This paper considers estimating wind using only the data of an inertial measurement unit without using any information from an air-data sensor and model parameters by estimating stability derivatives of a lateral-directional motion model of an aircraft. Assuming that the wind is constant, the relation between wind and stability derivatives, which allows the wind to be calculated, can be derived. An advantage of this method is that the estimated wind is relatively insensitive to the estimation error of the derivatives. The authors illustrate the effectiveness of the proposed method by simulation using NASA’s Generic Transport Model.

The effects of a wing dihedral on sonic boom reduction are systematically studied for a realistic supersonic transport. The LM1021, which was designed in detail by Lockheed Martin Corporation (U.S.A.), is used as the baseline analysis model. The aerodynamic coefficients and near-field pressure signatures are obtained using CFD for inviscid flows, and then the sonic boom intensity on the ground is calculated with the pressure wave propagation analysis by solving the augmented Burger's equation. The ‘Xnoise’ code developed by JAXA is used for the wave propagation analysis. The results clearly show a reduction in the sonic boom intensity not only on the undertrack, but also on the off-track. One representative result is that the pressure peak of the tail boom at the flight Mach number of 1.6 is reduced more than 15% by a 10-deg dihedral compared to a 0-deg dihedral at the cost of a 2% increase in drag. Variations of the lateral/directional static stability are also studied, and the results show improved lateral stability while there are mild directional instabilities caused by the dihedral.

Image-based terrain-relative localization is expected to play an important role in precision navigation in various small-body missions. In the Hayabusa2 mission, accurate navigation was achieved by manual matching between the asteroid image and a set of vertices of a shape model of the target body, called a “point cloud.” The manual process intentionally excludes invisible regions and adopts visible parts for matching. In this paper, an autonomous optical localization using the point cloud, which will take the place of the manually matching process, is proposed. The proposed method performs matching with the asteroid rims derived from the captured image and point cloud, respectively. Furthermore, the proposed method allows selecting the area used for matching by adding 1-bit information, representing the visible or invisible flag, to the point cloud. The proposed method has achieved the position estimation accuracy of 0.23 [px] (1σ) in simulations with various shading conditions. This paper applies the proposed method to the Hayabusa2 flight data and shows that the proposed method bears comparison with the Hayabusa2 team estimation results.

When a spacecraft fires its thrusters near the surface of a celestial body, objects on the surface of the body are scattered in the vertical direction and adhere to the cameras and ranging instruments mounted on the spacecraft, degrading their performance. In order to establish a future spacecraft design theory that is less sensitive to the scattering of surface objects, we first investigate the scattering factors and scattering tendencies of surface objects. We predict that celestial surface objects are scattered according to the wall angle of the crater created by the thruster plume. The relationship between the crater shape and the object dispersal angle is not fully understood. Mechanisms of crater formation include viscous erosion, which creates craters with a small wall angle, and bearing capacity failure, which creates craters with a large wall angle. Here, we experimentally clarify the transition point between the two crater formation mechanisms when the thruster plume penetrates soil with various shear strength values. We find that the objects disperse along the crater wall for both mechanisms. Based on the results, we examine measures for preventing the spacecraft from being hit by scattered surface objects.

A super-pressure balloon (SPB) is expected to provide cost-effective platforms for long-duration experiments in the stratosphere. The authors propose a new method to produce a light SPB, where the entire balloon envelope is covered by a diamond-shaped net; thereby effectively suppressing the stresses developed in the balloon envelope. The feasibility of the method was validated in 2010 through a ground inflation test using a prototype balloon. The development of the proposed SPB has progressed since then, involving the ground inflation test of a ∼6,000 m³ model balloon and the test flight of a ∼2,000 m³ balloon. Meanwhile, it has been realized that the inflated shape of the proposed SPB varies largely depending on the geometrical parameters of the cover net. The unique feature of the proposed SPB suggests that the optimal geometrical configuration of the cover net exists in that it maximizes the structural efficiency of the balloon. In this paper, the authors investigate the variation of the volume-to-weight ratio of the proposed SPB against the geometrical parameters of the cover net. The results show that the balloon volume will increase by a factor of three compared to that achieved by the current design practice without changing the balloon weight.

The escalating presence of space debris is becoming increasingly problematic due to the ensuing potential of damage to active spacecraft if a collision were to occur. The tether net has emerged as a possible solution for the capture of such debris. Although extensive studies have been conducted on the net's performance, the influence of initial debris velocity and net ejection on the tether net's interaction with and capture of debris has not been confirmed. The primary aim of this study is to investigate the net's behavior when it interacts with space debris moving at a range of velocities. The objective is to ascertain the permissible initial relative speed of the net necessary to facilitate successful contact and subsequent capture of the debris. This determination takes into account the initial velocities of both the ejection of the net and the debris. The results reveal that successful interaction between the net and the debris is influenced by several variables. These include the initial velocity of the debris relative to the net ejection system, the furthest distance from the net to the ejection system when the net commences contraction, the speed at which the net is ejected, and the direction of debris motion.