Pulsed Plasma Thruster (PPT) is one of the promising propulsion devices. It has characteristics which are simple composition, lightweight, and high durability. And small impulse bit can control precisely total impulse. Therefore PPT propulsion system has the advantage for the small, micro- and nano-satellite attitude control. This paper describes the result of the successive firing test 270,000 shots and over 500,000 shots. In experiments we got evaluation of PPT long-term performance trend, the function of feed mechanism, the electrode erosion and the durability.

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Micropropulsion is a key for the future of small spacecraft missions. There are a variety of thrusters including both chemical and electrical systems and each of them has its own advantages and shortcomings. Chemical thruster yields high impulse but low specific thrust. The thermal and pressure management in microscale are reviewed and several our own systems for micropropulsion are introduced.

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Based on a new concept, a low power electrostatic thruster is being developed for its application to 50 kg class satellite, which is named "Microwave Plasma Thruster". The proto-model (PM) of the microwave engine was manufactured and the qualification test (QT) was conducted. The estimated performances operated at 26.6W are 1250 seconds in specific impulse, 0.36mN in thrust and 10% in thrust efficiency, respectively. In future work, we started to research the new microwave engine which is operated at higher power using hydrazine as propellant for applications of geostationary satellites.

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The mainstream of the research and development of satellites in NASDA is for over 1 ton-class satellite. But, 50kg-class Micro satellites and under 10kg-class Nano satellites are researched, too. "μ-Lab Sat" -the first Micro satellite in NASDA- is planning to launch in 2002. The orbit of this satellite is LEO (low earth orbit) and the attitude of this satellite is the spin stabilization mainly, and the three-axis stabilization in the experiment. "μ-Lab Sat 2"-the next micro satellite in NASDA, is under conceptual study. It has 30kg-class mother ship satellite and 5〜10kg-class daughter-ship satellites. The orbit of this satellite is GTO (geostationary transfer orbit) and the attitude of mother ship satellite is the three-axis stabilization. Daughter-ship satellites will be formation flying in the experiment. The formation flying is the key technique for the interferometer.

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A MEMS (micro-electromechanical system) is batch-produced by micromachining based on semiconductor integrated circuit fabrication technology. It realizes high speed response, high sensitivity, low power consumption, electric circuit integration and multi-element configuration. A power MEMS is a new MEMS to supply electric power or kinetic power. The most important power MEMS application is an electric power supply replacing batteries in portable devices. Another important application is a micro-thruster for micro-spacecrafts. In future space missions, micro-spacecrafts with weight of less than 10kg will be mainly used, enabling cost reduction, formation flight and redundant system construction. For the miniaturization of spacecrafts, collaboration between space engineers and MEMS engineers is essential. As an example of such collaboration in Japan, the development of a solid propellant rocket array thruster under collaboration between Tohoku University and The Institute of Space and Astronautical Science is introduced.

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Solid-lubricated ball bearings are important mechanical parts for space satellites mechanism. The bearings are exposed to mechanical vibrational environments at launch. In the case, it is concerned about the damage to solid-lubricants of the bearings. Estimates of performances of the bearings exposed vibration are useful for to enhance reliability of satellite mechanisms performance. This reports describes the results of tribological tests in the air and thermal vacuum about ball bearings with a sputterd MoS2 film which were exposed to vibration test.

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Three tribological investigations related to vacuum or micro-gravity are presented in this paper. First, an adhesion phenomenon of clean metal surfaces in ultrahigh vacuum was microscopically analyzed using an AFM and TEM. It was shown that bonding stronger than the bulk strength of the softer metal arose at the real contact area due to diffusion of the mating metals. Second, a new solid lubrication technique called "tribo-coating" was applied to a ball bearing running in vacuum. The bearing showed longer life with low frictional torque compared with the existing Ag-lubricated bearing. Finally, performance of a gyroscope ball bearing in different gravity conditions was numerically investigated using a real-time dynamic simulation cord. It was demonstrated that the frictional torque and the retainer motion were more stable when the bearing operated in OG and in a vertical attitude in 1G compared with a horizontal attitude in 1G.

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Recently, a large side load is observed during start-up and shutdown sequences of Japanese LE-7A rocket engine nozzle. The objective of the present paper is to clarify the mechanism producing the large side loads during start-up process. The unsteady 3-D Navier-Stokes equations are solved for start-up process of three types of nozzle contours. That is, truncated perfect (TP) nozzle, 86% compressed truncated perfect (CTP) nozzle and CTP50-R5-L nozzle. The contour of TP nozzle and the contour of 86% CTP nozzle are LE-7 nozzle and the original LE-7A nozzle respectively. Asymmetric flow fields and large side loads are observed for LE-7A and CTP50-R5-L nozzles. There are two flow patterns which cause the large side loads. The first is the simultaneous occurrence of the Free Shock Separation (FSS) and the Restricted Shock Separation (RSS). The second is the oscillation of Mach disk under the RSS condition.

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This paper describes a method to predict accurate frequencies of structures in component mode synthesis. The current methods cannot necessarily provide accurate frequencies of structures becouse boudary modes obtained by using Guyan reduction are not accurate. A method to find boundary modes using dynamic reduction is proposed for improving frequency prediction accuracy. The proposed method is applied to a truss structure. Numerical example shows the effectiveness of the proposed method.

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In this paper, we study a design method of precise attitude controller of a LSS having problems of elastic oscillation and parameter variation. For the problem, H∞ robust control, μ synthesis or gainscheduling control are known to be efficient. In this study, we apply gainscheduling control to the problem. Although many types of gainsheduling controller have been studied, we adopt an approach based on spline-type parameter-dependent quadratic forms. At first we describe the algorithm of control system design with some extensions. Then we evaluate its perfomance by a numerical simulation for a typical LSS model.

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This study is devoted to investigate slew maneuver of a flexible space structure. The flexible space structure treated in the present study is a rigid body equipped with a flexible aluminum bean, and the control scheme is defined as a method to minimize the bending-moment at the root of the flexible appendage during slew maneuver. The hierarchical gradient algorithm is employed to obtain the optimal control profile. Original of the algorithm can only treat inequality constraints on the state variables, and not on the maximum value of control input. It is necessary in the present problem formulation to take into consideration constraints on the control input since maximum value of control input is naturally limited. This paper proposes a method to improve the hierarchical algorithm so that constraints on the control input can be treated. The method is analyzed numerically to verify the present modified algorithm, and to show that constraints both on the control input and bending-moment are satisfied. The resulting control profile is implemented in an experiment to verify its feasibility. Results of experiments show that bending-moment is effectively reduced in the case that constraint on the maximum value of bending moment is considered.

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A quite lot of satellites and spacecraft are being launched into some limited orbit. There is even fear of collision of each other. From this background, maintenance of orbiting satellite and orbit itself are becoming of high interest. To realize this, some new technologies, such as rendezvous and capture of orbiting satellite, are needed. This paper introduces NASDA's effort in the area of satellite servicing.

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Spaceborne GPS navigation technology is recently studied very actively because it is effective to enhance the autonomy of space vehicles on Low Earth Orbit (LEO). GPS attitude determination uses carrier phase measurements observed at multiple antennas, and especially it contributes to simplification of the GN&C sub-system. The major task of GPS attitude determination is to improve reliability and accuracy. Especially an initial attitude search algorithm, which resolves integer ambiguity of carrier wave length, should not be affected by measurement error. In this paper, we show the algorithm for initial attitude determination by integer search technique. Residuals to be evaluated for initial search are accumulated in order to mitigate the effects of measurement noise. It was proved to be effective by ground field tests. And we evaluated it by aircraft flight experiments, which were conducted in November 2001. Ambiguity solution and attitude can be obtained under dynamic attitude maneuvers.

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Development of an envelope with high specific strength is the critical key technology for the stratospheric platform (SPF) airship. In the Japanese SPF project, several laminate materials for the envelope have been manufactured and tested experimentally. The load bearing layers are made of Zylon (PBO fiber) and Vectran (PA fiber). These fibers are laminated with a gas retention film and protection layers. The tensile strength of lOOkgf/cm with weight about 200gram/m^2 is attained. Test results of coupon strength tests, pressure proof tests of manufactured gas bags and thermal characteristic tests are reported.

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National Space Development Agency of Japan (NASDA) has productively developed space technologies and dedicated itself to space activities for more than thirty years since it was established. In order to conduct much more advanced, productive, and reliable activities, a road map for development of space technology should be established and goals along with it should be achieved. This paper refers to NASDA's strategy in development of space technology as well as introduces its prioritized themes of study and research to enhance both fundamental and cutting-edge technologies. Besides, for enhancement of technological basis, it also refers to possibility of establishing collaboration with The Japan Society of Mechanical Engineers.

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