Yasuhisa Oda

Plasma generation using high-power millimeter-wave beam and its application for thrust generation

Propagation of an ionization front in the beam channel was observed after plasma was generated using a 170GHz millimeter-wave beam in the atmosphere. The propagation velocity of the ionization front was found to be supersonic when the millimeter-wave power density was greater than 75kWcm−2. The momentum coupling coefficient Cm, a ratio of the propulsive impulse to the input energy, was measured using conical and cylindrical thruster models. A Cm value greater than 350NMW−1 was recorded when the ionization front propagated with supersonic velocity.

An Experimental Study on a Thrust Generation Model for Microwave Beamed Energy Propulsion

In a microwave beaming thruster with a cylindrical tube, a plasma front propagates in the tube absorbing microwave power in a supersonic speed accompanying a shock wave. Therefore, the pulse detonation engine model is expected useful. In this study, pressure histories in the thruster were measured using pressure gauges and compared to pulse detonation engine (PDE) model. As a result, the propagation velocities of the shock wave and plasma front were found identical. Measured pressure at the thruster wall showed a similar history to that from the PDE model. These result shows that thrust generation model based on the PDE model would be applicable to the microwave beaming thruster.

An Experimental Observation for the Shock Wave Driven by Atmospheric Microwave Plasma in a Microwave Rocket

An experiment on microwave beaming propulsion with repetitive pulse was conducted. The microwave beaming thruster with forced breathing system was used. The forced breathing system supplies fresh air from thrust wall side into the thruster. The design flow speed in the thruster was 2.5-10m/s. A 170GHz high power gyrotron was used for microwave source. The pressure histories in the thruster were measured and propagation velocity of shock wave and thrust impulse were deduced. As a result, the velocity of shock wave in the thruster had small dependency on air flow speed because air flow speed in the thruster by forced breathing is lower than shock wave. At multi pulse operation, although at first pulse the propagation velocity of shock wave is identical to result of single pulse operation, after the second pulse propagation velocity was increased and the velocity became steady for latter pulses. As same, the impulse decrease at second pulse and steady impulse is obtained at latter pulses. Finally, the dependence of steady velocity of shock wave and thrust performance on partial filling rate of the thruster was compared to the thrust generation model with partial filling of air from the thrust wall. The experimental results on shock wave velocity and thrust impulse showed good agreement to the predicted dependency.

A Plasma and Shockwave Observation with Pulse Repetition in a Microwave Boosted Thruster

An experiment on repetitively pulsed microwave beaming propulsion was conducted. A 170GHz high power gyrotron was used for a repetitive-pulse microwave source. The propagation velocity of an ionization front and a shock wave in a cylindrical thruster model was. Pressure histories under multi pulse operationwith various repetition frequency from 15 Hz to 60 Hz. These propagation velocities were identical in any cases, and found decreased with the interval time. The velocity of shock wave and pressure in the thruster changed with the repetition frequency. Although impulsive thrust deduced from the pressure history was increased with the interval time, it was saturated at the repetition frequency about 20 Hz.

Propagating Structure Of A Microwave Driven Shock wave Inside A Tube

The thrust generation process of a microwave rocket is similar to a pulse detonation engine, and understanding the interactions between microwave plasma and shock waves is important. Shadowgraph images of the microwave plasma generated in a tube under atmospheric air were taken. The observed plasma and shock wave were propagating one-dimensionally at constant velocity inside the tube. In order to understand the flow field inside the rocket, one-dimensional CFD analysis was conducted. With the change of microwave power density, the structure of the flow field was classified into two regimes: Microwave Supported Combustion (MSC), and Microwave Supported Detonation (MSD). The structure of the MSD was different from the structure of a chemical detonation, which implied the existence of a preheating in front of the shock wave. Furthermore, the flight performance was estimated by calculating the momentum coupling coefficient. It was confirmed that the efficiency was nearly constant in the MSD regime, with the increase of microwave power density.

Pressure History Measurement in a Microwave Beaming Thruster

In a microwave beaming thruster with a 1‐dimensional nozzle, plasma and shock wave propagates in the nozzle absorbing microwave power. In this study, pressure histories in the thruster are measured using pressure gauges. Measured pressure history at the thruster wall shows constant pressure during plasma propagation in the nozzle. The result of measurement of the propagating velocities of shock wave and plasma shows that both propagate in the same velocity. These result shows that thrust producing model of analogy of pulse detonation engine is successful for the 1D thruster.

Competitiveness‐Analysis of a Future Space Transportation System: The Microwave Rocket

This paper evaluates the potential performance of a microwave propelled craft as a future space transportation system. The engine performance is evaluated on the basis of a the thermodynamic Lenoir‐cycle. Different propellants are discussed for the in‐space part of the ascent trajectory. A launch trajectory analysis with parameter variation is performed. Based on the results of the trajectory analysis the recurring launch cost is estimated. The study concludes with the derived margins for the vehicles airframe design.

Application of high power millimeter-wave to space propulsion

A microwave beaming thruster boosted by a 170GHz gyrotron was investigated. Plasma was successfully initiated by focusing the millimetre wave beam using a parabolic reflector. The plasma propagation velocity was increased with the beam power density; the velocity became supersonic at the power density beyond 80 kW/cm/sup 2/. Propulsive impulse was measured through the flight experiments, and resulting momentum coupling coefficient, a ratio of thrust to input energy, was found drastically increased when the plasma propagation velocity becomes supersonic.

A Multi Pulse Flight Experiment of a Microwave Beaming Thruster

An experiment on a multi‐pulsed microwave‐beaming thruster was conducted using a high power millimeter‐wave generator, gyrotron. Conical thruster models with various diameters and cone angles were tested. The momentum coupling coefficients Cm at the first and second pulses were separately estimated from the flight trajectory measurement. As a result, Cm was found decreased at latter pulses. The ratio Cm2 /Cm1 was varied mainly depending on the pulse repetition rate. The allowable maximum repetition rate for the optimum thruster scale would be lower than 60Hz.

An Experiment on Repetitive Pulse Operation of Microwave Rocket

Microwave Rocket was operated with repetitive pulses. The microwave rocket model with forced breathing system was used. The pressure history in the thruster was measured and the thrust impulse was deduced. As a result, the impulse decreased at second pulse and impulses at latter pulses were constant. The dependence of the thrust performance on the partial filling rate of the thruster was compared to the thrust generation model based on the shock wave driven by microwave plasma. The experimental results showed good agreement to the predicted dependency.