This paper proposes a way of quantitative evaluation for a system with design complexity defined by cyclomatic number, coupling, cohesion, scales of system and subsystems, and the number of interface and communication. Though the design complexity would eventually apply to the calculation of reliableness, it essentially enables a comparison between systems. Here, we adopted the design complexity to Japanese microsatellites, and obtained their characteristics and a guideline to improve them. Furthermore, we found a relation between the design complexity and success level of missions accomplished by the microsatellites, i.e. we should have an option to reduce the design complexity in order to increase the success level of a satellite. Thus, the design complexity affects the reliableness in reliability assessment or resource allocation in a project, so that it would establish an applicable reliability assessment specialized for microsatellite, so-called Hodoyoshi Reliability Assessment.
A novel drag reduction method for a cylinder using a pivoted airfoil is proposed in this study. The pivoted airfoil can rotate freely on a shaft so that the airfoil can head windward. First, we conducted a water tunnel test to validate the drag reduction method. Contrary to our expectation, the airfoil did not head windward completely. The airfoil started to move from an initial angle of 0º to a stable angle of about 14º. Next, we calculated the aerodynamic force of the airfoil by a computational fluid dynamics (CFD) method. The reason the airfoil did not head windward completely was revealed. This is because the sign of the moment coefficient around the rotating shaft changes with increasing angle of attack. The CFD simulation also revealed that the drag reduction method can decrease the drag by 34%.
This paper is concerned with flight controller design of D-SEND#2. D-SEND is a project to demonstrate a low sonic boom aerodynamic design concept. In the #2 part of this project, an unpowered test vehicle is lifted to an altitude of 30km by a balloon from which it then separates. After the separation, the vehicle's on-board flight control computer selects a target Boom Measurement System (BMS) according to the separation point. The vehicle then autonomously flies to the selected BMS and establishes prescribed sonic boom measurement flight conditions. The design of the GNC system for D-SEND#2 project is exceptionally challenging since 1) there is no nominal trajectory, 2) there is only limited control available to meet various requirements, 3) the flight envelope is quite wide, and 4) the development time is short. Dynamic inversion method and time-scale separation technique are applied to deal with these problems, and a systematic controller design procedure is presented. The controller is designed with this procedure and evaluated through linear analysis and Monte-Carlo simulations which shows it has sufficient performance and safety margines. This controller design method is confirmed to be a practical method for UAVs.
Radio frequency (RF) plasma cathodes have been researched and developed as an electron source to remove the drawbacks with dispenser hollow cathodes from ion and Hall thrusters. In this paper, we evaluate the electron-emission performance of a RF plasma cathode and the operating characteristics of the combination of a 1-kW class anode-layer-type Hall thruster and the RF plasma cathode. For the RF plasma cathode, an anode current of 3.5A is obtained at an RF power of 140W, a xenon mass flow rate of 0.2mg/s. The anode current is sufficiently high to operate the Hall thruster. Normal ion beam extraction and neutralization for the combination were experimentally confirmed. The anode efficiency of the RF plasma cathode is comparable to that of a hollow cathode. Based on this result, the feasibility of the RF plasma cathode for the Hall thrusters in ground tests was confirmed. However, because of the high RF power consumption, the total efficiency of the RF plasma cathode is lower than that of the hollow cathode at anode mass flow rates of 2.0mg/s and 2.9mg/s. This result indicated that for space-related applications, it is important to reduce the power consumption of RF plasma cathodes.
A hypersonic flight experiment using an S-520 sounding rocket as a launch vehicle is planned in order to demonstrate integrated control technologies for vehicle attitude and propulsion. Its primary mission requirement is to achieve experimental conditions for the installed ramjet engines (constant 50kPa dynamic pressure at not less than Mach 4.0) for a sufficient duration. In this paper, a feasibility study of the flight experiment is conducted using a multidisciplinary design optimization technique. The experimental vehicle shape and the flight trajectory are simultaneously optimized so that the duration of the required experimental conditions is maximized. In particular, consideration is given to the trade-off between a longitudinal static margin and trimming capability since it is a major concern for flight control of winged suborbital re-entry vehicles. Gross mass and launch angle of the sounding rocket are varied to obtain vehicle shapes and associated trajectories that successfully satisfy the mission requirement.
Shape estimation of space debris is an important task in evaluating its trajectory evolution and collision probability with resident objects in space. This paper shows the magnitude and rotation of space debris can be estimated by investigating the Doppler shift with a Single Range Doppler Interferometry (SRDI) method. The theory of SRDI method is discussed and its usefulness is confirmed by numerical simulations. Furthermore, fluctuation of Doppler shift of known space debris were successfully observed by the MU radar of Kyoto University and the size and spin rate of some space debris were successfully estimated.
In this paper, an immersed boundary method (IBM) and a cut-cell method on Cartesian grids are compared. In order to understand the characteristics of the two methods, two dimensional steady flow problems are solved. Near-wall pressure and shear stress distributions are investigated in detail. The results show that the cut-cell method is superior to IBM in grid convergence. However, the oscillation of the skin friction coefficient distributions was found in the cut-cell method, whereas IBM gave smooth distributions.