To elucidate complex flow phenomena in the solid rocket motor (SRM), it is beneficial to reduce development costs by employing computational fluid dynamics simulation, as conducting full-scale model experiments for SRM is expensive. This study focuses on numerically simulating the internal flow in the cylinder simulating the SRM geometry using the Building-Cube Method (BCM). First, the objective of this study is to develop a radial injection flow model (RIF model) for the BCM solver that can be utilized in the numerical simulation of internal flow in the cylinder simulating the SRM geometry. The numerical model geometry is based on the Ariane 5 SRM, which is a 1/30th scale axisymmetric model. The calculation results are validated through comparisons with experimental measurements, demonstrating the effectiveness of the RIF model using the immersed boundary method for accurate internal flow simulations of cylinder simulating the SRM geometry. Next, the effect of differences in wall injection conditions on the internal flow field of the cylinder simulating a solid rocket motor geometry was investigated using the BCM solver. The results indicate that the internal flow field and the vortex structure inside the cylinder simulating a SRM geometry change due to the effect of the injection velocity.

This paper discusses the flow characteristics of nitrous oxide, which is widely used as a self-pressurizing oxidant in small rocket engines, especially focusing on a pressure drop model. In a feed line with a tank pressure of 2.5–5.0 MPa, a flow rate of 200–550 g/s, and a pipe inner diameter of 10 mm, the pipe pressure drop was measured using a differential pressure gauge, the void fraction was measured using a capacitance meter, and visualization was performed using a high-speed camera. From the image obtained with a high-speed camera, many fine bubbles of a diameter of about 100–200 µm were observed in our test cases, resulting in a flow classified as a bubble flow. It was clarified that Dukler’s formula can predict the pressure drop within the mean absolute error of 15%.

Lunar exploration currently requires guidance and navigation based on satellite self-position estimation with an accuracy of 100 m or better to achieve pinpoint landing of spacecraft for scientific survey missions. Various terrain relative navigation methods have been proposed for estimating spacecraft position. For landing small spacecraft on a gravity target, simple and reliable methods are highly desirable due to the limited onboard computing resources available for optical navigation. Position estimation methods based on point pattern matching are promising for this purpose. The lunar landing project “Smart Lander for Investigating Moon” (SLIM) of the Japan Aerospace Exploration Agency (JAXA) plans to use line segment matching, which employs line segments created using the center coordinates of craters, for lander position estimation. Since the original method for the SLIM project may require direction matching to be performed twice for each line segment, the method can be improved by reducing the number of direction matches. In this study, an improved line segment matching method that uses crater size in addition to center coordinates is proposed to reduce the computation time for the original method for SLIM. The usefulness of the proposed method is confirmed by simulations.

This paper outlines the operation result of the reentry terminal guidance phase of the asteroid explorer Hayabusa2. Hayabusa2 successfully returned to Earth after 12 months of the return interplanetary cruise using the ion engine. The last 2 months of the return cruise required accurate trajectory control. In this phase, called the reentry terminal guidance phase, a series of precise trajectory correction maneuvers were performed to accurately guide the spacecraft to fly along a reentry corridor so that the sample return capsule could land within a designated zone in the Woomera desert, Australia. In this paper, the design methodology and operation result of the reentry terminal guidance, focusing on the trajectory guidance aspect, were discussed. The entire reentry terminal guidance operation was successful, and the sample return capsule was precisely guided and landed on the Woomera desert on December 6, 2020, contributing to the perfect success of the Hayabusa2’s asteroid sample-return challenge.

The Asia/Pacific region is recognized as an area of high air transportation growth, which will require increased air traffic management system efficiency. The Free Route Airspace (FRA) concept increases airspace user flexibility by allowing flight planning without reference to air traffic service routes. This enables more efficient flight plans and increases predictability by reducing the discrepancy between planned and flown trajectories. We propose introducing the FRA concept to the Incheon and Fukuoka Flight Information Regions, targeting a major international air traffic flow between Korea and North America. After analyzing the characteristics of the flow, we present the initial airspace design and concepts of operation. We estimate potential efficiency gains, and compare the air traffic complexity of the proposed FRA and the existing airspace. In addition to the EUROCONTROL complexity metric, a new complexity metric called “Hot Cell Ratio” is introduced to better represent complexity that arises from geographically dispersed traffic. The results show that there are potential flight plan distance reductions from FRA comparable to European targets, but the benefit is reduced by training and restricted-use airspaces. However, traffic complexity is not notably changed by FRA implementation.