Does Rocketry Work beyond Earth's atmosphere?

If NASA faked the moon landings, does the agency have any credibility at all? Was the Space Shuttle program also a hoax? Is the International Space Station another one? Do not dismiss these hypotheses offhand. Check out our wider NASA research and make up your own mind about it all.
patrix
Member
Posts: 712
Joined: Wed Dec 14, 2016 10:24 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by patrix »

kickstones » November 27th, 2017, 1:34 pm wrote:Patrix, working on the assumption that a water carrying rocket managed to get into space, what influences would vary in that medium to the ground level vacuum water / ice experiment?
For example, two phenomena documented to occur in space are solar radiation pressure and solar wind pressure, would they have any significant influences in water transformation and rocket mobility?
Dear kickstones,

I'm flattered you ask me, but I can only speculate as much as anyone. Supposing space is as described, I have no idea if that is the case since most likely nothing man made has went above the atmosphere, and if something have, the last thing the people responsible would probably do is to give us any factual information of the nature of space. Anyway, if space is a vacuum, a water mass would “cold boil” (dissipate to a gas in low temperature), this in turn will make it colder as it’s losing heat in that process. And if space is very cold in itself I’m not sure if the water will freeze instantly or if it will be able to dissipate first and become small ice droplets. If water was ejected with pressure behind it, there might be some Newtonian inertia enabling the object ejecting the water to move in the opposite direction. But I find the “Newtonian explanation” of rockets laughable since inertia alone cannot produce any significant movement. To achieve that, there has to be an energy release that can react with the surrounding environment. Say, for example, you have a ship and instead of using the diesel to fuel the engines you start throwing or catapulting the diesel barrels from the back of the ship. That would hardly produce any motion.
The_White_Lodge
Banned
Posts: 65
Joined: Tue Oct 31, 2017 2:01 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by The_White_Lodge »

Patrix,

You have oversimplified this "barrel thrown off of ships" thought experiment. If you are wondering why a bunch of people chucking barrels off a ship would produce very little motion in the opposite direction despite Newton's laws of motion being correct it is because most of the force generated by the throwers of the barrels when transferred to the ship would be along the vector perpendicular to the horizontal motion of the barrels flying off the ship. This is because the throwers of the barrels are connected to the ship via their feet which primarily push through the vertical plane. So, the ship would experience an increasing bounce, but not much directional motion, and indeed were you to carry this experiment out you would notice much greater bobbing of this respective ship immediately during and after these barrels were being thrown.
patrix
Member
Posts: 712
Joined: Wed Dec 14, 2016 10:24 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by patrix »

Dear WL,
Yes, I may not be very good at giving thought experiments around this. Earlier ones in this thread have been better. But the point is that Newtonian laws are perfectly fine, it's just that they cannot do much in terms of propulsion. Another example would be if the ship was a destroyer and you directed and fired all cannons aft. High energy, high velocity, but not much propulsion.
The_White_Lodge
Banned
Posts: 65
Joined: Tue Oct 31, 2017 2:01 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by The_White_Lodge »

Patrix,

If you don't believe in the laws of classical mechanics, I don't have a problem with that, but if you do believe in them then I do have a problem with you claiming they don't cover all forms of motion.

The ship destroyer example you cited has the same flaw in logic as your barrel example, except a ship firing a cannon will generate considerable directional motion in the opposite direction of the cannonball, the amount of this motion would depend on several factors the weight of the ship being one of them.

However, let us turn to a much simpler example of propulsion, the fire cracker. Are you suggesting that firecrackers are not driven upwards by propulsion?
Flabbergasted
Administrator
Posts: 1244
Joined: Mon Nov 12, 2012 12:19 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Flabbergasted »

The_White_Lodge » November 28th, 2017, 1:33 pm wrote:Are you suggesting that firecrackers are not driven upwards by propulsion?
TWL and patrix, if you read the entire thread you will see those scenarios have been covered ad nauseam. Each force (wheels, water, air) pushes most efficiently against an external medium of the same nature. No need to go there again, unless you have found something that pushes against the void.
simonshack
Administrator
Posts: 7341
Joined: Sun Oct 18, 2009 8:09 pm
Location: italy
Contact:

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by simonshack »

The_White_Lodge wrote:
However, let us turn to a much simpler example of propulsion, the fire cracker. Are you suggesting that firecrackers are not driven upwards by propulsion?
Dear WL,

As much as I have appreciated some of your contributions here on this forum, I don't think this particular topic ("Does Rocketry Work beyond Earth's atmosphere?") is your cup of tea. Let me explain:

For you to ask Patrix whether "firecrackers are not driven upwards by propulsion" - is frankly quite silly.

No one here is denying that firecrackers are driven upwards, you see? And no one is denying that propulsion methods are possible - within our atmosphere.

The question is: by WHAT SORT OF propulsion are firecrackers (or any skybound object) driven upwards? Is it solely "recoil propulsion"?

For instance, all you need to be driven upwards (and thus defy / annihilate gravity) is to fill a balloon with hot air: it will get you up to max 40km or so of altitude.
However, NO recoil force is involved with the ascension of a hot air balloon. Air -and only air (i.e. the interaction between colder and hotter air molecules) - is clearly the main 'actor' in this case.

Are you one of those who deny that firecrackers push on the surrounding air molecules? If so, let us know - and elaborate your thoughts about how much (or how little) you think that the surrounding air is responsible for firecrackers to be driven upwards. For now, I will kindly ask you to please refrain from asking senseless / silly questions such as:

"Are you suggesting that firecrackers are not driven upwards by propulsion?"
The_White_Lodge
Banned
Posts: 65
Joined: Tue Oct 31, 2017 2:01 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by The_White_Lodge »

Simon,

My question seemed entirely appropriate given Patrix's statement that:

"Newtonian laws are perfectly fine, it's just that they cannot do much in terms of propulsion"

I cannot intelligibly make out what this statement was suppose to mean, but my best guess is that Patrix is supposing that either propulsion does not exist as a real phenomenon, or that it does exist but it is not governed by Newton's laws of motion.
patrix
Member
Posts: 712
Joined: Wed Dec 14, 2016 10:24 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by patrix »

Dear WL,
As Simon points out, your comments show that you need to go back to the beginning of this thread and start reading. And this time you will not presuppose you actually know the physics involved when it comes to rocketry. Read up on the things Boethius mentions like Joule-Thomson, free expansion etc. In another thread you bring up hypnosis, referring to it at as magic. I don't know if that is correctly understood by me, but the reason I bring it up is not because I want you to explain what you mean again but because I want you to understand and consider that you yourself may be under the spell so to speak. You are in good company because so was I less than a year ago. The lies around space and space travelling have been so carefully crafted that I know of only one man - Simon, that has been able to unveil them fully. If you are able to break free from this spell, to use your own language, you will for one find that the claims of rocketry working in vacuum is nothing but pseudoscience, mesmerizing images and empty claims that phenomena we can readily observe, like GPS and "Sattelite TV", cannot possibly work without them.

I wish you good luck on your journey and hope you will be able to "break free". The keys to your mental prison have been handed to you thanks to the decades of work that Simon, Hoi and all the other fine Cluesforum researchers have carried out and documented on this forum. But only you yourself can put the key in the lock and turn it from the inside of your cell. Yelling for help on that part will only make it harder for you.

Vaya con Dios White Lodge.
kickstones
Member
Posts: 368
Joined: Wed Jan 16, 2013 1:15 pm

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by kickstones »

Patrix, I am inclined to agree with you about NASA spacecraft not being able to escape the earths atmosphere and apart from the satellite image I would say the NASA diagram below is fairly accurate. The diagram also gives me more of an understanding of the Project Highwater data mentioned earlier in relation to water expulsion in space and its relevance to the debate on propulsion of rockets in space.

Image

Diagram of the layers within Earth's atmosphere.

Troposphere
The troposphere starts at the Earth's surface and extends 8 to 14.5 kilometers high (5 to 9 miles). This part of the atmosphere is the most dense. Almost all weather is in this region.

Stratosphere
The stratosphere starts just above the troposphere and extends to 50 kilometers (31 miles) high. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer.

Mesosphere
The mesosphere starts just above the stratosphere and extends to 85 kilometers (53 miles) high. Meteors burn up in this layer

Thermosphere
The thermosphere starts just above the mesosphere and extends to 600 kilometers (372 miles) high. Aurora and satellites occur in this layer.

Ionosphere
The ionosphere is an abundant layer of electrons and ionized atoms and molecules that stretches from about 48 kilometers (30 miles) above the surface to the edge of space at about 965 km (600 mi), overlapping into the mesosphere and thermosphere. This dynamic region grows and shrinks based on solar conditions and divides further into the sub-regions: D, E and F; based on what wavelength of solar radiation is absorbed. The ionosphere is a critical link in the chain of Sun-Earth interactions. This region is what makes radio communications possible.

Exosphere
This is the upper limit of our atmosphere. It extends from the top of the thermosphere up to 10,000 km (6,200 mi).
Credit: NASA/Goddard

What is relevant to our water released in space scenario is the ionosphere and solar radiation absorbtion.

More specifically if we go back to the data report I linked to on the previous page it states...

"the ProJect High Water has provided essential Information relevant to a number of problems vital to --------- * explorations of space.
*(I could not make out the missing word)

Detailed knowledge of the dispersal of large quantities of liquids in space permits the determination of first order engineering parameters associated with an abort or explosion in space.

The first water release occurred in April 1962 at an altitude of 105 km (SA-2) and the second release was in November 1962 at an altitude of 165 km (8A-3)

The US Standard Atmosphere (1961) gives the atmospheric pressure at km at 105km l.3 x 10-4 torr (mm of Hg), and 2.4 x 10-6 torr at 165km

The water released, through ruptures to the container, expanded 'initially average expansion rate velocity of 1,05 km/seci. however, expansion rate velocities as high as 3.60 km/sec were observed.'

Laboratory experiments simulating the release of water into the ionosphere have been carried out in a Space Environment Simulator (SES).
These tests were performed with ambient pressures within the SES at 1.1 x 10-4 torr The pre-release chamber pressure was 1.4 x 10-4 torr.
Following the release, the chamber pressure rose to 3.2 x 10-2 torr."

An Analysis of the Second Project High Water Data
https://ntrs.nasa.gov/archive/nasa/casi ... 078055.pdf

Would the same result occur if water was released at the upper limit of our atmosphere (exosphere) and the boundaries of space where I would suspect solar radiation is at a greater level and the pressure would be less?

I realise people state there's zero pressure in a vacuum because there's no matter to be pressurised and as such no reaction would take place but wouldn't that change once matter was introduced?

For example from the Project Highwater....

Consider a spherical mass of fluid initially at rest in a region of zero pressure at time t=O the restraining membrane is instantaneously
removed allowing the fluid to expand into the evacuated region.


In the lab experiment reaction of water exposed to minimal pressure took place rapidly.

An examination of the film records showed that the water emerged as a multiplicity of minute droplets. These droplets rapidly dispersed.
A portion of the droplets were converted to ice particles. Freezing of the droplets probably commenced almost immediately. A significant
fraction of the droplets froze within five(5) milliseconds, and after 10 milliseconds, all of the remaining droplets were frozen
.

That there is now matter in the environment of space, ice droplets, would pressure be created on contact with them by solar radiation / solar wind?

The below from Wiki, and I realise that much of the data is gleaned from supposed satellites and spacecraft, however this is what's stated.....

Solar wind

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma consists of mostly electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude.

While early models of the solar wind relied primarily on thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required and likely relates to magnetic fields in the solar atmosphere.

The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of 300–500 km/s, a temperature of 1.4–1.6×106 K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of 750 km/s, a temperature of 8×105 K and it nearly matches the composition of the Sun's photosphere. The slow solar wind is twice as dense and more variable in nature than the fast solar wind.

https://en.wikipedia.org/wiki/Solar_wind

Radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. Radiation pressure implies an interaction between electromagnetic radiation and bodies of various types, including clouds of particles or gases. The interactions can be absorption, reflection, or some of both (the common case). Bodies also emit radiation and thereby experience a resulting pressure.

Johannes Kepler put forward the concept of radiation pressure back in 1619 to explain the observation that a tail of a comet always points away from the Sun.

The assertion that light, as electromagnetic radiation, has the property of momentum and thus it exerts a pressure upon any surface it is exposed to was published by James Clerk Maxwell in 1862, and proven experimentally by Russian physicist Pyotr Lebedev in 1900 and by Ernest Fox Nichols and Gordon Ferrie Hull in 1901.

https://en.wikipedia.org/wiki/Radiation_pressure

Comet

A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.

The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the "coma". The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous "tail" to form pointing away from the Sun.

The coma is generally made of  H2O and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun. The  H2O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization, with the solar wind playing a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path whereas smaller particles are pushed away from the Sun into the comet's tail by light pressure.

https://en.wikipedia.org/wiki/Comet

Would the above pressure created by solar wind /solar radiation have the same effect on a water releasing rocket and generate enough force to maintain continued momentum in space?
kickstones
Member
Posts: 368
Joined: Wed Jan 16, 2013 1:15 pm

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by kickstones »

Below is further information on the dynamics behind momentum of a comet, if correct and applied to a water emitting rocket in space it may help in determining if momentum beyond the earths atmosphere is plausible.

The first article is a simplified explanation and maybe unsound because the so-called expert does tell of space travel while the second has complex physics and as my physics knowledge is not of the highest order others, more proficient, will have to scrutinise it for validity.

What powers a comet?

Our friends at the Back Bay Astronomy Club in Virginia Beach, Virginia asked "What powers a comet?"

Well, that's a very interesting way to look at comets. It does seem as if they must be under some kind of power like a rocket or a spacecraft with thrusters. Comets travel very fast, loop around the Sun, and have long tails.

Because the comets are much smaller and lighter than planets, they are easily pulled this way and that by the gravity of the planets (or, in some cases, even by stars). So when we see them streaking through the solar system, they often aren't following the kind of neat, nearly circular orbits that most planets do.

The solid part of the comet, its "nucleus," is like a dirty, hard-packed snowball with pockets of air trapped inside. When a comet's orbit brings it into the inner solar system, where you and I live, some of the ice and gas are heated by the Sun, and they expand to form a cloud around the nucleus. Although the nucleus may be only a few kilometers across, the cloud, called a coma, can be thousands of kilometers across—even larger than Earth. The coma blocks our view of the nucleus, just as a cloud blocks your view of an airplane flying inside it.

Image

Light and other radiation from the Sun push on the gas and dust in the coma, blowing the material away to form a tail that can be millions of kilometers long. Now imagine you are wearing a scarf on a windy day. The direction the scarf blows does not depend upon the direction you are walking—all that matters is the direction the wind is blowing. The tail of a comet is the same—it points away from the Sun, regardless of whether the comet is on the part of its orbit that is taking it toward the Sun or away.

So one answer to what powers a comet is simply that the Sun does. It provides the heat that drives some of the material from the nucleus into the huge coma, and it provides the pressure to push some of that into the long and beautiful tail.

Now what powers the comet's orbit? Well, comets formed in the rotating cloud that produced the solar system, so that got them started on their orbits of the Sun. (This is the same reason Earth and the other planets orbit the Sun.) We already know that the comets are so light that the planets yank their orbits around, sending them just about every direction in the solar system. But still another force acts on comets. When gases inside the nucleus expand under the heat of the Sun, they often shoot through holes or weak spots in the crust of the nucleus, like the steam coming through the hole in a tea pot. The expanding gas and dust escape in jets, having the same effect as thrusters on a spacecraft. This force, like letting the air out of a balloon, will change the comet's path, making its orbit hard for astronomers to predict precisely.

http://fileserver.net-texts.com/asset.a ... &id=166316

Comet Tails

Comet tails come in two flavors: the ion tail and the dust tail.

The ion tail is thin, blue and linear - points directly away from the Sun.

The dust tail is white, broad and points generally (but not precisely) away from the Sun

What is happening?

Image

Physics of the Ion Tail


The ion tail is made up of ions (surprise!) - mostly CO+, N2+, CO2+. As the comet comes into the inner solar system, the Sun's radiation heats up the nucleus, "boiling off" and ionizing these gases.

These ions are electrically charged particles, and interact with the sun's solar wind (charged particles coming from the sun). The interaction between the comet and the solar wind distorts magnetic field lines, causing a cometary magnetotail which points away from the Sun. The charged ions stream along the magnetic field lines in the magnetotail, so the ion tail always points away from the Sun.

CO+ absorbs sunlight and flouresces, emitting energy at a wavelength of 4200 Angstroms, which is blue light.

Physics of the Dust Tail

The dust is not necessarily charged -- why should the dust tail point away from the Sun?

I. Radiation Pressure

Remember that photons (particles of light) carry momentum:

Image

And that force and momentum are related by

Image

Photons emitted from the Sun carry momentum outwards in a spherical shell (since they are radiated in all directions). Since pressure is force per unit area, the pressure these photons would place on an imaginary shell around the sun is

Image

Rather than assume an imaginary shell around the Sun, look at a single grain of dust. How much of a force would this grain feel. Force is the pressure applied times the grain's cross-sectional area, so it would feel a force

Image

So this is the force it feels from radiation pressure. But it also feels the force of gravity (from the Sun)

Image

If a grain is big, it has a lot of mass, so gravity wins. If a grain is small, it has less mass and radiation pressure wins. When does this balance occur?

Image

Putting in typical numbers, we get R=0.006 cm -- small! Grains smaller than this will be pushed away from the Sun. Grains larger than this will be left behind along the comet tail (what will they become?).

Actually, grains MUCH smaller than that won't absorb solar radiation as efficiently, so something else must be pushing on them -- solar wind collisions.

Both radiation pressure and solar wind collisions are less effective at pushing on dust particles than magnetic fields are at containing ions, so the dust tail is broader than the ion tail, and it is not as precisely aligned away from the Sun as the ion tail is.

Finally, the dust tail reflects sunlight, so it appears yellow/whitish in color.

http://burro.astr.cwru.edu/Academics/As ... tails.html
kickstones
Member
Posts: 368
Joined: Wed Jan 16, 2013 1:15 pm

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by kickstones »

More on solar radiation......

PREDICTING THE STRENGTH OF LEONID OUTBURSTS
https://leonid.arc.nasa.gov/MS033.pdf
LYYTINEN AND VAN FLANDERN

152
3.1. THE REGULAR RADIAL PRESSURE

What is usually called simply radiation pressure is here called “regular radial pressure”. It is a repulsive force, which is inversely
proportional to solar distance, effectively lowering the gravitational force. Other radiation pressure effects can be non-radial and can
have a different dependence on solar distance. Notably, variations in radiation force as a result of the particle's surface to mass ratio, rate
of rotation, etc., will lead to dispersion of particles,

The radiation force on a particle consists of three parts: due to absorption of solar radiation energy, due to re-radiation of the thermal energy, and due to reflection (scattering). The radiation pressure force on a totally absorbing particle of diameter d, neglecting the other two effects, at a distance r from the Sun is:

xxxxxxxxxxxxxx
(apologies due to formating problems I cannot post the formula in its entirety at present, interested readers should go to page 152 on the link below)
https://leonid.arc.nasa.gov/MS033.pdf

The constant S0 is the solar radiation constant at Earth’s distance and c is the light speed. In the ideal case where there is no absorption and all the energy would be reflected directly backwards (to the Sun) like a flat mirror put normal to the solar radius, the total effect would be twice that given by (1). Similarly, in the ideal case that all the energy would be re-radiated as thermal radiation directly backwards toward the Sun, the force by re-radiation would be the same as that of scattering. Hence, if the particle is non-rotating, spherical, non-conducting and homogenous on its surface, we can assume that the total force due to absorption, re-radiation, and scattering is directed away from the Sun and obeys an inverse square law.

Another scientific model can be found here...

https://ntrs.nasa.gov/archive/nasa/casi ... 004068.pdf
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Technical Memorandum 33-494
Mathematical Model of the Solar Radiation Force and Torques Acting on the Components of a Spacecraft
R. M. Georgevi

Although based on forces acting on a spacecraft it may help determine what forces would act on a body of water to ice transformation in space.

ABSTRACT
Solar radiation pressure exerts a mechanical force upon the surface of a spacecraft which intercepts the stream of photons coming from the
Sun. For high-precision spacecraft attitude control and orbit determination, it is necessary to generate a precise mathematical model of the
solar radiation force and the moment of that force; such a model must be more accurate than the currently used "flat surfaceIt model, based
on the radiation force on the effective cross-section area of the irradiated body. Another advantage of the model is that it can be used for the
effects of the air drag, solar wind, etc.


And of interest is ....

https://www.the-cryosphere.net/10/2541/ ... 1-2016.pdf
Reflective properties of white sea ice and snow
Aleksey Malinka et al

Who inform that.....

There can be different contaminants in ice. The particles of sediments from the atmosphere, which could be both long-distance-transferred (as with Sahara dust) or local (pollutionfrom industrial centers), can affect the sea ice albedo drastically (see e.g., Light et al., 1998; Marks and King, 2014; Lamare et al., 2016). For example, clay, slit, and sand particles are found in the ice situated far from a coastline in the Beaufort Sea (Reimnitz et al., 1993) and in the central Arctic (Nürnberg et al., 1994)

This raises the question what would happen if water released from a rocket in space containing such sediments collided with space dust, such as from a comet?

Because as this paper puts forward ...

Space Dust Collisions as a Planetary Escape Mechanism

http://online.liebertpub.com/doi/abs/10 ... alCode=ast

Abstract
It is observed that hypervelocity space dust, which is continuously bombarding Earth, creates immense momentum flows in the atmosphere. Some of this fast space dust inevitably will interact with the atmospheric system, transferring energy and moving particles around, with various possible consequences. An interesting outcome of this collision scenario is that a variety of particles that contain telltale signs of Earth's organic story, including microbial life and life-essential molecules, may be “afloat” in Earth's atmosphere. The present study assesses the capability of this space dust collision mechanism to propel some of these biological constituents into space.
kickstones
Member
Posts: 368
Joined: Wed Jan 16, 2013 1:15 pm

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by kickstones »

Would using seawater in a rocket in space have any benifits?

If this information posted on Wikipedia regarding water rockets is veryfiable then yes.

Image

A water rocket is a type of model rocket using water as its reaction mass. The water is forced out by a pressurized gas, typically compressed air.
The bottle is partly filled with water and sealed. The bottle is then pressurized with a gas, usually air compressed from a bicycle pump, air compressor, or cylinder up to 125 psi, but sometimes CO2 or nitrogen from a cylinder.

Image
Simplified animation of how a water rocket works. 1) A bubble of compressed air is added and pressurizes the contents of the bottle. 2) The bottle is released from the pump. 3) The water is pushed out through the nozzle by the compressed air. 4) The bottle moves away from the water because it follows Newton's Third Law.

Water and gas are used in combination, with the gas providing a means to store energy, as it is compressible, and the water increasing the propellant mass fraction and providing greater force when ejected from the rocket's nozzle. Sometimes additives are combined with the water to enhance performance in different ways. For example: salt can be added to increase the density of the reaction mass resulting in a higher specific impulse.

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

Specific impulse

Specific impulse (usually abbreviated Isp) is a measure of how effectively a rocket uses propellant or jet engine uses fuel. By definition, it is the total impulse (or change in momentum) delivered per unit of propellant consumed and is dimensionally equivalent to the generated thrust divided by the propellant mass or weight flow rate. If mass (kilogram or slug) is used as the unit of propellant, then specific impulse has units of velocity. If weight (newton or pound) is used instead, then specific impulse has units of time (seconds). Multiplying flow rate by the standard gravity (g0) converts specific impulse from the mass basis to the weight basis.

A propulsion system with a higher specific impulse uses the mass of the propellant more effectively in creating forward thrust and, in the case of a rocket, less propellant needed for a given delta-v, per the Tsiolkovsky rocket equation.

Rocketry

In rocketry, where the only reaction mass is the propellant, an equivalent way of calculating the specific impulse in seconds is also frequently used. In this sense, specific impulse is defined as the thrust integrated over time per unit weight-on-Earth of the propellant:


Image

where

Image is the specific impulse measured in seconds
Image is the average exhaust speed along the axis of the engine (in ft/s or m/s),
Image is the standard gravity (in ft/s2 or m/s2).

In rockets, due to atmospheric effects, the specific impulse varies with altitude, reaching a maximum in a vacuum. This is because the exhaust velocity isn't simply a function of the chamber pressure, but is a function of the difference between the interior and exterior of the combustion chamber. It is therefore important to note whether the specific impulse refers to operation in a vacuum or at sea level.

https://en.wikipedia.org/wiki/Specific_impulse

Whether or not salt will have an effect on the states (e.g. freezing ) of the emitted seawater in space is another matter.
patrix
Member
Posts: 712
Joined: Wed Dec 14, 2016 10:24 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by patrix »

kickstones » December 5th, 2017, 12:08 pm wrote:Would using seawater in a rocket in space have any benifits?
I'm getting a bit puzzled by these posts about water rockets, and this one does it since it implies rockets goes to space, which this thread in its very first post demonstrates they cannot. I suggest another thread for this matter.

And a “water rocket” is a pretty bad idea since water is not very compressible and cannot effectively turn into high volume gas through expansion or chemical reaction. The toy water rockets work by recoil. Compressed air forces the water out and the rockets go up ten, twenty meters or so.
Altair
Member
Posts: 90
Joined: Thu Feb 02, 2017 2:05 pm

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by Altair »

Anyway, I'm inclined to think that LEO sats (but no more than that) could be launched by just ballistic rockets, without need for them to work in the vacuum. I've been googling how it all began, with the Sputnik. If we have to believe Wikipedia, it was launched by a R-7 rocket, which was a missile launcher. Those could deliver some 5 tons to 12.000 km. Taking into account that Sputnik weighed only 45 kgs., maybe it was possible to get more height + momentum so that light objects could be put in LEO.

Now, this leaves open the question of orbital adjustments and of course, transfer to higher orbits (particularly geostationary), which undoubtely require rocket propulsion in a vacuum.

And of course, no way that something as heavy as the space shuttle can make its way above some 20 km or so...
FervidGus
Posts: 7
Joined: Sun Dec 03, 2017 12:45 am

Re: Does Rocketry Work beyond Earth's atmosphere?

Unread post by FervidGus »

PART 1

This will be my first contribution, although I have something in the pipeline for ‘The Rise & fall of ISIS’ too.

What follows will be an evaluation of the arguments for why rocketry will not work in a vacuum, as well as looking into misassumptions into the characteristics of the void of outer space as well. It will be made into 4 main parts, this being part 1. Even if rockets work in space, as I believe, this is does not by default lend credence to the warped images we encounter dressed as fact by NASA or whoever else.

I shall start with the first post of this topic, by Boethius:
“There are 4 major ideas on presented on the Internet, including NASA web sites, as to how rockets generate thrust in space
1. Newton’s 3rd Law : for every force there is an equal and opposite
2. Newtons’s 2nd Law : Force = Mass x Acceleration
3. Conservation of Momentum
4. The use of a specialized nozzle to accelerate the gas inside the ship, concentrate and aas jet”
Part 1 looks at the first point here, concerning Newton’s first law.
“The problem with applying Newton’s 3rd is that the rocket’s propellant does not generate force in a vacuum according to the laws of physics and chemistry. If the force of the propellant is 0 then Newton’s 3rd states that
Force on Rocket=-Force of Gas.
If Force of Gas = 0 the rocket does not move.”
[The logic here would be consistent, assuming that the force of the gas is indeed zero, although such is not the case]
“Why doesn’t the propellant generate any force, it's expanding, right?
There is something known as “Free Expansion” or the “Joule-Thomson” effect, named after James Prescott Joule and J.J. Thompson two of the founders of the field of Physical Chemistry.
(…)
Free Expansion states that when a pressurized gas is exposed to a vacuum the gas expanding into the vacuum without any work being done. The gas is not “pulled” or “sucked” into the vacuum nor is it “pushed” out of the high-pressure container. In other words no work is done, no heat or energy is lost.
This result has been experimentally verified numerous times since its discovery in the 1850’s.
[for example a paper in the Journal of Physical Chemistry from 1902: (…)”
Again, this is a good set of points that present a fair argument at first glance. But this is where the science stops, as it is incorrectly applied to the behavior of a rocket.

To start with, a rocket is a projectile that propels itself by ‘chucking’ its combustible load from its exhaust in order to move in the opposite direction of the ‘chucking’. If the exhaust may be manipulated, then the rocket is able to move in accordance to the shape of the exhaust manipulation. This is securely known to work for all missiles that work within the atmosphere.

So what about outer space? Wouldn’t free expansion halt the movement of particles as stated by Boethius? Not quite.

Remaining within the context of Newton’s third law, free expansion, and the non-existent push-pull action within a low gravity vacuum, the following explanation is given. All substances have a triple point, where there is a specific temperature and pressure wherein all three phases (solid, liquid, and gas) may exist at the same time. For water, it may sublimate (depending on the atmospheric conditions) or evaporate into a vapor between the temperatures of -50* C and about 350* C under a pressure curve. Depending on what the temperature of the water is, a certain pressure will result in the vapor phase.

Image
URL:http://cubeupload.com/im/Winterabstract ... ramofw.png

In general, gases are highly excited particles that may bounce around the walls of a vessel if a gas is to be contained- it is this very intensity of collisions which determines the pressure of a gas within a vessel. The more particles there are per unit volume, the higher the pressure. Now if you have liquid oxygen in space, it will most probably evaporate into a gas from liquid phases along certain temperatures and pressures. In the case of rockets purportedly used by NASA, liquid oxygen in kept in very cool conditions i.e. -182.7* C.

Now assume that you have an uninsulated, hollow sphere with 1 very small opening, so far sealed up. Inside this sphere is ordinary water, or liquid oxygen, and this sphere materializes into outer space. According to the laws of pressure, the liquid fluid inside will change phase into a gas due to the huge reduction in pressure. And the gas inside this sphere is now at a much higher pressure because it occupies all of the volume within the sphere; the energetic particles are colliding with the walls. Does low gravity affect the Brownian motion? Not at all (relatively)! The gas particles have too much energy to “link” with each other, and it’s unlikely that at the current temperature and pressure that the particles will settle.

So at this point the small hole is opened. The major point of contention is that free expansion will somehow negate the work done by the propellant exhaust of a rocket. According to Wolfram Alpha;
“In 1843, Joule did this simple experiment to show that the internal energy of a gas is a function of temperature, independent of pressure or volume. When the gas in the left sphere initially flows without resistance into the vacuum of the right sphere, no work is performed and no heat is transferred. Thus the temperature remains constant. It is now understood that this result is accurate only for an ideal gas.”


Image
URL:http://cubeupload.com/im/Winterabstract ... ansion.jpg

Now a few things taken from this are that this works best for an ideal gas, Independent of pressure and volume. This snippet can be applied to our sphere: after a period of time, the gas molecules will flow from the sphere via the small hole into the vacuum. There is a difference of pressure to be noted here- the vacuum has very low pressure, whereas the sphere has a much higher one.

So does this apply to the propellant exhaust of a rocket? Let’s see. First let us consider what a rocket does to produce the exhaust propellant. Through the mixing of liquid oxygen and rocket fuel, an explosive chemical reaction occurs to produce products. Now these exhaust products, usually gases, have a significant kinetic energy to them in contrast to the reaction products, which were fed through pipes using pumps etc. Where did this energy originate from? From the enthalpy change of combustion of course! The exothermic reaction, that was combustion, led to the products’ chemical bonds containing less bond enthalpy thus resulting to energy being lost to the system (the environment within the combustion chamber). Under the conservation of energy, this lost energy has to go somewhere. And so much of this energy is transferred to the products via kinetic energy, whereas a lot of also lost through heat, sound, light energy etc.

We have previously seen that Brownian motion of gas particles is not affected by low gravity, nor a vacuum; a vacuum neither pushes nor pulls. So this also applies to a rocket’s exhaust propellant. This high temperature, energetic exhaust is kept at high pressure by forcing it through a narrow pipe until it reaches the nozzle. Here it bursts out, pushing against the rocket. According to the third law of motion, as it pushes against the rocket, the rocket pushes back, and so the rocket is propelled. Free expansion plays no part here because this is a situation where the gas has a velocity component; it (the exhaust) is not isolated within a vessel with a small hole to pass through, rather it has been formed via a violent reaction and is being channeled to exit the rocket. I can find no scientific basis for other comments on free expansion that were mentioned in the first post of the topic. There is little difference between the process here taking place on earth, or in space.

So in summary, as the exhaust gases exert an upwards force on the rocket, an equal but opposite force downwards is exerted by the rocket body, thus resulting in the desired upwards motion. Neither free expansion nor an atmosphere plays a major role in this key model.

As long as the key points in part 1 are understood and stand without error, then I will progress to the successive parts relating to points 2, 3, and 4.

I will create the following parts soon, and in the meanwhile gladly anticipate debate on this.

(EDIT: Note for the admins: I have used cubeupload for the images, and used the share link URL...which after posting seems to have failed)
Post Reply