Low velocity impact performance analysis of fiber composite structure embedded with SMA was investigated. And, the energy-absorption of the structure due to tensile, shear, bending, and delamination effects was studied. In this study, Ballistic test is used to explore performances of fiber composite structure embedded with SMA under a low velocity impact. 9 mm Full Metal Jacket (FMJ) ammunition is used as projectile and 200 mm rectangular composite plate is used as target sample in this test. And, the control factors are number and arrangement of SMA material and thickness of the test samples. Taguchi method and ANOVA analysis method are used to explore the relevance and significance of each parameter to the energy absorption of the structure in this article. Furthermore, a multiple regression model was developed to fit the experimental data and to predict the energy absorption in changes of parameters effectively. Finally, the best combination of parameters used to resist a low velocity impact was obtained and discussed. The results reveal that the best combination of parameters enhances 19% of the energy absorption of the structure and SMA provides 18.47% contribution significantly.

View full abstract

Electric propulsion systems allow satellites to fly in very low-earth orbits. The rarefied atmosphere in such orbits consists mainly of atomic oxygen with kinetic energy that corresponds to the orbital velocity, and the reaction of atomic oxygen with spacecraft materials is a significant issue. Here we develop a hyperthermal atomic oxygen source using electron cyclotron resonance discharge plasma and a neutralization grid to simulate orbital conditions. The hyperthermal atomic oxygen is produced by surface neutralization of oxygen ions in the plasma. This paper reports on simulated beam properties. Atomic oxygen flux is measured by the erosion of a polyimide film on a quartz crystal microbalance. The flux is 2.55×10¹⁵ cm^-2 s^-1, which corresponds to orbital conditions at an altitude of 240 km. The neutralization efficiency, which indicates the performance of the neutralization grid, is much higher than 99%. The beam divergence angle is about 4°, as measured by the radial distribution of the atomic oxygen flux. From the ion energy, we estimate that the atomic oxygen beam has kinetic energy of about 3–7 eV.

View full abstract

Piecewise Straight Fold is proposed for large solar sail membranes to simultaneously realize the high packaging efficiency and the simple folding. The fold pattern is based on Spiral Fold to reduce the deviation of the fold line, which improve the packaging efficiency. In addition, the fold pattern consists of piecewise straight fold lines, which approximate the Spiral Fold line, in order to simplify the folding. A simple manufacturing process of Piecewise Straight Fold is developed based on the Z-fold membrane. The preliminary experimental results show the feasibility of the Piecewise Straight Fold and its simple manufacturing process, where the high packaging efficiency is also verified. The wrapping fold experiments for the solar power sail membrane is demonstrated by using the Piecewise Straight Fold. In the wrapping fold experiments, the applicability of the Piecewise Straight Fold to the solar power sail membrane is verified.

View full abstract

The small solar power sail demonstrator IKAROS was developed and launched in 2010 by JAXA and deployed its large membrane successfully. Through IKAROS's on-orbit operation, one of the most critical problems was a sail's shape imbalance during the sail deployment sequence. This paper focuses on the evaluation and consideration of the sail's imbalance through high vacuum experiments using a scale-down sail model. The experimental results obtained using the specially designed rotating mechanism and a small scale model lead to a hypothesis of the reason for the IKAROS's imbalanced deployment. The experimental results are extrapolated up to IKAROS's scale, using dimensionless analyses.

View full abstract

Solar sails are a form of spacecraft which deploys a large sail in space and uses solar radiation pressure for propulsion. IKAROS is a spinning solar sail developed by JAXA and was launched in 2010. As demonstrated with IKAROS, it is extremely effective to place various devices, such as thin-film solar cells for power generation, on the sail membrane of a solar sail. Such devices, however, contribute to the thickness of the sail, and may hinder the deployment of the sail. In this paper, the sail deployment method of IKAROS is reviewed and its dynamics, which may result in an asynchronous deployment of the sail, is investigated.

View full abstract

As a future high-precision space structure system, smart structure systems which measure and correct their shape on orbit have been studied. In the smart structure systems piezoelectric ceramics are often used as an actuator. To correct and retain the shape of the structure, electric voltage must be applied continuously. To reduce the amount of electricity usage, a new control method was proposed, where the fact that strain of the piezoelectric ceramics remains without applied voltage after a pulsed voltage input was utilized effectively. In the previous study, the feasibility of the proposed method had been verified for a piezoelectric ceramic plate and a beam with the piezoelectric ceramic plate bonded. The result had shown that the strain of the piezoelectric ceramic plate and the tip displacement of the beam had remained after the pulse, although the beam had vibrated. In this study the strain response for the pulsed voltage was observed for various types of piezoelectric ceramic plates including hard type and soft type, and the vibration of the beam was suppressed by applying a feedback control or a trigonometric shaped pulse input.

View full abstract

This paper proposes a method to store a large solar-sail membrane while ensuring repeatability of its stored configuration. Large membranes used as a solar sail should be stored compactly to save the launch volume; in addition, their stored configuration should be sufficiently predictable in order to guarantee reliable deployment in orbit. However, it is difficult to store a large membrane compactly because of the finite thickness of the membrane. This paper demonstrates the feasibility of the proposed “bulging roll-up” method experimentally using 10m-size membranes, and evaluates the repeatability of its stored configuration quantitatively.

View full abstract

Membrane structures are intensively paid attention as large deployable and light-weight structures. Membranes are vulnerable to wrinkles resulting in the degradation of structural performance. We suggest a new wrinkle detection method using elastic wave propagation on the membranes as an alternative and supplementary way of optical methods using cameras. In this paper, elastic wave propagation behavior in the wrinkled membrane is analytically investigated by simplifying a wrinkle as the combination of thin plane plates and circular plates. Effects of the frequency of elastic waves and the curvature of wrinkle on the reflection/transmission of the waves at the wrinkle are investigated. The wave transmittance across the wrinkle is calculated and discussed to propose a detection method of wrinkles in membranes. Experimental demonstration of wave propagation in wrinkled membrane is performed using piezoelectric actuators and Multi-axis Vibration Evaluating System (MaVES). It is confirmed that elastic waves with frequencies below the circular frequency cannot propagate across the wrinkle, while waves with higher frequencies can transmit through the wrinkle.

View full abstract

Deployable membrane structures are hopeful to develop future lightweight large space structures. In order to predict the dynamic behaviors of the structures in the preliminary design phase, simple and fast numerical simulation is necessary. For this purpose, multi-particle approximation method has been studied which models membranes with spring-mass-damper systems. In this study, polygonal membrane structures integrated with extendible booms are investigated. The membranes are deployed by the elasticity of the booms in a stepwise manner. A multi-particle model for one-dimensional elastic body is introduced as the boom model to the multi-particle method. Each boom is released from the tip end by several particles and the dynamic behaviors of the stepwise deployment can be obtained. The behaviors are compared with deployment experiments of booms without a membrane. Numerical simulation of the deployment of a hexagonal membrane with booms is also demonstrated. Finally, the effect of the stepwise pattern on the vibration motion of the central body due to deployment is studied.

View full abstract

In order to support various future activities using spacecrafts, we need to develop a re-entry system which is useful, safe and low-cost. We have studied the structural strength of an inflatable aeroshell, which is a novel re-entry system currently under development within JAXA. In this paper, we investigate the structural strength characteristics of the inflatable aeroshell with respect to its configuration, scale effect and initial out-of-plane deformations. The investigations are carried out by both numerically and experimentally; the results are in good agreement with each other and will benefit efficient structural design of the aeroshell in a future development.

View full abstract

This study estimates the effect of creases, or plastic wrinkle lines, on the out-of-plane stiffness of solar sails. A method to simulate the crease effects using reduced-order finite-element (FE) models is proposed, and is applied to a practical solar sail architecture. A detailed crease shape is determined by a geometrically nonlinear FE analysis using a simple model first; the effect of creases is then replaced by beam elements. This method substantially reduces the computational effort required for the FE analysis of a solar sail model. The result suggests the significant impact of creases on membrane's out-of-plane stiffness when the tension level in the membrane is small.

View full abstract

In this study, a fuel-efficient, low-thrust transfer problem is considered. The low-thrust transfer occurs continuously and its magnitude is constant through the transfer. Then, injection methods that enable spacecraft to transfer from any initial orbits to the geostationary orbit are proposed. The effectiveness of the proposed injection methods is evaluated via numerical simulations, with respect to velocity and fuel mass. Moreover, the dependence of the velocity increment on the initial argument of perigee is clarified through an analytic expression, which is useful in selecting a fuel-efficient initial orbit.

View full abstract

This study deals with the orbital motion of a follower satellite controlled by a few thrusters relative to a target satellite in a circular orbit. The thrusters of the follower are fixed to its body and generate constant unilateral forces. To generate control forces in the required directions, the follower attitude is controlled using the thruster forces only. Furthermore, the follower attitude needs to be controlled to estimate the relative position of the follower satellite from the time profile of the line-of-sight (LOS) angle. First, controllability using constant inputs in one direction is examined on the basis of modal analysis. Thereafter, the energy efficiency of controllers is discussed according to the direction of the control forces. Finally, numerical simulations are performed to verify the effectiveness of the controller and its energy efficiency.

View full abstract

Single Gimbal Control Moment Gyro (SGCMG) is an effective actuator for three axis attitude control of the satellites. Since satellite missions conduct with limited energy supplies in space, it is required to reduce the energy consumption during attitude maneuvers. However there are two problems with finding the optimal solutions for minimum energy maneuvers: the initial assumption and the calculation cost. To solve these problems, this study introduces a new sub-optimal control law to achieve the sub-minimum energy maneuvers without both initial assumption and iterative calculation. Compared to conventional steering law, the sub-optimal control law results in decreasing the energy consumption by more than 80 percent for all maneuver axis.

View full abstract

Solar sails are a form of spacecraft which deploys a large sail in space and uses solar radiation pressure (SRP) for propulsion. The spin-axis direction of a spinning solar sail is known to rotate around an equilibrium point near the Sun direction due to the influence of the SRP. This unique attitude motion can be controlled by the spin rate of a spacecraft, and may help in reducing fuel consumption for attitude control. In this paper, attitude control of a spinning solar sail via the spin rate is optimized and compared with a general attitude control method. The comparison shows a powerful effectiveness of the attitude control via the spin rate.

View full abstract

A kinetic impact to the asteroid 1999 JU3 by a 300kg-class impactor spacecraft is studied. This study is a part of conceptual studies conducted within the mission design of “Hayabusa-2”, the second Japanese asteroid sample-return mission. In contrast with the finally selected “Small Carry-on Impactor(SCI)” concept, the present paper shows a feasibility of a different option, the kinetic impact by a 300kg class dedicated spacecraft. This option is valuable in terms of its scientific outcome, as the impact energy is 100 times larger than the current SCI concept. This paper discusses the feasibility of the terminal impact guidance and navigation using an onboard optical telescope. The study assumes a ground operator-in-the-loop guidance scheme, which is deemed to be the lowest development risk within the limited schedule before launch. It is shown that the ground-based terminal guidance is achievable with the accuracy of 200-300m with a realistic amount of fuel and operational load.

View full abstract

This paper applies Wide-Field integration (WFI) of optic flow to the state estimation of a space probe. By utilizing nonlinear forms for optic flow instead of linearized expressions used in a standard method, this study enables the estimation of the probe’s attitude angles as well as its velocity components. First, this paper describes the estimation principle of a new WFI method for three-dimensional motion of a space probe. Then, numerical simulations are conducted to verify the effectiveness of the proposed method. Through the simulation results, this paper discusses the effects of the following three factors on the estimation accuracy: resolution of optical images, roughness of target surface, and noise included in optic flow.

View full abstract

In case of a failure on a Hohmann-type translunar trajectory, a reconfiguration of the trajectory that utilizes the three body dynamics of the interior realm of Earth-moon system is proposed. The stable manifold and unstable manifold of a periodic orbit around L1 point extended toward the Earth side have homoclinic intersections. In the proposed method, after detection of a failure on the nominal trajectory, the trajectory is modified by small maneuvers so that the spacecraft can be kicked back by the moon and transferred to the unstable manifold. Then the spacecraft is returned to the moon side through the intersection with the corresponding stable manifold on the Earth side. The periodic orbit is used as a parking orbit so that the amount of delta-v at the moon orbit insertion can be reduced. Since the required amounts of delta-v at each individual maneuver are small throughout the reconfigured trajectory, it can serve as a solution for a backup trajectory in case of a main engine failure. Additionally, the long transfer time of the low-energy trajectory and good operability conditions in the interior realm provide an opportunity for diagnosis and repair of the failure.

View full abstract

The attitude motion of the spinning solar sail IKAROS was unique. Its behavior is highly dependent on the deformation of the flexible sail, which is easily changed by the attitude motion. Therefore, it is important to understand the relation between the sail deformation and the attitude motion in order to obtain better knowledge of sail design and management. In this study, a consideration is made about how the sail deformation varies according to the spin rate of the solar sail and how it changes the attitude motion from the view point of the structure. As a result, it was revealed that the variations of the parameters of the sail deformation and the attitude motion are proportional to the squares of the spin rate. The theory is evaluated by using the flight data of IKAROS, its sail shape is estimated, and its equivalent Young's modulus is calculated, which is an index of how much the sail with wrinkles stretches when the force is applied to it.

View full abstract

This paper introduces a new faults detection and diagnosis (FDD) subsystem for microsatellite attitude determination systems which use one three-dimensional rate gyro and two vector sensors. This FDD subsystem includes two filters for residual generations, hypothesis tests for fault detections and a reference logic table for fault isolations and fault recovery. This automatic FDD subsystem helps to enhance the automatic ability of attitude determination flight software and to reduce the dependence on ground support.The scheme developed in this paper resolves the problem of the heavy and complex calculations during residual generation parts and therefore the delay in isolation process is also reduced. The numerical simulations for TSUBAME, a demonstration microsatellite of Tokyo Institute of Technology, are conducted and analyzed to demonstrate the working of this FDD subsystem.

View full abstract

An improved sliding mode control (SMC) strategy for the attitude control problem of a nonlinear spacecraft with an elastic appendage is investigated. Since conventional sliding mode controllers include a discontinuous function, a significant problem called chattering can occur. In this study, a new switching function is used to minimize the effects of chattering, which will excite critical oscillations in the modal coordinate. The designed controller is derived using Lyapunov’s second method, which keeps a system stable. The simulation results confirm the effectiveness of the proposed controller in tracking the attitude maneuver and damping the oscillations.

View full abstract

In this study, the formation flying of two spacecraft in near-circular orbits under the influence of a J₂ perturbation is considered to obtain a control strategy for maintaining formation flying while minimizing fuel usage. This study utilizes a state transition matrix that describes the relative motion of a deputy spacecraft with respect to a chief spacecraft in terms of the argument of latitude of the chief spacecraft. Owing to the J₂ perturbing force, the actual position of the deputy with respect to the chief deviates from the nominal position. The abovementioned state transition matrix enables the analytical calculation of the secular terms of the deviation, providing the strategy for optimized fuel position maintenance. In this study, a two impulsive control is considered to compensate for the secular terms of the position error. Additionally, the conditions for the chief spacecraft's argument of latitude that minimize the velocity increments for the two impulsive controls are derived. The velocity increments are effectively reduced by adjusting the chief spacecraft's argument of latitude while taking the influence of the J₂ perturbation into account.

View full abstract

The solar power sail is a deep space probe that will be powered by a hybrid propulsion system with solar photon acceleration and ion engines to explore the outer planetary regions of the Solar System without having to rely on nuclear power. The Japan Aerospace Exploration Agency (JAXA) launched the world's first solar sail demonstration spacecraft, “IKAROS” (Interplanetary Kite-craft Accelerated by Radiation Of the Sun), in 2010. This spacecraft successfully demonstrated several key technologies related to the use of a solar power sail in a deep space flight environment. JAXA is currently planning an outer Solar System exploration mission using the demonstrated solar power sail technology, where the spacecraft will fly to Jupiter and perform a swing-by for a Jovian Trojan asteroid. This study undertook a trajectory design and system feasibility analysis for this mission. Candidate target asteroids were selected based on ballistic trajectory analysis, and then, electric-propulsion, continuous-thrust trajectory design was conducted to verify the conditions assumed for the ballistic analysis (e.g., estimate of steering loss due to the low-thrust trajectory). It was found that out of over 4000 Trojan asteroids, only 7 are feasible candidates considering the preliminary system design results. To broaden the choice of target asteroids, it will be necessary to reduce the weight of the solar power sail itself, its deployment mechanism, and the bus electronics.

View full abstract

In future surveys, planetary exploration spacecraft will need to land on rock beds and slopes. Therefore, spacecraft should be equipped with landing methods to facilitate soft landings in these severe regions. However, conventional landing methods have problems such as high rebound, the impossibility of reuse, and excessive resource consumption. To overcome these problems, the authors previously invented several landing methods, but these have practical limitations. Thus, this paper proposes a novel landing mechanism called the base-extension separation mechanism (BESM), which focuses on energy conversion using springs and separable units, and discusses a single-axis falling-type small-scale model of a spacecraft with the BESM. Then, the rebound and acceleration suppression performance is evaluated through simulations. These reveal that the BESM realizes good performance under nominal conditions. The BESM is shown to have good robustness against variations in the ground stiffness, ground damping, spacecraft mass, and installed mass. The study findings reveal that the BESM is a promising method: it overcomes the drawbacks of the conventional methods and our previous inventions. In addition, the BESM generally performs better in soft landings than our previous inventions.

View full abstract

In an interplanetary mission, the influence of solar radiation pressure (SRP) is a dominant disturbance in terms of the attitude control of a spacecraft, and a continuous disturbance due to the SRP shortens their mission life time. On the other hand, practical uses of the SRP are rapidly developed such as in Hayabusa and IKAROS, and their effectiveness is increasingly acknowledged. The objective of this study is to establish attitude control methods of a spacecraft by actively using the SRP. Moreover, we derive general and precise control methods by taking into account that the principal axes of inertia of a spacecraft are usually inclined from its symmetrical axes slightly, and verify the control methods by applying it to a model of Akatsuki.

View full abstract

Spacecraft internal disturbances are defined as internal forces or torques generated within the spacecraft that produce undesirable movement or behavior of the mission payload and/or the spacecraft. The line-of-sight pointing error of the optical payload caused by internal disturbances is often one of the most critical issues for a satellite with very high payload pointing requirements. The control and management of internal disturbances are, however, not simple, since disturbance forces and torques as well as their transfer characteristics affect the final performance. The transfer characteristics are strongly related to the attitude/structural dynamics, the attitude/pointing control system and the optical properties, and are therefore also affected by the properties of the disturbance itself. Consequently, for a given target performance, the individual disturbance sources must be specified, taking all these factors into consideration. In this paper, it is discussed how to specify transient disturbances, and a set of control parameters is proposed.

View full abstract

In this study, the application of direct current arc plasma discharge is discussed through computational analysis on the flow around a bump-up shape over a surface of a typical hypersonic vehicle under 20-km altitude and Mach-5 flight condition. Numerical simulation based on our simple plasma model suggested that the front pressure over a bump-up slope could be decreased by the use of plasma actuation method proposed in this study. The plasma source generated at 7 cm ahead of the bump successfully reduced the drag coefficient for more than 56%, changing the surface flow to go smoothly along the surface of the bump shape.

View full abstract

The EHD (electro-hydrodynamic) thruster seems suitable for a device of mobility at planetary exploration because of its propellant-less nature. In this paper, the fundamental characteristics of the EHD thruster are investigated from a viewpoint of the applicability to the planetary exploration. The numerical analysis of the drift-diffusion equations shows that it works irrespective to the polarity of the electrodes because the polarity of the produced ions is also changed. This fact implies that it will work in different atmospheric composition with different polarity of the produced ions. It is also numerically found that the thrust tends to increase with the decrease in the ambient pressure. For simplicity of discussion, a simple analytical model to describe the energy conversion efficiency is derived, and it indicates that higher efficiency is expected in higher Knudsen number regime. Both the above results suggest that the EHD thruster is promising especially in planetary atmosphere with low density.

View full abstract

For improvement of prediction of acoustics waves from a rocket plume, validation studies of numerical simulation are performed using experimental data of acoustics waves from subscale rocket motors, and prediction accuracy of numerical simulation is discussed. Experimental data of flow and acoustics fields of a solid motor and a H2-AIR liquid motor are used as the reference. The computational results of the far-field OASPL agree with experimental data within the error of approximately 5dB. The result shows that the current numerical methods well predict Mach waves at downstream side even though the results of far-field PSD are slightly overestimated. Meanwhile, it is difficult to capture shock associated acoustic waves and fine-scale turbulence acoustic waves at upstream side and the results of far-field PSD are underestimated. In addition, difference between single and multicomponent in the computational results is also small.

View full abstract

Dr. D. Pettit, a NASA Astronaut, carried out a thermocapillary flow experiment in a thin water film on-board the International Space Station (ISS) in 2003. The thin water film containing milk powder tracers was formed in a stainless-steel wire ring. The heating of a section of the ring by a soldering iron induced a thermocapillary flow in the water film. This flow was towards the heated part of the ring (outward flow); in the opposite direction (from hot to cold) to the ordinary thermocapillary flows observed in a liquid bridge and a liquid film. To shed light on the discrepancy observed between the space experiment and the ordinary thermocapillary flow, we have carried out a three-dimensional numerical simulation study. In the simulation we have also included the effect of meniscus shape. The simulation results showed that the meniscus shape determines the flow direction. Its consideration in the simulation also led to the prediction of an outward flow (from center to the heated part of the ring) in the water film as observed in the space experiment of Dr. D. Pettit.

View full abstract

In this study, an experiment was performed to clarify the flow field, in which the rods were normally inserted into a main supersonic flow with a porous cavity. In the experiment, a porous cavity is attached to a bottom wall of a main duct. A thermal tuft probe was adopted to detect a vertical flow direction in the cavity to monitor the flow behavior in the cavity. The experiments show that the three rods aligned spanwise retard the downstream displacement of the starting shock wave. It also reveals that the interaction among the rods, the porous cavity, and the starting shock wave changes the flow in the cavity suggesting the strong circulation between the cavity and the main supersonic flow. Moreover, the frequency shift of the cavity flow from about 370Hz to 400Hz is confirmed during the displacement of the starting shock wave from upstream to downstream of the porous cavity.

View full abstract

Behaviors of flame propagation in a detonation tube were observed by the schliren system with a high-speed video camera, and the flow velocity, flame velocity and propagation velocity of the pressure wave and the maximum pressure were measured to clarify the combined effects of a vortex flow on flame propagation and the deflagration-to-detonation transition (DDT) process. The flame is accelerated and the flame velocity is rapidly increased when the Shchelkin spiral is inserted in the tube. The accelerating flame acts as a piston producing the compression wave and it proceeds to the shock, then transition to detonation is accomplished. The DDT distance in the case with the Shchelkin spiral becomes shorter due to the combined effects of a VF and Shchelkin spiral.

View full abstract

We have numerically analyzed the asymmetric separation flow control over a slender body aiming to improve the controllability of high-angle-of-attack flight; in this study, the dielectric barrier discharge (DBD) plasma actuator is used as flow control device. A Reynolds averaged Navier Stokes/large-Eddy Simulation hybrid method (RANS/LES) is adopted with a high-order compact spatial difference scheme. First, the characteristics of flow field were investigated for various angles of attack. The asymmetricity of the flow field becomes stronger with higher angle of attack. In addition, the flow separation point is changed depending on the angle of attack, axial position and body side (starboard or port side). Next, numerical simulations of the flow field controlled by the plasma actuator were conducted. Plasma actuators are located circumferential position of ±80 degrees, ±100 degrees or ±120 degrees. We investigated the influence of the positional relation between the flow separation point and the actuator location on the side force control. As a result, it is shown that the circumferential position of the plasma actuator is important and should be chosen from the position and distance from the flow separation point. In addition, it is considered that the plasma actuator at closer position to the body apex has a stronger impact on the flow field.

View full abstract

In an attempt to study the oxidation phenomena of the thermal protective materials, test on carbon fiber reinforced carbon (C/C) composite have been conducted in plasma arc facility under the similarly MARS and other planet entry conditions. An arc heated wind tunnel used for thermal protective testing of ablation materials for capsule, probe and space vehicle. The study of attempts of ablation phenomena related the plasma characteristics to the thermally decomposed gas, the chemical composition and material structure after an arc heating test. Sample heating test during virgin C/C and C/C composite penetrated with dimethyl silicone oil target in a CO2 arcjet flow is experimentally investigated on measurements of emission spectra in shock layer and internal temperature distribution in the ablation materials.

View full abstract

Mixing between the injected fuel and high speed free stream air is challenging at supersonic speeds. Placing cavities downstream of injection holes or slots addresses the problem of flame holding and stabilisation, however there are still open questions related to mixing enhancement, uniformity and efficiency. The present study examines experimentally the flow field interactions due to a transverse jet - cavity combination with shock impingement at supersonic speeds using PIV, Schlieren photography, and oil flow surface visualisation. The oblique shock lifts the shear layer over the cavity and combined with the instabilities generated by the transverse jet injection creates a highly complicated flowfield with numerous vortical structures. The interaction between the oblique shock and the jet leads to a relatively uniform velocity distribution within the cavity. The lifting of the shear layer is also believed to reduce the drag created by the cavity.

View full abstract

This paper presents the basic research for establishing the qualification test (QT) level a unit has to pass to be sold as a product for space usage. A laboratory test campaign was conducted to study how the mechanical stresses distribute within a satellite body so as to define the unit QT level. We carried out random vibration tests using two types 50cm/50kg class satellites and measured the distribution of acceleration inside the satellites. The research focuses on the provision of the physical basis of the test conditions to be defined in the new standard. We tried to identify the range of natural frequency and amplification of acceleration in various launching environment through statistical analysis of the test results. The detailed test procedure, analysis method and primary results are herein reported.

View full abstract

A new procedure for the thermal design of micro- and nano-satellites is proposed for completing the thermal design of micro- and nano-satellites within about one year. First, two concepts of thermal design are considered for maintaining the temperature change of units within an allowable range. One concept involves decreasing the temperature change of units by using the whole thermal capacity of the micro- and nano-satellite. The other concept involves decreasing the temperature change of the inner structure on which units with a narrow allowable temperature range are mounted and which is insulated conductively from the outer structure. Then, the temperatures of micro- and nano-satellites designed with the former concept are calculated using a one-node analysis method. The temperatures of micro- and nano-satellites designed with the latter concept are calculated using a two-node analysis method. The combinations of optical properties of the structures and units to maintain the temperature of units within the allowable range are obtained by using one- or two-node analysis. Finally, the multinode analyses are carried out to obtain a detailed design based on the optical properties obtained from the one-node analysis or two-node analysis. This thermal design procedure is applied to the Hodoyoshi-1 satellite, which is about 50 cm wide, 50 cm deep, 50 cm high, has a mass of about 50 kg, two inner plates, and solar cells on the body, flies on the Sun-synchronous orbit at the altitude of 500 km, and is pointing to the Earth. The thermal design of this micro-satellite was completed within about ten months. Possible problems with the procedure are tested, and the procedure is verified.

View full abstract

The number of micro- and nanosatellites has rapidly increased in recent years. The tracking of some satellites can be insufficient if orbits are not determined by the development institutions. This is especially true in the case of low-altitude satellites, in which the orbit frequently changes. In this paper, the activities of the international Orbit Determination Network (ODN) system are described, and the feasibility of tracking is quantitatively evaluated on the basis of simultaneous observations in two countries. The hardware and software architecture required for a conventional low-cost ground station to become a node of the network is also described in detail.

View full abstract

The lithium-ion secondary cells/batteries are commonly used for the spacecraft, today. ‘REIMEI’ satellite is also an example using lithium-ion secondary battery. It used 3 Ah-class off-the-shelf lithium-ion secondary cells, which used the spinel LiMnO4 for the positive and graphite for the negative electrode. Seven cells were connected in series, and two series strings were connected in parallel. The satellite was launched in August, 2005, and injected into the low earth polar orbit. Initially, the battery performance was simulated based on the dependency of the cell performance on temperature. Considering the impedance and discharge performance depending on temperature, the end-of-discharge-voltage during the operation had been precisely controlled. Seven years operation of the lithium-ion secondary battery under the micro-gravity conditions have been demonstrated through the REIMEI operation in space.

View full abstract

To provide data rate more than 100 Mbps for nano satellite communications, we have developed an X-band downlink system with a modulation symbol rate of 100 Msps. The received signals of nano satellites tend to suffer much more distortion due to the transmitter and channel constraints. Several effective techniques based on turbo equalizer/decoder have been developed and verified via computer simulation therefore, the obtained results apply to the downlink system design.

View full abstract

Considering the cost reduction of the space transportation system, suborbital spaceplane, which flights ballistically to the altitude of 100 km, is considered one of a promising approach. Because of the avoidance of the orbital revolution, which leads to the reduction of the initial loading fuel, going to and returning from the space at low cost becomes possible. Due to the reduced re-entry speed, the ablator material is unnecessary and the reusability of the spaceplane is increased. SpaceShipOne, which is one of the suborbital spaceplane, has already reached to the step of the commercial use. The suborbital spaceplane seems possible to enter the orbital revolution by building a Maglev Guide Rail in the form which encircles the earth in Low Earth Orbit, and the Maglev Vehicles, which are driven along to the Guide Rail, berth with the suborbital spaceplane. It considered possible to maintain the Maglev Vehicle stationary in the space by adapting the configuration of the Orbital Ring. In this paper, the orbit of the Guide Rail, which supports not only the Maglev Vehicle but also the suborbital spaceplane, is calculated by astrodynamics. The results demonstrate that, sustainable movement around the earth is possible for Guide Rail in spite of the increase in the weight of Maglev Vehicle due to the docking with the suborbital spaceplane.

View full abstract

This paper describes the evaluation method of the new Japanese thrusters design, balancing and verification of interface compatibility with the HTV system and operation design. Thruster performance directly affects the performance of the space craft. Therefore, the thruster replacement from the imported thrusters to the new Japanese thrusters required the evaluation from the view point of high-order system level. It is important to select the appropriate elements, verify their relationships, and create a feedback mechanism which allows modification of each element. This method will facilitate the overall systems design for future inter-orbit transfer vehicles.

View full abstract

Multi-objective aerodynamic design exploration for the statically stable shape of the vertical-takeoff-and-landing rocket is conducted through the multi-objective evolutionary computation with the Newtonian method. The Newtonian method is one of the evaluation methods of aerodynamic forces in the supersonic region. Four objective functions are considered; 1)maximization of the lift to drag ratio(L/D) in return flight phase, 2)minimization of the launch drag coefficient(C_{D_Launch}) in ascent phase, 3)maximization of the volume of the body and 4) maximization of the distance from the nose to the center of gravity(x_cg). The maximum-lift-to-drag-ratio and minimum-launch-drag-coefficient shapes are almost the same each other, and they are close to bi-conical shape with small kink angle, similar to the previous study. On the other hand, the shape of the maximum distance from the nose to the center of gravity is found to be a narrow-front-body and wide-aft-body shape. The results also illustrate that the upper limit of the position of the center of gravity, with which the rocket is a statically stable at the angle of attack for the maximum lift-to-drag-ratio,is located at the position of 66% longitudinal length from the top of the body in the shapes considered in this study.

View full abstract

Present study investigated the effects of the geometry changes of the waveriders on aerodynamic characteristics by using the numerical simulations. This study introduces the two types of waveriders which have simplified lower surface; one is composed from two planes (Two-flat waverider) and the other is from one plane (Flat waverider). The ideal waverider, which has the ideal lower surface shape, is designed from the conical flow field for the angle of attack of 0 degree and Mach number of 4.0. The numerical simulations for three waveriders each shape are performed in inviscid and viscous cases. The numerical results for ideal waverider show that the rate of decrease of L/D between viscous and inviscid cases is the largest in the three waveriders. Therefore the ideal waverider designed by the inviscid assumption is affected by the viscous effect. The L/D of flat waverider decreases at the positive angle of attack because its drag coefficients increase. The longitudinal stability of three waveriders is not obtained as the center of gravity is placed at 70% of fuselage length.

View full abstract

The ice crystal growth experiments were carried out from December 2008 to February 2009 to understand the mechanisms of the morphological transition. However, the transition was not observed at all in space. Hence, we introduce a two-dimensional model to understand the stabilization mechanisms. From the comparison between the numerical and experimental results, it is found that the stabilization mechanism is the Gibbs-Thomson effect. The convection influence on the ground is also investigated. From the estimation of the Nusselt number, it is found that the convection strongly affects the temperature distribution even though the small supercoolings.

View full abstract

In order to obtain the particle temperature in complex plasmas, a new method based on the pair distribution function (PDF) is investigated. From the PDF, the mean square displacement is obtained. To estimate the temperature, the particle motion is also traced. The fast Fourier transform (FFT) analysis of the motion data indicates that the fundamental and second harmonic frequencies are found. The model for a single frequency is expanded to calculate the temperature under the multiple frequencies conditions. The temperature is estimated to be 0.08 to 0.17 eV. This is consistent with the temperature obtained from the conventional method.

View full abstract

As a fundamental study on the droplet-interaction effect in the fuel-spray ignition, spontaneous ignition of an n-decane droplet pair in hot air was experimentally studied in normal gravity and microgravity. Two suspended droplets initially at room temperature were brought into a hot furnace filled with air and ignited spontaneously. In the previous studies, cool-flame and hot-flame ignition delays were evaluated thorough thermocouple measurement, and their dependence on inter-droplet distance was discussed thorough the development of temperature and fuel-concentration distribution around a droplet pair. However, two-dimensional observation of cool-flame and hot-flame behavior was not possible with thermocouple measurement. In the present study, interferometry was applied in order to detect cool flame, which emits almost no visible light. Density field around a droplet pair was qualitatively observed with a high-speed camera, and the locations of cool-flame and hot-flame appearance were evaluated. Pressure was 0.3 MPa, and ambient temperature was between 560 and 680 K. The ambient conditions are in the range where two-stage ignition occurs. Initial droplet diameter was either 0.8 mm or 1 mm. In normal gravity, cool flame always appeared on the lower side of the droplet pair, and hot flame appeared on the upper side in most cases, which is obviously the effect of buoyancy. In microgravity, cool flame appeared on the outer side of the pair, and hot flame appeared on the inner side of the pair, which corresponds with the discussion in the previous studies.

View full abstract

We improved the method of measuring method of interdiffusion coefficients using the Foton shear cell technique and stable density layering by adding the normalization of the measured concentration, reducing the segregation in the alloys, and improving the fitting method of the theoretical diffusion formula. We measured interdiffusion coefficients of Sn-Pb alloys using two different diffusion pairs (Sn and Sn-10at%Pb, Pb and Pb-10at%Sn) at 773K and investigated the dependence of diffusion coefficients on the solute concentration. The measured values agreed well with the theoretical curve obtained using Darken’s equation. Therefore, we supposed that Darken’s equation is also applicable to diffusion in liquid.

View full abstract

Recently, researches on bulk glass and glass-ceramics have attracted the attention due to their low cost optical materials of the future. In this study, the formation of bulk spherical RAlO₃ (R=rare-earth elements) glass and crystalline phases have been investigated due to their unique features in terms of the solidification process, glass structure and optical properties. Aerodynamic levitator was used to undercool the melt below the melting temperature. RAlO₃ sample was levitated and completely melted by a CO₂ laser and then cooled by turning off the CO₂ laser and solidified. In the RAlO₃ system, La, Nd and Sm aluminum perovskites solidified as glass and Eu to Lu aluminum perovskites solidified as crystalline phases. The as-prepared glasses showed a high refractive index of ~1.89, suggesting that containerless levitation is an elegant technique for the fabrication of new glass and crystalline ceramics from an undercooled melt.

View full abstract