Fuel droplet array combustion experiments of a fuel droplet array were performed at microgravity to investigate the mechanism of fuel droplet group combustion. The purpose of this research is to understand the dependence of flame spread speed on droplet spacing and initial droplet diameter. Ten fuel droplets were generated using a thin glass needle and suspended at the crossing points with SiC fibers of 7.5 and 14 μm in diameter, respectively. Sequential backlit-images of the droplet suspension fibers and the droplets were taken at the time of flame spread. n-Decane was employed as the fuel. The effect of initial droplet diameter on the normalized flame spread speed were examined with varying droplet spacing. In the case of 3.75 in nondimensional droplet spacing showed that the normalized flame spread speed increased less than 0.48 mm in initial droplet diameter and remained constant above 0.48 mm. In the case of short flame spread induction times, which is the time for a flame to travel between two droplets, the normalized flame spread speed increased as the initial droplet diameter increased. The reason for this believed to the flame spread induction time is dominated by the premixed-flame propagation time.
We developed a tool for visualizing the spatial geometry of objects and field-of-view (FOV) of scientific instruments for mission plans and data analysis of Hayabusa and Hayabusa 2, and named “HARMONICS (Hayabusa Remote MONItoring and Commanding System).” We also implemented a graphical user interface to simulate a changing FOV. Displaying arbitrary viewpoints over a time sequence helps determine the geometry observed and supports later data analysis. HARMONICS loads ancillary data with the SPICE kernel format: position and attitude of the spacecraft, properties of scientific instruments and target's shape model, etc. Here, we report on the system details and enhanced functions of HARMONICS compared to the original version in 2005.
A highly maneuverable and reusable spaceplane, which is remarkable for its ability to send payloads and data back to Earth in the volatile environment, is attached with high priority in responsive reconnaissance missions. In view of the fact that a classical nonlinear optimization algorithm is mostly restricted in discovering the optimum solution of a multi-stage trajectory-design problem, a two-level optimization algorithm is established to enhance the convergence of the solution. By means of dividing the entire trajectory into ascending, on-orbit, deorbit, and reentry segments, respective optimizations of the four segments above compose the sublevels of the optimization scheme and are associated elaborately one after another by transmitting the terminal value of a former segment to its following segment. A genetic algorithm, which is employed in the top level of this scheme, will incorporate the intermediate solution and state quantities from sublevels as the fitness function of the GA and generate the new optimized value for the first segment in each sublevel during each iteration. This two-level iteration will be operated under given constraints and will eventually acquire the optimum trajectory with a maximum target coverage time. Furthermore, a Monte Carlo simulation is conducted to observe the robustness of the optimized solution.
A robust aeroelastic optimization design methodology for hypersonic wings considering uncertainty in heat flux is presented and applied to a design process of a typical hypersonic low-aspect-ratio wing. An interval analysis method is used to perform the transient heat transfer analysis with uncertainty in heat flux within the newly developed aerothermoelastic framework. A genetic algorithm is used to build the framework for robust optimization, and it is also used to determine the critical thermal load case from an interval temperature field obtained using interval heat transfer analysis. Aerothermoelastic analysis of the hypersonic wing shows that the structure may bear a severely worsening thermal environment when there is uncertainty in heat flux during hypersonic flight. Not merely the average temperature, but also the temperature gradient distribution of the structure rises, which might make designs created using deterministic analysis methods unreliable. Optimization results show that the robust optimization design methodology can provide a relatively light structural design and simultaneously make sure it is capable of satisfying multiple constraints under severe thermal environments with uncertainty.
A novel Out-of-Sequence High-degree Cubature Huber-based Filtering (OOS-HCHF) algorithm is presented and utilized to estimate the trajectory of a ballistic target in the ballistic phase. This novel algorithm makes use of the 5th-degree cubature rule to numerically compute Gaussian-weighted integrals, which are propagated through a nonlinear state equation, and then a weighted mean and covariance are taken. As the radar measurements are accentuated with corrupting glint noise which is essentially non-Gaussian and arriving out-of-sequence, usually caused by communication and processing latency, the novel filtering is carefully designed with the consideration of these factors. First, the solution to the OOSM problem is derived in combination with the 5th-degree cubature rule in time update equations. Second, the Huber technique, which is a combined minimum l1 and l2-norm estimation technique, is used to design the measurement update equations. Therefore, the proposed OOS-HCHF could exhibit robustness with respect to deviations from the commonly assumed Gaussian error probability, for which conventional cubature Kalman filtering (CKF) exhibits a severe degradation in estimation accuracy. Furthermore, the out-of-sequence measurements could be incorporated optimally. Finally, in contrast to extended Kalman filtering (EKF), more accurate estimation and faster convergence could be achieved by OOS-HCHF from inaccurate initial conditions. Simulation results are shown to compare the performance of OOS-HCHF with CKF and EKF.
NACA conducted extensive tests of z-stiffened panels under compressive load in the 1940s and 1950s in order to create direct-reading design charts. Because of the asymmetry of z-stiffened panels, the buckling behavior is complex and buckling analysis of the NACA data has not been conducted. In order to analyze the buckling of z-stiffened panels, a new tool for the buckling analysis of thin-walled structures is developed. This paper presents the results of the buckling analysis of the NACA data and investigates the buckling behavior of z-stiffened panels. It is found that the lateral buckling of the stiffener is critical in the short column region, while the torsional buckling of the stiffener is not critical.
This paper describes development strategies and on-orbit results of the attitude determination and control system (ADCS) for the world's first interplanetary micro-spacecraft, PROCYON, whose advanced mission objectives are optical navigation or an asteroid close flyby. Although earth-orbiting micro-satellites already have ADCSs for practical missions, these ADCSs cannot be used for interplanetary micro-spacecraft due to differences in the space environments of their orbits. To develop a new practical ADCS, four issues for practical interplanetary micro-spacecraft are discussed: initial Sun acquisition without magnetic components, angular momentum management using a new propulsion system, the robustness realized using a fault detection, isolation, and recovery (FDIR) system, and precise attitude control. These issues have not been demonstrated on orbit by interplanetary micro-spacecraft. In order to overcome these issues, the authors developed a reliable and precise ADCS, a FDIR system without magnetic components, and ground-based evaluation systems. The four issues were evaluated before launch using the developed ground-based evaluation systems. Furthermore, they were successfully demonstrated on orbit. The architectures and simulation and on-orbit results for the developed attitude control system are proposed in this paper.