The uncontrolled reentry of space object is one of the serious problems that the space agencies face. This paper presents a new reentry prediction method which estimates the reentry time and point using multiple sets of orbital elements and an error-propagation model. In the low-altitude orbit, the dominant perturbing force is air drag. Analyzing how the air drag affects the accuracy of the orbit propagation, we constructed an error-propagation model. Combining the multiple orbital elements with this model, this method estimates the optimal air drag and predicts a reentry time accurately. To demonstrate the performance of this method, a reentry prediction experiment was conducted. The experimental prediction took an example of the H-II Rocket 2nd Body that actually reentered on 27 January, 1999. Results show that the method can provide accurate predictions of reentry.

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Quasi-steady MPD (Magnetoplasmadynamic) arcjet PF-series were developed to understand the cathode jet structures, i.e., to mainly understand pumping acceleration processes of an MPD thruster. The ring anode of PF arcjets is located downstream from the cathode enough to generate a high axial current. Spatial current distribution, electron temperature and electron number density were measured in order to examine the plasma features in the cathode jet region. They were sensitive to the gas species and the anode radius of PF arcjets. Especially, a high-energy region was formed along the center axis of the PF-II arcjet with H2. The current distribution on the cathode cone and the pressure at the cathode tip were also measured with a divided cathode and pressure tap, respectively. Current fractions entering an inner cathode rod at large discharge currents were hardly dependent on gas species and the anode radius of PF arcjets. The pressure at the cathode tip of the PF-II arcjet was good agreement with the JJ²-dependence curve derived from the electromagnetic acceleration theory.

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An in-situ observation of small planetary bodies (asteroids or comets) has been of great interest for planetary science. The authors have proposed a small rover for MUSES-C asteroid exploration mission of the Institute of Space and Astronautical Science. The proposed rover adopts a novel and innovative mobility that drives a rover by hopping, which has a lot of advantages under the micro-gravity environment on the surface of small planetary bodies. A test model of the proposed rover was developed and the micro-gravity experiments were conducted. This paper describes the experimental results, which are compared with the simulation analysis.

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Lifetime is one of the urgent problems in ion thrusters. In these circumstances, most of the ion thruster researches have been focused on lifetime problems. In practice, performing actual lifetime tests requires devastating time and money, computer simulation is a powerful tool which enables parametric study for various operating conditions and grid geometries. The paper presents efficient two-dimensional and three-dimensional optics codes which have been developed to analyze life-limiting mechanisms of ion thruster optics such as grid structural failure and electron backstreaming due to charge-exchange ions. Calculation results showed that the codes predicted grid erosion with good accuracy within a reasonable computation time.

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An in-plane co-location method for geostationary satellites is improved so that it does not need multiple-part maneuvers even when there are various effective cross-section to mass ratios. The relative eccentricity-vectors between the satellites are controlled as if repulsive interaction with frictional force were applied to the terminal points of the vectors in the eccentricity-vector space. Numerical experiments confirm the validity of the improvement in a nine-satellite system,

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