Spallation particles emitted from an ablating test model mounted in a supersonic arc-heated air flow was investigated experimentally and computationally. Emission spectra of CN violet band and C2 swan band, that were attributed to spallation particles, were identified not only inside the shock layer of the ablator but also outside of it. Since the evidence of the presence of spallation particles was found, the trajectory of a spallation particle was simulated to reveal the conditions for the flight to the upstream of the shock layer. The simulation was made by ejecting a solid particle at various speeds from the front surface of the ablator.
The purpose of this paper is to design a control system for an integrated laser propulsion/tracking system to achieve continuous motion and control of laser-driven micro-vehicles. Laser propulsion is significant in achieving miniature and light micro-vehicles. A laser-driven micro-airplane has been studied using a paper airplane and YAG laser, resulting in successful gliding of the airplane. High-performance laser tracking control is required to achieve continuous flight. This paper presents a control design strategy based on the generalized Kalman-Yakubovic-Popov lemma to achieve this requirement. Experiments have been carried out to evaluate the performance of the integrated laser propulsion/tracking system.
Orbital motion under a continuous outward radial acceleration as a function of the distance from the central body is investigated analytically. The attainable maximum radial distance is given as a function of the radial acceleration, and numerical experiments are carried out showing some periodic orbits under radial acceleration. Three representative cases are treated: constant radial acceleration; radial acceleration proportional to inverse radial distance; and radial acceleration inversely proportional to square of radial distance. This paper focuses on the second case, which has not been reported in the literature. The results are applicable for mini-magnetospheric plasma propulsion.
Foreign object impact damage is a serious problem for ceramic gas turbines. In this paper, a series of finite element analyses with an elastic assumption was made to estimate the plausible damage behavior of axial and radial ceramic blades. Foreign objects were assumed to impact the leading part of the blade suction surface. The present analysis showed that the stress peaking process is strongly influenced by the interaction of various stress waves, leading to structural damage. The locations of the peak principal tensile stress (peak stress) in the axial blade corresponded well with the damaged parts of the blade observed experimentally. The maximum peak stress appeared in the suction surface and the averaged peak stress value in this surface was roughly double that in the pressure surface. Unlike the axial blade, the radial blade reached maximum peak stress in the pressure surface. The value was much larger than the initial impact stress due to the wave interactions. For the effect of the rotation, centrifugal force did not change the basic distribution of peak stresses, but it caused additional stress peaks near the hub in the pressure surface. Moreover, the centrifugal force caused appreciable differences in the averaged peak stresses in the suction and the pressure surfaces. The present finite element analysis with elastic assumption seems useful for understanding structural fracture behavior, when designing ceramic blades.
In the MUCES-C mission conducted by JAXA (Japan Aero Exploration Agency), a microwave neutralizer is mounted with a microwave ion engine on the HAYABUSA space probe. The neutralizer consists of an L-shaped antenna to inject microwaves and samarium cobalt magnets to provide ECR (electron cyclotron resonance). Plasma production of a higher density than the cutoff density is expected in the discharge chamber, but the neutralizer is so small that high-precision measurements using a probe are difficult. To clarify the plasma production mechanism in the microwave neutralizer, numerical analysis was conducted using a code coupling PIC (particle-in-cell) method, and a FDTD (finite-difference-time-domain) method. This paper describes effects caused by varying magnetic field configuration and antenna position in the neutralizer. The calculation results show that bringing the antenna closer to the ECR region is effective for plasma production.
A Whale Ecology Observation Satellite (WEOS) was successfully launched on December 14th, 2002. We adopted a single-axis magnetic torquer damping control and gravity gradient attitude stabilization for WEOS. It is the first trial in Japan for pointing communications antennas towards Earth, and the GPS antenna towards zenith. The damping control and attitude stabilization system of WEOS consists of a three-axis magnetometer, a magnetic torquer coil, a deployable mast with a fixed mass at the tip, and attitude control software. This system carried out rate damping control of the principal axis of the maximum moment of inertia and earth pointing attitude stabilization. Immediately after separation from the H-IIA-4 launch vehicle, WEOS tumbled due to the imbalance force of the three separation springs. The tumbling was reduced by the closed-loop damping control and then the mast was deployed. After 1 week, we confirmed the establishment of the gravity gradient attitude stabilization. This paper describes the attitude control system, operation procedure, and control results.
We analyzed a small coaxial helicopter developed for entertainment in 2002. The upper and lower rotors are rigid rotors. The upper rotor is connected to a stabilizer bar. The cyclic pitch of the upper rotor is controlled by the stabilizer bar when the attitude of the helicopter is varied. The angle between the upper rotor and the stabilizer bar is 41°. The cyclic pitch of the lower rotor is controlled by servo motors and the inputs of the cyclic pitch from the servo motors are at the azimuth angles of 45°, 225° and 135°, 315°. This paper clarifies how the angle between the upper rotor and its stabilizer bar and the azimuth angles of the inputs of the cyclic pitch to the lower rotor are determined.
The aim of this study is to examine a magnetohydrodynamic (MHD) power generation system for the space applications using a nuclear fission reactor as the heat source. This MHD system uses He/Xe mixed gas as coolant instead of alkali-metal-seeded inert gas. The interrelation between the specific heat of the coolant and the mass flow rate was examined. When the specific heat decreases due to increase of the Xe fraction, the mass flow rate must increase to keep the output power and plant efficiency constant. A regenerator efficiency of 100% and reactor output temperature of 1800 K or higher should be chosen for the highest plant efficiency of 56% and lowest specific mass of 1.4 kg/kW. This highest plant efficiency and lowest specific mass were also expected by optimizing parameters for enthalpy extraction and radiator temperature. This means achieving high plant efficiency or low specific mass gives different values for enthalpy extraction and radiator temperature. With a higher net electrical output power, lower specific mass is obtained. This explains why the present space MHD power generation system is better than other conventional space power generation systems for the high MW-range output power.
Numerical simulations of the flow around a periodically vibrating airfoil and the two-degree-of-freedom (TDOF) bending-torsion flutter characteristics were carried out. An unsteady, two-dimensional, incompressible Navier-Stokes flow solver was coupled with a two-degree-of-freedom structural model for a flutter computation. To simulate unsteady phenomena, the Navier-Stokes equations are described by the ALE method. The Baldwin-Lomax turbulence model was implemented for high Reynolds number calculations. Computations of the periodically vibrating airfoil show agreement with Theodorsen’s linearized theory and the existing results of some numerical analyses. Flutter was observed in the TDOF model coupled with the flow solver when the rigidity of the airfoil was small. A control method for the flow field was studied and the airfoil flutter was stabilized by a PID (Proportional-Integral-Derivative) control algorithm.