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Integrated Propulsion and Power Missions amenable to electrolysis propulsion can gain from having both the electrolyzer and the batteries replaced with a URFC. 7 In this case, the weight of the unitized system is shared by the power and propulsion system thus providing a savings over conventional systems. Recent results have demonstrated that URFCs are capable of many energy storage cycles without significant degradation. 6 Results from recent accelerated cycle testing are shown in Fig. 3 along with a description of the single cell URFC polysulfone cell frames. The unit was designed to operate at pressures as high as 1 MPa. With the water tower filled up to 15 cm, the total impulse of this system was estimated to be 1000 N-s if an lsp of 330 s is assumed. Hydrogen, generated inside the electrolysis cell percolated to the top of the tower. A compression fitting installed in the tower wall connected to a 3.18-mm diameter propellant line, which supplied hydrogen to a 300-cc storage tank, rated for 20 MPa. Oxygen generated inside the electrolysis cell accumulated inside the base. Another fitting in the side of the base connected to a 3.18-mm diameter propellant line, supplying oxygen to a 150-cc storage tank. The tanks were designed to assure nearly equal pressures based on the decomposition. Solenoid valves installed between the electrolysis unit and the storage tanks were opened during the electrolysis cycle and then closed during thruster firing. The valve closing prevented water from being drawn from the electrolysis tower into the propellant lines by sudden depressurization following ignition. This valve would be eliminated in a true flight design by the use of a zero gravity compatible water vapor feed electrolyzer. Nitrogen purge lines between the tanks and the electrolysis unit allowed the propellants to be purged, exhausting through the rocket nozzle. This feature was only required in ground testing. Sonic venturis installed inside the propellant lines downstream of the storage tanks fixed the propellant mass flow rates to the thruster. The venturis were designed for specific mass flow rates at inlet pressures of 0.68 MPa to achieve a stochiometric mixture ratio of eight. However, the venturis were calibrated over a range of inlet pressures. The mass flow rates, and thus the chamber pressure, decreased during a blowdown test, as the inlet pressures vary from 1.0 to 0.5 MPa. Calibration data assured that the venturis were choked at all points during blowdown tests for these operating conditions. Opening of thruster valves, installed downstream of the venturis, caused the venturis to choke, controlling hydrogen and oxygen mass flows to the injector. The injector available for these tests was optimized for a 20-N thruster. As a result, the injector did not provide optimum performance for the current tests, but was good enough for the purpose of this study. The oxygen was injected into a center annulus, where it was excited by a spark ignition system. Six cycle test cycles of operation power levels. Critical system parameters did not change over the course of the test, indicating that life and also the system operated over a wide range. conditions. More than 2010 alternate fuel cell (FC) and electrolyzer (EC) were accomplished at four different These results indicate that URFCs should be able to power satellites through many thousands of eclipse periods. Unlike battery power systems which require shallow depth of discharge to achieve systems throughout long cycle life, URFC energy storage should be capable of deep discharges their entire service life. Table I gives a summary of the status of the different demonstrated technology technologies. All technologies performance at readiness level 4 or higher. have NASA's Tests Electrolysis Propulsion Breadboard As a proof of concept, a complete electrolysis propulsion system was assembled. A schematic of the electrolysis breadboard system is shown in Fig. 4. For simplicity, power was obtained from a 35 V power supply, to simulate the small spacecraft bus. The maximum available power was 700 W. The system was designed to operate in blowdown mode (i.e. no regulators were used). A description of the system components follows. In a flight qualified system, the electrolyzer used would be a zero gravity compatible water vapor feed electrolyzer. The electrolysis unit used in the current experiments, however, was not a flight-type percolating, 5- cm high base. The electrolysis cell was housed in the base of the unit and was a 45.2-cm 2, platinized Nation 117 membrane with NASA TM-113157 electrolyzer This unit provided consisted Standard. unit, but was a cathode commercial, liquid feed by Hamilton a 5-cm diameter, 20-cm of high, plexiglass water tower on a 12.5-cm square, gravity 6PDF Image | Electrolysis Spacecraft Propulsion Applications
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