This paper describes the aerodynamic characteristics of the flapping motion of a dragonfly wing model. The orbit and feathering angle of a dragonfly wing were measured using a high-speed video camera. The measurement data was used to formulate two mathematical models: linear and Fourier models. The aerodynamic characteristics of a thin plate and dragonfly wing models, which were investigated using a numerical simulation, revealed that the linear model generated a high vertical force during descent and high thrust force during ascent. Although the Fourier model could not generate a high thrust force during ascent, it generated a higher vertical force than the linear model. During the flapping motion in both the models, a marginal difference was observed between the forces generated at the top and bottom. When the feathering angle approached the stroke angle, the resultant force direction acting on the wing models was reversed.
At an early stage of development, LE-7A engine suffered from high side loads. One of them was caused by the transition between Free Shock Separation (FSS) and Restricted Shock Separation (RSS), and the other was caused by the stagnation and sudden movement (‘jump’) of the separation point at a small step inside the nozzle extension. This paper focuses on this stagnation and jump phenomenon of separation point caused by the step inside LE-7A engine nozzle during the startup and shutdown transients.
LE-7A engine encountered two troubles at an early stage of development, associated with the extension of the nozzle. One of them is large side loads during start up and shut down and the other is the damage on the nozzle tube, both caused by the occurrence of Restricted Shock Separation (RSS). The largest side load occurred when the separation point jumped from the nozzle cooling step inside the nozzle to the nozzle exit, after the stagnation of the separation point at the step. These phenomena such as ‘the RSS annihilation and occurrence’ and ‘the separation stagnation and jump’ indicate a significant suggestion for the RSS suppression by a small step inside the nozzle. This paper presents a focus on the LE-7A engine specific separation phenomena during the startup and shutdown transients and a method of RSS suppression with a step inside nozzle.
Variations of pitot pressure were observed at Mach 10 nozzle calibration tests of the Japan Aerospace eXploration Agency 1.27m hypersonic wind tunnel. The nozzle calibration data were examined and the non-isentropic condensing flow was suspected by humidity in the working gas of air. In order to decrease the humidity amount, the facility was modified to suppress the water condensations in the heating parts and the steady-state pitot pressures were obtained. Before and after the modifications, the tunnel flow condition were statistically assessed to confirm the repeatable isentropic flow. As a result, the efficient humidity management combined with the operation cycle was established. Both the humidity amount and the nozzle exit wall pressure should be monitored to assure the water-effect free flow.
A strategy to realize the tropospheric delay correction in satellite based augmentation systems is presented. The tropospheric delay is one of the major error sources of the GNSS signals. It is attempted to generate the correction information from the numerical weather prediction data to realize the tropospheric delay correction in real-time for mobile positioning. To introduce the correction information into the satellite based augmentation system, the amount of the correction data must be minimized without degrading the correction accuracy. In this paper, through several statistical evaluations using the long-term observation data, the appropriate contents and the data amount of the correction message are investigated. It is shown that the correction message should consist of the information of the tropospheric zenith delay and its average gradient in height. The amount of the correction data is also successfully minimized, and users in the region of Japan can receive the sufficient correction information by receiving only 3 messages. The results of the analyses clearly show the feasibility of the presented strategy.
We have developed an OmniDirectional Vision system (ODV) using two reflecting mirrors to monitor a spacecraft on orbit. Recently, a spacecraft is loaded with many deployable structures. The ODV provides a panoramic image of 360 degree surroundings in real time and is possible to monitor two or more deployable structures at the same time. Moreover, the CCD and the lens are not exposed to cosmic rays, because these are covered with metallic mirrors. Therefore, a loss of the CCD element and a blur of the lens due to the cosmic rays are not occurred easily. We have designed the ODV for the Unmanned Space Experiment Recovery System (USERS) spacecraft which was launched on September 10, 2002. The optical characteristics of the ODV has been evaluated and the results show that the ODV can acquire a sharp image. Two ODVs were adopted as monitor cameras of the USERS. From the input images of the ODVs on orbit, the deployment of the paddles and the Capillary Pumped Deployable Radiator (CPDR) and the separation of the Re-entry Module (REM) were confirmed.
Numerical investigation on the transient phenomena of the plasma flows in a pulsed MPD thruster has been conducted. Argon is used as a propellant and the mass flow rate is fixed to 0.8g/s. Just after the discharge is initiated, a shock wave is induced in the thruster due to the intensive Joule heating around the cathode, and then the shock wave is propagated to a downstream region at a speed of about 3,000m/s. This numerically evaluated velocity of the shock propagation agrees with the shock velocity derived from the Rankine-Hugonio relation including an electromagnetic effect. When the discharge duration time is too small, for example, 120μs, the specific impulse is almost half as long as that in the steady operation due to low propellant utilization. To enhance propellant utilization efficiency, the discharge duration of the pulsed MPD should be large (> 600μs).