The time-spectral (TS) method to numerically predict self-excited oscillation due to the fluid dynamics-- rigid body dynamics coupling is developed and validated through the comparison with the time-marching (TM) method. A residual of the TS equation of motion of a rigid body is found to be a useful indicator to realize limit-cycle oscillations. It is minimized by repeating the frequency update by the Newton iteration, where the gradient of the residual with respect to the frequency is obtained from the flow simulation, and the displace update by solving the TS equation of motion. The developed method is validated by two problems: one is an oscillating cylinder due to the Karman vortex, and another is a transonic, pitching wing due to the movement of the shock wave around the wing. In both problems, the TS methods quantitatively reproduce free oscillations by the TM method. The simulation time is shortened by a factor of 4 for the transonic wing problem.
This study explores the minimum-time attitude maneuver of satellites using Control Moment Gyros (CMG). The CMG system is able to generate high torque and run for longer term than other actuators. However, it is known that the singular input that cannot generate effective torque appears in the optimal control for the minimum-time maneuver of a rigid spacecraft with a pyramid type SGCMG system. In previous studies, a new system equipped with variable speed CMG (VSCMG) to the CMG where the singular input appeared has been proposed. It is shown that the new system can rotate faster than the normal pyramid type SGCMG system in the simulation based on the optimal control law. However, for applications in actual satellites, numerical optimization cannot be used due to the high calculation cost. The objective of this study is to make the new semi-optimal control law for the minimum time attitude maneuver of the satellite equipped with the VSCMG. The new control law is designed using a rule-based feedforward control combined with feedback control. The result by numerical simulation has shown that the proposed control law enables the satellite to achieve faster maneuver without iterative calculations.
In this paper, we propose two estimators to compensate the target's maneuver and uncertain vehicle dynamics including uncertain system lag; one is an extended state high-gain-observer-based estimator to estimate an uncertainty and disturbance term (UDT) which affects the line-of-sight (LOS) rate dynamics, and the other is a novel filter to estimate the uncertain system lag. Generally, a linearized system from its original system for the estimation of the uncertain system lag is unobservable, whereas, we can make the system observable with the filter. The effectiveness of those compensation methods are shown by conducting some representative numerical simulations and comparing with a conventional compensating method. The filter which estimates the uncertain system lag used in combination with the high-gain-observer-based estimator has made better performance than the one used in combination with the conventional method in terms of convergence time and resulting miss distance.
This paper is concerned with the control of the dual-spin turn (DST) of a spacecraft to regulate the spacecraft attitude. The DST is a method for attitude stabilization of a rotating spacecraft by transferring the angular momentum of the spacecraft to a single wheel. The proposed control law consists of feedforward (FF) and feedback (FB) control phases. The FF control is designed by optimizing the driving pattern of the wheel using the Differential Evolution (DE). In the FB control, the rate damping control and the attitude control around the wheel rotation axis are proposed based on the linearized error system around the stationary state of the spacecraft. By using the proposed control law, the DST is controlled step by step, and the spacecraft eventually becomes stationary at an arbitrary angle around the wheel rotation axis. The validity of the proposed method is verified by numerical simulations.
This paper proposes an optimal planning method of imaging multiple points on Earth from a spacecraft that is equipped with a pyramid type Control Moment Gyros (CMGs) as the attitude control actuators. The purpose of the planning is to maximize the number of cities to be imaged with better quality during multiple orbiting. The problem results in the optimization of selection of target cities and imaging orders under the constraints of the candidate cities, position of the spacecraft and the attitude maneuvering time. In order for better quality of the images, we consider minimization of the sum of the distance between the spacecraft and the target cities in the city selection procedure. Estimating the attitude maneuvering time with CMGs usually takes long due to the complexity, therefore, we also propose a faster estimation method of the maneuvering time by approximation. The proposed planning method is applied to the imaging of 292 cities around the world along 10 satellite paths, and its validity is evaluated through numerical simulations.
A neural network for prediction of discharge current, which shows nonlinearity and hysteresis dependent on coil current, has been developed to build auto control system of Hall thrusters. The prediction accuracy dependence on training data sets composed of operational parameters (previous work), 250 images of plume shape and both, operational parameters and images, are investigated. The network using only plume images can describe the non-linear mode hop jump and hysteresis that the network using only operational parameters cannot describe. The predicted discharge current, however, is fluctuated up and down, while that observed in experiment shows smooth curve. The prediction using both operating parameters and plume images as the training data, can describe mode hop jump and hysteresis with 0.8% difference between prediction current and that observed in experiment.
Compressibility effects on aerodynamic characteristics of a Mars airplane is investigated at a low Reynolds number flight condition. The aerodynamic characteristics are evaluated by using Reynolds-Averaged Navier-Stokes simulations with SST κ—ω turbulence model and γ—Reθ transition model. Numerical results show that the lift coefficient increases as the Mach number increases at angles of attack of 2 to 6 degrees, but it decreased at angles of attack of 0 and 8 degrees. The drag coefficient also increased as the Mach number increased. The pitching moment coefficient significantly decreased as the Mach number increased. The main reason of these changes is that the reattachment point of the separated flow on the main wing moves to downstream due to the compressibility effect.
OMOTENASHI is a CubeSat that will be launched by NASA SLS rocket. Its mission is to demonstrate that a CubeSat can make a semi-hard landing on the Moon. The 6U-size spacecraft, which weighs 12.6kg, and consists of an orbiting module (OM), a rocket motor (RM) for deceleration on approach to the moon, and a surface probe (SP) as the landing module. Under tight resource constraints, a unique structure and separation mechanism is designed for a small space and a low mass. A validity of these designs has been verified through a vibration test. The margin of safety under the launch vibration is calculated by the structure analysis. In addition, to increase the impact resistance, all components of SP are filled with an epoxy resin. This performance had been evaluated by the drop impact test. As the result, this test model endured more than 16,158G with no function failure. In this paper, the design overview and test results are described.
System integration plays an important role in the aerospace product development, especially in the development of commercial aircraft as large-scale and complex system. We describe and study the definition and importance of system integration. In the present technical note, we evaluate the effectiveness of conventionally proposed evaluation indices for technology readiness and system integration maturity, etc. and propose a new Maturity Index for System Integration, SIML (System Integration Maturity Level).
Spin-type solar sails have the advantage of being lighter compared to other deployment methods, but can exhibit complex deployment dynamics. Severe asymmetric dynamics was observed in the deployment experiment in a vacuum chamber. In this study, this deployment behavior is reproduced by numerical simulations using multi-particle techniques that take into account membrane collisions. We propose a simple method to predict whether a significant asymmetry will occur by calculating the energy change of the membrane. The conditions for realizing symmetric deployment are presented.
The visualization of flow field around NACA0012 airfoil under constant-pitch-rate motions was conducted using a towing tank. The effects of the pitch rate on the flow field were investigated by PIV, PTV, and pathline visualization at a Reynolds number of 50,000. The non-dimensional pitch rate r was set to 0.01 and 0.02. It was found that the effect of the pitch rate appeared at the pitch angles far smaller than the static stall angle. The separation point and the position of the separation bubble deviated from those in the steady condition. The angles at which the laminar separation bubble was observed under unsteady conditions were different from the angles under the steady condition. Due to the pitching up motion, the unsteady laminar flow separation was observed at r = 0.02. The delay in the formation of the laminar separation bubble was also observed at the smaller pitch rate (r = 0.01), although the unsteady laminar flow separation was not observed.
Discharge current oscillations, especially a frequency range of several tens kilohertz, have been a significant problem in Hall thrusters from the viewpoint of electromagnetic interference because a discharge-current frequency and amplitude are unpredictable. A pulsating boost chopper power supply (chopper PS) has been developed to adjust a discharge-current frequency to a chopping frequency of the chopper PS. In our previous studies, for both SPT and TAL-type Hall thrusters, the chopper PS shifted the oscillating frequency to the chopping frequency and successfully suppressed the amplitude of the discharge current. However, the discharge-current spectrum showed a sharp peak on the chopping frequency. In this study, a spread spectrum was applied to the pulse signal, which switches the field-effect transistor of the chopper PS, with the aim to reduce the spectrum intensity on the chopping frequency. As a result, the spectrum peak was attenuated with improved thrust performance and suppressed discharge-current amplitude and ion wall loss.
In this study, a focusing schlieren PIV system of the LED light source was used to estimate the flow vector of free jets, as a first step toward the application of wind tunnel testing. The system was constructed by an extended light source, a Fresnel lens, source and cutoff grid, focusing lens and a camera. A source grid of the lattice configuration was prepared to visualize the vertical and horizontal density gradients at the same time. The light source was designed by consisting of 4 LEDs. The helium gas was used as the test gas to obtain large density gradient in low speed flows. As a result, the image of the flow pattern by the lattice grid was different from the image of the vertical and horizontal grids. By utilizing the lattice grid, the radial velocity distribution by PIV analysis of the jet showed good agreement with the empirical formula.
This paper proposes a method for evaluating the attitude accuracy of an inertial measurement unit (IMU) using an optical motion capture system. The most valuable feature of this method is that it can evaluate the accuracy of the IMU in a free-fall condition. Two independent coordinate systems, i.e., the reference coordinate systems of the IMU and the motion capture system, are made to correspond using a rotation matrix that is obtained through a static pretest. Two types of accuracy evaluation methods are displayed. One is the difference of Euler angles in each component, and the other is the difference of measured three-dimensional attitudes, which is calculated using Rodrigues' rotation formula. The demonstration result indicates that the proposed method can evaluate the accuracy of the IMU in free-fall conditions effectively.
The local shock wave velocity modulation phenomena due to the interaction with the discharge field was investigated by using high speed camera with the frame rate of 4×105fps. From the experimental results, it was observed the phenomena of the shock wave acceleration in the direction toward the electrode center and of the deceleration in the direction away from it. By comparing the numerical simulation, it was suggested that the shock wave can be accelerated in the temperature increasing region and it can be decelerated in the temperature decreasing region. In this study, the local shock wave velocity modulation phenomena due to the interaction with the DC discharge field was clearly indicated.
This paper shows results of designing grid system using numerical simulation with genetic algorithm. Furthermore, the search processes were visualized using principal component analysis, a dimension reduction technique for deeper understanding of the search processes and evaluation of the searched area. Assuming the design of the μ 10 engine, grid parameters were optimized according to an objective function. However, the result of visualization showed that the search area was not comprehensive. In addition, verification of the population size in the genetic algorithm indicates the multimodality of the search space, which clarified the direction of future improvements.
In this study, tensile tests were conducted for the fastener consisting of aluminum (or bakelite) female thread and chromoly male thread. The results showed that the maximum loads in the tensile tests were proportional to the nominal diameter d, fit length l and the shear strength τu of the female thread material. Therefore, it was found that if dimensionless female thread strength KsFmax/(τuπ dl) was measured in the certain (d, l), the maximum loads Fmax at any (d, l) could be accurately predicted. In addition, strength analysis of female/male fasteners were performed using finite element method. As a result, the analysis maximum load Fmax became higher as the fitting length l and the nominal diameter d were larger, as in the experiment. However, the analysis was stopped halfway due to an error, and the analysis result of the maximum load was smaller than the experiment, and it was found that the prediction was limited. To get accurate results, it is necessary to eliminate the analysis error and to consider the roundness of the thread valley of the analysis model.
The use of phased array antenna (PAA) with a power taper in a space solar power systems requires a configuration that can be mass-produced. However, there was no conventional method of constructing a PAA with power taper, which suitable for mass production. Therefore, this paper proposes a method of constructing a PAA with a single type of amplifier and uniform spacing between antenna elements, which gradually increases the number of elements in the subarray. As a result of applying the proposed method to a 10-dB truncated Gaussian taper, the power transmission efficiency is equal to or higher than that conventional methods. In addition, the proposed method was demonstrated in experiments using a one-dimensional patch antenna array.
After tests using actual oxidizer, for example firing tests, the valves for propulsion system should be enough cleaned. If the cleaning was not appropriate, it would be able to cause of problems such as a leaking by corrosion cracking. But now, valve cleaning methods are based on the experiences of each manufacturer and those are not unified. We conducted some tests to verify the efficiency of cleanings method for oxidizer valves. Especially, we focus on the method to remove residual oxidizer from polymer for seals inside valve. In this paper, we describe our results and propose a policy for efficient valve cleaning methods.
System integration plays an important role in the aerospace product development, especially in the development of commercial aircraft as a large-scale and complex system. eVTOL vehicle that attracts attention as a new aircraft development program these days is a small and concise system compared to the commercial aircraft. The development of eVTOL vehicle greatly differs from the development of conventional commercial aircraft in various aspects of development. In addition to clarifying its characteristics and differences, the waterfall-agile hybrid development processes suitable for eVTOL vehicle is proposed in this technical note.
This paper describes the concept validation process of an onboard inertial platform by means of a motion stage as the low-cost supplementary device for the attitude control subsystem of ISAS/JAXA sounding rockets. The proposed device is a HEXA 6 DOF parallel robot consisting of parallel links with one moving plate to make up a motion stage, aiming at achieving the resolution of changing in its attitude angle is 0.1 degree. In addtion, this device is equipped with a single axis spin table installed on the top of the moving plate to enhance the spin dump/suppressing ability. The flight experiment has been performed January 2020 using S-310-45 rocket with successfully obtained telemetry data enough to conclude that this approach can be one of options for the low-cost attitude control assistant device.
Accurate and reliable flight data is indispensable for research and development to explore new findings which will be of assistance in establishing a new system of air traffic management (ATM). Although radar data called CARATS Open Data and Automatic Dependent Surveillance Broadcast (ADS-B) data are currently available, these data have limitations in accuracy and number of parameters; therefore, they are not so sufficient for the research in which detailed parameters such as airdata, take-off weight and cost index are required. The purpose of this study is to verify whether commercially available flight simulator software: X-Plane in which function of Flight Management System (FMS) is replicated, is usable for studies on ATM. To validate whether the flight simulator software can reproduce accurate flight profiles and aircraft parameters, mimicked flight data gained by the simulator is compared with calculated data and real data. In the flight simulation by X-Plane, weather data is input by a piece of software, FS Global Real Weather (FSGRW) which provides the simulator with weather data from National Ocean and Atmospheric Administration's (NOAA) server every 5 minutes.