Quote from: Shevek23 on 09/14/2016 07:23 pm In some ways the MHD-driven-motor concept can be far simpler and more reliable, and also controllable, than the ingenious all-mechanical systems we use. There is no way that is true, see the H-1.a. how do you start a MHD-driven-motor? All it takes a turbine engine is head pressure, simple start cartridge, or gas bottle.
In some ways the MHD-driven-motor concept can be far simpler and more reliable, and also controllable, than the ingenious all-mechanical systems we use.
Quote from: Jim on 09/14/2016 07:40 pmQuote from: Shevek23 on 09/14/2016 07:23 pm In some ways the MHD-driven-motor concept can be far simpler and more reliable, and also controllable, than the ingenious all-mechanical systems we use. There is no way that is true, see the H-1.a. how do you start a MHD-driven-motor? All it takes a turbine engine is head pressure, simple start cartridge, or gas bottle. You start such an engine using power from batteries that are sized to run the engine long enough for the MHD power to start running the pumps and refilling the batteries. Since they only need to run for maybe 3-10s, and possibly at a lower throttle setting, they don't need to be that big. Could also be ultracapacitors.~Jon
I dont think anyone will dispute that you will get better performance ( thrust to weight, ISP ) out of a turbopumped engine. And it's very likely that scaling up electric pumping will make little sense.....
EDIT: Nah, HTS-motors are around 20.0 kW/kg apparently now, or higher. Source: Brown, G. V, “Weights and Efficiencies of Electric Components of a Turboelectric Aircraft Propulsion System,” 2011
...(But batteries work pretty well.)
Digging around more, NTRS has this paperDesign study - Rocket based MHD Generator, 1997, ERC Inforporated
Siemens flew a 260kw, 50kg air-cooled motor in "Extra 330LE" aerobatic plane. So 5KW/Kg. NASA research from a few years ago peaked with 10KW/Kg with motors submerged in LN2. I don't think i've seen higher projections than that.
Ambitious Goals, Different ApproachesGoals are ambitious, with NASA Research Agreements (NRAs) awarded to the University of Illinois and Ohio State University to develop electric systems that can achieve 13 kilowatts per kilogram and efficiency greater than 93 percent. NASA Glenn’s target is 16 kW/kg and 98-percent efficiency.General Electric and the University of Illinois share an NRA to make power converters that produce 19 kW/kg and an efficiency target of 99 percent. Boeing’s working on a cryogenic converter with goals of 26 kW/kg and an efficiency of 99.3 percent. Compare these goals with the Energy Department’s 2020 goal of 14.1 kW/kg for vehicle power electronics.
Quote from: savuporo on 09/14/2016 09:43 pmAgain, nobody has yet fired a turbopump in space, after any significant loiter times.Not an issue for the RL10
Again, nobody has yet fired a turbopump in space, after any significant loiter times.