Does Rocketry Work beyond Earth's atmosphere?

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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby brianv on Wed May 29, 2013 3:56 pm

Yes, haven't you noticed?

I thought the Sun was a super compressed giant ball of gas whose molecules radiate heat and light from the extreme pressure. You are saying it's a giant camp-fire in space?

Why don't I get a suntan sitting in front of my log fire?
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby hoi.polloi on Wed May 29, 2013 4:00 pm

brianv wrote:I thought the Sun was a super compressed giant ball of gas whose molecules radiate heat and light from the extreme pressure. Why don't I get a suntan sitting in front of my log fire?


The Sun isn't fire. Fire isn't the spectrum of radiation coming from our Sun. Some evidence indicates the Sun is electric, and not a fusion reactor.

But this is off topic. Stick to rocketry please. We're not recreating Suns inside rockets.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby lux on Wed May 29, 2013 4:03 pm

brianv wrote:
It not widely understood that Earth's atmosphere is described as a Fluid! That is where your thrust also comes from! A rocket expels gases against fluid causing forward motion, much like a fish! They can swim up and down and even horizontally.


Rockets are swimming through the air like fish?

So, these are rockets then?


full link: http://www.youtube.com/watch?v=vIJINiK9azc
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby brianv on Wed May 29, 2013 4:07 pm

I'm not going to look at some stupid fucking video as evidence of anything.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby simonshack on Wed May 29, 2013 4:09 pm

Lux,

Any thoughts on my Hydrojet Funicular? Would it work? if not, why?
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby lux on Wed May 29, 2013 4:32 pm

simonshack wrote:Lux,

Any thoughts on my Hydrojet Funicular? Would it work? if not, why?


If you turned that hydrojet around it would make a great jacuzzi. :D

But, would it work? If all you wanted to do was get a lot of people wet, yes, it would work. But, I doubt it would move very much.

I think this is a better design:

Image

It has diesel assist!

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

Unread postby lux on Wed May 29, 2013 4:38 pm

Sorry, Brian. My comment about the sun = fire was wrong. Let there be peace.

The air swimmer video I posted is partly in fun and partly for science as it does illustrate a type of propulsion through the air that many believe applies to rockets but I believe that to be a mistaken understanding. My belief is that rockets do not move by pushing against the air.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby Flabbergasted on Wed May 29, 2013 4:43 pm

First of all, I have to say I agree with Boethius that no propulsion is possible without gravity and an atmosphere (or surface contact). The principle that makes a rocket work under these two conditions (as at the moment of launch) would be inapplicable under any other conditions (such as in "space").

Having said that, I would like to add a perspective more akin to traditional cosmology and metaphysics. This is not directly relevant to the analysis of the feasibility of propulsion in so-called "space", which I think has been satisfactorily dismissed by Boethius, Hoi and others, but may be worth a few minutes of meditation.

Modern science has adopted or inherited certain assumptions, or paradigms, about time and space and matter which may be useful and go a long way in organizing knowledge for the sake of practical applications, but which do not necessarily correspond to ultimate reality.

For example, based on our everyday physical perception of "empty space" between macroscopic objects (despite our knowledge of the invisible gas that fills it), we imagine that the space between what we define as the "nucleus" and the "electrons" of an atom is absolutely empty. Likewise, we imagine the space between celestial bodies to be "empty" (or near-empty, which doesn´t really make a difference). In short, we assume the existence of a preexisting three-dimensional nothingness called "space", in which things (particles, bodies) move and have their being.

In reality, space and matter are two sides of the same coin. There is no matter without spatial extension, and no spatial extension which is not also an expression of "matter", whether it is perceptible to our physical senses or not.

There can really be no transition from "nothingness" (which would necessarily be non-dimensional, although a purely intellectual construct) and "somethingness". It is inconceivable to move from one object to another separated by absolute nothingness. Nothingness, or "empty space", is merely a sensory appearance which is necessary for our practical life, but not a metaphysical possibility. In the physical world there can really be no discontinuity.

It would be interesting to look at the connection between the introduction of the "empty three-dimensional space" world view and the promotion of zero to the status of number. Just as you cannot derive "something" from nothing, you cannot derive the series of numbers from zero by multiplication. The Universe "begins" with something, like the number 1, or else it is non-manifest.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby Boethius on Wed May 29, 2013 5:09 pm

Heiwa wrote:
Boethius wrote:Heiwa, are you saying we can burn fuel in the vacuum of space without the benefit of an atmosphere or gravitational field like we have on the earth or the sun? Even if we bring along our own liquid oxygen I don't see how we can burn anything in the vacuum of space except inside of a closed container. Having an open nozzle would violate the integrity of our closed container.


Yes, you can burn stuff in vacuum without the benefit of an atmosphere or gravitational field. The stuff must only be combustible. And if you burn this combustible stuff in vacuum inside a container in vacuum and, if the container is open at one end, the gases due to the combustion will escape there and produce a FORCE ... that will affect the container. BASIC. KISS. :P


Heiwa, first of all it is my understanding that liquid can't exist inside a vacuum. Any liquid exposed to a vacuum is immediately converted to gas and any gas is immediately spread out into the void. So any combustion would have to take place in a sealed container and hence not in a vacuum in the strict sense.

Secondly, you mention the possibility of opening one side of a container, exposing it to the vacuum, while combusting gasses inside the container. In this case we have to consider that combustion can't occur anywhere near the opening because any liquids in that area are being instantly converted to gas by the vacuum and spread out into the void via free expansion. When combustion occurs at the far side of the container the force is going to push the remaining liquid out before it can be combusted. This seems like a terribly inefficient use of fuel as the combustion itself is forcing unspent fuel into space.

Another problem is that gas enters a vacuum at an average speed of about 2,000 meters a second. A 25 meter long Saturn 5 stage 2 fuel tank with over 1,000,000 liters of fuel would have it's contents drained in about 1/100 of a second if exposed to the vacuum of space.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby Boethius on Wed May 29, 2013 5:19 pm

Speaking of Saturn V rockets, after looking at some data provided by the Smithsonian I have some questions...

Times and distances traveled by a Saturn V
    Stage 1: 912 mph (38 miles in 2.5 minutes)
    Stage 2: 770 mph (77 miles in 6 minutes)
    Stage 3: 17,500 mph (achieved in 2.75 minutes) an acceleration of nearly 372,000 m/h^2

Questions:

1. Why does the rocket slow down between stages 1 and 2? I would expect it to pick up speed if it were powered by thrust because
    a. the thinner atmosphere reduces wind resistance
    b. it is now lighter, having discarded stage 1
    c. the pull of gravity against it's climb is reduced the higher it goes
    d. ...what is the point of stage 2 if does not increase the speed of the rocket?
2. How does stage 3 accelerate at such a tremendous rate without
    a. killing the astronauts?
    b. ripping apart the capsule?

http://airandspace.si.edu/collections/i ... aturnv.htm
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby simonshack on Wed May 29, 2013 5:25 pm

lux wrote:But, would it work? If all you wanted to do was get a lot of people wet, yes, it would work. But, I doubt it would move very much.


And now? Would it move? If so, why?

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

Unread postby lux on Wed May 29, 2013 5:31 pm

Boethius wrote:Heiwa, first of all it is my understanding that liquid can't exist inside a vacuum. Any liquid exposed to a vacuum is immediately converted to gas and any gas is immediately spread out into the void. So any combustion would have to take place in a sealed container and hence not in a vacuum in the strict sense.



In a vacuum water boils and then freezes as illustrated here:


full link: http://www.youtube.com/watch?v=pOYgdQp4euc

As you can see the water is not converted into a gas in a vacuum. As the narrator notes ...

At atmospheric pressure water boils at 100 degrees Celsius. That's because that is the point where water vapor pressure is equal to atmospheric pressure and water begins to change phase from liquid to vapor.


Notice that he says "At atmospheric pressure ...at 100 degrees C ... water begins to change phase from liquid to vapor" but as you can see the vapor stage does not occur in a vacuum at lower temperatures.
Last edited by lux on Wed May 29, 2013 6:02 pm, edited 2 times in total.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby lux on Wed May 29, 2013 5:44 pm

simonshack wrote:
lux wrote:But, would it work? If all you wanted to do was get a lot of people wet, yes, it would work. But, I doubt it would move very much.


And now? Would it move? If so, why?

Image


It could move to some degree depending on the thrust, weight and frictional forces involved.

Squid, for example, move through the water by squirting water out to the rear as explained here. They fill up a cavity in their bodies with water and squeeze it out causing them to dart forward.
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby Heiwa on Wed May 29, 2013 5:54 pm

Boethius wrote:
Heiwa wrote:
Boethius wrote:Heiwa, are you saying we can burn fuel in the vacuum of space without the benefit of an atmosphere or gravitational field like we have on the earth or the sun? Even if we bring along our own liquid oxygen I don't see how we can burn anything in the vacuum of space except inside of a closed container. Having an open nozzle would violate the integrity of our closed container.


Yes, you can burn stuff in vacuum without the benefit of an atmosphere or gravitational field. The stuff must only be combustible. And if you burn this combustible stuff in vacuum inside a container in vacuum and, if the container is open at one end, the gases due to the combustion will escape there and produce a FORCE ... that will affect the container. BASIC. KISS. :P


Heiwa, first of all it is my understanding that liquid can't exist inside a vacuum. Any liquid exposed to a vacuum is immediately converted to gas and any gas is immediately spread out into the void. So any combustion would have to take place in a sealed container and hence not in a vacuum in the strict sense.

Secondly, you mention the possibility of opening one side of a container, exposing it to the vacuum, while combusting gasses inside the container. In this case we have to consider that combustion can't occur anywhere near the opening because any liquids in that area are being instantly converted to gas by the vacuum and spread out into the void via free expansion. When combustion occurs at the far side of the container the force is going to push the remaining liquid out before it can be combusted. This seems like a terribly inefficient use of fuel as the combustion itself is forcing unspent fuel into space.

Another problem is that gas enters a vacuum at an average speed of about 2,000 meters a second. A 25 meter long Saturn 5 stage 2 fuel tank with over 1,000,000 liters of fuel would have it's contents drained in about 1/100 of a second if exposed to the vacuum of space.


Hm, liquid? Gunpowder or similar rocket fuel is solid and contains its own oxygene and will burn anywhere, incl. in vacuum. You just have to ignite it! Like dynamite. I have done it many times when I was a military elite soldier/killer/officer defending king/country! But a solid exposed to vacuum will it ... maybe evaporate? Disappear?

The ignition of a combustible in a container can be done in many ways, e.g. in the middle and all of it and the whole thing blows up. BOOM! :angry:

Or, you arrange a nozzle opening in the container and slow down the ignition of the combustible fuel so exhaust gases can escape into the vacuum and produce the FORCE that will change the velocity of the container ... in vacuum.

You see - the combustion does not take place in vacuum ... and that's why rockets work in vacuum. :)
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Re: Why Rocketry Doesn't Work in the Vacuum

Unread postby Heiwa on Wed May 29, 2013 6:10 pm

simonshack wrote:*


my HYDROJET FUNICULAR

Heiwa,

I have fitted this funicular with a hydrojet (such as those propelling modern high-speed ferries) and a giant water tank. Knowing the power of this jet, the weight of the fully loaded funicular and the angle/degree of ascent, would it be possible to estimate how fast - if at all - this thing would be propelled uphill, by spraying water into the air?

Image

Technical specs of the Kamewa high-speed ferry (cruising speed 30knots):
http://www.celebritycruisess.com/1997-1 ... 0-pax.html

The Schwebebahn funicular in Dresden (built in 1901)
http://www.flickr.com/photos/hrs51/4727175923/


Surely, this machine would obey to Newton's laws of motion - as the water ejected would push against the water in the tank - which is, if I am getting this right, the same principle by which NASA's rocket's function in near-vacuum? If not - what am I missing?

How do rockets work in the vacuum of space?
"The truth is that the rocket does have something to push against: namely, its own fuel."
http://www.straightdope.com/columns/rea ... m-of-space


Simon, when I was a soldier/killer/officer defending king/country 45+ years ago, serious fire fighting was a part of the fun. It, the fun, was to extinguish a fire a the bottom of a ship with me/us at the open deck 20 meters above. Thus I and some other crazy persons were supposed to descend down into the smoke filled ship/hell with a fire hose, open the fire hose nozzle at the bottom of the ship ... and extinguish the fire.
Great fun.
You had to open the fire hose nozzle slowly because the water splashing out of the nozzle produced a force on the hose/nozzle opener that could throw him backwards. Newton got it right!
It also works in vacuum. :P
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