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.     

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.     

Early development of Xenopus embryos is affected by simulated gravity.

Early amphibian (Xenopus laevis) development under clinostat-simulated weightlessness and centrifuge-simulated hypergravity was studied. The results revealed significant effects on (i) "morphological patterning" such as the cleavage furrow pattern in the vegetal hemisphere at the eight-cell stage and the shape of the dorsal lip in early gastrulae and (ii) "the timing of embryonic events" such as the third cleavage furrow completion and the dorsal lip appearance. Substantial variations in sensitivity to simulated force fields were observed, which should be considered in interpreting spaceflight data.     

Solar power sail membrane prototype for OKEANOS mission

This paper reports on the manufacturing and evaluation of a solar power sail membrane prototype for the OKEANOS project. The in-house prototype was built by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. Mechanical and electrical evaluation tests were conducted. The membrane, thin-film solar cells, reflectivity control devices were good condition after the manufacturing and handling. The improvements in the manufacturing process and design were found. The manufacturing process and design were fundamentally established. After the prototype, improvement plans for the manufacturing process and design were tried. We have a prospect of manufacturing the flight model sail and continue to the development.     

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.     

A balloon-borne very long baseline interferometry experiment in the stratosphere: Systems design and developments

The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20?GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage (“uv-coverage”) by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging.     

Night side lunar surface potential in the Earth’s magnetosphere

In the Earth’s magnetotail, Japanese Moon orbiter Kaguya repeatedly encountered the plasmoid or plasma sheet. The encounters were characterized by the low energy ion signatures including lobe cold ions, cold ion acceleration in the plasma sheet-lobe boundaries, and hot plasma sheet ions or fast flowing ions associated with plasmoids. Different from the previous observations made in the magnetotail by the GEOTAIL spacecraft, the ions were affected by the existence of the Moon. On the dayside of the Moon, tailward flowing cold ions and their acceleration were observed. However, on the night side, tailward flowing cold ions could not be observed since the Moon blocked them. In stead, ion acceleration by the spacecraft potential and the electron beam accelerated by the potential difference between lunar surface and spacecraft were simultaneously observed. These electron and ion data enabled us to determine the night side lunar surface potential and spacecraft potential only from the observed data for the first time.