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.