In recent years, research is actively being conducted on unmanned air vehicles (UAVs), micro-air vehicles (MAVs), and Mars airplanes. In these flights, there is a common problem that laminar separation likely occurs due to the low Reynolds number (Re = 104–105) flight conditions. Laminar separation causes a reduction in the lift-to-drag ratio and hence needs to be controlled. In this study, we utilize the “moving surface method” to resolve this problem. This method supplies momentum to the separation part and controls flow near the wing surface by actively moving the upper surface in the direction of uniform flow; the 2D effect of this method has been demonstrated in a previous study. In this study, we successfully extended this effect to 3D wings. Upon applying the moving surface method, the NACA0006 wing achieved the largest lift-to-drag ratio improvement at an angle-of-attack of 6° and this was achieved by the Ishii wing as well. This is because, in this method, the laminar-separation bubble disappears, thus leading to a large drag reduction. In addition, as the angle-of-attack increases, differences in the 2D flow field become prominent and a strong 3D flow field appears, even when the moving surface method is not applied; at an angle-of-attack of 9°, many small vortices are generated, which complicates the flow field. The aerodynamic coefficient also varies; especially, the 3D drag coefficient is larger than its 2D counterpart. The moving surface method thus successfully suppresses 3D flow and flow separation, leading to a 2D attached flow field.
The amount of debris in space is increasing every year, and its effect on satellite missions is worsening. In this research, a method for removing debris using laser radiation pressure from a ground station is proposed. This method does not require a satellite to be launched to remove debris, and the system applied is less likely to be considered as a threat because it is relatively safe even if the laser erroneously irradiates another satellite, because the laser intensity is no more than 108 W/m2. However, the power applied to debris is small, such that it requires a great deal of time and energy to deorbit the debris. Therefore, this study aims to evaluate the feasibility of debris removal by laser radiation pressure from the view point of energy consumption and time. In addition, in order to increase feasibility of this method, a sub-optimized laser irradiation method for reducing the time and energy consumption required for removal is proposed. This study addresses how much energy and time is needed for a particular piece of debris to be removed by laser under three parameters: power of the laser, time that the laser is powered, and the location of laser station. By sub-optimizing these parameters, the energy needed to remove a particular piece of space debris within a particular time is minimized. Furthermore, a laser irradiation method for deorbiting multiple pieces of debris using multiple laser stations is discussed. This study contributes to show that the new debris removal method using laser radiation pressure from ground station can effectively and practically remove multiple debris in terms of time and energy cost.
Recently, large space structures using thin films have attracted widespread attention. Finite-element analysis using tension-field theory is expected to be a practical tool for analyzing a nonlinear wrinkled-membrane behavior in large space structures with low computational cost. Aiming to extend functionality of wrinkling analysis using tension-field theory, a simplified formula capable of estimating a wrinkle amplitude using tension-field solutions was proposed in past research. In the current study, we investigated the applicability of that proposed formula to the wrinkling behavior on a square membrane subjected to corner tension loads.
A theoretical and numerical study has been conducted on an electrodeless thruster which uses a traveling magnetic field for effective thrust generation. The physics behind the thrust generation mechanism was studied theoretically, and the theory was validated by 1D electrostatic particle-in-cell simulations. The thrust generation was found to be due to the formation of a Double Layer (DL). The magnetic pulse pushes the electrons in the magnetic front forming a small charge separation. The localized electric fields arising due to this separation causes significant acceleration of the ions, and the electrons in opposite directions. However, this leads to further charge separation, deepening the potential well across leading to the formation of a DL which in turn generates mono-energetic ion beams. The energy required for sustaining the DL is derived from the trapped electrons in the leading front of the DL. The theory predicts a drop in the temperature of trapped electrons. This temperature decrease is confirmed by the electron thermal energy distribution obtained from the simulation.
Mixtures of ammonium dinitramide (ADN), monomethylamine nitrate (MMAN), and urea form stable ADN-based energetic ionic liquids (EILs), even below room temperature. These mixtures, referred to as EIL propellants, can be highly energetic and yet are easy to handle. This study focuses on the ignition of ADN-based EILs in a thermal apparatus. We consequently ignited ADN-based EIL droplets within 590 ms using 2 W of the continuous-wave laser. The results suggest that laser ignition is a feasible new ignition system for thrusters. The condensed-phase reaction of the ADN-based EILs started immediately after heating, and gases evolved from the reaction ignited when the droplet temperature reached approximately 400°C. Thermal analyses indicated that the amount of heat generated by the condensed-phase reaction of the EILs affected their ignitability. The analysis of the evolved gases indicated that methyl nitrate gas generated from the condensed-phase reaction of MMAN ignited first, followed by the ignition of other gases because of heat from the flame of the methyl nitrate. These results clarify the ignition requirement of ADN-based EILs and should be useful in the design of new EIL compositions.
The RF plasma thruster is studied to improve the lifetime issue caused by electrode erosion. Our previous study reported that the non-uniform magnetic field near the RF antenna improves the thrust performance. It is important for the optimization of thruster configuration to clarify why the magnetic field configuration strongly influences the thrust performance. The objective of this paper is to numerically investigate the influence of externally applied magnetic field configuration on the plasma. We adopt the three-fluid plasma model which considers ions, electrons and neutral particle. As a result, it is found that the plasma diffusion is significantly affected by the external magnetic field configuration, and although the non-uniform magnetic field does not contribute to the plasma generation efficiency. It is effective to suppress the plasma wall loss.
In this study, a voltage waveform comprising the steep and gradual slopes is optimized to maximize the thrust of the induced flow by a dielectric barrier discharge plasma actuator. Our aim is to experimentally determine the effects and the improvement mechanism of the flow strength and efficiency by the voltage waveform. For this purpose, measurements and analyses of the thrust, power, and body force are conducted. Especially, the body force was analyzed by particle image velocimetry. The proposed waveform improved the thrust and efficiency by more than 50% and 40% compared with the sinusoidal waveform, respectively. We determined that the improvement is due to the dense plasma generation and acceleration; accompanied by the strong discharge in the steep voltage slope and the maintained electric potential in the gradual voltage slope.
In this paper, we develop a new gain-scheduled (GS) controller for attitude control of spacecraft when the plant models are given as linear parameter-varying (LPV) systems. Avoiding trial and error in determining the weighting matrices of the H2 performance evaluation, we introduce the inverse linear quadratic (ILQ) method, while generalizing the existing theory for linear time-invariant (LTI) systems to that for LPV systems. The existing optimality condition is also rebuilt in a linear matrix inequality (LMI) condition and generalized for LPV systems. As a numerical example, in this paper, we deal with angular velocity control of a spacecraft with reaction wheels (RWs) and demonstrate the effectiveness of the proposed controller through a numerical simulation.
Every year, the Geospatial Information Authority of Japan collects improved Administrative Zone vector data from the administrative divisions of Japan and uses them to update the National Land Numerical Information (NLNI). The purpose of this study was to use the full polarimetric ALOS-2/PALSAR-2 data to qualitatively evaluate the accuracy of shoreline detection for updates to the NLNI. We also evaluated the shoreline data using ASTER/VNIR data with a spatial resolution similar to that of the ALOS2/PALSAR-2. The combined image of edge images, i.e., surface scattering power (Ps), double-bounce scattering power (Pd), volume scattering power (Pv), and helix scattering power (Pc) were generally capable of identifying the shoreline on various types of coasts. The combined image has the advantage of being able to detect various terrain features and coastline orientation, which is not possible when using single polarization image analysis. The results of this study suggest that it is possible to update the NLNI Administrative Zone vector data using the full polarimetric ALOS-2/PALSAR-2 data.
This study proposes a method for attaching a deorbit device to non-cooperative satellites. The proposed capture system consists of convex springs as grasping arm or finger. The convex springs wrap and hold the target when the contact force is applied. In addition, combination with a membrane improves the tolerance of the target position. This paper focuses on the characteristics of the convex spring, which is the main component of this capture system. The dynamics and control methods of motion are also clarified.
The National Institute of Information and Communications Technology in Japan has developed vehicle earth stations equipped with an antenna system for the automatic tracking of the Wideband InterNetworking engineering test and Demonstration Satellite “KIZUNA” (WINDS), making it possible to form a satellite link while moving. However, shadowing can have a large impact on satellite communications using directional Ka-band antennas with high rectilinearity. It is estimated that the degree of shadowing due to trees varies with seasons, which is a function of seasonal leaf cover. Therefore, we measured the potential seasonal difference by comparing the attenuation of the received signal from the satellite during a year-long experiment with shadowing from several kinds of trees. No attenuation fluctuations were observed from evergreen trees, whereas seasonal attenuation fluctuations were confirmed from deciduous trees.
In this paper, the completion conditions for a latch mechanism with a kinematic coupling, which consists of three v-groove/sphere pairs (Maxwell type), are approximately derived as a relationship between the slope angle of v-grooves and friction coefficient. The kinematic coupling is an economical and suitable method for attaining high repeatability in fixtures. Therefore, the kinematic coupling is used in various types of deployable space structures, such as the James Webb Space Telescope and the extensible optical bench of ASTRO-H (Hitomi). In previous studies, numerical simulations were carried out to determine the amount of additional force that should be applied to complete the latch from the incomplete state. However, it is difficult to use such numerical solutions as general design criteria. In this paper, approximated completion conditions are described using analytic functions. As a result, the derived completion conditions are intuitively clear and usable as design guidelines. The most severe condition, where two v-groove/sphere pairs are latched and only one pair remains unlatched, is clarified. It is shown that there are an optimum slope angle and upper limit of the friction coefficient for latch completion. Finally, the most severe completion condition is verified through experiments.
The demand for electrical pump-fed propulsion systems increases due to the need for higher thrust and higher specific impulse. In this study, system mass modelling for various missions has been conducted to investigate the quantitative merit or demerit of adopting the electrical pump-fed propulsion systems. A new model for the tank mass, calculated by its volume, diameter, the internal device (PMD or diaphragm) and the shape (cylindrical or spherical), is proposed. These models are embedded into the new system mass model, allowing the assessment of the quantitative effect by adopting the electrical pump-fed solution for future propulsion systems.
Small satellites are opening radical new possibilities for space utilisation, especially in low-Earth orbit (LEO). Due to their compactness, many small satellites have no active attitude control systems. A method for passive stabilisation would be useful to regulate attitude without requiring the mass and volume of powered sensors and actuators. In this paper, passive aerodynamic stabilisation of a 3U nanosatellite is investigated using an in-house coupled orbit-attitude simulation platform. The objective is to evaluate the robustness of satellite stabilisation in the 200-400 km altitude range, including in the presence of a perturbing magnetic torque, and initial spin motion. The results show that at 400 km altitude, aerodynamic stabilisation is not a realistic method for attitude control, but that its potential increases lower in the atmosphere.
SAR (Synthetic Aperture Radar) has been popular in Earth remote sensing because this is available for all-weather and night time, unlike optical sensors. Identification and classification of ships have been remarked from viewpoints of coast guard such as finding and monitoring marine accidents and poaching boats without Automatic Identification System (AIS). This research uses SAR data provided by PALSAR2/ALOS2. This research adopts the Convolutional Neural Network (CNN). The label is given to ship SAR image using AIS. Results with PALSAR 2 data with a resolution of 100 m/pixel showed high accuracy of 95%. This research showed the availability of a method to identification of ships from SAR images using CNN.
The high-energy electron experiments (HEP) instrument on board the Arase satellite employs two sensors, HEP-L and HEP-H, and was designed to measure electrons with energies from 70 keV to 2 MeV. The recent Van Allen Probes observations indicate that MeV electron flux is very small in the inner radiation belt, while the HEP has detected significant counts at MeV energy channels in the inner radiation belt. Counts in the inner radiation belt are registered similarly at different energy channels of HEP-H and higher energy channels of HEP-L, and show no clear energy dependence. Their properties suggest contamination of high-energy protons that populate densely the inner radiation belt. In order to identify the energy of the penetrating protons we compare the spatial distribution of the HEP counts with NASA's AP9 mean model. We find that the primary peak of the count distribution measured with HEP in MeV energy range is located at L = 1.5 at the magnetic equator, which in in agreement of > 60 MeV inner belt protons of AP9 mean model. The secondary distribution is also found at higher L values, which can be attributed to MeV protons. We have been conducting Geant4 simulation for penetrating protons into the HEP. Our result of the simulation is consistent with suggestions of analysis on the spatial distribution.
Self-deployable tape springs made of CFRP feature significant effect from relaxation, mainly happening during long time stowage in coiled configuration prior to launch. The stored strain energy contained within the structures during stowage tend to modify the polymer matrix mechanical properties. The research introduced here aims to develop an efficient numerical process capable of determining the evolution of the deployed shape, after deployment, of such structures due to viscoelastic relaxation happening during on Earth stowage. A two steps homogenization process is devised to compute the plain weave mechanical properties. The process is first based on an analytical model to determine the strand's properties, before using a finite element based numerical model for the plain weave pattern. Properties are fitted with Prony series to display the variations over a long time range. Results from this homogenization are then used in an Abaqus numerical model to predict the deployed shape evolution of the tape springs, and its recovery capabilities after full deployment. Validity of the model is checked using results from experimental stowage conducted on bistable tape springs.
The two-grid ion optics of a water propellant miniature ion propulsion system (MIPS) was numerically studied by full-aperture ion-optics simulation considering an inhomogeneous plasma source in the discharge chamber. Three dominant ion species (H2O+, OH+, and H+) of water vapor plasma were included in the model. Their trajectories were tracked considering charge-exchange and elastic collisions between ions and neutral water molecules. The model was validated by experiments using the MIPS with two grids having 295 apertures each. The calculated accelerator impingement current agreed reasonably well with those obtained from the experiment. To increase its low propellant utilization efficiency, a new grid design method was introduced. This successfully improved neutral confinement by decreasing the diameter of the accelerator grid apertures without causing direct impingement of ions by optimizing the grid thickness distribution using the Particle In Cell-Monte Carlo Collision (PIC-MCC) calculation results.
Tri-electrode plasma actuator (TED-PA) has two high voltage electrodes (AC and DC) and a grounded electrode. It can induce a stronger jet than the conventional plasma actuator (DBDPA), that is attributed to jet generation not only at the AC electrode but also at the DC one. Especially, the jet from the DC electrode dominantly contributes to the stronger jet. In this study, for obtaining the guideline to optimize the design of the TED-PA, we conduct the experiments aiming to verify the mechanism of the DC discharge enhancement by the interaction with the dielectric barrier discharge at the AC electrode, that is important phenomena to achieve strong jet generation. As a result, the discharge photograph shows that the discharge at the DC electrode becomes stronger when the dielectric barrier discharge at the AC electrode becomes stronger. In addition, the jet from the DC electrode also becomes stronger with the DC discharge. The results support the results reported in our previous numerical work showing that the mechanism of the DC discharge enhancement is the electrons supply from the DBD at the AC electrode to the DC discharge.