This paper proposes a Hybrid Genetic Algorithm (Hybrid-GA) which is suitable for a large scale multidisciplinary optimization problem such as Two-Stage-To-Orbit (TSTO) spaceplane optimal design problem. The Hybrid-GA is implemented by combining Sequential Quadratic Programming (SQP) method with GA. When constructing the Hybrid-GA, there are three problems that should be solved; 1) decision of optimized variables and discrete method, 2) how to use results of local search, and 3) selection for survival method. These problems are discussed and solved in order to effectively combine SQP method with GA. In order to demonstrate the effectiveness of the proposed Hybrid-GA, the TSTO spaceplane optimal design problem, which consists of weight, aerodynamics, propulsion, and flight trajectory analyses, is investigated using the proposed Hybrid-GA, and the optimal results of Hybrid-GA are compared with that of Simple-GA, and SQP methods. Finally, strategy to achieve the TSTO spaceplane is proposed by comparing the optimal results of changing payload weight and maximum wing load factor of booster.
Both experiment and calculation demonstrated to clarify the effect of a column wall jet in uniform fluid flow on the characteristic of wake oscillation. The vortex intensity decreased and the oscillations attenuated when the jet direction matched the uniform flow. When the jet flow was reversed, the vortex intensity grew and the oscillations increased in magnitude. It has been found that the Strouhal number based on the half width of the flow velocity distribution was nearly constant. Also, the frequency depended on the vortex structure of the wake, which was further dependent on the jet flow velocity. In addition, the situations that gave twin peaks in the oscillation spectrum were found both in experiment and in calculation.
Space tethers are subject to high collision risk due to the very large collision cross-sectional area and they can be cut easily by impacts of small particles because of the thin diameter. Therefore, double-line tethers have been proposed to extend their life. The previous works assessed the survivability of double-line tether treated two wires independently. This treatment assumed that the distance between two wires is infinite. Physically, the distance between two wires is finite, however. Therefore, two wires could be cut simultaneously if the particle cutting through the first wire has or the remnant melted or vaporized at impact on the first wire have still enough energy to cut the second wire. As a result, unfortunately, once we consider that two wires can be cut simultaneously by a single impact, the merit of double-line tether disappears. Double line tether without sufficient clearance between two lines would not survive longer than expected. In this paper we will describe how to treat double line tether with a finite clearance between two lines and provide some results from applying this technique to a micro tether satellite named QTEX, being developed at Kyushu University.
To meet the expected increase in air traffic demand, airport expansion programs are currently underway. For the programs, prior assessment of the effect is indispensable. Conducting fast time simulation experiments provides valuable information for the prior assessment of airport surface capacity. To obtain more reliable information, the simulation experiments should be conducted on valid models. As a result, validation process for simulation models is required. In consideration of aspects specific to modeled airports, the simulation models should be validated. In this paper, a Japanese airport was modeled. Compared to the field observation data, the model was validated. As an application of the model, a series of fast time simulation experiments was conducted. The experiments were to evaluate the impact of air traffic increase on the current airport layout. The results from the experiments were also discussed.
This paper proposes a novel “knowledge-free” anomaly detection method for spacecraft based on regression techniques. This method learns a linear or nonlinear probabilistic regression model in the learning phase by applying a regression technique to a massive telemetry data of spacecraft, and then monitors the real-time telemetry data using the constructed model. This approach can be seen as adaptive limit-checking because it sequentially predicts proper envelop of a target time-series based on the past data of itself and other relevant series. We have confirmed the effectiveness of the proposed anomaly detection method by applying it to the telemetry data obtained from a simulator of an orbital transfer vehicle designed to make a rendezvous maneuver and from actual space operation of Engineering Test Satellite VII (ETS-VII).
This study aims to obtain the optimal flights of a helicopter that reduce ground noise in its landing approach with an optimization technique and to conduct flight tests for confirming the effectiveness of the optimal solutions. Past experiments of JAXA (Japan Aerospace Exploration Agency) shows the noise of the helicopter varies significantly according to its flight conditions, especially depending on the flight path angle. We therefore build a simple noise model of the helicopter, in which the level of the noise generated from a point sound source is a function only of the flight path angle. By using equations of motion for flight in a vertical plane, we define optimal control problems for minimizing noise levels measured at points on the ground surface, and obtain optimal controls for specified initial altitudes, flight constraints, and wind conditions. The obtained optimal flights avoid the flight path angle which generates the large noise and decrease the flight time, which are different from the conventional flight. Finally, we verify the validity of the optimal flight patterns by the flight experiments. The actual flights following the optimal ones also result in the noise reduction, which shows the effectiveness of the optimization.