Takao Koura’s research while affiliated with Kyushu Institute of Technology and other places

Solid rocket motors are mainly used for launching small satellites because they have a small number of parts, simple structures, and high responsiveness. However, there are concerns about solid rocket motors, which release solid rocket motor slag (SRM slag). The SRM slag is derived from aluminum powder in a solid matrix and released as agglomerated alumina into outer space before and after the solid rocket motor is cutoff. It has been confirmed that voids inside themselves in combustion tests in a vacuum conducted by JAXA. In this paper focusing on SRM slag with voids, we simulated its impact with diameters ranging from 1 mm to 10 mm, with porosities ranging from 0 % to 80 %, and with impact velocities of 2-15 km/s towards enough thick targets. We investigated the potential danger of SRM slag with voids using AUTODYN-2D. In addition, we calculated the ballistic limit curve (BLC) for each porosity of SRM slag based on the penetration depths obtained by the numerical simulations and compared BLCs in SRM slag and space debris made of aluminum alloy.

Potentially dangerous asteroids (PHAs) are asteroids that have orbits approaching the Earth and are a threat to humankind. Among them, Apophis and Bennu have been attracting attention in recent years. It is necessary to prevent PHAs from impacting the Earth, so this study focuses on asteroid deflection by hypervelocity impact as an impact avoidance. In this method, a projectile such as a spacecraft is impacted into a PHA at hypervelocity and its orbit will be changed. This method is considered to be the best method because it can achieve asteroid deflection instantaneously and it will cause less secondary disasters by asteroid split.

One of the promising ways to remove space debris is to attach an electrodynamic tether (EDT) to debris by shooting a harpoon from an active debris removal satellite. There is a possibility for the harpoon to be removed from the surface of debris because of the tensile load of the EDT. The purpose of this research is to evaluate the pull-out force in a novel harpoon designed for the debris capturing system. This new harpoon with a barb is composed of an inner harpoon and an outer harpoon. After the penetration, the outer harpoon is deformed by the inner harpoon and so creates a barb on the tip. Harpoon shooting tests were conducted using a debris capture gun in order to study the impact of the harpoon into the aluminum alloy plate. After firing tests, pull-out tests were conducted by the universal tensile testing machine. During these tests, the harpoon was deformed after the penetration and opened a barb on the tip so the function of barb system could be confirmed. Moreover, the maximum pull-out load the harpoon can handle without being separated from the plate is measured. For some harpoons with the barb system, pull-out load was superior to the non-barb systems. In this way, the efficiency of this design of harpoon is proved, with a maximum loading of 7000 to 16000 N.

Near Earth Objects (NEOs) are asteroids and comets which come close to Earth’s orbit each year. So there is a high possibility of impacts for example, in February 2013, an asteroid created an airburst near Chelyabinsk State in Russia, causing an estimated damage of approximately 33M$ and injuring an estimated damage of approximately 1500 people. To avoid asteroid impacts it is necessary to change NEO’s orbit. Impacting at a hypervelocity is one of the methods that we consider to change NEO’s orbits. Hypervelocity impacts intend to change the orbit by making a spacecraft impacts on the NEO. In our study we examined the orbit change induced by hypervelocity impacts and explosives to further improve the effect. The influence on the orbit by explosives depends on the shape of the crater created by an impactor. Thus we will optimize its shape by making impact tests with a Two Stage Light Gas Gun in order to accelerate impactors with different shapes. As a result, we analyzed of the influence by explosive with AUTODYN from the shape of craters obtained by the experiment and we found that the shape of crater has an optimum condition.

At present, Space debris have a lot of problems in the space industry. They are the crush to spacecrafts and making the restriction of orbit in space. ISO 112227 was enacted in 2012 as a measure against microscopic secondary Space debris called Ejecta among space debris. However, this protocol did not take into account oblique impacts of projectiles, and a draft revision is made for the purpose of implementing oblique impact experiments. In this research, as a verification of the revision proposal, a 1 mm diameter projectile simulating micro debris is collided with a two-stage light gas gun at a speed of 5 km.s⁻¹ using a target of A2024-T3, usually used as a spacecraft material. The impact angles are 0 (vertical impact), 45, 60 and 75 degrees. About the evaluation method, it is based on the generation amount of Ejecta and its distribution throughout impact marks. Since the target is a ductile body, the amount of Ejecta generated is small, and so it is difficult to calculate accurate ejecta mass at 60 and 75 degrees. Since the angle also increases the distribution of impact marks, scavenging of Ejecta is insufficient. In order to solve this problem, the way of collecting Ejecta is reviewed in oblique impact experiments.

To reduce fuel consumption on airplanes, we need nowadays lighter materials which absolutely need to withstand bird strikes. CFRP (Carbon fiber reinforced plastic) is one of the best materials for this, considering its high strength modulus and low density, but still lacks impact resistance. In this study, we simulated a fragment of aircraft impacting on a fan case in order to develop a CFRP with a better strength and impact resistance than conventional CFRP. For this experiment, we used the gas gun installed in our laboratory, and a rigid rectangle projectile as an impactor. Then, we compared our new lamination structure with conventional CFRP according to the amount of absorbed energy and to the delamination area (internal separation of layers). The amount of energy is obtained by the difference of energy before and after the impact, and the higher the energy absorbed, the more resistant the material is. In the case of the delaminationarea, the smaller it is, the lower the damages are. In new CFRP (called E2-E), the conventional [45, -45] degree layer is changed to a [30, -30] degree layer and a 0 degree layer is added between the 30 and -30 layers. The conventional lamination structure is [(0/45/-45/0)3(45/-45)(0/-45/45/0)3], and the E2-E’s lamination structure is [(0/30/0/-30/0)2(30/0/-30)2]s. As a result, for the same amount of energy the CFRP E2-E was not penetrated unlike conventional CFRP. Moreover, the absorbed enegy was higher and the delamination area was smaller, which means the E2-E materialshowed better performances than coventional CFRP.

NEO (Near Earth Object) are the celestial bodies which pass near the Earth. One NEO deflection method is spacecraft impact. In order to estimate its results, it is necessary to clarify mechanism of momentum change of NEO. Generally, β is used as an evaluation index in this field and affected by various factors, so this study focuses on spacecraft shape. Five types of projectile shape were tested and compared in term of two aspects. In addition, we made comparison by using scaling law in order to compare the shape effect in the speed region which is assumed to using actual NEO deflection.