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Much space debris exists in orbit around the Earth. The amount of the space debris increases annually with the disposal of space crafts and collision between pieces of space debris (NASA, 2015). The speed of the space debris at a geosynchronous orbit is approximately 3 km/s, and approximately 7-8 km/s at a low Earth orbit distance. The speed with which space debris impacts the Earth is approximately 10 km/s. Space debris greater than 10 cm across can be observed from the ground, and space crafts are able to avoid collisions with debris of this size. However, space debris under 10 cm across is not able to be observed or avoided. Even these small pieces of space debris colliding with space crafts induce functional loss or destruction because their impact energy is proportional to the square of the debris speed. One example of such a space debris collision occurred to an artificial satellite in 2009 (NASA, 2009). Therefore, countermeasures addressing space debris collisions are an important focus for the future of space development. In 2009, a high-speed impact experiment was performed on aluminum foam to develop a debris shield that could defend spacecraft against space debris (Ryan et al., 2009). In this experiment, a uniquely shaped crater was formed around the impact point. The crater had a narrow entrance and then a large internal cavity, like a turnip. Figure 1 shows the cross section of such a turnip-shaped crater, where the red line outlines the shape of the crater. Traces of compaction and melting were confirmed on the surface of this crater: the compaction was caused by the spreading of the debris cloud, and the melting was caused by the high-speed impact. However, it is very difficult to measure the temperature at the Abstract It has been reported that when a high-speed projectile collides with aluminum foam, a unique crater with a narrow entrance and large cavity is formed, shaped like a turnip. In the case of a material with higher porosity, it is considered that a debris cloud is produced by the impact, and the crater is created by scattering the debris cloud inside of the target material. In addition, melting traces have been observed, and it is predicted that these are caused by the heat created by the impact. It is conceivable that the temperature of a plasma induced by highspeed impact is associated to indicate the temperature at impact, although this relationship has not yet been proven. Measuring temperature at impact point is difficult since the measuring device will have to avoid collision with the projectile. Therefore, it is essential to measure plasma apart from impact point and observe diffusion of plasma. In this paper, high-speed impact experiments in which plasma was measured with a triple probe and a high-speed camera was performed to confirm the above. The high-speed impact experiment was performed with a vertical gas gun at Ritsumeikan University’s Impact Engineering Laboratory. The impact speed was 400 m/s,

Measurement of plasma for elucidation of crater formation mechanism on aluminum foam under high speed impact