Talk:Water

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: http://www.asi.org/adb/06/09/03/02/095/al-o-propellants.html and http://www.projectrho.com/rocket/rocket3c2.html

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. http://www.omnibraze.com/wire.html A research paper by A. Gerlich et al. gives the melting point of an aluminum magnesium eutectic as 437 degrees centrigrade. http://www.materialsaustralia.com/Materials_Forum/Vol29/GP%2046.pdf 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)