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This paper presents the design methodology and performance testing of an additively manufactured resistojet operating on hydrogen as propellant. Additive manufacturing allows to produce complex monolithic resistors, resulting in reliable high efficiency thrusters. The concept, to be used in combination with advanced cryogenic storage technologies, is proposed for short time and high specific impulse orbit transfers. The simplified two-dimensional thermal design approach adopted is discussed, and its application to the engineering of the resistor is shown for both Inconel 718 and tungsten. The paper reports the performance testing of the proof-of-concept version of the thruster, manufactured in Inconel 718. Experiments on hydrogen show near ideal performance, demonstrating a peak thermal efficiency of 96%. The thruster proves the validity of the design methodology proposed, and the feasibility of the approach to develop monolithic additively manufactured hydrogen resistojets as main propulsion units.

A hollow cathode is an efficient electron source in the self-heating mode utilizing the discharge power. However, in sub-ampere currents, it needs keeper power to maintain the thermionic electron discharge, which could decrease the thrust efficiency. To address this problem, we propose using a microwave cathode, which is based on the flight model of a microwave ion thruster neutralizer cathode, as an alternative to a hollow cathode. First, we redesigned the magnetic field of a microwave cathode discharge chamber and tested it in the diode mode configuration. The electron emission current is doubled compared to the original performance. Next, we coupled the improved microwave cathode with a 200-W class Hall thruster and compared the characteristics and performance with a hollow cathode. We confirmed that the magnetic field polarity affects the ignition characteristics. We measured the thrust by an inverted thrust stand, the ion energy distribution functions by a retarding potential analyzer, and the beam profiles by an ion collector. The thrust and thrust efficiency are equivalent for both types of cathode. The specific impulse is 10% higher in the case of the microwave cathode. Since the potential difference between the microwave cathode and ground rapidly increased at currents above 600 mA, this could be taken to be the trade-off point against the hollow cathode., [Highlights] / • Electron current of a microwave cathode doubled by redesign of magnetic circuit. / • Magnetic polarity of microwave cathode and Hall thruster affected plasma maintenance. / • Thrust was equivalent in the both cases of microwave cathode and hollow cathode. / • Performance trade-off point between the two cathodes was about 600mA. / • Efficiency analysis by IEDF and beam profile showed different plasma characteristics.

Accepted: 2019-09-18, 資料番号: SA1190110000

An advanced background-oriented schlieren (BOS) method, named as the speckle beam-oriented schlieren technique, was newly developed to measure the distribution of refraction angles in transparent media. A speckle pattern is generated by passing a coherent laser beam through a holographic diffuser, a pinhole, and a lens, generating a collimated background image that is projected directly onto the image sensors. Since the intensity of the background image is maintained at a high level, this method is, in principle, useful for diagnosing fast and/or low signal-to-noise phenomena, such as high-temperature gasses with radiation emission. Moreover, by splitting the background beam into two imaging paths with different focal lengths, the refraction angles can be measured for a schlieren object with uncertain location, and the depth position of the refraction angles can be resolved. This technique was demonstrated by measuring the refraction angle and the depth position distribution in a sonic jet with different injected locations., Published: 08 January 2021 ファイル公開：2022/01/08

Nanosecond-pulsed surface dielectric barrier discharge plasma actuators are used to control shock-wave/boundary-layer interactions. Characterization of the separation region without plasma actuatio...

A 3D-printed resistojet, wherein the heater and flow path were united, was produced. The heater consists of multi-layer shells and is difficult to break down. In this paper, the thermal design and the results of the thrust measurement are reported. The measured electrical resistance matched with the predicted one. Both the heater and the thrust reached 70 percent efficiency when paired with a nitrogen propellant at a mass flow rate of 0.2 g/s., AIAA 2018-4907 Session: Micropropulsion II

資料番号: PA1210040000

Ultimate weight reduction and low manufacturing cost are strongly required in the development of next-generation launch vehicles. It is one of effective methods for these purposes to change structural materials from conventional aluminum alloys to composites, such as CFRP (Carbon Fiber Reinforced Plastics). Under these situations, we developed a launch vehicle structure by using CFRP/honeycomb sandwich panels in order to achieve both weight and cost reduction. FEM (Finite Element Method) simulation was utilized to effectively carry out the structural design. Metallic structures are applied for the flanges (joining interfaces between the other structures) in general; however, we used CFRP structures also for the interface flanges for the weight reduction and manufacturing simplicity. The designed CFRP structure was fabricated and a static load test was conducted considering flight loads during actual launch. The strain distribution was obtained by FBG (Fiber Bragg Grating) sensors and three-dimensional displacement was measured by laser tracker as well as normal strain gauges in the limit load test. These measured data were compared with the FEM simulation results and they show good agreement. We will apply these manufacturing, testing, simulation and sensing techniques for the future launch vehicle developments.

This study numerically explores the flow physics associated with nanosecond pulsed plasma actuators to control shock-wave induced boundary-layer separation. By using two actuators, parallel and canted with respect to the main flow direction, a previous experiment suggested the actuator worked in two ways: boundary layer heating and vorticity production. The heating effect was enhanced with the parallel electrode and made the separation stronger, while the canted electrode produced vorticity and suppressed the separation due to the momentum transfer. Because the detailed physics is still unclear, a numerical investigation is undertaken with a large eddy simulation and an energy deposition model for the actuator. The flow without the actuation corresponds to the experimental observation, indicating the calculation successfully resolves the separation. With the actuation, as with the experiment, the calculation successfully demonstrates definite difference between the parallel and canted electrodes: the parallel electrode causes excess heating and increases the separation, while the canted electrode leads to a reduction of the separation, with a corresponding thinning of the boundary layer due to the momentum transfer. The counter flow created by the canted actuator plays an important role in the vortex generation, transferring momentum to the boundary layer and, consequently, mitigating the separation., Accepted manuscript for publication in Physics of Fluids

The ionized exhaust plumes of solid rocket motors may interfere with RF transmission under certain flight conditions. To understand the important physical processes involved, we measured microwave attenuation and phase delay due to the exhaust plume during sea-level static firing tests for a full-scale solid propellant rocket motor. The measured data were compared with the results of a detailed simulation performed using the frequency-dependent finite-difference time-domain ((FD)2TD) method. The numerically derived microwave attenuation was in good agreement with experimental data. The results revealed that either the line-of-sight microwave transmission through ionized plumes or the diffracted path around the exhaust plume mainly affects the received RF level, which depends on the magnitude of the plasma-RF interaction.

Velocity and temperature measurements were conducted for a two-dimensional magnetoplasmadynamic arcjet with hydrogen propellant. To obtain the velocities of both atoms and ions, laser absorption spectroscopy was employed for atom, and time-of-flight technique was used for ions. In a quasi-steady operation at 13kA/0.65g/s, larger ions velocity (33km/s) than that of the atoms (13km/s) was found in the case of flared anode configuration, which implies that large mean free path between the ions and atoms prohibited momentum transfer from the ions to the neutral particles. This velocity difference was not observed in the case of converging-diverging anode, where the high-density plasma inside the discharge chamber enhances momentum transfer from ions to atoms. In addition to the velocity difference, diagnostics by probe methods revealed high ion temperature in comparison with that of electrons at the thruster exit. Using the velocities and temperatures together with the densities of each particle, energy flux of the magnetoplasmadynamic arcjet was discussed. The large energy deposition into thermal and internal energy modes near the thruster exit indicated a large amount of pressure energy that should be converted to velocity energy by an appropriate nozzle design to further improve the thrust performance.

The Japan Aerospace Exploration Agency launched the S-310-43 sounding rocket from the Uchinoura Space Center on Aug. 04, 2014 for the purpose of investigating such behavior as boiling and flow of cryogenic liquid rocket propellant in an environment simulating coasting flight on orbit by using the sounding rocket's sub-orbital ballistic flight. In the low-gravity state, the cryogenic fluid (liquid nitrogen) was introduced into the test sections of similar shapes to the flow channels in the cryogenic propulsion systems. The boiling of liquid nitrogen inside the test-sections and the transition of flow regimes from gas/liquid two-phase flow to liquid mono-phase flow were visualized. The temperatures, pressures and void fractions of each channels were measured as well. Development of the experimental equipment for S-310-43 sounding rocket is described in this paper., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: DS1540301003

資料番号: SA1005060000