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Plat
2007-Jun-26, 11:53 AM
I want to know more about spacecrafts, like are there engines on spacecrafts? I would figure that if they did they would probably have to be the most powerful on Earth. What different kinds of energy does get used when lifting off the rocket into space?

NEOWatcher
2007-Jun-26, 12:40 PM
I want to know more about spacecrafts, like are there engines on spacecrafts? I would figure that if they did they would probably have to be the most powerful on Earth. What different kinds of energy does get used when lifting off the rocket into space?
Do you have some more specific questions about this? It's a rather general question considering all the different spacecraft that have been made.
But;
The Saturn-V rockets were the most powerful engines ever made. You may want to peruse that if you're looking for power information.
Basically, all rocket technology uses a chemical reaction (a burn) to create the energy. There have been many different fuels used.

Plat
2007-Jun-26, 12:42 PM
How about the Space Shuttle? the manned spacecraft.

NEOWatcher
2007-Jun-26, 12:46 PM
How about the Space Shuttle? the manned spacecraft.
How about what aspect?
Saturn-V was manned...
I don't understand your question...

Plat
2007-Jun-26, 01:03 PM
Nevermind...here is another question, what happens when the rocket gets our of the Earth's atmosphere and gravity, does it still put on the afterburners or what?

Do we have the technology now to send a rocket to lets say Pluto

R.A.F.
2007-Jun-26, 01:11 PM
Do we have the technology now to send a rocket to lets say Pluto

I googled rocket to pluto (http://www.google.com/search?hl=en&q=rocket to pluto&btnG=Google Search). The very first result is the New Horizons missions page.

Ya know, Platinum...you "could" use google yourself to answer your questions...just a thought.

Argos
2007-Jun-26, 01:12 PM
Do we have the technology now to send a rocket to lets say Pluto

Yes (http://pluto.jhuapl.edu/)

NEOWatcher
2007-Jun-26, 01:15 PM
Nevermind...here is another question, what happens when the rocket gets our of the Earth's atmosphere and gravity, does it still put on the afterburners or what?

Do we have the technology now to send a rocket to lets say Pluto
The fuel has it's own oxidizer, either part of the fuel, or part of the burn (with an oxygen tank to mix with it).
Therefore, no air from the atmosphere is needed.
The rocket does not "get out of our gravity". It just goes fast enough against gravity that it's neutralized (free fall). And since there is nothing slowing you down in space, it's best to get up to speed as quickly as possible.
New horizons (http://www.bautforum.com/showthread.php?t=37223) is on it's way to Pluto...
I suggest you do some of your own research. It's fairly clear that you need a little more education on the subject than a Q&A can provide. I know that I tend to learn a lot more this way, because I always discover related topics that make things a lot more clear.
Here's a start on orbital mechanics (http://aerospacescholars.jsc.nasa.gov/HAS/cirr/ss/3/2.cfm).

Argos
2007-Jun-26, 01:16 PM
RAF beat me on that...

Remember the Pioneers and Voyagers too.

cudachaser
2007-Jun-26, 01:22 PM
The space shuttle uses 2 solid rocket boosters and 3 main engines to get into orbit. The main engines use liquid hydrogen and liquid oxygen. Once in space the orbiter maneuvers with 44 thrusters and 2 larger OMS engines. These engines are powered by mono-methyl hydrazine and nitrogen tetroxide which are hypergolic meaning they ignite on contact requiring no ignition system

Nicolas
2007-Jun-26, 01:32 PM
Considering power of a rocket engine (or jet engine or other reaction engine), it isn't really relevant to express that in horsepower. It gives a huge number, sure, but simply stating thrust is more relevant as (unless I'm mistaken) you can't really compare these HP's with the HP's of say a car engine.

btw also the turbopumps feeding the rocket engines are enormously powerful, and one of the difficult parts in designing and building a working rocket engine. Jut ask the N-1 rocket ;).

Bob B.
2007-Jun-26, 05:21 PM
I want to know more about spacecrafts, like are there engines on spacecrafts? I would figure that if they did they would probably have to be the most powerful on Earth. What different kinds of energy does get used when lifting off the rocket into space?

Please give my web page a look, it should give you a good introduction to the subject and answer many of your questions:

Rocket & Space Technology (http://www.braeunig.us/space/index.htm)

_

Nicolas
2007-Jun-26, 06:46 PM
If your website is as good as some of your general rocket info in your replies, it is a good start indeed :).

tofu
2007-Jun-26, 07:17 PM
wow, that is a great website. kudos to you Bob.

Bob B.
2007-Jun-26, 08:51 PM
Thank, guys.

I wish I had time to do more with it, but job and home responsibilities always seem to get in the way. I have an outline of a bunch of sections I want to add but I seem to be able to get only about one done a year. By the time I finally consider the site complete I'll probably have spent 20 years working on it. I suppose that's what makes it a good hobby; there is always more to learn and do.

Jens
2007-Jun-27, 06:53 AM
Ya know, Platinum...you "could" use google yourself to answer your questions...just a thought.

Not just google, either. Try going to your public library, and find a book on rockets. They're bound to have them. You'll find a great amount of interesting knowledge.

And if you're an interested kid, why not get an Estes rocket? Simple, but it's the same principle. Plus they're really cool to watch, and not that expensive.

Nicolas
2007-Jun-27, 08:17 AM
I've checked on ESTEC rockets, and they're in the two hundred million dollar range. Oh, Estessss. My bad.

cjl
2007-Jun-28, 03:15 PM
Do you have some more specific questions about this? It's a rather general question considering all the different spacecraft that have been made.
But;
The Saturn-V rockets were the most powerful engines ever made. You may want to peruse that if you're looking for power information.
Basically, all rocket technology uses a chemical reaction (a burn) to create the energy. There have been many different fuels used.

Actually, they were the most powerful liquid fueled engines ever made. They put out 1.5 million pounds of thrust each. The Shuttle SRB's are the highest thrust rocket engines ever, at 2.8 million pounds of thrust each.

NEOWatcher
2007-Jun-28, 04:13 PM
Actually, they were the most powerful liquid fueled engines ever made. They put out 1.5 million pounds of thrust each. The Shuttle SRB's are the highest thrust rocket engines ever, at 2.8 million pounds of thrust each.
An important distinction...Thanks for the correction.
I may have heard it with some technical semantic with the word motor or something that doesn't apply to solid rockets.

cjl
2007-Jun-28, 04:27 PM
Possibly...

I will say this - IMO, they are both incredible achievements, and to see the nozzle of an F1 is an amazing sight (as is the entire saturn V). The SRB's are inherently simpler, but there's still a lot of work that went into making the thrust curve exactly as needed - it isn't a simple matter like throttling a liquid.

(on a side note, this (http://www.csar.uiuc.edu/) is an amazing site to see some simulations of large solid rocket motors, including the Shuttle SRB's)

Nicolas
2007-Jun-28, 06:21 PM
The SRB's are the most advanced candles in the world. ;)

Bob B.
2007-Jun-28, 08:36 PM
An important distinction...Thanks for the correction.
I may have heard it with some technical semantic with the word motor or something that doesn't apply to solid rockets.

Although it is not a hard and fast rule, generally...

Engine = liquid propellant
Motor = solid propellant

cjl
2007-Jun-28, 09:34 PM
The SRB's are the most advanced candles in the world. ;)
When did they start including oxidizer with candles?

;)

matthewota
2007-Jun-29, 11:51 AM
The Saturn V had many different types of rocket engines, ranging from the Rockedyne F-1 Kerosene/LOX engines to the solid propellant ullage and retrorocket motors on the upper stages. Specifically you are meaning the F-1 engines which were installed in a five engine cluster at the base of the first stage. Total thrust was 7.5 million pounds.

Matthew Ota
space history buff


Do you have some more specific questions about this? It's a rather general question considering all the different spacecraft that have been made.
But;
The Saturn-V rockets were the most powerful engines ever made. You may want to peruse that if you're looking for power information.
Basically, all rocket technology uses a chemical reaction (a burn) to create the energy. There have been many different fuels used.

NEOWatcher
2007-Jun-29, 12:50 PM
When did they start including oxidizer with candles?

;)
That's what makes them so advanced.
SRB > flare > candle

Bob B.
2007-Jun-29, 06:18 PM
Platinum Rhymer, are you planning to return to this thread? You started it and yet you seem not to be much of a participant. Working on the premise that you are paying attention, I will try to answer some of your questions.


I want to know more about spacecrafts, like are there engines on spacecrafts?

When you use the word ďspacecraftĒ I assume you are talking about the vehicle that is put into space and not the rocket that launched it. Your questions seem to wander back and forth between spacecraft and launch vehicles, thus Iím not sure what it is you are looking for. I define the terms as follows:

Spacecraft - A piloted or unpiloted vehicle designed for travel in space.

Launch Vehicle - A rocket used to launch a satellite or spacecraft into orbit.

Obviously there are engines on launch vehicles since they must power their payload into orbit. Most spacecraft have some combination of engines as well depending on the mission they are designed to perform.

Virtually all satellites and spacecraft have some means of attitude control. Attitude refers to the orientation of the vehicle, which is important for aiming instruments and engines, etc. In some cases attitude is controlled by non-propulsive means, such as reaction wheels, but more often there is some form of three-axis control (pitch, yaw, and roll) using small engines called thrusters. The thrusters may be cold gas type (e.g. nitrogen), monopropellant type (e.g. hydrazine), or bipropellant type (e.g. monomethyl hydrazine [MMH] and nitrogen tetroxide [N2O4]).

In addition to attitude control, some spacecraft have an engine(s) for performing a variety of maneuvers. For instance, a manned vehicle may need an engine to alter its orbit and maneuver to a rendezvous with another space vehicle. An interplanetary spacecraft has an engine for mid-course corrections and to provide the decrease in velocity required to enter orbit around its target planet. A geostationary satellite may have an engine to perform the maneuver needed to settle into its final geostationary orbit.


I would figure that if they did they would probably have to be the most powerful on Earth.

Are you now talking about spacecraft or launch vehicles?

Launch vehicles certainly need powerful engines to lift the full weight of the rocket, propellant, and payload; however the engines donít necessarily have to be the most powerful available. It all depends on how big the fully assembled rocket is. The engines have to powerful enough to lift the rocket, but you donít want to oversize them or else the acceleration loads will be too great. There is a balancing act that must be performed to determine the right sized engine for the specific application. Launch vehicles come in all sorts of sizes for launching a wide range of payloads.

Spacecraft, on the other hand, most certainly do not need the most powerful engines. Attitude control thrusters are very small, and most maneuvering engines are of fairly low thrust. It does not take an especially powerful engine to maneuver a spacecraft around once it is in space.


What different kinds of energy does get used when lifting off the rocket into space?

The chemical energy stored within the propellant is released as thermal energy which is then converted to kinetic energy, however I have a feeling this isnít the answer you were looking for. If your intention is otherwise, please clarify.


How about the Space Shuttle? the manned spacecraft.

The winged part of the Space Shuttle is called the Orbiter. It is both a spacecraft and part of the launch vehicle. The three large engines on the aft end of the Orbiter, called the Space Shuttle Main Engines (SSME), are used only during launch and are fed liquid hydrogen and liquid oxygen propellant from the large External Tank (ET). The SSME provide a thrust of 470,000 pounds each in a vacuum. Once the Orbiter is in space, the SSME are no longer used until the next time the Shuttle is launched.

The Space Shuttle is also equipped with two smaller engines that are part of the Orbital Maneuvering System (OMS). The OMS engines are also on the aft end of the Orbiter, burn MMH and N2O4, and have a thrust of 6,000 pounds each. The Orbiterís Reaction Control System (RCS) consists of 38 each 870-pound thrusters and six 24-pound thrusters. These thrusters are scattered about at both the forward and aft ends. The larger thrusters are for coarse attitude control while the smaller ones are for fine attitude control. The very small thrusters are sometimes called verniers.


...here is another question, what happens when the rocket gets our of the Earth's atmosphere and gravity, does it still put on the afterburners or what?

A spacecraft does not need to continually thrust as is often depicted in science fiction movies and television. Traveling in space is simply a matter of transferring between orbits of different sizes and shapes until you get to where you want to go. The orbit transfers require engine burns of short duration, but then the spacecraft just coasts along the new trajectory until it reaches the next transfer point. Most transfers can be performed with a fairly small engine.


Do we have the technology now to send a rocket to lets say Pluto

Yes Ö see New Horizons.

Extravoice
2007-Jun-30, 01:14 AM
Nice explanation Bob. I certainly learned a few things :)

A follow-on question, though.
You wrote:
The thrusters may be cold gas type (e.g. nitrogen), monopropellant type (e.g. hydrazine), or bipropellant type (e.g. monomethyl hydrazine [MMH] and nitrogen tetroxide [N2O4]).

Does a monopropellent such as hydrazine "burn" to generate more energy than a cold-gas thruster? If so, what starts the "burning?" Is the stuff just explosive below a certain pressure, or is there a spark generator or similar device to start the process?

Bob B.
2007-Jun-30, 02:53 AM
Does a monopropellent such as hydrazine "burn" to generate more energy than a cold-gas thruster? If so, what starts the "burning?" Is the stuff just explosive below a certain pressure, or is there a spark generator or similar device to start the process?

Although hydrazine (N2H4) burns when combined with an oxidizer, in a monopropellant application it "decomposes" when brought in contact with a catalyst. The resulting high-temperature gases (nitrogen, hydrogen and ammonia) are then accelerated through the nozzle. This type of engine is called, appropriately, a catalytic decomposition engine. The performance is much better than cold gas but not as good as bipropellant engines -- hydrazine decomposes at a temperature of about 1,200o K while bipropellants burn upwards of 3,000o K.

The following is the description of monopropellant engines from my Web page:


Monopropellant Engines

By far the most widely used type of propulsion for spacecraft attitude and velocity control is monopropellant hydrazine. Its excellent handling characteristics, relative stability under normal storage conditions, and clean decomposition products have made it the standard. The general sequence of operations in a hydrazine thruster is:


When the attitude control system signals for thruster operation, an electric solenoid valve opens allowing hydrazine to flow. The action may be pulsed (as short as 5 ms) or long duration (steady state).
The pressure in the propellant tank forces liquid hydrazine into the injector. It enters as a spray into the thrust chamber and contacts the catalyst beds.
The catalyst bed consists of alumina pellets impregnated with iridium. Incoming hydrazine heats to its vaporizing point by contact with the catalyst bed and with the hot gases leaving the catalyst particles. The temperature of the hydrazine rises to a point where the rate of its decomposition becomes so high that the chemical reactions are self-sustaining.
By controlling the flow variables and the geometry of the catalyst chamber, a designer can tailor the proportion of chemical products, the exhaust temperature, the molecular weight, and thus the enthalpy for a given application. For a thruster application where specific impulse is paramount, the designer attempts to provide 30-40% ammonia dissociation, which is about the lowest percentage that can be maintained reliably. For gas-generator application, where lower temperature gases are usually desired, the designer provides for higher levels of ammonia dissociation.
Finally, in a space thruster, the hydrazine decomposition products leave the catalyst bed and exit from the chamber through a high expansion ratio exhaust nozzle to produce thrust.

Monopropellant hydrazine thrusters typically produce a specific impulse of about 230 to 240 s. Another suitable propellant for catalytic decomposition engines is hydrogen peroxide, however the performance - about 150 s specific impulse - is considerably lower than that obtained with hydrazine.

Monopropellant systems have successfully provided orbit maintenance and attitude control functions, but lack the performance to provide weight-efficient large delta-V maneuvers required for orbit insertion. Bipropellant systems are attractive because they can provide all three functions with one higher performance system, but they are more complex than the common solid rocket and monopropellant combined systems. A third alternative are dual mode systems. These systems are hybrid designs that use hydrazine both as a fuel for high performance bipropellant engines and as a monopropellant with conventional low-thrust catalytic thrusters. The hydrazine is fed to both the bipropellant engines and the monopropellant thrusters from a common fuel tank.

Cold gas propulsion is just a controlled, pressurized gas source and a nozzle. It represents the simplest form of rocket engine. Cold gas has many applications where simplicity and/or the need to avoid hot gases are more important than high performance. The Manned Maneuvering Unit used by astronauts is an example of such a system.


SOURCE: Space Mission Analysis and Design, 2nd Ed.; Wiley J. Larson & James R. Wertz (editors), Microcosm Inc., 1992.

cjl
2007-Jun-30, 03:50 AM
Nitrous Oxide is another usable monopropellant IIRC, with a potential Isp of about 170 seconds...

Maksutov
2007-Jun-30, 06:27 AM
One thing I've always wondered about. I've never had much to do with the design and manufacture of large solid fuel rockets. Looks like there are some experts in that field on this thread.

Check out this photo of an Honest John launch. (http://www.redstone.army.mil/history/systems/images/honest_john_01.jpg)

Note how the exhaust is grayish black until it's well beyond the nozzle and then brightens into a white plume. What's the reason for this? I would expect the exhaust to be uniform since the combustion is happening in the chamber, not aft of the nozzle. Is this perhaps a peculiarity of the fuel/oxidizer blend being used? Interaction with atmospheric water vapor?

cjl
2007-Jun-30, 07:52 AM
There are several possible explanations for this...

One is that the fuel is substantially under oxidized, and the excess fuel is being burned with atmospheric oxygen in the flame (which can't happen immediately on exiting the nozzle, as the mixing with atmospheric oxygen takes some time).

Another would have to do with pressure effects - that motor appears to be significantly underexpanded, which would create alternating high and low pressure regions with shock waves separating them. The flame appears to start at one of these shock waves.

Sometimes, in hobby motors, there is a substantial gap between nozzle and flame because the flame does not start until the flow is subsonic. That does not appear to be the case here however, unless the visible flame is really only occurring on the outer edge of an otherwise supersonic flow. This is a possibility, but a rather unlikely one IMO.

I can't think of any other options off the top of my head, but I'll post any more if I think of them.

Here's a picture of the phenomenon I was talking about in hobby motors - in this case, J800's. They put out roughly 250 pounds of thrust each, and have a total impulse of about 1280 newton seconds each (Isp of about 205). Note how far back the flame starts (clickable thumbnail):


http://s27.photobucket.com/albums/c183/chris_lapanse/th_RG1S2903_USDuece4x6.jpg (http://i27.photobucket.com/albums/c183/chris_lapanse/RG1S2903_USDuece4x6.jpg)

ASEI
2007-Jun-30, 02:44 PM
I want to know more about spacecrafts, like are there engines on spacecrafts? I would figure that if they did they would probably have to be the most powerful on Earth. What different kinds of energy does get used when lifting off the rocket into space?

Spacecraft and launch vehicles typically use some sort of rocket motor, meaning the motor puts out a jet of material from a stored propellant tank. Of course, the type of rocket motor you are going to use depends on the application.

There are booster motors, designed to put out extremely high amounts of thrust. Second stage motors are towards the booster motor point of fitness, but are usually biased towards higher Isps. (Internal specific impulse is a measure of fuel efficiency of a rocket, measured in seconds. The Isp*9.8m/sec^2 is your exhaust velocity. Isp*gravity*mass-flow-rate is your thrust).

(PS - typically "spacecraft" refers to a sattelite - the object that maneuvers in orbit, launch-vehicle refers to the rocket that gets it into orbit. LV motors are orders of magnitude more powerful than spacecraft motors due to the fact that they have to push that giant tower of fuel into the air)

Then there are spacecraft manuevering motors (for orbital changes) which are usually some form of monopropellant engine, and hopefully someday, ion drive. Hydrazine monopropellant can be stored at a wide range of temperatures in space, and the engines which use it can be lightweight and simple, they basically only have to push the hydrazine across a catalyst and get it to react with itself.

Hydrogen, as a counterexample, needs to be refridgerated to cryogenic temperatures, which is typically maintained by boiling off a portion of the hydrogen in the tank with time - not the sort of loss you would want to have for a multi-year space mission. That's why sattelites and spaceprobes use hydrazine rather than hydrogen/oxygen fuel.

In most rocket engines, the propellant and the fuel are one-and-the-same (the propellant being the gas the rocket reacts against, the fuel being the source of energy that energizes the propellant jet). Ion drives though use an external energy source to ionize the propellant gas (usually some form of heavy element, due to the ease of ionizing the first electron). Ion drives and other forms of Electric propulsion (Such as arc-jets or plasma jets) sacrifice mass-flow-rate and thrust for Isp and fuel efficiency. They put out piddling miniscule thrust, but do it in such a way that they don't have to expend as much fuel in the end to get a certain impulse out of it (and hence change in velocity).

Arcjets are a common type of attitude control jet (controls the spacecraft orientation, and unloads reaction wheels, which are another attitude control mechanism).

--------------

As for launch vehicle engines, since you were asking questions about the more powerful rocket engines,

Typically a liquid 1st stage engine will be some form of bipropellant rocket, (due to the fact that hydrazine is deadly-poisonous and no one wants to be near the exhaust, among other things like higher Isp for bi-propellants). Liquid hydrogen/liquid oxygen and kerosene (or some other hydrocarbon)/liquid oxygen are the most common modern launch vehicle fuel combinations.

The rocket motor is composed of turbomachinery, a combustion chamber, and a supersonic nozzle. The nozzle expands the gas to try to convert most of the gasses energy into kinetic energy. You want the gas jet going as fast as possible (with caveats due to wanting the jet exit pressure to match atmospheric pressure) because this is how you end up with the most thrust and fuel efficiency. Thrust due to pressure is nowhere near as significant as thrust due to the momentum of the gas jet, and so the big bell-nozzle part of the motor is trading the temperature and pressure (internal energy) of the gas jet for speed (kinetic energy).

The combustion chamber is where the reaction takes place with the fuel. The fuel gets burned in here, releasing the energy of the chemical reaction. The gas in here is under hundreds of atmospheres of pressure and thousands of degrees. There is usually much concern about the injector types and the fuel-impingement geometries here, because the goal of the injectors is to get fuel to react and mix as completely as possible in the milliseconds that it is within the chamber.


The turbomachinery is the critical part of the engine. The turbomachinery raises the pressure of the fuel and oxidizer from the tanks up to the chamber pressure, in order to be able to push it into the chamber. It does this by burning a portion of the fuel with a portion of the oxidizer, expanding it through a turbine to get the energy, and then using it to run turbo-pumps which draw the fuel and oxidizer from the tanks and compress it to the chamber pressure. Without the turbo-pumps, you couldn't operate the chamber at such extreme pressures in a continuous manner. All the plumbing you see above the nozzle and chamber is the turbomachinery.

Cooling:
Usually the turbomachinery is convolved with some sort of regenerative cooling schemes. Often, you will see the nozzle composed of some sort of copper tubing. Basically, a booster rocket or second stage rocket will generate tremendous temperatures as it launches - temperatures too high for metals to retain enough strength for the motor to operate. Before the cryogenic fuel is injected into the rocket chamber, it is pumped around the chamber and nozzle through the "basket" of copper cooling tubes - this cools the nozzle and allows it to operate at temperatures that it otherwise couldn't.

Recently though, a phenolic ablative liner has also been used to cool the nozzle. This method assumes the nozzle will only be in operation for a short period of time, so a coating of phenolic material slowly chars off the nozzle/chamber walls, taking the energy of the reaction with it.

PS - I have with me here Rocket Propulsion Elements, 7th Ed. by George P. Sutton and Oscar Biblarz - this is the book I used during one of my rocket classes in college.

Bob B.
2007-Jun-30, 03:58 PM
Nitrous Oxide is another usable monopropellant IIRC, with a potential Isp of about 170 seconds...

Ah, yes ... I can see that. I don't recall having read about nitrous oxide being used as a monopropellant, so I never bothered to research it. I just performed some calculations on it and it certainly seems like a very adequate monopropellant. I think it is possible to get a specific impulse in the 180-190 170-180 s range with a high enough expansion ratio. I just modified my Web page to include a blurb about it.

EDIT: Recalculated specific impulse -- used wrong specific heat ratio.

cjl
2007-Jun-30, 08:08 PM
Actually, in some fast burning hobby hybrid motors, the vast majority of the thrust comes from the nitrous oxide acting as a monopropellant, with the fuel adding only slightly (mainly because of the high mass flow rate and short burn time). Most of these are in the range of 150-160s, but they are also optimized generally towards low cost, ease of use, and reliability, rather than absolute maximum performance.

Bob B.
2007-Jun-30, 09:21 PM
Actually, in some fast burning hobby hybrid motors, the vast majority of the thrust comes from the nitrous oxide acting as a monopropellant, with the fuel adding only slightly (mainly because of the high mass flow rate and short burn time).

Sounds like the Mythbusters' salami rocket.

BTW, your 170 s specific impulse estimate was closer than my 180-190 s figure. I reviewed by calculations and found I used the wrong specific heat ratio. Might be able to hit 180 s or a little more in a vacuum with a really big expansion ratio.

cjl
2007-Jun-30, 10:15 PM
Yeah - I bet that's what the salami rocket was - a combination of simply escaping pressure with some slight effects as a monopropellant, with basically no contribution from the salami itself. That's one of the few episodes of that show that I feel they truly and completely botched, but oh well...

Noclevername
2007-Jul-01, 01:04 AM
Yeah - I bet that's what the salami rocket was - a combination of simply escaping pressure with some slight effects as a monopropellant, with basically no contribution from the salami itself. That's one of the few episodes of that show that I feel they truly and completely botched, but oh well...


They revisited that myth a few episodes later and determined the same thing. After which they actually got one (eventually) to ignite.

cjl
2007-Jul-01, 02:28 AM
Nope - I saw the revisit, and they still never got one to really ignite. The one that made the huge spike in thrust did in essence one thing - the igniter lit the black powder, and the huge overpressure that resulted blew the nozzle out. The nozzle blowout then created the massive thrust spike that they measured. It's that simple. They never burned salami (and they never will burn wet salami - it would only work with fuel that didn't have any water - it would need to be dried salami). I'd also like to note that hybrids absolutely MUST have the tank of nitrous oxide vertical for it to work, so a sideways test stand is only OK if the tank is vertical and has a tube down to the sideways combustion chamber.

Bob B.
2007-Jul-01, 08:28 PM
There are several possible explanations for this...

One is that the fuel is substantially under oxidized, and the excess fuel is being burned with atmospheric oxygen in the flame (which can't happen immediately on exiting the nozzle, as the mixing with atmospheric oxygen takes some time).

Another would have to do with pressure effects - that motor appears to be significantly underexpanded, which would create alternating high and low pressure regions with shock waves separating them. The flame appears to start at one of these shock waves.

Sometimes, in hobby motors, there is a substantial gap between nozzle and flame because the flame does not start until the flow is subsonic. That does not appear to be the case here however, unless the visible flame is really only occurring on the outer edge of an otherwise supersonic flow. This is a possibility, but a rather unlikely one IMO.

I can't think of any other options off the top of my head, but I'll post any more if I think of them.

I know a similar effect is observed in liquid fueled engines that utilize film cooling. The F-1 engine is a notable example, shown here in a test firing (http://upload.wikimedia.org/wikipedia/en/9/97/F-1_engine_firing.jpg). The low-temperature (relatively speaking) exhaust from the gas generator is injected into the nozzle around its perimeter. The gas then flows along the inside surface of the nozzle below the injection point, forming a barrier between the nozzle wall and the hot gas from the combustion chamber. This helps to keep the nozzle from getting too hot. In the F-1 photo, the tappered duct that wraps the nozzle circumference is where the gas generator exhaust is injected. Normally there is a nozzle extension that attaches below this point, but it is removed in this photo. It is the nozzle extention that is meant to be cooled by this technique.

The darker exhaust that you see coming out of the nozzle is just a thin layer around the outside and appears darker because it is cooler and contains un-combused fuel (the gas generator operates fuel-rich to keep the temperature down). A short distance beyond the end of the nozzle this dark exhaust ceases. I'm not absolutely certain what happens at this point, though I suspect the un-combusted fuel ignites due to contact with oxygen in the atmosphere. I suppose other explanations include mixing of the hot and cool gases, or heating of the cooler gas to the point of incandescence.

The reason I mention this is because the effect looks similar to the photo posted by Maksutov. I think you've suggested some good explanations for the effect, however the simularity to the appearance of the F-1 engine makes me wonder whether or not nozzle ablation could have anything to do with it. Perhaps the darker area is a thin layer of cooler gas containing residue from the nozzle. I reckon your explanations are more likely, but I throw this out there as a possibility. What do you think?

Nicolas
2007-Jul-01, 10:32 PM
When did they start including oxidizer with candles?

;)

Candles requiring an oxygen rich atmosphere are sooooo last millennium. The candles I use nowadays include their own oxidizer, which is very handy:

-you can give yourself some light when doing repairs on the bottom of a filled swimming pool

-if there's a power outage and you light one of these candles -do keep it vertical- next thing you know you'll find yourself in (what's left of) the basement, right next to the fuse box.

;) :D

On a more serious sidenote: do emergency road flares and ship flares include their own oxidizer or not? As most are used in air, I see no immediate reason for it, but then again SRB's are also used in the atmosphere...I assume that's mainly because the used mixture including oxidizer burns far more powerful, the atmosphere couldn't give enough oxygen to the SRB. Plus the amount of oxygen is better to control without atmospheric air inlet, and you don't get supersonic inlet problems. But anyway, if they burn brighter with a mixture including its own oxidizer, I see why flares would have oxidizer. Or if it's based on gunpowder, like fireworks, then it also includes its own oxidizer because apparently that mixture burns more violently. I doubt flares are based on gunpowder though :), magnesium or some other metal seems more likely to me.

cjl
2007-Jul-02, 01:26 AM
Flares usually do...


The reason the SRB uses its own is simply that there is no real way to use atmospheric oxygen - the only flow is outward.




The reason I mention this is because the effect looks similar to the photo posted by Maksutov. I think you've suggested some good explanations for the effect, however the simularity to the appearance of the F-1 engine makes me wonder whether or not nozzle ablation could have anything to do with it. Perhaps the darker area is a thin layer of cooler gas containing residue from the nozzle. I reckon your explanations are more likely, but I throw this out there as a possibility. What do you think?

That actually sounds like a possibility - I hadn't thought of it, but as you said, the picture you have of the F1 does bear a striking resemblance to the effect in Makustov's picture.

The only thing that I don't know about there is the material of the nozzle - that would obviously be the main determining factor in ablative properties. I've never heard of this as a possibility before with solids, but all the solids I normally work with are a tiny fraction of this size (usually a few thousand newton seconds and below).

Nicolas
2007-Jul-02, 08:19 AM
The reason the SRB uses its own is simply that there is no real way to use atmospheric oxygen - the only flow is outward.

Well, obviously to use atmospheric oxygen you'd have to add an inlet, that's what we do in scramjets :).

But first of all, it's very hard to make a good inlet for such a range of mach numbers, second it may induce loads of extra drag, third it's hard to have a constant amount of oxygen supply, fourth I don't think you'll ever get as much oxygen as you get out of burning with your own oxidizer so you won't get the optimal mixture, and fifth: it works "easily" and excellent as it is: no inlet, bring your own O2. :)

I thought the black thing at the nozzle was due to incomplete combustion or expansion. You can indeed see it in the F1 when it is still at low altitude. You can see it very clearly when they tested the F1 without the largest part of the nozzle, so I seriously doubt it's nozzle material.

Bob B.
2007-Jul-02, 01:18 PM
But first of all, it's very hard to make a good inlet for such a range of mach numbers, second it may induce loads of extra drag, third it's hard to have a constant amount of oxygen supply, fourth I don't think you'll ever get as much oxygen as you get out of burning with your own oxidizer so you won't get the optimal mixture, and fifth: it works "easily" and excellent as it is: no inlet, bring your own O2. :)

Using air also adds a large amount of nitrogen to the mix. Adding nitrogen does two bad things to decrease performance: (1) it increases the average molecular weight of the exhaust gas, and (2) it lowers the chamber temperature because some of the heat of combustion goes into heating the nitrogen.


I thought the black thing at the nozzle was due to incomplete combustion or expansion.

I think that is the most likely explanation as well.


You can indeed see it in the F1 when it is still at low altitude. You can see it very clearly when they tested the F1 without the largest part of the nozzle.

You can seen it in the F-1 because the low-temperature, fuel-rich exhaust from the gas generator is injected into the lower part of the nozzle. If not for this film cooling, the dark region of exhaust wouldn't exist. What we see in the F-1 is not the result of incomplete combustion of the gas ejected from the combustion chamber. On the other hand, the later explanation does seem to be a likely reason for the dark exhaust in Makustov's photo.


... so I seriously doubt it's nozzle material.

I didn't mean to suggest that the dark region is nozzle matrial per se. I suggest the possibility that it is a shell of lower temperature material. If the nozzle is cooled ablatively, I wonder if there could exist a shell of gas/ablated material cool enough in temperature to be noticeable darker than the incandencent high-temperature exhaust. Probably not, but I thought I'd mention it.

Nicolas
2007-Jul-02, 04:10 PM
Good points about the disadvantages of nitrogen when using atmospheric oxygen in combustion.

Bob B.
2007-Jul-02, 09:20 PM
Good points about the disadvantages of nitrogen when using atmospheric oxygen in combustion.

Nitrogen in the air has a big affect on flame temperature, etc., but there is a huge advantage to not having to carry the oxidizer on board our vehicle. Here are some quick numbers for comparisonÖ

Letís say weíre burning a stochiometric mixture of methane and gaseous oxygen at a combustion chamber pressure of 1,000 PSI:

CH4 + 2 O2 --> CO2 + 2 H2O

This reaction yields an adiabatic flame temperature of 3,634o K, the average molecular weight of the products is 22.69 (dissociation will occur), and the specific heat ratio is 1.20.

Letís now say we are burning the methane using air, where there are 4.3 moles of nitrogen for every 1 mole of oxygen:

CH4 + 2 O2 + 8.6 N2 --> CO2 + 2 H2O + 8.6 N2

In this case the flame temperature is 2,155o K, the molecular weight is 27.63, and gamma equals 1.25.

If we were to exhaust the products through a nozzle expanding to one atmosphere pressure, the specific impulse in the first case is 290 seconds.

In the second case, how do we calculate the specific impulse? If we base it on the combined mass of the methane and oxygen as we did in the first case, the specific impulse is 196 seconds, which is a significant decrease. However, since we are drawing the oxygen from the air we have to carry only the methane fuel and not the oxidizer. If we calculate the specific impulse as a function of the mass we are actually carrying on our craft (i.e. the methane), then the specific impulse jumps up to 980 seconds.

Clearly there is a big advantage in using atmospheric oxygen even with the presence of nitrogen. However, as you explain is post #42, there are other considerations that make it largely impractical for use in rockets. A launch vehicle has to operate through a very large range of ambient conditions in a very short period of time. Engineering an air-breathing engine that can operate through that range of conditions is a real problem. Furthermore, unlike an aircraft that is designed to operate in the atmosphere, the goal of a launch vehicle is to get above the atmosphere as quickly as possible and then perform most of the acceleration while in a near vacuum. Obviously air-breathing engines donít work too well in a vacuum.

Nicolas
2007-Jul-02, 09:41 PM
A launch vehicle has to operate through a very large range of ambient conditions in a very short period of time. Engineering an air-breathing engine that can operate through that range of conditions is a real problem.

I can certainly second that. It's a real problem indeed, gave me headaches more than once :). But IMO it's the most interesting aerospace problem of the moment. And we're making progress. Maybe, someday in the future we'll see airbreathing boosters. It all depends on those many things that are yet to be determined to be "problems" or "show stoppers".

Bob B.
2007-Jul-02, 10:11 PM
But IMO it's the most interesting aerospace problem of the moment. And we're making progress. Maybe, someday in the future we'll see airbreathing boosters.

Yeah... I've heard some ideas that certainly sound interesting. It will be exciting to finally have a technology breakthrough that significantly reduces the cost of delivering a payload to orbit.

Nicolas
2007-Jul-02, 10:19 PM
If the technology ever breaks through, my CV will get a silver lining: "and I was part of that!" :)

Well, it does beat everything else on my quite empty CV...

publiusr
2007-Jul-03, 12:41 AM
In short. The bigger the rocket--the bigger the spacecraft--and the more it can do in a mission. Avoid assembly--build large.

cjl
2007-Jul-03, 05:09 AM
Also, somehow, the intake would need to pressurize the oxygen and nitrogen up to chamber pressure (around 800 psi for the SRB's on the shuttle, 1000 for most liquids, and 2500 or so for SSME's IIRC) without allowing any of the high pressure gases from the chamber out. This is one of the most difficult things - you would need an incredible pump or inlet do do this, especially across a wide range of mach numbers and altitudes.

Nicolas
2007-Jul-03, 09:35 AM
Except for the ramjet (and excluding piston engines), current airbreathing engines use a shaped inlet and compressor to compress the inlet air. A ramjet only uses a shaped inlet. The current approach for scramjets also is to work with a shaped inlet. I can tell you, it's an art to design a scramjet inlet that gives nice compression accross a range of mach numbers, whether it has variable geometry or not.

I don't remember the exact numbers, but I thought that scramjet engines worked with a somewhat lower chamber pressure than for example SRB's. Of course, the chamber mixture isn't stationary in a scramjet, so that's a first reason to have less pressure.

Bob B.
2007-Jul-03, 12:10 PM
(around 800 psi for the SRB's on the shuttle, 1000 for most liquids, and 2500 or so for SSME's IIRC)

The SSME, which uses a staged-combustion cycle, operates at a combustion chamber pressure of 204 atmospheres (3,000 PSI). Staged-combustion engines routinely operate at higher chamber pressures (about 150-250 atm) than the simpler gas-generator cycle engines (<100 atm). The highest chamber pressure I can recall for a gas-generator engine is 95.9 atm for the RS-68*. For comparison, the staged-combustion RD-180** engine has a chamber pressure of 253 atm!

* Made by Rocketdyne for the Delta IV, and proposed for use in the Ares V.
** Made by NPO Energomash / Pratt & Whitney for the Atlas V.

m1omg
2007-Jul-03, 08:40 PM
Do you have some more specific questions about this? It's a rather general question considering all the different spacecraft that have been made.
But;
The Saturn-V rockets were the most powerful engines ever made. You may want to peruse that if you're looking for power information.
Basically, all rocket technology uses a chemical reaction (a burn) to create the energy. There have been many different fuels used.

The non-chemical engine - ion engine - was used in some unmanned probe missions.

NEOWatcher
2007-Jul-05, 01:24 PM
The non-chemical engine - ion engine - was used in some unmanned probe missions.
Yes; that's why I was looking for more clarification. The OP was referring to lift-off, so that rules out the ion, solar sail, and any other non-chemical idea we can think of (at least as of today).

Bob B.
2007-Jul-05, 02:24 PM
The OP ...

Speaking of the OP, where is Platinum Rhymer? I have to say I'm rather upset that he/she would start this thread, abandon it after only a couple hours, and not acknowledge any of the responses. How rude!

Noclevername
2007-Jul-05, 06:03 PM
Speaking of the OP, where is Platinum Rhymer? I have to say I'm rather upset that he/she would start this thread, abandon it after only a couple hours, and not acknowledge any of the responses. How rude!


Well, don't jump to assumptions. He might've had a run-in with some Real Life, or lost his computer in a poker game, or been grounded, or something.

Bob B.
2007-Jul-05, 06:14 PM
Well, don't jump to assumptions. He might've had a run-in with some Real Life, or lost his computer in a poker game, or been grounded, or something.

I've considered that possibility and I'm prepared to apologize to Platinum Rhymer should it be appropriate. In the meantime ... it's been 9 days!

publiusr
2007-Jul-21, 06:50 PM
Now there was at least one air-breathing solid concept--the GNOM, a very small ICBM concept:
http://www.astronautix.com/lvs/gnom.htm Specific impulse at 550 sec

And here was what was meant to shoot warheads down:
http://www.astronautix.com/lvs/sprint.htm

"The motor ignited after the missile had been ejected from its silo by gas pressure, and accelerated the Sprint with more than 100 g. Within seconds, the missile reached a speed of Mach 10+, and the extreme thermodynamic heating demanded sophisticated ablative shielding (the nose was already glowing red-hot less than a second after launch)."

I wonder if you could combine these two. oohh....

Delta II's kerosene is warmed for more energy. Somethimes kero is cooled in other rockets to make it a bit denser and to get more fuel in.

Grashtel
2007-Aug-04, 11:42 PM
Now there was at least one air-breathing solid concept--the GNOM, a very small ICBM concept:
http://www.astronautix.com/lvs/gnom.htm Specific impulse at 550 sec
http://www.astronautix.com/lvs/pr90.htm the tactical missile version that was actually built.

mugaliens
2007-Aug-05, 11:24 PM
The Saturn V had many different types of rocket engines, ranging from the Rockedyne F-1 Kerosene/LOX engines to the solid propellant ullage and retrorocket motors on the upper stages. Specifically you are meaning the F-1 engines which were installed in a five engine cluster at the base of the first stage. Total thrust was 7.5 million pounds.

Matthew Ota
space history buff

I agree with you that 7.5 million pounds is the correct figure for the Saturn V stage one rocket, thus should retain the title.

Similarly, we measure how powerful automotive engines are by the horsepower of all eight cylinders, not by each cylinder.

mugaliens
2007-Aug-05, 11:30 PM
On a more serious sidenote: do emergency road flares and ship flares include their own oxidizer or not?

Yes, and they do burn not only in wet conditions, but also underwater (a little difficult to ignite them underwater, though, unless they're specifically made to do so).

cjl
2007-Aug-08, 10:21 PM
I agree with you that 7.5 million pounds is the correct figure for the Saturn V stage one rocket, thus should retain the title.

Similarly, we measure how powerful automotive engines are by the horsepower of all eight cylinders, not by each cylinder.

However, if you put three engines in a car, and then ask which car has the most powerful engine, you don't add all three engines together and say it is the most powerful engine. You look at each separately. That is why the SRB is the most powerful rocket motor ever made. Not that the saturn V is weak :)