Ginga observations of Seyfert galaxies

We observed twenty-eight Seyfert 2 galaxies with the Japanese X-ray satellite, Ginga, and found Seyfert 2 galaxies, in general, have the X-ray spectral characteristics of obscured Seyfert 1 nuclei. This result agrees with the predictions from Unified Seyfert model proposed by Antonucci and Miller /1/. However, among the observed Seyfert 2 galaxies, there are a few galaxies with no evidence of an obscuration, contrary to the general predictions of the unified model. We note that type 2 AGN will contribute to the Cosmic Diffuse X-ray Background, if the unified Seyfert model can be extended to the far distant AGN such as quasars.     

Oxygen line mapping of SN 1006 with Suzaku

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region.     

Deriving the Absolute Reflectance of Lunar Surface Using SELENE (Kaguya) Multiband Imager Data

The absolute reflectance of the Moon has long been debated because it has been suggested (Hillier et al. in Icarus 151:205–225, 1999) that there is a large discrepancy between the absolute reflectance of the Moon derived from Earth-based telescopic data and that derived from remote-sensing data which are calibrated using laboratory-measured reflectance spectra of Apollo 16 bulk soil 62231. Here we derive the absolute reflectance of the lunar surface using spectral data newly acquired by SELENE (Kaguya) Multiband Imager and Spectral Profiler. The results indicate that the reflectance of the Apollo 16 standard site, which has been widely used as an optical standard in previous Earth-based telescopic and remote-sensing observations derived by Multiband Imager, is 47% at 415 nm and 67% to 76% at 750 to 1550 nm of the value for the Apollo 16 mature soil measured in an Earth-based laboratory. The data also suggest that roughly 60% of the difference is caused by the difference in soil composition and/or maturity between the 62231 sampling site and the Apollo 16 standard site and that the remaining 40% difference can be explained by the difference between the compaction states of the laboratory and the actual lunar surface. Consideration of the compaction states of the surface soil demonstrates its importance for understanding the spectral characteristics of the lunar surface. We also explain and evaluate data analysis procedures to derive reflectance from Multiband Imager data.     

The effect of neglecting VLBI reference station clock offsets on UT1 estimates

Very Long Baseline Interferometry (VLBI) allows to monitor universal time (UT1) by conducting regular international experiments. Such dedicated observation networks are equipped with different hardware components, which require different processing strategies when the data are correlated. As the timing units at each stations are usually offset with respect to universal time (UTC) this effect should be considered during correlation processing. Thus, it is investigated how neglecting of these offsets theoretically impacts the estimation of UT1. Three different strategies for the proper handling of the timing offset will be discussed and their advantages/drawbacks will be pointed out. Moreover, it is studied how neglecting of these timing offsets affects UT1 time-series and how such a missing correction can be applied a posteriori. Although the discussed effect is for most of the UT1 experiments smaller than the formal error of the estimates, it is important to consider station clock offsets properly in next-generation VLBI systems, which are expected to improve accuracy of results by about one order of magnitude.     

Increasing Frequency Spectrum Utilization in Mobile Systems

In mobile radio communication systems, one of the most significant problems is to use the radio frequency spectrum as efficiently as possible, because the radio frequency spectrum is finite. This paper classifies a variety of techniques for increasing frequency spectrum utilization. Next, it is clarified that our proposed ``new channel assignment algorithm' is more efficient than other algorithms through simulation analysis.     

Concept study on Deep Space Orbit Transfer Vehicle

In this paper, the concept of Orbit Transfer Vehicle for Deep Space Exploration (Deep Space OTV) is proposed, and its effectiveness and feasibility are discussed. Basic concept is the separation of two functions required for the deep space exploration, the transportation to the destination, and the exploration at the destination. Deep Space OTV is a spacecraft specialized for the transportation to the deep space destination. It is an expendable spacecraft propelled by solar electric propulsion. The payload of Deep Space OTV is Explorer, which is a spacecraft specialized for the exploration at the deep space destination. The effectiveness of the concept is discussed qualitatively, focused on the merits of the separations of two functions. The feasibility of Deep Space OTV is discussed based on the conceptual design of the spacecraft and its applicability to deep space missions. Several deep space missions are modeled and the payload capacity of Deep Space OTV is estimated. The missions include Asteroid rendezvous, Mars orbiter, Lunar lander, and so on.     

Structure and thermal control of panel extension satellite (PETSAT)

Panel ExTension SATellite (PETSAT) [S. Nakasuka, Y. Nakamura, Panel extension satellite (PETSAT)—a novel satellite concept consisting of modular, functional and plug-in panels, in: 24th International Symposium on Space Technology and Science, invited talk, 2004-o-2, 2004 [1]] is a satellite which is made of several “functional panels”. Each panel has a special dedicated function and various combinations of different kinds of functional panels enable PETSAT to deal with various mission requirement. Development of PETSAT requires four interface requirements. These are mechanical interface, thermal interface, electrical interface and information interface. In this paper, mechanical interface and thermal interface of PETSAT are especially focused on and introduced. In the development of PETSAT issues about mechanical interface corresponds to panel structure and deployment mechanism. The structure of PETSAT is designed so as to have light weigh, enough space for devices and high stiffness. And deployment system has simple mechanism to avoid vacuum metalizing and improve reliability. On the other hand, approaches for thermal interface [K. Higashi, S. Nakasuka, Y. Sugawara, H. Sahara, K. Koyama, C. Kobayashi, T. Okada, Thermal control of panel extension satellite (PETSAT), in: 25th International Symposium on Space Technology and Science, 2006-j-02, 2006 [2]] are homogenization of temperature within panel and between panels. Homogenization of temperature within panels can be realized by heat lane plate, and that between panels is realized by magnetic fluid loop with magnetic heat pump. These approaches for mechanical and thermal interface are demonstrated in SOHLA-2 [Y. Sugawara, S. Nakasuka, T. Eishima, H. Sahara, Y. Nakamura, K. Koyama, C. Kobayashi, T. Okada, Elemental technologies for realization of panel extension satellite (PETSAT), in: 25th International Symposium on Space Technology and Science, 2006-J-01, 2006 [3]] that is satellite of technology demonstration for PETSAT.     

Optimization of fault-tolerant thruster configurations for satellite control

The fault tolerance of spacecraft actuators significantly affects the reliability of satellites and the likelihood of successful missions. To enhance the fault tolerance of the actuators, this study derives optimal fault-tolerant configurations of fixed thrusters that maximize the controllability of a fully-actuated or underactuated satellite. The proposed method optimizes thrust and torque directions generated by the thrusters. Thus a cost function in terms of the thruster locations and directions is defined as the summation of the generated control forces and torques with respect to the body-fixed frame. The optimal configuration is obtained by the successive use of an energy potential method that is motivated by Thomson’s problem. Some numerical examples are provided that show the effectiveness of the proposed formulation and optimization method.     

Lunar apex–antapex cratering asymmetry as an impactor recorder in the Earth–Moon system

The degree of apex–antapex cratering asymmetry of a synchronously rotating satellite primarily depends on the mean encounter velocity of impactors with respect to the planetary system and the orbital velocity of the satellite. This means that we can estimate the mean encounter velocity of impactors by observing the apex–antapex cratering asymmetry, if the relationship between these is known. To apply this technique to the Moon, we attempt to derive the relationship between the mean encounter velocity of impactors and the degree of the lunar cratering asymmetry as a function of time, considering the temporal variation in the lunar orbital velocity during the last 4.0 Gyr. We used the cratering asymmetry of Zahnle et al. [Zahnle, K., Schenk, P., Sobieszczyk, S. et al. Differential cratering of synchronously rotating satellites by ecliptic comets. Icarus 153, 111–129, 2001] to obtain the relationship. Applying this relationship enables us to estimate the impactor’s velocity of the Earth–Moon system from an investigation of the spatial distribution of lunar craters. Furthermore, we re-evaluate the cratering asymmetry’s influence on lunar cratering chronology.