In-Situ Propellant Production - Revision history

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Aluminum

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Sulfur

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Aluminum

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 One proposed solution to this problem is to mix finely powdered aluminum with liquid oxygen, adding a small amount of fumed silica to the mix. The result would be a gelled monopropellant which would provide an estimated specific impulse of 285 seconds<ref>[http://www.asi.org/adb/06/09/03/02/095/al-o-propellants.html Larry Jay Friesen. "LUNAR ALUMINUM and OXYGEN PROPELLANTS to SUPPORT LUNAR BASES and PLANETARY FLIGHT". Moon Miners Manifesto #95, May 1996]</ref>, the same as with sulfur. This approach has been tested on a small scale, and was determined to be reasonably stable.<ref>[http://www.wickmanspacecraft.com/moon1.html John Wickman. "Using Lunar Soil For Propellants & Concrete". Wickman Spacecraft & Propulsion Company]</ref><ref>[http://www.wickmanspacecraft.com/lsp.html Rocket Propellant From Lunar Soil]</ref>
-One potential issue with this approach is the production of dust. As the exhaust cools, particles of aluminum oxide would form, which could be an issue for heavy use. Proper design of the engine could mitigate this however. If the combustion was complete and all products were entirely vaporized upon ejection, the resulting dust should be quite small, perhaps microscopic in size, and traveling at sufficient speed to allow for wide dispersal. Current spacecraft are already designed to handle dust of this size, and its generation should not endanger their use.
+Tests were also conducted by NASA, with actual tested ISP's of about 130 seconds. "Powdered Aluminum and Oxygen Rocket Propellants: Subscale Combustion Experiments".
 == Silicon ==

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 One disadvantage of this approach is the complexity of producing silane. The process used terrestrially for silane production is long, rather complex, and requires a number of reagents that are quite rare on the moon. Methane and hydrogen production are quite straightforward by comparison.
-== Sulfur ==
+== Sulphur ==
-Another proposed solution is to use [[sulfur]] as a propellant, in what is sometimes referred to as a "Brimstone Rocket". Sulfur melts at about 115 °C, which could be easily achieved by preheating the fuel tank before launch. Burning this molten sulfur with liquid oxygen would produce sulfur dioxide as exhaust, with a specific impulse of around 285 seconds. Sulfur is present in the lunar regolith in much higher quantities than both hydrogen and carbon, some mare soils containing as much as .27% by weight.<ref>[http://library.lanl.gov/cgi-bin/getfile?00261154.pdf V. T. Vaniman, D. R. Pettit, G. Heiken. "Uses of Lunar Sulfur" Los Alamos National Laboratory, 1988]</ref>. In addition, unlike [[hydrogen]] and [[carbon]], [[sulfur]] compounds may be extractable by magnetic benefication rather than heating the regolith, greatly reducing both the complexity and energy requirements of gathering them.
+Another proposed solution is to use [[sulphur]] as a propellant, in what is sometimes referred to as a "Brimstone Rocket". Sulfur melts at about 115 °C, which could be easily achieved by preheating the fuel tank before launch. Burning this molten sulphur with liquid oxygen would produce sulphur dioxide as exhaust, with a specific impulse of around 285 seconds. Sulphur is present in the lunar regolith in much higher quantities than both hydrogen and carbon, some mare soils containing as much as .27% by weight.<ref>[http://library.lanl.gov/cgi-bin/getfile?00261154.pdf V. T. Vaniman, D. R. Pettit, G. Heiken. "Uses of Lunar Sulfur" Los Alamos National Laboratory, 1988]</ref>. In addition, unlike [[hydrogen]] and [[carbon]], [[sulphur]] compounds may be extractable by magnetic benefication rather than heating the regolith, greatly reducing both the complexity and energy requirements of gathering them.
 == Aluminum ==

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 ==Superoxide Solid Fuel==
-This sort of rocket could be used for a one shot orbital maneuver such as circularization of orbit of a payload launched by a mass driver.  Powdered aluminum or magnesium would be mixed with powdered sodium superoxide (NaO<sub>2</sub>) in such quantities as to provide both the oxidizer and excess oxygen to serve as reaction mass.  It would provide only a small number of meters per second impulse with the main advantages being ease of manufacture and the ability to store the rocket without fuel evaporating or corroding its container.
+This sort of rocket could be used for a one shot orbital maneuver such as circularization of orbit of a payload launched by a [[Mass_Drivers#What_Will_Work|mass driver]].  Powdered aluminum or magnesium would be mixed with powdered sodium superoxide (NaO<sub>2</sub>) in such quantities as to provide both the oxidizer and excess oxygen to serve as reaction mass.  It would provide only a small number of meters per second impulse with the main advantages being ease of manufacture and the ability to store the rocket without fuel evaporating or corroding its container.
 ==See Also==
 *[[List of Propulsion Systems]]

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 == Ammonia ==
 Ammonia does not exist naturally on the Moon.   Yet it would be expedient to synthesise it as follows. Once volatiles are extracted from lunar regolith, some nitrogen will be released, together with a large quantity of Hydrogen.   Both hydrogen and Nitrogen are difficult to store.   Ammonia can be produced by heating hydrogen and nitrogen in the presence of certain catalysts.
-In that case it might be very efficient to use Amonia as reaction mass for solar thermal rockets.    It would be a  somewhat lower specific impulse than hydrogen, but much easier to store than hydrogen, and no oxidizer is needed.
+In that case it might be very efficient to use Amonia as reaction mass for solar thermal rockets.    It would be a  somewhat lower specific impulse than hydrogen, but much easier to store than hydrogen.
 Ammonia of course has many other uses, such as a refrigerant fluid, important for heat engines and temperature control in space and on the Moon.

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 This fuel would be used in a [[Liquid Metal Alloy Oxygen Rocket]]
 ==See Also==
 *[[List of Propulsion Systems]]

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 Lunar [[silicon]] could possibly be used in the same manner as [[aluminum]], as they are similar in both atomic weight and potential energy, and hence could have similar specific impulses. Silicon has been utilized in test mixtures, powdered and mixed in a liquid oxygen gel as with aluminum<ref>[http://ae-www.technion.ac.il/~rocketw3/benny5.pdf Benveniste Natan and Shai Rahimi. "THE STATUS OF GEL PROPELLANTS IN YEAR 2000". Technion - Israel Institute of Technology, Faculty of Aerospace Engineering. Table 6]</ref>. As silicon dioxide is the most common component of the lunar crust (nearly half by weight), it's use in this manner is attractive.
-==Liquid Metal Alloy Oxygen Rocket==
+==Liquid Metal Alloy Fuel==
+This fuel would be used in a [[Liquid Metal Alloy Oxygen Rocket]]
 ==See Also==

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 ==Liquid Metal Alloy Oxygen Rocket==
-Another possible solution to the high melting point of Aluminum is to alloy it with portions of calcium, magnesium, sodium, potassium, and silicon to get a low enough melting point for the alloy for convenient use while still using materials that are relatively abundant on Luna.  As a bi-propellant this alloy would need to be mixed with a large excess of oxygen for combustion to provide sufficient gas for a working fluid to expand as exhaust through a bell nozzle.  The oxygen could also be used as to cool the combustion chamber wall and expansion nozzle.  The resulting hot gas would drive the oxygen and fuel pumps before being injected into the combustion chamber.  Having a single shaft for the for the oxygen and fuel pumps would be a problem since there would need to be a rotary seal where the shaft penetrates the oxygen housing to prevent oxygen from contacting the fuel before the combustion chamber.  Having an electric generator driven by the hot oxygen as well as the oxygen pump might provide a solution.  Then the fuel pump would be electrically driven.
+Another possible solution to the high melting point of Aluminum is to alloy it with portions of calcium, magnesium, sodium, potassium, and silicon to get a low enough melting point for the alloy for convenient use while still using materials that are relatively abundant on Luna.  As a bi-propellant this alloy would need to be mixed with a large excess of oxygen for combustion to provide sufficient gas for a working fluid to expand as exhaust through a bell nozzle.  The oxygen could also be used to cool the combustion chamber wall and the expansion nozzle.  The resulting hot gas would drive the oxygen and fuel pumps before being injected into the combustion chamber.  Having a single shaft for the for the oxygen and fuel pumps would be a problem since there would need to be a rotary seal where the shaft penetrates the oxygen housing to prevent oxygen from contacting the fuel before the combustion chamber.  Having an electric generator driven by the hot oxygen as well as the oxygen pump might provide a solution.  Then the fuel pump would be electrically driven.  The fuel tank could be pressurized with hydrogen from a small tank of liquid hydrogen which would be used as necessary to maintain the pressure to the fuel pump input.  A portion of that hydrogen could also fill the housing for the electric motor that drives the fuel pump.  The oxygen tank could be pressurized with initially with a small amount of helium gas.  After engine start, some of the hot oxygen from the combustion chamber cooling could be diverted back to the oxygen tank through a loop that would heat the oxygen just enough to maintain pressure.  Then oxygen from this loop would go on to the combustion chamber injector.
 The proportions of the various metal components of the liquid fuel would be determined by the cost and availability of each component on the moon and its contribution to keeping a low melting point and providing high specific impulse.  NaK eutectic mixture is 22% sodium and 78% potassium.  It melts at 9.4 degrees Farenheit or -12.6 degrees Celsius.  So it is certainly not a difficult mixture to keep at a temperature at which it remains liquid to be handled by rocket engine turbo pumps.  Aluminum and magnesium would raise the melting temperature of the alloy but would be added for the high energy they provide when burned in oxygen and their relative local abundance.  Silicon would be added in such a proportion as would lower the melting point in a cost effective way.  The whole alloy would be maintained in the fuel tank at a temperature well above its melting point to be sure that some local variation did not cause plating out of a higher melting composition.  Multiple sheets of aluminum foil in lunar vacuum would provide adequate insulation so that the liquid metal fuel and the liquid oxygen would each stay at its proper temperature until pumped into the combustion chamber to be burned.