Spacecraft charging occurs in space environment. There are two types of spacecraft charging. “Surface Charging” and “Internal Charging.” The former has been investigated for about 30 years. Until now, however, the latter has not been studied deeply enough and, as far as we know, measurement of internal charging in the spacecraft has not been made yet. Under these circumstances, we tried to develop equipment for measurement of internal charging in space environment, applying PIPWP (Piezo-electric Induced Pressure Wave Propagation) method, which enables us to measure electric charge distribution in dielectrics. The equipment was designed smaller and lighter in order to be able to be installed into spacecraft. The specific feature of this equipment is that it is capable of measuring charge distribution continuously in real-time. Using the equipment, we succeeded in measuring charge distribution in PMMA (Poly Methyl Methacrylate) film during and after electron beam irradiation and, we could obtain basis data to proceed to spacecraft borne equipment.
Three kinds of carbon fibers-reinforced carbon matrix (C/C)-SiC functionally graded materials (FGM) chambers were cyclically tested using the bipropellant of nitrogen tetroxide (NTO)/monomethyl hydrazine (MMH) to evaluate the durability on life aiming for use in future reusable reaction control system (RCS) engines. The SiC/C FGM was applied to the layer between SiC and C/C base material in order to relax the difference in the thermal expansion of the two materials. The coating damage modes were inspected after each of the chamber dulability tests. On the first developed chamber, it has been found that the great damage was observed at contraction surface, and unexpectably, the damage was prematurely increased at near the impingement point, which showed the most low heat load, of the film cooling. On the second developed chamber, it also has been found that the damage especially at throat section was observed after 500 cycles of combustion. In the third developed chamber which was applied both of the 8-harness satin fabrics arrangement of the fibers and 40 μm FGM layer/C-SiC matrix, the damage seemed to be decreased compared with that of the first/second chambers.
The behavior of exhausted plasma from ion thruster in the near earth orbit was analyzed to find its influence on the earth's environment. It was found by the analysis of the motion of beam plasma using PIC method that the quasineutral state of the exhausted plasma was broken and the charge separation occurred soon after their exhaust because their density much decreases by the beam divergence and the electric field in the plasma can not keep the electrons to stay in the plasma. So, the ions will be trapped by the geomagnetic field for a long period. It was also found by the analysis using the plasma density distribution model and the ion thruster mission analysis model that the plasma components density distribution near the earth will change by the energy input of these trapped ions if the large scale operation of ion thruster is performed.
In order to analyze dynamics of space systems, such as cluster satellite systems and the capturing process of damaged satellites, it is necessary to consider such space systems as reconfigurable multibody systems. In this paper, we discuss the numerical computation of the dynamics of the ground experiment system to simulate the capturing and berthing process of a satellite by a dual-manipulator on the flat floor as an example. We have previously discussed the efficient dynamics algorithm for reconfigurable multibody system with topological changes. However, the contact dynamics, which is one of the most difficult issues on our study, remains to be discussed. We introduce two types of the linear complementarity problem (LCP) concerned with contact dynamics. The difference between two types of the LCP is whether impacts can be considered. Dynamics systems with impacts and friction are non-conservation systems, moreover the LCP is not always solvable. Therefore we must check if the solutions of the numerical computation are correct, or how accurate those are. In this paper, we derive the method of numerical computation with guaranteed accuracy of the LCP for contact dynamics.
A fundamental strategy for libration control of tethered systems in elliptic orbits is developed. Periodic libration, which is of the same period as orbital period, is shown to be proper as the cotrol objective of libration of tethered systems in elliptic orbits. Periodic control to accelerate or decelerate librations at certain points in orbit is shown as the basic control, which leads libration to be asymptotically stable to converge on the periodic libration. Libration controls by tether length rate and on-board thruster are formulated based on this fundamental strategy, and its validity is shown through numerical simulations.