Does Rocketry Work beyond Earth's atmosphere?

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Re: Does Rocketry Work in the Vacuum?

Unread postby hoi.polloi on Thu Jul 23, 2015 4:35 am

Well, pmb, you didn't bother to finish your post, but I guess we are meant to assume you were about to type something about what you appreciate about us. It would have been a welcome comment since you entered waving your finger at everyone.

I for one would love to hear what you have to say about rocket formulas that take into account atmospheric resistance and pressure and so on. Please lay it on us. You don't have to read all threads on the entire forum to get a picture of the problems with rocketry. You can simply read this thread. The one you are commenting on. (If you had actually read it in instead of just bursting on the scene making accusations, you would see that there have already been attempts to explain and design vacuum experiments. And you would know that the experiments that you imply as being authoritative are actually very ineffectual, and in quite an amateur way at that.)

To summarize for those wishing to catch up with pmb's out-of-context complaints, the "free expansion of gas in a vacuum" (as Boethius posited) is one explanation for gaseous rocket fuels (which already conceptually would have to be shown to be capable of igniting adequately) escaping an implement with no work being done on the implement. In short, bursts of spray would not navigate anything. Since the bursts are also said to occur in the near perfect void of outer space, this would be nigh impossible to test on Earth, especially with the rocket models of several stories (heh, stories) in height that we are shown. Therefore, the enigma of the claims of NASA and ESA and other so-called "space explorers" is that their formulas cannot actually be tested without a great deal of money and/or access to incredibly special privileges. Many of those privileges are, in turn, actually also not possible for the average person to test, making even the claims of the science of "space explorers" as dubious as the claims made without adequate scientific explanation.

By the way, some mathematical proofs are not very good explanations about how something works. Telling us, for example, that a telescope's ability to read a stop sign from 12 miles away is derived from the formula for the arbitrary resolution of any device with a resolution, does not answer the question of how the resolution is achieved.

A simpler way of putting it is: please do not dodge questions by forwarding us to a different question that apparently grants access to the knowledge you claim there is. Especially when it does not actually do so but only claims to. Use and respect and answer respectfully the questions asked.

Moving on, another issue with rocketry is the lack of strong visual evidence to replace all the fake footage. Since many of the rocket launch videos appear to be manipulated imagery, and people who search for it cannot seem to come up with reliable, undoctored evidence of an actual rocket launch to space, many people have also come to ask questions about why space-faring rockets cannot be filmed or video taped presuming they were real.

As for topics not having to do with rocketry, and for which you can actually speak on with any expertise or speciality/specialty, I have made this special thread for you. Since you seem content to enlighten us about so many topics, feel free to change topics quickly and do not be afraid to try to convince people that your knowledge of outer space is based on a solid foundation (excepting of course if your only argument will be that many people agree with you so explanations are unnecessary) : viewtopic.php?f=23&t=1812

As for being open minded, I am not sure what you mean exactly. I think we may use those words differently. To us, open minded means lending some brain waves to hard questions and working on answering them. To you, it might mean accepting (and widely promoting) the most well-funded looking answer. No offense or judgment is meant at all in this statement. I am simply observing that that may be the case based on your posts so far.

Please, proceed with your rocket explanation using your own words on how we're all wrong in doubting that they achieve what NASA claims. Text book explanations are welcome, as long as you yourself are prepared to demonstrate your understanding of any given text. Useful understanding of a text (as opposed to the understanding of an insane individual or someone with a disabling mental handicap) would be qualified as something which you can explain to others in your own words so that they can understand it and confidently know that they understand it.

If you used to be able to explain it, but — due to injury — you can now no longer explain it, I am afraid nobody will find much use for that. And it would be a pretty convenient excuse to hide behind, for someone who just wanted to berate innocent researchers who are genuinely curious about the world they inhabit.
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Re: Does Rocketry Work in the Vacuum?

Unread postby simonshack on Thu Jul 23, 2015 9:49 am

*

This is the forum mentioned by pmb, "The Naked Scientists" - where they have a (now locked) 9-page thread titled:

"Topic: thrust does not work in space": http://www.thenakedscientists.com/forum ... #msg449749

Our new member Pmb (who I assume is "PmbPhy" on that forum) seems to have been quite active on that thread - and has worked hard to share his views about physics and how rocketry would work in space. Here are some interesting excerpts of pmb's reasonings :


PmbPhy wrote:"(...) Sit down on the skate board and make sure its on a very flat smooth surface. Make sure that you and the skateboard are at rest before you throw the stone. Then throw the stone as hard as you possibly can parallel to the ground. The exact moment the rock leaves your hands the whole system of thrower + skateboard will recoil. You and skateboard won't wait until the rock see if there's something to hit because the rock and skateboard doesn't think."

"The easiest way to understanding this is to look at the simplest situation. In a vacuum, think of a coin with a firecracker next to it right above its flat side. When the firecracker detonates the fragments smash against the coin and bounce off of it. Newton's third law tells us that the coin will rebound. You can look at a rocket engine as a controlled continuous explosion. This has nothing to do with the presence of an atmosphere. In fact it doesn't work as well with an atmosphere present."

[in response to a Naked Scientist forum member who doubts that rockets would work in the void of space]:
"The example I myself gave to him is the fact that in order for the space shuttle to achieve orbit the thrust of the rocket's engine must work in the absence of an atmosphere. Otherwise it wouldn't work. When the space shuttle wants to return to earth it must ignite the engines so that the thrust will slow it down enough to enter the earth's atmosphere".


Impeccable logic, n'est-ce-pas? Let's take a deep breath - and read that again: "(...)for the space shuttle to achieve orbit the thrust of the rocket's engine must work in the absence of an atmosphere. Otherwise it wouldn't work." In other words: it HAS to work, otherwise it WOULDN'T work, you see? :P

Something I have noticed in various forums discussing the subject of space propulsion is exemplified by this other comment - by "alancalverd", a supporter of PmbPhy's arguments on the Naked Scientists forum. At one point, alancalverd says :

"Have you ever fired a rifle? The recoil force is exactly the same whether you fire it under water or in air. Recoil force is independent of the surrounding medium. Conservation of momentum is demonstrated in many ways: billiard balls, "Newton's Cradle", spinning tops and skaters.... and in no case is there any requirement of "something to push against". Rockets work by conservation of momentum, nothing else. You chuck stuff out of the back and the rocket moves forward so that the net change in momentum is zero."

In fact, I have often seen this 'bullet-recoil' argument being brought up by folks convinced by the feasibility of space propulsion - and I remember reading on some other forum that burning rocket fuel basically works like the flow of bullets fired out of a machine gun: what propels a spacecraft, it is argued, is the mass of the exploding fuel recoiling against the combustion chamber coupled with the momentum of the exhausts rapidly expelled out of the nozzle, yet - ( and this is clearly / strongly argued ) - these same, supersonic exhausts do no work whatsoever as they impact the atmosphere (not even at sea-level). As it is, the consensus among these people seems to be that rockets work exclusively by 'recoil effect' and 'rapid mass / momentum transfer' (excuse my figurative layman's terminology) - and that no analogy whatsoever can be made between a jet engine and a rocket engine - as far as the very nature of their propulsion forces is concerned. I believe the following sentence (that I once read and saved in my 'space notebook') correctly sums up their basic theory: "If you know the rocket's mass, the amount of fuel burnt per second and the exhaust velocity then you can calculate the rocket's gain in velocity per second interval which is also therefore equal to its acceleration."

Fair enough. So with this theory in mind, I have decided to set up an experiment. On the beach.


THE MIDGET-SOLDIER ROCKET PROJECT

I have this midget soldier (my little Italian trooper only weighs in at 50kg or so) that I wish to launch and briefly propel upwards (in the atmosphere, that is - am not even thinking of reaching the 'vacuum' of space for now!). Looking around for the 'world's fastest machine gun' I have also found this remarkable Russian machine gun, the "SKHAS Ultra" used in WWII - capable of firing 3000 (yes, three-thousand) rounds per minute - i.e. 50 rounds per second.

ShKAS machine gun specifications: https://en.wikipedia.org/wiki/ShKAS_machine_gun

Image


Now, I already know the basic specifications of the Ariane 5 rocket - having already looked into it / discussed in this thread some time ago:
Image

Weight of Ariane 5 rocket: 760.000 kg
Mass of fuel ejected per second : 2000 kg / s
Ratio of fuel-weight expelled per second / vs vessel weight: 1/380
(in other words, 0.263 % of total vessel weight is expelled every second)
Exhaust velocity (at sea level) : 2749 m/s

As compared to :

Weight of midget soldier + machine gun + 650 rounds of ammunition: 50+10+40 = 100 kg
Mass of 50 rounds (of 24g each) fired per second : 1.2 kg
Ratio of rounds expelled each second / vs soldier+gun assembly: 1/83
(in other words, 1.2 % of total vessel weight is expelled every second)
Muzzle exit velocity : 825 m/s


So, let's see: my 'vessel' (i.e. the midget soldier and his machine gun & ammunition) is :

About 4.5 X superior (more efficient) in terms of mass expelled per second / vs vessel weight
About 3.3 X times inferior (slower) in terms of 'muzzle / exhaust exit velocity'.

By the looks of it - and since my mass-ejected-per-second-ratio is 4.5 X superior to that of the Ariane rocket - this looks promising, yet I'm a bit worried that my exit velocity (of my 'rocket fuel' - i.e. the bullets of my machine gun) is inferior to the Ariane rocket's.

However, not being a physicist, I'm currently stuck at a more profound / momentous question:

Will my midget soldier take off at all - and briefly soar up in the skies? If not - WHY NOT?

Hopefully, Pete (our new member 'pmb') or any other helpful physicist will be able to help me out here. Anyone?
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Re: Does Rocketry Work in the Vacuum?

Unread postby Farcevalue on Sun Jul 26, 2015 4:57 pm

Simon, aside from your midget soldier rocket being propelled by the mass ejection of shells (perhaps plausible, however marginally, when he is already in the vacuum) he also has to escape the gravitational field of the earth. According to Wickipedia, the ShKAS machine gun fires cartridges with muzzle velocity of a paltry 2710 ft/s, as opposed to, say a .220 Swift Cartridge that can exceed 4000 ft/s (commonly cited as the fastest available production model cartridge).

Regardless, both of these speeds are still quite short of the escape velocity required to leave the gravitational field of earth which according to NASA, is 36,960 ft/s. (http://www.nasa.gov/audience/foreducato ... ty_prt.htm)

At some point after your midget soldier rocket leaves the ground, he will have to gain more than 13 times the rate of speed his ammo is leaving the barrel of his "propulsion system".

(Incidentally, regarding the Apollo rockets, it just me or is the idea of executing the untested maneuver of the untethering, rotation and re-attachment of of the command module pictured below at the speed of 36,960 ft/s a tad fanciful?)

Image

Anyway, last month there was a bit of buzz about the possibility of new unmanned "hyper sonic" rockets changing the nature of warfare by the year 2040, the projected date of the perfection of these projectiles that can reach the currently unprecedented (except when talking about Apollo rockets, that is) 5573 ft/s:

http://www.ibtimes.co.uk/arms-race-betw ... ft-1508241

We have all seen the slow acceleration of the Apollo rockets that the camera follows until they are out of sight, yet they are evidently all the while picking up enough speed to become virtually invisible to any cameras that might attempt to capture them as they entered the "vacuum". And yet, if all goes according to plan, the military will have unmanned rockets capable of achieving speeds approaching less than one sixth the speed of Apollo rockets by the year 2040. That gives them another thirty years or so to achieve what they had already done one hundred years prior.

So, I submit my vote in favor of your midget soldier rocket achieving orbit. Maybe next we will see pigs achieving orbit by ejecting cotton candy from their snouts, why not?
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Re: Does Rocketry Work in the Vacuum?

Unread postby Kham on Wed Jul 29, 2015 8:56 am

Came across this first video and thought it had promise as a demonstration of Newton's 3rd Law of Motion. I also thought the video did a good job of explaining the differences between the two camps, Pro Spacers versus Pro Earthers, in layman's terms. My diagrams are not nearly as eloquent as Simon's, probably because they were lifted from the video, but I too am waiting for a physicist to explain the results of the demonstration from the video.

Definitions: Pro Spacer believes rockets can fly in a vacuum. Pro Earther believes rockets need atmosphere to fly.

Image

Image

Consider the standard balloon car.

Image

When you fill the balloon with air and release it out the back, what will happen?

Image

What will happen if the air exiting the balloon gets diverted, will the balloon still move forward?

Image

You will have to watch the video to see if the balloon car moves forward when the exiting air is diverted.

NASA SPACE PROGRAM HINGES ON 1 LIE

The big question is this: Is this a valid experiment? Does it demonstrate that for movement to take place, the air exiting the balloon must push against the atmosphere? Watch the whole experiment at the link below which will start at 6:27. The explanations, should you care to listen to them, are at the beginning of the video.

There is another video that demonstrates the idea of how thrust works also using a standard balloon car. Although this clip does not disprove that rockets can operate in a vacuum, it does demonstrate the pushing against air idea, in that air exiting the balloon must push on the atmosphere behind it in order for the balloon car to move forward. I included this link because it was a second demonstration of that same idea from the first video and it’s entertaining. The experiment at the link below will start at 9:20. The explanations are at the beginning of the video.

NERD ACCIDENTALLY PROVES ROCKETS DON'T WORK IN SPACE!
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Re: Does Rocketry Work in the Vacuum?

Unread postby rusty on Wed Jul 29, 2015 7:13 pm

Kham wrote:
There is another video that demonstrates the idea of how thrust works also using a standard balloon car. Although this clip does not disprove that rockets can operate in a vacuum, it does demonstrate the pushing against air idea, in that air exiting the balloon must push on the atmosphere behind it in order for the balloon car to move forward. I included this link because it was a second demonstration of that same idea from the first video and it’s entertaining. The experiment at the link below will start at 9:20. The explanations are at the beginning of the video.

NERD ACCIDENTALLY PROVES ROCKETS DON'T WORK IN SPACE!


Thanks so much for bringing this up. Amazing experiment - so simple and yet so telling.

You're right that it does not fully "disprove that rockets can operate in a vacuum". But it's probably the closest we can get under atmospheric conditions. We know that the defenders of "rocket science" will come up with some lame excuses, something along the line of "we already told you that rockets are less effective in vaccuum, but they still work quite well, and you can't simulate that with something as simple as a balloon and a vacuum cleaner, yadda yadda yadda...".

To me that's pretty much it. Game over for all of THEIR space clown fantasies. Once and for all.
Last edited by rusty on Thu Jul 30, 2015 5:04 am, edited 1 time in total.
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Re: Does Rocketry Work in the Vacuum?

Unread postby Flabbergasted on Thu Jul 30, 2015 1:12 am

Kham wrote:Image
The big question is this: Is this a valid experiment?

It´s a simple and clever experiment and I am not surprised it shows that the "opposite reaction" is insufficient to move the balloon cart. In any case, the experiment is not valid in the sense that the wheels are in contact with a surface to which energy (if any) can be transferred. The drawing above shows equally distributed vectors hitting the inside of the "combustion chamber", but the wheels of the balloon cart will only allow forward movement.
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Re: Does Rocketry Work in the Vacuum?

Unread postby hoi.polloi on Thu Jul 30, 2015 8:34 am

A slightly more ideal version could involve pseudo-frictionless ball bearings as a conveyance. However, yes, the point is interesting.
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Re: Does Rocketry Work in the Vacuum?

Unread postby ICfreely on Thu Jul 30, 2015 12:55 pm

We know that cold water boils in a near perfect vacuum chamber:

Boiling cold water In a Vacuum Chamber

full link: http://www.youtube.com/watch?v=glLPMXq6yc0
https://www.youtube.com/watch?v=glLPMXq6yc0

It’s a foregone conclusion that Earth is suspended in the vacuum of space. At the risk of sounding too simplistic, I just can’t seem to figure out what sort of barrier between Earth’s atmosphere and the vacuum of space (which is penetrable by rockets) prevents the water on Earth’s surface from boiling.
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Re: Does Rocketry Work in the Vacuum?

Unread postby hoi.polloi on Thu Jul 30, 2015 4:35 pm

Well, air thins as we go higher, that's true enough. As for anything up there or beyond where we've been being a foregone conclusion, I think we are having that discussion in another thread or two — and will likely discuss for centuries to come, or until we actually get there.

Still, that's a pretty profound inquiry. Boiling ... hmm.
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Re: Does Rocketry Work in the Vacuum?

Unread postby pov603 on Fri Jul 31, 2015 10:48 am

Boiling is only the change of 'water' into 'water vapour'?
If so, is it safe to assume then there is plenty of water vapour at higher altitudes due to lower temperatures but lower pressures?

Edited higher to lower...
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Re: Does Rocketry Work in the Vacuum?

Unread postby I, Gestalta on Tue Aug 04, 2015 5:18 pm

I do not recall as to whether or not I actually voiced this curiosity of mine, but since the early days of this thread, I'd always humored the idea that one could devise an experiment on combustion within a vacuum by using a Magdeburg sphere.

Forgive any oversimplification on my part---and I am certainly open to being corrected on any misunderstanding(s) I might have---but:

If you placed some sort of remote-controlled or automatic camera inside the sphere (one which would not collapse after vacuum or near-vacuum is achieved), and took several instances of video footage of various, NASA-styled combustion examples, (remote-controlled or automated), wouldn't we at least learn something?

I'd try two things, basically:

1.) Try to ignite several types of lighters (possibly even matches with some sort of rigged up self-striking system) within the sphere at gradually-reduced degrees of atmospheric pressure. Is combustion achieved? For how long?

2a.) Suspend a sort of makeshift rocket from a string attached to the inner ceiling of the sphere, and set its engine(s) to ignite (or attempt to ignite), and see what happens. Does it rock back and forth? If so, why? Is it because the string is attached to the sphere and there's a vibrational interaction taking place?

2b.) Try it without the string. Place the "rocket" inside the sphere unattached, and see what happens when you attempt to ignite whatever engine you've fashioned. Perhaps it would clank around on the inner surface due to internal vibration, I don't know.

To take it a step further, perhaps all of this would be moot, and would need to be tested in some sort of "zero G" environment, such as extremely high-altitude and/or one of those fancy chambers.
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Re: Does Rocketry Work in the Vacuum?

Unread postby Flabbergasted on Wed Aug 05, 2015 2:57 am

I am sure the experiment would be exciting to watch, but...

1) unlike "interplanetary space", chambers and spheres have inner walls against which the rocket exhaust will push, much like a launch pad. I would surprised if the rocket didn´t move.

I, Gestalta wrote:Place the "rocket" inside the sphere unattached

2) unless you can replicate conditions of perfect weightlessness, the rocket won´t be able to float or otherwise "remain unattached" inside the sphere but will be in contact with some structure or surface with which it will interact the moment force is applied.

Also:
viewtopic.php?f=23&t=1632&p=2393845#p2393845
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Re: Does Rocketry Work in the Vacuum?

Unread postby I, Gestalta on Wed Aug 05, 2015 4:57 am

Well, a primary aspect of the experiment would be to determine whether or not a flame would actually be possible to create within these conditions. It would be an attempt at creating a combustion reaction with lesser and lesser degrees of oxygen.

The attachment-to-matter aspect of the experiment would be secondary, and would require separate observations. For instance, what if the experiment determined that, no matter what degree of oxygen were present at a particular stage of air/oxygen reduction, a flame could not be produced?

Finally, what would be the harm in seeing if a flame could be created in an environment which has been entirely relieved of oxygen?

Depending upon the results, the rest of my conditions could be tested (and expanded upon) fairly easily. The primary objective of my supposition is to test the possibility of combustion even occurring in vacuum, let alone creating "work".
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Re: Does Rocketry Work in the Vacuum?

Unread postby brianv on Wed Aug 05, 2015 1:18 pm

I, Gestalta wrote:Well, a primary aspect of the experiment would be to determine whether or not a flame would actually be possible to create within these conditions. It would be an attempt at creating a combustion reaction with lesser and lesser degrees of oxygen.

The attachment-to-matter aspect of the experiment would be secondary, and would require separate observations. For instance, what if the experiment determined that, no matter what degree of oxygen were present at a particular stage of air/oxygen reduction, a flame could not be produced?

Finally, what would be the harm in seeing if a flame could be created in an environment which has been entirely relieved of oxygen?

Depending upon the results, the rest of my conditions could be tested (and expanded upon) fairly easily. The primary objective of my supposition is to test the possibility of combustion even occurring in vacuum, let alone creating "work".


One of the first "Science" experiments we did as school-children was to put a candle inside a Bell Jar and extract the air. The candle went out. :rolleyes:
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Re: Does Rocketry Work in the Vacuum?

Unread postby rusty on Wed Aug 05, 2015 1:36 pm

Well, our rocket scientists tell us that space rockets have some sort of combustion chamber which is separated from the vacuum by some sort of nozzle with some sort of valve. They tell us that the combustion takes place in the combustion chamber and then, pffft, the hot combustion products press the valve open and push the rocket forward. Or something like that.

However, I think it's a valid question to ask, if there's a vacuum outside and some gaseous sort of oxygen/fuel mixture inside if this would not automatically lead to a pressure difference that opens the valve and pulls all our precious propellant gases out before they can be ignited.

I guess that's a purely speculative and theoretical question which can hardly be corroborated by any sort of experiment.
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