| Lunar Derived Propellant Rockets By David Dietzler 2008 Abstract: Mass drivers can launch millions of tons of cargo per year. They will launch at high accelerations of hundreds of Gees. This is unsuitable for humans. Space workers will travel in rockets that accelerate at only a few Gees for lunar sub-orbital “hops,” and flights between lunar orbit and the lunar surface. Three propellant combinations are of interest for simple pressure fed rockets operating between LO and the Lunar surface- Al+LUNOX, Silane + LUNOX and LH2+LUNOX. Calculations show that SiH4+LUNOX uses somewhat less than 60% as much hydrogen as LH2 and LUNOX and could conserve or extend rare and valuable lunar hydrogen resources. Aluminum+LUNOX uses no hydrogen (1) Basic Rocket Math e^v/c = mass ratio v= rocket velocity c=exhaust velocity e= 2.718 ISP*0.0098= c ISP=specific impulse 0.0098= acceleration of gravity m/s divided by 1000 to get c in km per second Tankage and motors typically amasses 20% of propellant mass For pressure fed rockets this may reach 30% of propellant mass ISP of Aluminum+LUNOX = 280 seconds c= 2.744 km/sec “ “ Silane+Lunox = 340 seconds c= 3.332 km/sec “ “ LH2+LUNOX = 450 seconds c= 4.41 km/sec To reach 1.6 km/second, lunar orbital velocity, and ascend to low lunar orbit or retro down from LO, a rocket needs a mass ratio of: Aluminum+LUNOX 3.83 Silane+LUNOX 3.02 LH2+LUNOX 2.31 If we have a payload mass of 20 tons, knowing the payload mass and mass ratio to reach 1.6 km/sec is given by: MR = (Mp + 0.3Mp + payload mass)/ 0.3Mp + payload mass Mp = mass propellant (0.3Mp) = rocket structure mass (30% of propellant) For Al+LUNOX 3.83 = (Mp + 0.3Mp + 20 tons)/(0.3Mp + 20tons) Solution: 3.83(0.3Mp+20) = (Mp + 0.3Mp + 20) 1.149 + 76.4 = Mp + 0.3Mp + 20 57.55 = 1.3Mp Mp = 44.268 Thus the Al+LUNOX rocket have a payload of 20 tons, a propellant mass of 44.268 tons and a rocket tank, motor and frame mass of 13.3 tons (30% of propellant mass) Using the same formulas we can determine that a silane+LUNOX rocket with a payload of 20 tons will have a propellant mass of 31.77 tons of propellant and 9.53 tons of rocket mass For a LH2+LUNOX rocket with a payload of 20 tons we find that we need 20.7 tons of propellant and 6.9 tons of rocket structure to reach 1.6 km/sec. Stochiometery How does silane+LUNOX compare to LH2+LUNOX? SiH4 + 2O2 = SiO2 + 2H2O or 32 gr SiH4 + 64 gr O2 = 32 gr SiO2 + 36 gr H2O 2H2 + O2 = 2H2O 4gr H2 + 32 gr O2 = 36 gr H2O 31.77 tons of SiH4 and LUNOX will consist of 1 mass of SiH4 per 2 masses of LUNOX or 10.6 tons of Silane 20.7 tons of LH2+LUNOX will consist of 1 mass of LH2 and 8 masses of LUNOX or 2.3 tons of LH2 Here’s where it get’s interesting. If 10.6 tons of Silane for the SiH4 and LUNOX rocket is 4 masses hydrogen and 28 masses of silicon, the silane only needs 1.325 tons of hydrogen to produce on the Moon. 10.6 * (4/32) = 1.325 Result Silane+LUNOX uses just a little more than half as much precious hydrogen. 1.325/2.3 = 0.576 By making silane with abundant silicon and precious hydrogen and making LUNOX which is also abundant on the Moon, once we get industry and resource processing going, we can extend and/or conserve our precious hydrogen obtained by volatile mining and ice mining in polar shadowed craters. With Aluminum and LUNOX we don’t have to sacrifice any hydrogen at all !!!! Pressure Feed Why run simple pressure fed rockets? Because silane burns to silica and water vapor and silica deposits would ruin the pump turbos. How do we run simple pressure fed rockets on the Moon when helium is more rare than hydrogen by far? And argon is even more rare than helium. I suggest using high pressure gaseous oxygen to push LOX into the engine and gaseous silane to push the SiH4 into the engine. There will be some heat exchange between silane, LUNOX, gaseous silane and gaseous oxygen, but the mass of the gaseous oxygen and silane will be far lower than the mass of liquid silane and oxygen so there will not be a tremendous heating of the liquid propellants. That is to say that the greater mass of liquid propellants will have a far higher specific heat capacity than the gaseous O2 and silane. Heat flows from substances of higher temperature to lower temp.,so the gas will lose heat into the liquid and if it is cold enough, that is well below it's boiling point, the mass of liquid won't boil when it absorbs heat from the gas..It's more likely that the liquids will cool the gas and reduce tank pressures, but before this happens the brief few minute rocket engine burn will be over with. Despite objections, I think gaseous O2 and silane can work in pressure fed rockets. Note: Silane ignites spontaneously in air. If we pressurize liquid SiH4 with gaseous O2 there might be an explosion! We must pressurize liquid silane into the rocket engine with gaseous silane at high pressures, several thousand psi. The upside is that silane and oxygen will be hypergolic for sure fire rocket motor ignition. The Moon seems to be "burping" radon and there may be pockets of this mildly radioactive gas in the Moon but radon is no good as a pressurant because it has a half life of only 3.8 days and decays into polonium and lead. The upside of this is that radon forms by the decay of U238, so there could be richer sources of uranium inside the Moon than KREEP that only has 4ppm U and 10ppm Th. We might mine this for nuclear rockets, reactors and RTGs. Lead can be used to stain glass red and add color to Moon bases(2). 1) http://www.wickmanspacecraft.com/lsp.html 2) http://en.wikipedia.org/wiki/Radon |
| Rocket designs will vary. Tanks will be insulated from frame by ceramics at frame contact points. The frame and tanks will be wrapped in aluminum foil for protection from solar rays that could warm the supercold propellants. Computers will monitor tank temperatures and pressures and gaseous oxygen and silane flow into tanks will be automatically regulated and fuel flow will also be regulated to maintain correct thrust levels during brief burn. At one gee it will take just 163 seconds or 2.7 minutes to reach 1.6 kps.So there will not be much time for cold liquid propellants to condense the gaseous O2 and silane and cause loss of pressure. Engineers who understand the kinetics of heat flow between gaseous O2 and LUNOX and gaseous silane and liquid silane could make this work. Silane will flow thru gimbaled rocket engine cooling jacket and the engine will be designed for reusability. Rocket engine lifetime might be limited by silica deposit build-ups in the firing chamber and nozzle. |
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| HCl + Si |
| Chlorine is recycled, new silicon and hydrogen are put into system to make more silane and O2 is generated by magma electrolysis |
| Si + 3 HCl ==> HSiCl3 + H2 or 4Si + 12 HCl ==> 4HSiCl3 + 4H2 4HSiCl3 ==> SiH4 + 3SiCl4 see: http://en.wikipedia.org/wiki/Silane All plumbing, pumps, compressors, valves. chemical reactors and storage tanks are made of titanium because titanium has excellent chlorine corrosion resistance. see: Lunar Titanium |
| Note: For every 4 atoms of silicon inputed only 1 atom becomes part of silane and 3 atoms become part of SiCl4 that is decomposed to Si and chlorine. Or, in terms of molar masses: H2 = 2gr Si = 28 gr Cl = 35 gr HSiCl3 = 134 gr SiH4 = 32 gr SiCl4 = 168 gr .4Si(112) + 12HCl(432) ==> 4HSiCl3(536) + 4 H2(8) 4HSiCl3(536) ==> SiH4(32) + 3 SiCl4(504) 3SiCl4(504) ==> 3Si(84) + 12Cl(420) For every four masses of silicon we input we get 1.143 masses of silane and three masses of hi quality silicon that just needs to be zone refined and can be used for solar panels. It seems that if we are mass producing silane/LUNOX on the Moon for rocket propellant there will also be lots of hi quality silicon as an additional benefit. |
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| Raw Regolith inputed to magma electro. |
| resin? From hemp or creosote bushes? |
| HCL |
| hot HCL + Si |