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Other substances, such as aluminum or magnesium and oxygen can be used for rocket fuel. We have plenty of those.

Oxygen has been used for decades as rocket oxidizer. Although magnesium and aluminium are good fuels, and are used in solid rockets, they can not be used in a liquid rocket, as they have to be kept very hot to be a liquid, leading to compatibility issues with supercold LOX. An alternative would be to have a hybrid rocket: a tank of LOX, and a tube filled with metal powder. However, the metal powder will fall out the nozzle. This is why solid rockets use a binder to keep the fuels together. The binder will have to be shipped from Earth. T.Neo 08:42, 11 August 2008 (UTC)

Response from Bryce: T.Neo raises a good point. Solid and even hybrid rocket fuel here on Earth is mixed with a binder, which is often a high hydrocarbon rubberlike substance. That's pretty pricey on the Moon and, again, we hate to "throw away" hydrogen (and carbon) in this way. Maybe given the vacuum and anhydrous environment of the Moon, we could do some sort of "sintering" process to cause our fuel to stick together until used, and yet have the oxidizer reach it when needed.

The reason the metal fuel is in powder form is because there is more surface area. If the aluminium was just one solid sheet, the reaction with oxygen would create an impervious barrier of aluminium oxide, preventing further reaction. Sintering the fuel would, I imagine, decrease the surface area and lead to the same problem. But, maybe the ratio of fuel to binder could be changed, with the binder being just a thin layer holding the powder together. What would this material be? What about the remaining fuel left in cargo lander fuel tanks? T.Neo 07:43, 12 August 2008 (UTC)

That could be a possibility. NASA is currently working on ways to scavenge unused fuel from the lunar landers so it can be used in an outpost. I've heard mention of hybrid engines which would use hexagonal cross-section metal rods in addition to hydrogen/LOX in the combustion chamber to add additional boost, but that is for interplanetary/cislunar ships which would not land. - Jarogers2001 14:08, 12 August 2008 (UTC)

Abundance of oxygen could be an advantage for a "direct ascent" lander. It does not have to carry the oxidiser for the return trip, only the fuel. I am weary about any potential hybrid/solid rocket for manned transportation. T.Neo 07:10, 13 August 2008 (UTC)

liquid aluminum / liquid oxygen rockets

T.Neo should not give up too easily on liquid aluminum / liquid oxygen rockets. The liquid oxygen in the tanks would be used to cool the combustion chamber wall in a tube wall construction design. So before it is injected into the combustion chamber it will be a hot gas. Liquid hydrogen is used to cool the combustion chamber wall of the space shuttle main engine. The temperature differences there are greater than there will be in the aluminum oxygen rocket. Oxygen is not as good a coolant as hydrogen so the aluminum oxygen rocket will not be able to run up to as high a temperature or pressure as the space shuttle main engine. The rocket would not reach that temperature any way because of all the excess oxydizer necessary to keep sufficient gas in the combustion chamber to serve as a working fluid. People at the following web sites think aluminum/oxygen rockets are worth considering: and

mass drivers

All of this rocket stuff is just a preliminary expedient anyway. See the Mass Drivers article to see what ought be the economic method of getting stuff from Luna to lunar orbit when things are more fully developed.--Farred 22:59, 13 August 2008 (UTC)

I don't have a problem with cooling the engine, I have a problem with keeping the aluminium liquid, and keeping the LOX cold, all while trying to keep the rocket in one piece. The binder in use in a hybrid rocket can be a thin film holding the fuel together. Importing volatiles is not so hard. We can make lander stages out of volatiles, we can make our Earth Departure stages out of volatiles, so that when we crash them into the Moon to calibrate our tectonic sensors we can provide future generations with volatiles. The Ranger probes used balsa wood to cushion lunar impact. Why not send huge chunks of plastic to crash into the moon? No landers, etc. This approach could even be used to land "dumb" payloads on the Moon. Do not confuse "Reuseable" with "reuturn to Earth". I think Mass drivers are the way to go to lift payloads off the Moon, cargo at least. I was thinking of a rocket second stage, if not that, some sort of device for orbital manuvering. I think that a solar thermal rocket using LOx as a working fluid could fit the job nicely. T.Neo 12:30, 14 August 2008 (UTC)

problems, problems

There is a tendency of lunar base enthusiasts to go off on tangents worrying about problems that turn out to be irrelevant and ignoring serious problems. This situation is a result of our ignorance. With what little information we have I am not convinced that the maintaining the aluminum liquid and oxygen liquid in separate tanks on one rocket vehicle will be the big problem. Lacking proper reference works at hand at the moment, I looked up a couple of web pages that incidentally touched on the liquid temperature of aluminum. Omni Technologies gives a temperature for melting their aluminum based brazing material as 582 – 604 degrees centigrade. A research paper by A. Gerlich et al. gives the melting point of an aluminum magnesium eutectic as 437 degrees centrigrade. With some aluminum, magnesium and silicon in the pot the melting temperature might be managably low. Vacuum insulation is not difficult to come by or maintain on Luna. Even though the actual fuel that is put into such a hypothetical rocket just prior to launch must be considerably hotter than the melting point to insure that some higher melting point phase does not freeze out to coat the inner surface of tubing, the temperature involved should not melt insulation materials available.
A concern that must be addressed is the tendency for metals from which one might otherwise construct a combustion chamber to burn away in a high temperature high pressure pure oxygen environment. I can not say off hand what alloy or ceramic might be suitable for the combustion chamber wall. There is also the problem of aluminum oxide particles in the rocket exhaust abrading the throat of the combustion chamber. Perhaps expendable ceramic inserts to line the combustion chamber throat would be called for.
My main point is that until there is more definite data, we can not completely rule out a liquid aluminum / liquid oxygen rocket. Have you got a rocket test stand in your garage that operates in a high vacuum?
Just putting in capital letters fixed the link to the Mass Drivers article. --FARTHERRED
Why not use powdered aluminum in a straight tube and feed it into the combustion chamber by pushing on the other end? Aluminum could disperse when blown by the oxygen. - Jarogers2001 03:04, 15 August 2008 (UTC)

You mean push the powder into the combustion chamber? Could work. I am looking at this from the perspective of ACPC propellant. -Do away with Ammonium perchlorate oxidser, and turn the device into a hybrid rocket with oxygen oxidizer. -Reduce the amount of binder to a bare minimum. Yes, the binder has to be imported from Earth, but only a small amount is used. As I said in my previous comment, getting volatiles to the moon is not as hard as you might think. Even with some Aluminium/Magnesium/silicon fuel, I am unsure about what the rocket might be contructed of, etc. Remember how small the apollo lunar module was, getting off the Moon SSTO. Now, if there was a hybrid, with a mass driver accelerating a rocket powered second stage, the two could be much smaller then a pure rocket or pure mass driver system. This means that the colonists only need to build a mass driver that is half the length, and a rocket stage that is half the size. We have not tested aluminium rocket technology. The safest, cost effective way would be a hybrid rocket. No, I do not have a working test model in my garage, but I am working on it. I have several crazy propellant ideas. Now, where can I find some liquid Flourine? T.Neo 07:17, 15 August 2008 (UTC)

Pumping Aluminum Powder

In response to Jarogers2001’s suggestion of feeding powdered aluminum into the combustion chamber of a rocket

Let us take the transfer of powdered aluminum to the combustion chamber of a rocket one step at a time. First, if the aluminum powder were in a vertical cylinder opening at the bottom into the combustion chamber, that cylinder would need to be pressurized with a nonoxidizing gas to the same pressure as the combustion chamber to prevent the oxygen from the combustion chamber moving into the stored aluminum powder bringing the flame front with it. Otherwise the cylinder would be just a portion of the combustion chamber and not the type of rocket engine being discussed. To keep the aluminum powder from just falling into the combustion chamber prematurely there would need to be a door between the fuel chamber and the combustion chamber that would open or disintegrate into a number of pieces that could fall through the combustion chamber when the rocket was ignited. The aluminum would not need to be pushed into the combustion chamber, it would fall in. There would be very poor control of the rate of fuel injection.
Second, the aluminum powder could be pushed through a cylinder with a horizontal axis by an auger and fall at one end into the combustion chamber. Again, the aluminum storage chamber would need to be pressurized.
Third aluminum powder in cans could be pushed into the combustion chamber through a port with a set of seals preserving combustion chamber pressure. The cans, perhaps made of aluminum titanium alloy, would need to retain structural integrity just long enough get through the port seals, and then burn completely with their contents.
Fourth cans of aluminum powder could be added to the combustion chamber by a positive displacement pump having two rotors of two or more lobes each. Although such pumps are usually used for liquids they might serve for cans of aluminum powder. Check out an example at the Pump World web page. A set of springs might be added to the pump so cans of aluminum powder would be positively ejected from the pump cavity as the cavity opens onto the combustion chamber rather than having the can squashed by the vane that tries to close the cavity. The ends of the rotor vanes might be lubricated with gold to prevent excessive blow-by. It would cost about twice as much as grease on Luna because in addition to transportation costs the raw material cost would be significant. The cost would be justified only if the rocket engine provided great advantages over competing types.
In summary, although it does not seem to be proven that pushing aluminum powder into the combustion chamber of a rocket is absolutely physically impossible, there does seem to be the lack of any great motivation for putting money into pursuing this idea.--FARTHERRED 11:43am central daylight time on the 16th of August

So that leaves hybrid rockets and liquid rockets. What about so called "flashbulb" rockets? Are they only for orbit circularization? And solar thermal for orbital manuvering? T.Neo 08:23, 18 August 2008 (UTC)

Locally Made Lunar Rockets

As T.Neo suggests, flashbulb rockets are only for circularizing the orbit into which a payload is placed by a mass driver. This is not a high specific impulse or a low empty weight rocket. The delta v requirement is small. The matters of concern are ease of manufacture and reliable performance.
For a solid fuel, lox oxidizer rocket the binder does not necessarily need to be a polymer. Keep in mind that the finished chunk of solid fuel should burn at a high controlled rate and maintain a large enough surface area to provide the desired burn rate and provide sufficient heat transfer to the exhaust gas. An advantage of pumped oxygen as the oxidizer is that it allows control by valves. A disadvantage is the requirement of power for the pump. The chunk of fuel might reasonably contain aluminum, magnesium, titanium and alloy flakes sintered together with a low melting alloy of mostly aluminum with magnesium, silicon, and perhaps sodium and calcium thrown in. The manufacturing process should result in a high porosity closed cell structure that breaks down by melting and oxidation in the rocket engine to leave a rough porous surface that burns at a high controlled rate. Adding hydrogen gas to the fuel mix to hold open pores would also provide some combustion rate control as escaping steam would form hydrogen again as it reacts with metal fuel components in a quasiequilibrium fashion. Steam and hydrogen would interfere with the oxygen reaching the burning surface. Adding silicon dioxide might provide rate control if the hydrogen is too expensive. This sort of technology can only be developed by a long series of tests, if it is at all possible.
A solar thermal rocket using oxygen reaction mass is certainly possible. It might be desirable to boost the specific impulse by electrically heating the oxygen after it was preheated by direct solar energy. The advantage of the orbit to orbit transfer mission is that high thrust to weight ratio is not such a stringent requirement. I can only guess how far this advantage might be pushed. Electrodes used to heat the oxygen would absorb heat from that oxygen on one side and be cooled by the incoming liquid stream on the other. The expansion nozzle could be radiatively cooled because the engine would operate at low pressure.
The potential for development is great. If NASA sticks to a reasonable budget, it can not all be done by 2020. NASA should see if 2030 works. Instead, the last I heard is that they want to use a nitrogen tetroxide and monomethylhydrazine assent stage after having astronauts waltz around on Luna for a while. If there is a need to put on a show for the yokels, it would be better handled by the National Rocketry and Canyon Jumping Administration. If someone is not impressed enough with the noise of the rockets, he can be given a seat closer to the path of the rocket motorcycle rider that charges out over the take-off ramp. Something of this nature could be jerry rigged in about a year, and if we loose one canyon jumper there would be other volunteers. It would provide a better demonstration of American technical superiority than the stupid death-warmed-over program that NASA's political bosses have forced upon them. --Farred 18:03, 19 August 2008 (UTC)

Sintering the fuel together with a low-melting point binder might do the trick. Pumping the LOX is a problem. Could pressurized oxygen gas be used to force the LOX into the engine? Right now NASA is doing everything wrong. I think that a first step in the right direction would be for them to be sensible, dump Constellation and adopt DIRECT. T.Neo 08:51, 20 August 2008 (UTC)

Pressure feed rockets do not have as great a specific impulse potential as turbo pumped rockets. Perhaps the lox could be mixed with ozone and the ozone be catalytically decomposed to provide power for the oxidizer pump. Required engeneering data would include the solubility of Ozone in liquid oxygen at operating temperatures, the energy availabel per kilogram of ozone and the concentration of ozone in solution at which it becomes an explosion hazard. We do not want some ozone freezing out in nearly pure form on a tank wall and exploding from some stray vibration. I hear that if one were to strike a tank of liquid ozone with a hammer, one would never hear the clang.
What is this DIRECT T.Neo writes about? Is that Mars Direct? --Farred 19:33, 21 August 2008 (UTC)
DIRECT 2.0. Personally, I don't buy into the idea. All I've heard is NASA bashing, repetitive accusations of foul play in op-eds, and outrage over non-compliance with congressional mandates with little substance and not enough study to back it up. I read the ESAS study front to back and I find myself agreeing with it's conclusions. My personal preference is for COTS. Playing the "congress said" mandate card is a quick way to kill any rational effort, because congress doesn't understand the word "rational." The DIRECT people don't see this. I honestly suspect that Direct is an effort carried out by NASA engineers who are afraid of losing their jobs, which is very understandable. However, NASA is not the end all, be all of aerospace. The best engineering talent will be able to find higher paying work in the private sector. People forget that government jobs pay {insert fecal-referencing profanity of your choice}. - Jarogers2001 05:29, 22 August 2008 (UTC)

You make a good point about DIRECT, but I still think that Constellation is not applicable to the SDLV category anymore. No SSMEs*, no 4-segment boosters, differant tank diameters, etc. Meanwhile Ares I has run into problems. Weight constraints, etc. How much more harder is it to man-rate a Delta-IV heavy then it is to create a new launcher? We do not neeed NASA to return to the Moon, we should not want NASA to return us to the Moon. The shuttle was a mistake, Constellation is a bigger one.

  • I am not saying that an SSME would be a better choice then a RS-68 or J-2X.

T.Neo 07:53, 22 August 2008 (UTC)