We demonstrate the motion of a space robot in microgravity with use of the drop shaft at the Japan Microgravity Center (JAMIC). The drop shaft could provide 10-second microgravity. The technique used to stably levitate a robot is the most important element in experiments with robot motions using a drop shaft. Therefore, we developed a holding mechanism with grippers and tested it first. We then propose a sensorbased path planning method to control the orientation and the arm position of a space robot. This method compiles a database of current sensory outputs, motion and next sensory outputs, and searches the path using breadth-first search. This method is an application of a finite state automaton. We proved the above results by experiments using a drop shaft.
The authors have developed a method for the estimation of the pitch and roll angles of small aircraft such as RPRVs (Remotely-Piloted Research Vehicles) and UAVs (Unmanned Aerial Vehicles) which are too small to carry vertical gyros. The method uses three angular rate sensors with drifts, two accelerometers and air-data sensors. The attitude data obtained from the outputs of the accelerometers, which are corrected for translational and centripetal accelerations, contain high frequency errors due to the correction error for centripetal accelerations using body-axis angular rates. Similarly, the attitude data obtained from the integration of the outputs of the angular rate sensors contain low frequency errors due to sensor drifts and integration errors. Correct pitch and roll angles can be estimated by filtering out and combining the meaningful frequency regions of the two.
The dynamic instability of an elastic supported sphere in the uniform flow is studied experimentally by using the low speed open wind tunnel. If the oscillation was made by an initial deformation due to the outer disturbance, the oscillation was damped when the wind speed was below the some critical wind speed. However, if the wind speed increased over that critical wind speed, the limitcycle oscillation appeared. This oscillation disappeared and the small amplitude randam oscillation appeared, when the wind speed increased over the another higher critical wind speed, and the oscillation of the sphere damped rapidly even if the oscillation was made by the initial deformation due to outer disturbance. In the present study, eight series of the wind tunnel tests were done i. e. the two spheres and the four pairs of the spring were used. The limitcycle dynamic instability were observed in the Reynolds number range 3×103<Re<4×104. The ratio of the limitcycle dynamic instability disappearing critical wind speed to the one appearing wind speed was between 4.8 to 2.2 in the each wind tunnel test. The maximum vibration amplitude of the sphere oscillation was about 0.5d in the each test.
The interaction of a streamwise vortex with a fin is investigated experimentally using high-image-density particle image velocimetry, which allows determination of the instantaneous distributions of vorticity over entire planes of the flow. The vortex distortion past the fin is described in terms of averaged patterns of velocity field and instantaneous vorticity contours at two different locations of the fin. The instantaneous structure of the broken-down vortex upstream of the leading-edge of the fin exhibits the classical staggered pattern of alternating positive and negative concentrations of vorticity. Along the leading-edge of the fin, however, including the edge of the tip, positive concentrations of vorticity dominate. Averaging of these instantaneous vorticity concentrations shows that a time-averaged, positive vorticity layer exists along the leading-edge and tip of the fin. Over the surface of the fin, the averaged levels of vorticity are significantly lower than those on the edge.
Preliminary analysis is performed on the stability of a periodic orbit around an irregular shaped body. The latus rectum (the amount of the angular momentum) and the semi-major axis (the amount of the total energy) of the orbital motion are chosen as indices of the orbit stability. Analytical approximations for the two indices are derived for orbits of an arbitrary inclination angle with a small eccentricity using a proposed perturbation method and are validated by numerical simulations of a dumbbell model. The relationships between the orbit stability and the inclination angle as well as the ratio of the rotation period of the body to the orbital period of the spacecraft are clarified through the analysis. An example of designing the orbit injection based on the derived analytical approximations is also given.
The purpose of this paper is to obtain the optimum trajectory for the fuel minimum guidance phase of lunar soft landing experiments NASDA is planning. In this phase the lander descends to a few km altitude from 15km altitude realized by the Hohmann transfer from the circular orbit of 100km altitude. Characteristics of the phase are thrust direction constraints near the terminal point, which are (A) thrust direction at the terminal point must be vertical and (B) change rate of the thrust direction must be smaller than the specified value. It was obtained the minimum thrust should be used for the latter half of the interval just before the terminal point where the thrust direction is changing largely. The optimum thrust direction except the region where the thrust direction is changing largely coincided with the one for no constraints. This fact will ease the derivation of guidance law.
The lateral movement of three-dimensional (3-D) cellular flames is numerically studied. The numerical model includes compressibility, viscosity, heat conduction, molecular diffusion, chemical reaction, and convection. We superimpose hexagonal disturbances on the plane flames and calculate the evolution of disturbed flames. When the Lewis number is unity, i. e., only the hydrodynamic effect has an influence on the flame instability, stationary cellular flames are formed. When the Lewis number is smaller than unity, i. e., the diffusive-thermal and hydrodynamic effects have an influence, laterally moving cellular flames are obtained. The lateral movement of cellular flames is due to the diffusive-thermal effect. The laterally moving velocity of cells in 3-D flames is larger than that in two-dimensional (2-D) flames. Because, the increase of local temperature at the convex surface in 3-D flames is great compared with that in 2-D flames.