This paper demonstrates the optimization process of a satellite constellation for disaster detection by the use of serviceability function as evaluation criteria. The study is conducted on constellations of synthetic aperture radar (SAR) satellites for detecting damaged area following a disaster. In the optimization process which comprises three steps, 1) choosing candidate constellations through sensitivity analysis, 2) adjusting detailed orbital parameters by compatibility evaluation among major target places, 3) checking adaptability to the various situation of topography around the targets, serviceability function is employed as the criteria for evaluation of tradeoffs. As a result of the study, it was indicated that the constellation comprised of two satellites in the sunsynchronous sub-recurrent orbits and two satellites in the inclined orbits will be an optimized choice for the observation of Japan within six hours following a disaster.
One DGVSCMG can achieve 3-axis attitude control of a spacecraft. However, in attitude control problems, it is difficult to avoid singularities of a DGVSCMG system when there is no redundancy. In this paper, we develop a singularity robust controller to avoid singularities of the system. This technique considers singularity avoidance by not a steering law but a control law while introducing an extra term into the Lyapunov function. Through a numerical simulation, effectiveness of the singularity robust controller is demonstrated.
Green monopropellant thrusters, such as HAN-based and ADN-based monopropellant thruster, have been continuously developed as replacement for conventional hydrazine thrusters. A green monopropellant reaction system by utilizing discharge plasma of swirling noble gas has been proposed in substitution for the solid catalyst. Objective of this study is to evaluate the thrust performance of HAN-based monopropellant thruster with discharge plasma system by the measurement of combustion chamber pressure under vacuum. As a result, stable operations were confirmed by the measurement of combustion chamber pressure and internal pressure of argon-tube. At argon mass flow rate of 0.13g/s, HAN-based monopropellant mass flow rate of 0.31g/s and nozzle expansion ratio of 1, power consumption, c-star efficiency and rising time of combustion chamber pressure were 484W, 54% and 597ms, respectively. In addition, predicted thrust and specific impulse by the measured combustion chamber pressure were 282mN and 93s, respectively.
Accurate prediction of aircraft trajectory is indispensable for efficient air traffic management under trajectory-based operation concept. Aircraft are vectored to make an efficient arrival sequence to Tokyo International Airport, and the trajectories of aircraft depend on the order of arrival sequence. Prediction of order of arrival sequence contributes accurate prediction of aircraft trajectories. The author developed a model that predicts the order of arrival sequence to Tokyo International Airport when aircraft pass 50 nautical miles, 100 nautical miles and 150 nautical miles points to the airport. The model includes a support vector machine (SVM) model that predicts which of a pair of aircraft is a leader in the sequence. The accuracy of prediction by our SVM model at 150 nautical miles point is 92.3 percent. The order of arrival sequence is predicted by the integration of the SVM model and quick-sort algorithm. The accuracies of predictions of arrival sequence at 50 nautical miles, 100 nautical miles and 150 nautical miles points are 95 percent, 89 percent and 76 percent, respectively. They are much higher than the accuracies of predictions based on first-come-first-served principle, which are 85 percent, 66 percent and 49 percent, respectively. This shows the effectiveness of our model.
The feasibility of the flight time uncertainty modeling in 4-dimensional trajectory is discussed. The flight time uncertainty causes due to the difference between both the estimated and actual wind speeds and the control input and the output of the flight speed. According to the standard deviation analyses using the actual operation data, it has been demonstrated that the model of the flight time standard deviation is able to describe the tendency of its magnitude. It is further clarified that the correlation between the true air speed and the estimated wind speed should also be considered in the modeling to improve its accuracy. It is indispensable to take this correlation into consideration in the uncertainty modeling in the 4-dimensional trajectory operation.
Time series data of aerodynamic characteristics obtained by flight tests have large variances compared with data obtained by ground testing tools such as wind tunnel tests and numerical simulations. It is necessary to examine the uncertainty of the data obtained by flight tests in order to minimize random and systematic errors. We investigated on-board measuring instruments of the aircraft, and analyzed systematic uncertainties of the aerodynamic coefficients obtained by the flight tests using the JAXA Flying Test Bed ``Hisho''. This paper discusses the result of the systematic uncertainty analysis and the contributing factors to the uncertainty of aerodynamic coefficients.