Numerical analysis of O3 depletions by exhaust plume from stratospheric flight at the altitude of 25km was conducted. Expanding box method was employed to simulate a diffusion of exhaust plume in the stratosphere. Concentrations of chemical species and normarized sensitivities of O3 concentration for reactions were estimated by fifth-order BDF method. Chemical kinetics include NOx, HOx and Ox chemistry. As results, it takes over two days that O3 concentration within a plume becomes ambient lebel within 1ppb. O3 perturbations were changed by an effect of plume-emission time, and they are bigger in daytime than in nighttime. Distributions of sensitivities of O3 concentrations for reactions are also changed for the plume-emission time. O3 depletion is greater by NOx than by HOx in exhaust plume.
We analyzed the small coaxial helicopter recently developed for entertainment. The upper rotor is connected with a stabilizer bar alone and the lower rotor is not connected with it. The cyclic pitch of the upper rotor is controlled by this stabilizer bar, and that of the lower rotor is controlled by servo motors. We investigated how this stabilizer bar varies the cyclic pitch of the upper rotor and how it contributes to attitude control of a fuselage.
The present paper treats a technique of vibration measurement and control based on the optimal placement of sensors and actuators. In the first report of this paper, we discuss the validity of an optimal design of modal sensor and actuator through numerical simulations. The modal sensor is designed by the optimal placement of accelerometers which are located on the optimal location minimizing an observation spillover. In order to build up a simple and efficient vibration control system using PZT piezoelectric materials as actuators, the modal actuator is constructed by the optimal placement of actuators based on the criterion of minimization of control spillover. To examine the effect of the optimal design of modal sensor and actuator, numerical simulations are presented using CFRP cantilevered plate. We consider the relation between a location of sensors/actuators and the efficiency of modal control. The results of simulation show that the optimal placement of sensors and actuators is indispensable to measure and to control the vibration of plate precisely.
Satellite communication systems have entered into the mobile multimedia communication era. To support small earth terminals, the satellites must have high levels of effective isotropic radiated power. Onboard high-power amplifiers are not only needed to generate high RF output power, but also to generate as less heat as possible. To address this issue, we present a new technique reducing an amount of heat generated in high power amplifiers on a satellite. The technique makes use of heat suppression signals so as to maintain the amplifier’s power efficiency. The dissipation heat has been conventionally evaluated by consumption power of loaded FETs. However, the validity of this method has not yet been clarified on an experimental basis. Therefore, the dissipation heat from SSPAs was evaluated by other measurement technique, that is, we measured temperatures of SSPA and of air cooling. Furthermore, an effect of heat suppression was demonstrated.
The air breathing ion engine (ABIE) is a new type of electric propulsion system which can be used to compensate the aerodynamic drag of the satellite orbiting at extremely low altitudes. In this propulsion system, the low-density atmosphere surrounding the satellite is taken in and used as the propellant of ion engines to reduce the propellant mass for a long operation lifetime. Since feasibility and performance of the ABIE are subject to the compression ratio and the air intake efficiency, a numerical analysis has been conducted by means of the direct-simulation Monte-Carlo method to clarify the characteristics of the air-intake performance in highly rarefied flows. Influences of the flight altitude, the aspect-ratio of the air intake duct, the angle of attack, and the wall conditions are investigated.
Aluminum alloys have been widely used in the constructing various space structures including the International Space Station (ISS) and launch vehicles. For space application, welding experiments of an aluminum alloy were conducted by the GHTA (Gas Hollow Tungsten Arc) welding processes using a filler wire feeder in vacuum. We investigated the melting phenomena of a base metal and a filler wire, bead formation phenomena and effects of wire feeding speed on melting characteristics. The melting phenomenon of melt-run welding with a filler wire was basically the same as that of without a filler wire. It was clarified that the effects of wire feeding speed on bead sizes and configurations. Furthermore the butt welding joints were welded by the optimum wire feeding speed and the tensile strengths of those joints were evaluated. The mean value of tensile strengths of butt welding joints that were made using d.c.-pulsed GHTA welding with filler wire in vacuum was almost same value as that was welded by GTA (Gas Tungsten Arc) welding in air.
In recent years, concern has been raised about the interference phenomena (chemical reaction, sputtering etc.) between ionospheric plasma and high-voltage space systems such as the International Space Station and so on. In order to solve the physical mechanisms of these phenomena and establish the prevention technology, it is important to accumulate experimental data based on ground simulation tests. Therefore we have developed a cathode-less microwave discharge oxygen ion source for an ionospheric plasma simulator. The oxygen ion source for ionospheric plasma simulation demands plasma density more than 1012m- 3 and high durability (our target is more than 70hours). This ion source is capable of generating oxygen plasma of the order of 1014m- 3 for more than 100hours with 25W microwave power and 3sccm oxygen gas. In order to investigate the operational performance of the oxygen ion source, we conduct various measurement tests such as plasma diagnosis using a single probe, ionic mass spectroscopy by a Quadrupole Mass Spectrometer (QMS), atomic oxygen flux measurement using a silver coated QCM (Quartz Crystal deposition Monitor) and 70hours operating test etc. This paper reports the experimental results of each measurement tests and assesses performance as an ion source for ionospheric plasma simulator.