This study proposes a new approach to estimating micro-debris distribution from solar array images. In Geosynchronous Earth Orbit (GEO), enough debris measurement has not been done because of long distance from the Earth to the orbit. On the other hand, most of the satellites have solar panels as an indispensable power source, and they become the reasonable target of micro-debris and cosmic dust. From diameters of impact craters on the surfaces of the solar arrays the debris’ size distribution can be estimated with Bayesian approach, whereas the real shapes of the impact craters from the camera images arbitrarily taken from slant views should be obtained. We apply projective invariant properties to the original images to recover the images taken from front views which similarly express the real shapes of the craters. The effectiveness of the proposed method is demonstrated by a series of the numerical simulations using artificial camera images.
It is widely known that a self-field MPD thruster changes from an electrothermal acceleration mode to an electromagnetic one as the discharge current is increased. Such transitional behavior is numerically studied with argon propellant using a two-dimensional TVD Lax-Friedrich scheme incorporating multiple ionization processes. As the discharge current J is increased from 4 to 10kA under a mass flow rate of 0.8g/s, a steep rise of the voltage, which indicates the transition, occurs between low and high current modes of operation around J=7kA, which is equivalent to the Alfvén’s critical ionization current. The steep voltage rise is attributed to the increase in the work of the Lorentz force around the cathode. The radial distributions of the heavy particles and electrons are examined and compared with the past experimental results. Additionally, in the electromagnetic mode, the ratio of the ionization energy to the input power decreases with increasing input power, and the maximum ratio of the kinetic energy to the input power is 0.57. This high thrust efficiency can be attributed to the idealized model, in which the effects of the sheath as well as the heat loss to the electrodes are neglected.
An increasing number of small satellites and hybrid rockets are proposed for miscellaneous space applications, many of which assume the use of Global Positioning System (GPS) for positioning. Some of those platforms are designed and developed by university students and require very low power consumption and also low cost. This paper describes the adaptation of small GPS receivers and open source receiver firmware for space and high dynamics applications, including software performance validation using a GPS signal simulator.
The subject of this paper is a space robot that has a manipulator arm mounted on a satellite body. This paper investigates the problem for stabilizing the attitude of both the main body of a space robot and the joint angles of a manipulator independently and simultaneously. Two control methods are proposed here for the solutions of this problem. One is a time-varying feedback controller, and the other is a time-invariant feedback controller. The former controller has the theoretical success for the topological obstructions, but has the practical disadvantage. In contrast, the latter controller has the practical usefulness in spite of the theoretical incompleteness. Furthermore, it is shown that each control method has the robustness against the presence of parametric uncertainties such as model errors and signal noises. The effectiveness of each controller is verified by numerical simulations.
Cyclic zero-tension tests for symmetric angle-ply CFRP laminated specimens were carried out to investigate the low cycle fatigue behavior of graphite/epoxy and graphite/PEEK composites. Two types of stacking sequences were tested: [+θ/-θ]4s (Distributed ply) and [+θ4/-θ4]s (Blocked ply), where θ was 30º or 45º. Stress-strain curves of specimens under cyclic loadings were obtained by means of an extensometer. A mechanical ratcheting, which means progressive increase in plastic strain at each cycle, was observed on the cyclic stress-strain curves. Comparing the stress-strain curve of static tensile test with one of the cyclic zero-tension test, we made the assumption that the fatigue failure occurred when the ratcheting strain by cyclic loadings reached the static failure strain. Results of an ultrasonic scanning test revealed that the distributed ply specimens differed from the blocked ply specimens in an internal fatigue damage progress.
In practical fluid computation with structured grids around complex geometries, singular points can be frequently found where abrupt grid line changes exist. The grid singularities cause troublesome problems when some finite difference scheme with high accuracy and resolution is applied. Excellent theory has been proposed, which solve the above singular problem by decomposing a computational domain into two blocks along a line or a surface which contains the singular points and by imposing the characteristic interface conditions (CIC) at the block interface. However, the original theory has constraints on a combination between the adjacent computational coordinate definitions; these two coordinates have to be the same direction on the block interface. For a flexible coordinate arrangement without the restriction, the original CIC is further extended, and the generalized characteristic interface conditions (GCIC) are newly derived. Consequently, the coincidence of the computational coordinate definitions becomes unnecessary, and more flexible multi-block computation can be realized successfully. In this paper, vortex convection problems with grid singularities are solved to validate the GCIC. Besides, conventional multi-block treatment with overlapped domain technique and that with averaging procedure are also tested and compared to investigate their superiorities and inferiorities. As a result, it is confirmed that the GCIC have excellent performance in the multi-block computation and can be straightforwardly applied to a detailed unsteady flow simulation such as direct computation of aero-acoustics.