ConclusionsThe analytical techniques used during the test program permitted accurate pretest predictions. These techniques are being applied in the NERVA flight-engine program and will greatly reduce the number of tests required at the subsystem and engine level. This proven analytical approach grants a higher confidence of success with a limited number of tests.Studies of the pulsed plasma thruster used for stationkeeping in the LES-6 satellite are described. Current waveforms were measured, from which circuit parameters were deduced, an energy balance made, and thrust was computed. Each current pulse ablates ^10~8 kg of Teflon (6 X 10 16 molecules of C 2 F 4 ), exhausts it at 3000 m/sec (specific impulse 300 sec) with an impulse bit of 31.2 jj, N-sec (7 julb-sec). Langmuir probe measurements of electron density and temperature, a K-band microwave interferometer measure of density and collision frequency, spectroscopic analysis of ion species, and a Faraday cup measurement of ion velocity were all made. Ion velocities of approximately 40,000 m/sec indicate that the gas is only partially ionized. A thrust stand was constructed to measure impulse bit and specific impulse. The impulse bit is linear with capacitor energy (1.85 joules, normally). Modifications in the current return path to the capacitor which changes the magnetic field behind the exhaust were made. Specific impulse could be tripled, but impulse bit dropped by a like factor, with no improvement in efficiency.
A ten megawatt rocket driven MHD disk generator system has been designed as part of the feasibility study of multimegawatt MHD space power systems for SDI0 mission applications. The experimental system consists of a plasma generatodinjector, a supersonic nozzle, a parallel wall disk channel, and a diffuser. The magnetic field is provided by a heat sink cryogenic magnet coil. Facility support systems include a reactant feed system, a cooling system, an excitation and power extraction system, an exhaust system, and the required instrumentation and control system.The fuel is an aluminum-MMH gel. The oxidizer is a potassium nitrate-IRFNA solution. At the design oneto-one mixture ratio, the specific enthalpy is 10 MJkg. The products of combustion are expanded from the stagnation combustion pressure of 11 atmospheres to supersonic/ sub-atmospheric flow conditions at the inlet of the channel. The supersonic nozzle consists of 24 water cooled vanes which impart a 45 degree swirl to the working fluid at the entrance of the MHD channel. The MHD channel operates in the impulse mode with a nearly constant plasma conductivity in the range 40 to 50 mho/m from the channel inlet to its exit. The magnetic induction is tapered from an inlet value of 5 Tesla to an exit value of 3.25 Tesla. For atmospheric pressure exhaust and a diffuser recovery of 50 percent, an enthalpy extraction of 1 MJkg is predicted so that at the design flow rate of 10 kg/sec, a power output of 10 MW is projected. Following initial excitation, power for the magnet is provided by the channel itself. Fabrication of the system components was initiated early in 1989. Testing is planned for the second half of 1989.
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