An experimental study of the aerodynamic characteristics of a vertical landing rocket during the landing phase is conducted with emphasis on the interaction between the supersonic nozzle jet and the ground surface. Because of the large base area, variations in the base pressure distribution have a significant effect on the aerodynamic forces acting on the body. When the distance between the base and the ground surface is small, the base pressure decreases and downward force acts on the body. The generation of such downward force is quite unfavorable from a viewpoint of the safety of the vehicle. This effect can be reduced to some extent by modifying the outer edge of the vehicle base and roughening the ground surface. Moreover, it is observed that the static stability in pitch motion vanishes near the ground. Consequently, careful control during the landing phase is necessary to ensure vehicle safety.
To date more than 800 spacecraft, upper stages, and apogee kick motors are known to reside in geosynchronous and nearby orbits, including geosynchronous disposal (i.e., collection) orbits. U.S. and European ground-based sensors have detected an even larger number of debris greater than 10cm in diameter. Using projections of geosynchronous deployment characteristics and disposal rates, NASA and Kyushu University models of the geosynchronous and super-geosynchronous orbital regimes have examined the sensitivity of the long-term satellite population to various scenarios. Emphasis has been placed on the rate of collisions in the geosynchronous orbit and in the higher collection orbits and on the significance of cross-regime contamination. The sensitivity of the long-term environment to low velocity (0–1km/s) collision breakup model parameters and on the minimum height of collection orbits has also been explored. Results are presented in terms of both satellite population and spatial density.
Two-dimensional Navier-Stokes simulations have been performed for three types of flows at stall conditions about NACA633-018, NACA631-012 and NACA64A-006 airfoils. The Baldwin-Lomax algebraic eddy-viscosity model was applied in three different manners. First, a fully turbulent flow was assumed. Second, a transition point from laminar to turbulent was set manually. Third, the Degani-Schiff modification was applied. The fully turbulent computations predicted maximum lift coefficients much higher than experiment in all the cases, while the computations agreed well with experiment when specifying transition points properly. The computations with the Degani-Schiff modification predicted the stall angle close to experiment, but showed different behaviors at post-stall conditions. It is important to capture a laminar separation bubble at the leading-edge for predicting stall angles and post-stall behaviors correctly.
In this paper, the dynamics of tether winding target is analyzed. This problem is not peculiar to capture of an uncontrolled satellite with tether. It contains the common technology to casting the tether in order to moor the floating object in space, or to operating tether in the ground. This paper presents three-dimensional model of a tether and a target. The tether is divided into concentrated masses in order to consider the tether motion. The target is regarded as a prism. In formulation of the system, the friction and the normal reaction between the target and the concentrated mass is defined as contact force. And the impulse equations applied to the case that more than two concentrated masses collide with the target in the same time, is derived. In numerical simulations, the verification of this model is presented by the comparison with fundamental two-dimensional model of a tether and a target, and three-dimensional winding motions, the sideslip and the gyro effect, are shown.
The shock shapes, boundary layers, and temperature layers around a model of HOPE-X traveling at a hypersonic speed were visualized utilizing the electric discharge method. The experiments were carried out under the condition that the angles of attack were 0°, 15°, 30°, and 45°. To visualize 3-D shock shapes around the model, the observation of shock shapes were conducted from the side and back of the model. From the experimental results, it was confirmed that the two kinds of shock shapes interacted with each other. The various kinds of shock shapes according to the model angles of attack were also obtained. Subsequently, the visualized results of temperature layer around the model were described. Furthermore, the boundary layers generated around the model were visualized and compared with the temperature layers. A hypersonic gun tunnel was used in these experiments. The main characteristics of the tunnel were the Mach number was 10 and the duration was 10ms.
A preliminary life test of a low-power DC arcjet anode was conducted using a 500-W-class laboratory-model arcjet. After a continuous operation of 90-h, we compared the degradation of two types of anodes: one is a conventional pure tungsten anode, which is made of multiple fine grains of several tens of micrometer in size; another is a tungsten anode made of only four coarse grains. Both materials showed nearly the same amount of degradation from the viewpoint of so-called a constrictor closure phenomenon, in which the radius of the constrictor decreases during the continuous operation. However, micrograph analyses showed different degradation features for the two anodes: for the conventional tungsten anode, grains were severely embrittled in the recrystalization processes after the thruster operation accompanied by many cracks or even drops out of grains; in contrast, the anode made of four coarse grains showed a few cracks only along the grain boundaries, and its thrust performance was unchanged before and after the 90-h test. Hence there is a possibility to suppress the grain embrittlement by completely removing these grain boundaries from the tungsten anode by making the anode from one huge grain.