Koji Tanaka

<p>Ejecta from hypervelocity impact includes not only fragments but also luminous vapor cloud with plasma. The plasma (i.e. plasma density) is an important parameter for estimating the risk of discharge on solar array paddle or power harness of spacecraft. We carried out hypervelocity impact experiments using a two-stage light gas gun to analyze luminous vapor cloud and plasma from impacts of the different projectile and target materials. We measured luminous vapor cloud and plasma by using a high-speed video camera and a streak camera spectroscopy, which gives time-resolved spectra and a plasma probe. From the time-resolved spectra, the temperature of the luminous vapor cloud was calculated by fitting the black body radiation from a continuous spectrum of the luminous vapor cloud. Also, we compared and investigated the temporal change of each emission line spectrum from impacts of different target and projectile materials. </p>

<p>New artificial Lagrange points for spacecraft with a tethered anchor are presented in this paper. The positions of conventional artificial Lagrange points generated by solar radiation pressure are restricted depending on the sail lightness number. Using a tethered anchor, that restriction can be relaxed. Around the L2 point, the new artificial Lagrange points for spacecraft with a tethered anchor are derived based on the circular restricted three-body problem. The dependence of the position of the new artificial Lagrange point on the parameters such as mass ratio and tether's length is investigated for spacecraft with a tethered anchor. The trajectories of spacecraft with and without tethered anchors are calculated numerically. Results show that the tethered anchor can halve the offset of artificial Lagrange points. The effect of tethered anchor on the shift of artificial Lagrange point increases if a tether is long and the mass ratio m_anc /m_sc is large.</p>

The technologies for the Solar Power Satellite (SPS) have been well studied on the ground and now it is highly required to make demonstration experiments in space as the next logical step. One of the important subjects to be verified in space is the microwave power transmission pointing at the rectenna site on the ground. It includes verification of high-power microwave power transmission through the ionosphere and demonstration of the retro-directive phase control technology for the microwave beaming. These studies can be conducted by the "Small Satellite" that is currently promoted as one of the near future space programs in Japan. The conceptual study for the demonstration experiment has shown that 1 kW class microwave power transmission experiment at 5.8 GHz in the low earth orbit is worthwhile and feasible under constraints of current concept of the "Small Satellite" program.

Light-weight thin film (plate) structure is expected to play an important role in space development in the near future. Thin film solar array, large planar antenna, inflatable structure, and Solar Power Satellite (SPS) are the typical examples. We have carried out hypervelocity impact experiments on thin materials using the railgun accelerator at the Institute of Space and Astronautical Science, with the aim of clarification of the process of the plasma generation in case of the thin target. In our experiments, the velocity of the projectile is around 4.5 km/s. Copper (Cu), Aluminum (Al) and Silver (Ag) were used as the thin plate targets. Propagation of the impact-generated plasma was observed by a high-speed video camera and plasma probes. In the front side of the target, a spherical-shape plasma was observed, which propagated near the same velocity as the projectile. On the other hand, the impact-generated plasma propagating along the surface of the target was observed in the rear side. In particular, the plasma propagating along the plate surface in the rear side is practically important in the design of solar array paddle.