pippin - 5/5/2007 10:33 AMAnybody an idea, what kind of ISP you can get from methane engines?(...)
TyMoore - 5/5/2007 3:42 PM...I am assuming of course that a nuclear reactor main base powersource will provide process energy to synthesize the necessary ingredients to make the methane, atleast on Mars. ...
TyMoore - 6/5/2007 3:31 AMYou send up a small one (about 100KWe, or about 500 KWt--total system weight maybe about 7-10 tons) and send that along as a part of the payload manifest. They aren't really that heavy, not for what they give you which would be years of power and heat. The mass comes from power conversion systems, and heat rejection systems. The main bulk of the radiation shielding will be made from Mars itself: you bulldoze up a burm around the reactor--bingo, instant radiation shielding. Also you locate the thing some distance away from the rest of your base.
pippin - 7/5/2007 12:17 AMQuoteTyMoore - 6/5/2007 3:31 AMYou send up a small one (about 100KWe, or about 500 KWt--total system weight maybe about 7-10 tons) and send that along as a part of the payload manifest. They aren't really that heavy, not for what they give you which would be years of power and heat. The mass comes from power conversion systems, and heat rejection systems. The main bulk of the radiation shielding will be made from Mars itself: you bulldoze up a burm around the reactor--bingo, instant radiation shielding. Also you locate the thing some distance away from the rest of your base. "bulldoze" requires a bulldozer, doen't it. Icluding power supply. Might even be lighter to send all the stuff from earth.
What kind of reactor are you envisioning? Pressurized water reactor as seafaring vessels? That's the "light" ones of today but requires extensive external cooling. Lots of water around a ship. None at all on mars. Hmmm. By the way... lot of mass comes from pressurized containment.Pebble bed reactor (or similar high temperature design)? That's the one you WANT to use since it's got a non-critical design (no rapid unsccheduled disassemblies contamining your whole base due to your reactor going critical) and you can get away with radiation cooling and a gas turbine instead of a (heavy) steam turbine and you don't need a (heavy) pressurized containment. However, it's not operationally proven, so count 20 year of development time, no need to start developing methane engines for that scenario today...
Then there is fuel. You still need a few tons of that (we are not talking about "pure" U235 or something, but a mixture in a containment). How do you send it there? You probably don't want to contamine half of your current habitate due to one of those (rare) chemical launcher failures so you need LOTS of containment around that while sending it up...I don't think you will see a large scale nuclear reactor (that is: more then a pem or something of similar size) on mars until you have enough infrastructure up there to at least assemble it there and find your fuel locally...
Use of a new high radiation-safety orbit was also demonstrated. The Topaz used a new thermo-emission conversion method to convert heat to electricity. This would also power a range of new systems including electrostatic manoeuvring engines, ion orientation/stabilisation engines, solar sensors, magnetic momentum compensators, multi-channel wave devices, and special plasma weapons to provide a defence against anti-satellite weapons. The Plazma-A satellites carried instruments to map the magnetic field of the earth, with an eye toward developing a magnetic navigation system. Topaz provided over 10 kW of power and had long endurance and storage in a radiation-safe orbit. A follow-on Plazma-2 would have been equipped with the even safer Topaz-2. The spacecraft would be orbited by a Tsyklon 2 booster and have a mass of 3550 kg. Despite these encouraging tests, the US-AM nuclear-powered component of the Pirs system was abandoned on the instructions of Gorbachev in 1988 due to continued reliability problems and international incidents when the reactor cores of the satellites crashed to the earth.
TyMoore - 6/5/2007 2:23 PMThis is getting way off topic--but I didn't say tons of fuel. I said total system weight--reactor pressure vessel, control systems, coolant circulation, power conversion, heat rejection, and oh yeah, the bulldozer. A small reactor no bigger than refrigerator using highly enriched uranium as fuel, probably straight Uranium-235 (93% enriched) alloyed with Zirconium to brind the Uranium content down to about 10%, cald again with zirconium, and then stuck in a tungsten cermet structure. It could be cooled with a pressurized water loop, or it could be helium cooled for a relatively high efficiency Brayton conversion system using gas turbines and an alternator. You'll get good cycle efficiency, long life, and lots of process heat for everything from a green house, to oh yeah, making methane in a Fischer Tropsch process, which you can then burn in those neat little methane engines.
TyMoore - 5/5/2007 7:55 AMI think the main advantage with methane is storability. Liquid methane's boil point is close to that of liquid oxygen, which is a lot 'wamer' than liquid hydrogen--so the boil off should be quite a bit less. Also, you can save weight on a booster by thinning the insulation over the fuel tank a bit from liquid hydrogen...
As far as making methane on Mars--it's not as much balogny if there's plenty of water up there. Water can be electrolyzed into hydrogen and oxygen. The hydrogen can be reacted with carbon monoxide in a Fischer-Tropsch synthesis reaction to create methane. No problem really--you just need a power source to supply process heat.
privateer - 7/5/2007 7:43 AMQuoteTyMoore - 5/5/2007 7:55 AMI think the main advantage with methane is storability. Liquid methane's boil point is close to that of liquid oxygen, which is a lot 'wamer' than liquid hydrogen--so the boil off should be quite a bit less. Also, you can save weight on a booster by thinning the insulation over the fuel tank a bit from liquid hydrogen...In this case, propane may be better:___________ Methane PropaneMelting point -182.5 -187.6 (LOX boiling point is -182.95)Boiling point -161.6 -42.09 (all temps are in Celsius)Liquid density 0.42 0.58See? Propane will also stay liquid at LOX boiling temp (with larger margin), but it will remain liquid in much wider range of temps. (Heh, -42 celsius is a normal ambient temperature in many areas on Mars!) Density is also notably higher. Two reasons why tanks can be lighter.Isp of methane, ethane and propane (with LOX) is virtually the same IIUC.QuoteAs far as making methane on Mars--it's not as much balogny if there's plenty of water up there. Water can be electrolyzed into hydrogen and oxygen. The hydrogen can be reacted with carbon monoxide in a Fischer-Tropsch synthesis reaction to create methane. No problem really--you just need a power source to supply process heat.Now this can be a problem for propane. How hard it will be to produce it instead of methane?