The authors have proposed the A*-EC hybrid path planning method which can generate a 3D flight path quickly considering terrain and obstacle avoidance. This paper proposes two methods to improve its calculation time in order to apply it to a larger scale problem in real time. Using the two methods, the calculation time reduces approximately from half to quarter. The authors measure the calculation times to examine the performance of the improved A*-EC method by changing the number of waypoints and ``nodes'' which are the apexes of the 3D cells expressing terrain and obstacles. Calculation time is about 10—100 seconds in case of 50—100 waypoints and 2000—7500 nodes. The authors apply the method to a large scale problem in which there are 61 waypoints and about 7000 nodes, and actual topological information and recorded weather information are used as obstacles. The simulation result shows the method can be used in real time.
Clear air turbulence (CAT) affecting safety operation of aircraft is one of essential problems when the number of aircraft operations increases and we have to reduce the accident rate. To suppress the dynamic motion of aircraft with high acceleration in turbulence, we consider an optimal preview controller which uses prior information of turbulence measured by a certain air speed sensor such as LIDAR (Light Detection and Ranging). The analysis which simulates the dynamic motion of MuPAL-α in actually observed turbulence shows that the proposed optimal preview controller can reduce the impacts on aircraft motion by turbulence such as 60% reduction of maximum acceleration comparing a controller without prior information. The robustness of the proposed controller to uncertainties is also examined.
A numerical analysis program is created to research effect of heat transfer for propellant flow in Laval nozzle and estimate improvements of thrust and specific impulse. Several types of gases are assumed as propellant. The energy ratio is defined as ratio of energy supplied to propellant by convective heat transfer to enthalpy of propellant at the inlet of nozzle. The energy ratio increases with elongating length of divergent nozzle, and finally becomes maximum value that depends on Prandtl number, propellant temperature and wall temperature at the inlet of nozzle. The conversion efficiency is defined as ratio of energy conversion to kinetic energy with nozzle to energy supplied to propellant. The conversion efficiency increases with elongating of divergent nozzle, and depends on profile of supplied heat.
Research and development of small spacecraft have advanced extensively throughout the world and propulsion devices suitable for the small spacecraft, microthruster, is eagerly anticipated. The authors proposed a microthruster using 1—10-mm-size solid propellant. Small pellets of solid propellant are installed in small combustion chambers and ignited by the irradiation of diode laser beam. This thruster is referred as to a laser ignition microthruster. Solid propellant enables large thrust capability and compact propulsion system. To date theories of a solid-propellant rocket have been well established. However, those theories are for a large-size solid propellant and there are a few theories and experiments for a micro-solid rocket of 1—10mm class. This causes the difficulty of the optimum design of a micro-solid rocket. In this study, we have experimentally investigated the effect of thruster configurations on a laser ignition microthruster. The examined parameters are aperture ratio of the nozzle, length of the combustion chamber, area of the nozzle throat, and divergence angle of the nozzle. Specific impulse dependences on those parameters were evaluated. It was found that large fraction of the uncombusted propellant was the main cause of the degrading performance. Decreasing the orifice diameter in the nozzle with a constant open aperture ratio was an effective method to improve this degradation.