part (which we may just agree to disagree about), it seems we're all pretty much in agreement: rockets simply cannot work in space - and certainly cannot perform the way NASA portrays it.

How droll. Here we are, seemingly entertaining a heated debate - while we're all cool and syntonized as to the fundamental implications of it: NO space travel is possible. It's a bit like a reverse situation of those funny scientists in "A Trip To The Moon" (1902) who first quarreled vigorously with each other - only to eventually nicely collaborate to build their successful, moonbound spaceship...

Although we may never be able, for obvious reasons, to collaborate towards building our own spaceship to test our diverging views (as to exactly why it would not work), I find our debate worthwhile and interesting nonetheless. So let me just summarize in a few paragraphs what, in my view, constitute the primary hurdles for mankind to propel a rocket beyond our atmosphere or, if you will, into the vacuum of space. This will also serve as a response to Hoi's last post - and as a wide tip of my hat to Boethius for having greatly helped my understanding of the problems / physics involved.

- A rocket rising through the atmosphere will nicely proceed upwards in its escape from gravity - as long as certain conditions are maintained: the relative pressures at the rocket's nozzle and the outside atmosphere need to be as equal as possible, in order to obtain maximum 'mileage' / efficiency from the rocket's fuel.

- In fact, NASA clearly states that the optimal running conditions of their rockets occur only ONCE, at a certain unspecified (mid-range) altitude, when the above-mentioned pressures are identical. This, in perfect accordance with Newton's 3d law - what with its notion of "equal and opposite forces". Clearly, these rockets are designed to work best in our earthly atmosphere - and the atmospheric pressure IS in fact "the equal and opposite force" which the rocket thrust pushes against. To deny this fact is pure, outlandish and deceptive NASA hogwash-babble. Ironically, it is NASA itself that claims that their rockets work BEST when those two pressures are equal !

- Aerodynamic drag will of course be a factor in the equation, yet only a minor one - given the pencil-shaped, streamlined vessel. As the atmosphere pressure thins out with altitude, some more speed will probably be gained (out of a given power output) - but this fact would, obviously, have no incidence whatsoever in alleviating the forces needed for the weight of the rocket to escape the pull of gravity.

- Now, as we have previously seen, the atmospheric density range which our spacebound rocket is supposed to operate in, spans from a pressure of 0,001 (the average air density in our atmosphere) to a staggeringly inferior pressure of 0,000000000000000000000001 (the density of space vacuum). Thus, as the rocket climbs ever higher, it will have to exponentially increase its output/thrust (and, of course, its fuel consumption), in order to keep going - and combating the pull of gravity which, contrary to public belief, does NOT decrease exponentially with altitude.

- The rocket (at a given, high altitude which I cannot pretend to calculate precisely) will eventually be overpowered by the force of the exponentially decreasing outside pressure, its fuel being sucked out into the infinite 'vacuum of space' at stratospheric rate/speed - and faster than you can say "Houston-we-have-a-prob...---". Much like a champagne bottle popping its cork here on Earth (due to a minimal pressure difference), the rocket fuel will flush out with explosive force. Moreover, this force will expand in ALL directions (a bit like the diffused spray of your garden waterhose nozzle set on 'broad, soft mode') and provide little or no thrust. The rocket, from there on, will be doomed - and plunge back to Earth.

And for those willing to argue that NASA may have found a way to 'pinch' their rocket nozzles, so that the fuel doesn't get sucked out in a flash : well, you can always open a champagne bottle with great care, making the force inside it fizzle slowly out in the atmosphere. But such a subdued, impotent fizzle would hardly provide the necessary energy to propel a rocket away from Earth's gravity, would it?

Only a pinched fart would produce the same amount of 'power'(odor-power, in this case) as a vigorously expelled bowel-gas sample. We all know that much!
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### Re: Why Rocketry Doesn't Work in the Vacuum

CitronBleu wrote:So Boethius,

If you were somehow floating in space with a rifle in your hand, and fired that rifle, do you think you would feel any recoil?

Hello CitronBleu,

Yes, a gun will recoil and no, this has nothing to do with how a rocket works.
Boethius
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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote:
Boethius wrote:
I can see how a rocket is pulled towards a planet/star via gravitational attraction. But I don't see what this has to do with rocket propulsion.

Gravity is just a force applied to the rocket by masses in space/vacuum. Same with a rocket engine attached to the rocket. It can also apply a force on the rocket = propulse the rocket in space/vacuum. Most rocket engines use liquid fuel/oxygene that, when burnt in the engine combustion chamber, ejects gases through a nozzle into space/vacuum that in turn provide the propulsion force.

You can't eject gas into a vacuum. This is at the heart of the space rocket fantasy. As soon as gas from the combustion chamber enters the nozzle and comes in contact with the vacuum it is whisked away into the void. Regard the equation for work done by a gas: Work = Pressure x Volume. When pressure is 0 work is 0. Gas provides no force in a vacuum.

Problem is just not to run out of fuel, as you cannot top up in space/vacuum. Evidently no rocket or space ship cannot carry enough fuel to brake into Moon orbit, land on Moon, start again from Moon and accelerate out of Moon orbit and try to get back to Earth (and brake there) as explained at http://www.heiwaco.tripod.com/moontravel.htm . But apart from that rocketry actually works in vacuum.

Do you have any proof that rocketry works in a vacuum?
Boethius
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### Re: Why Rocketry Doesn't Work in the Vacuum

Boethius wrote:
You can't eject gas into a vacuum.

Just open the valve of the Magdeburg hemispheres and air enters the vacuum. Vacuum is just lack of air.
Heiwa
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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote:
Boethius wrote:
You can't eject gas into a vacuum.

Just open the valve of the Magdeburg hemispheres and air enters the vacuum. Vacuum is just lack of air.

So you're saying if a hatch opened and gas left the ship to equalize the pressure, with no extra force applied to the gas, this alone could potentially move the ship.
hoi.polloi

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### Re: Why Rocketry Doesn't Work in the Vacuum

Well, with what I suppose would be somewhat basic physics, it would be possible to determine just how much air---intended to be blown into the vacuum---would be required to produce the distances and rates of travel proposed to us by NASA.

A chamber of gas relative to the size of say, Dublin, would fit the bill, no? On that note: bollocks.
I, Gestalta
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### Re: Why Rocketry Doesn't Work in the Vacuum

hoi.polloi wrote:
Heiwa wrote:
Boethius wrote:
You can't eject gas into a vacuum.

Just open the valve of the Magdeburg hemispheres and air enters the vacuum. Vacuum is just lack of air.

So you're saying if a hatch opened and gas left the ship to equalize the pressure, with no extra force applied to the gas, this alone could potentially move the ship.

Yes, say that 1 kg of compressed air (no combustion) is leaving the ship into vacuum through a nozzle at 100 m/s velocity, this alone produces a force of 100 N that propulse the ship forward in the vacuum.
Heiwa
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### Re: Why Rocketry Doesn't Work in the Vacuum

*

So, if this works on Earth and in the vacuum of space...

...we should sell the idea to NASA asap!

Q&A with NASA:

Inflating a Balloon in Space
Q: Is it possible to blow up a balloon in space? I would like to know more about the gas laws in space.

A: Yes, it is easy to blow up a balloon in space. The way you inflate a balloon is to put a larger pressure inside the balloon than outside, which is easy to do when the outside pressure is near zero. (...)
Dr. Eric Christian
http://helios.gsfc.nasa.gov/qa_sp_ev.html
simonshack

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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote:
hoi.polloi wrote:So you're saying if a hatch opened and gas left the ship to equalize the pressure, with no extra force applied to the gas, this alone could potentially move the ship.

Yes, say that 1 kg of compressed air (no combustion) is leaving the ship into vacuum through a nozzle at 100 m/s velocity, this alone produces a force of 100 N that propulse the ship forward in the vacuum.

Gas can't exist in a boundless, low-pressure, low-gravity vacuum like interstellar space. So it can't be used to move a rocket.

Gas only exists under pressure; in an atmosphere, in a container, in an extremely strong gravitational field, etc... Without pressure individual gas molecules fly away distancing themselves from each other at thousands of meters a second (depending on the specific heat) and no force is exerted in the process (no work done).

Using gas in space is like using ice cubes on the surface of the sun.
Boethius
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### Re: Why Rocketry Doesn't Work in the Vacuum

Heiwa wrote:
Yes, say that 1 kg of compressed air (no combustion) is leaving the ship into vacuum through a nozzle at 100 m/s velocity, this alone produces a force of 100 N that propulse the ship forward in the vacuum.

So when the *ahem* Lunar Module was depressurized for extra-vehicular activities it trembled and quaked and maybe even went skittling off across the highly reflective surface of the moon.
arc300
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### Re: Why Rocketry Doesn't Work in the Vacuum

Boethius wrote:
Gas can't exist in a boundless, low-pressure, low-gravity vacuum like interstellar space.

The gas will evidently continue to exist, when you eject it into zero pressure vacuum. It cannot POUFF POUFF disappear! BTW - what is low-gravity vacuum? I have a feeling you are not serious.
Heiwa
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