A new identification procedure in discrete time systems is proposed. This method identifies the unknown parameters in the system by using the pulse response time history which is reconstructed through an ARMA model. With this identification, the excitation requirement on input is relaxed, and it results in easy installation. As this identification is done totally in time domain, it is applicable to the time variant systems. The sufficient conditions are obtained within which the identification is performed for such systems. A number of numerical simulations are conducted to confirm the availability. In the simulations, the simplified model of a launch vehicle in flight is treated to show the ability of the identification of the time variant system.

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The present paper deals with the numerical investigation of autoignition region between a backward-facing step and perpendicular wall injectors in a supersonic combustor. A series of simulation changing the dynamic pressure ratio of the injectant to the main stream is carried out. Wall pressure profiles and injectant concentration in the recirculation region between the step and the injectors show agreement with experimental results. The results by tracking streamline clarifies the correlation between the ratio of circulating cycle to the variation of injectant concentration in the horseshoe vortex and the residence time of mixture measured at the fixed point. The residence time increases from 0.3 msec at the dynamic pressure ratio of 0.1 to 1.2 msec at 0.7. When the dynamic pressure ratio exceeds 0.7, the residence time becomes constant because the size of the horseshoe vortex and injectant concentration does not vary.

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A 60cm Magnetic Suspension Balance System (MSBS), which has been developed in the National Aerospace Laboratory of Japan (NAL), is described in detail. Magnetic field in the MSBS is evaluated analytically and is compared with measured one. Available magnet kinds for the MSBS are selected analytically. The optimum ratio of diameter to length of cylindrical magnet for the MSBS is also evaluated. A model position sensing and the control systems are described with calibration test results. A model holding system is also shown, which is necessary for worker’s safety at suspending a large and massive model. The control system is presented and the measured model position during suspension is examined. The balance accuracy is examined and its error of drag force can be improved by restricting the calibration test to an expected drag range. Flow of the 60cm low-speed wind tunnel equipped with the MSBS is examined to be available for wind tunnel tests.

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Here is presented an experimental and analytical study on a precooler for hypersonic air-breathing engines. Precooling of the incoming air breathed by an air-inlet gives extension of the flight envelope and improvement of the thrust and specific impulse. Three precooler models were installed into an air-turbo ramjet engine and tested under the sea level static condition. When the fan inlet temperature was down to 180K, the engine thrust and specific impulse increased by 2.0 and 1.2 times respectively. Thick frost formed on the tube surfaces at the entrance part of the precooler blocked the air-flow passage. On the other hand, very thin frost formed at the exit part because the water vapor included in the air was changed to mist particles due to the low temperature of the air in this part. Parametric studies on the precooler design values and a sizing analysis were also performed. Decrease of tube outer diameters on the precooler is only way to increase heat exchange rates without increase of its weight and pressure loss.

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Irradiating a nano-second laser pulse on a solid surface, a GH₂/GO₂ combustion chamber was operated to measure the minimum ignition energy for three parameters: the spot diameter, the thruster pressure, and the target material. It was confirmed that this method is useful since the minimum ignition energy can be much less than that of the laser spark ignition. It turned out that the minimum ignition energy increases as the spot diameter increases, and decreases monotonously as the thruster pressure increases. In addition, it was suggested that the ignition is possible even after the irradiation of a million laser pulses by applying the metallic targets (tungsten and stainless). On the other hand, the carbon target provided poor ignition probability.

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The stability of the orbits around the sphere of influence of the secondary body in the circular restricted three-body problem is discussed. This orbit is called “Pseudo Orbit” here. Though there exists a stability limit for the inclination of the pseudo orbit, the whole story of the instability was not resolved. In this paper, it is shown at first that the out-of-plane motion of the pseudo orbit causes disturbances in the in-plane motion by the method of virtual energy. Then, it is shown that the disturbances are governed by the Mathieu’s equation which has the periodic coefficient, and the rigorous mathematical property of the instability of the pseudo orbit is presented.

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