牧 謙一郎

Martian Moons eXploration (MMX) is a mission to Martian moons under development in JAXA with international partners to be launched in 2024. This paper introduces the system definition and the latest status of MMX program. “How was water delivered to rocky planets and enabled the habitability of the solar system?” This is the key question to which MMX is going to answer in the context of our minor body exploration strategy preceded by Hayabusa and Hayabusa2. Solar system formation theories suggest that small bodies as comets and asteroids were delivery capsules of water, volatiles, organic compounds etc. from outside of the snow line to entitle the rocky planet region to be habitable. Mars was at the gateway position to witness the process, which naturally leads us to explore two Martian moons, Phobos and Deimos, to answer to the key question. The goal of MMX is to reveal the origin of the Martian moons, and then to make a progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer-part of the early solar system. The mission is to survey two Martian moons, and return samples from one of them, Phobos. In view of the launch in 2024, the phase-A study was completed in February, 2020. The mission definition, mission scenario, system definition, critical technologies and programmatic framework are introduced int this paper.

A solar power satellite (SPS) is a renewable energy system that converts the sun's energy into electricity in space and transmits it to Earth using microwaves. The SPS concept, first proposed in 1968 in the United States, has recently started attracting increased public attention as a promising energy system that can be used to resolve global environmental and energy problems. One of the most challenging technologies for the SPS is microwave power transmission from the geostationary orbit to the ground. The technologies for microwave power transmission have been studied for more than 40 years since the initial demonstrations in the 1960s; however, for SPS application, considerable research, especially on high-efficiency power conversion between direct current (dc) and radio frequency (RF) and on high-accuracy microwave beam control over a long range, is still needed. This paper introduces the concept of SPS and presents the technologies and issues associated with microwave power transmission from space to ground. Current research status and the future development prospects for microwave power transmission toward commercial SPS use are also described.

We are developing a phased-array antenna system as a bread board model (BBM) for space experiments using a small scientific satellite toward the solar power satellite (SPS). The purposes of the space experiments are to demonstrate a precise directional control of wireless power transmission (WPT) technology from space to the ground and to clarify the propagation characteristics of the microwave power in the ionosphere. A phased-array antenna possesses a potential for precise beam directional control and beam forming by controlling an amplitude and phase of the microwave from each antenna element. We designed and fabricated the BBM in order to evaluate an effect of amplitude and phase error of the microwave circuits produced at the time of the manufacturing and generated by temperature fluctuation on the microwave beam control. Copyright © 2013 by the International Astronautical Federation. All rights reserved.

The commercial life of Solar Power Satellite (SPS) is usually considered to be 30-40 years. However the disposal plan after expiration of its life has not been well studied so far. This paper describes the life analysis of SPS by evaluating the radiation and debris (meteoroid) environment, and proposes a replacement scenario at the end of life to prevent generating space junk. The SPS basic model (tethered-SPS) is used for this study. If we set an allowable degradation level at 15-20 % for the commercial life 5-10 % by radiation degradation, 5 % by hyper-velocity impact loss, and 5% by spontaneous electrical failure, 40 years life is expected in the following assumptions (1) photovoltaic cells with high radiation-resistance (5-10 % degradation at 2.5 × 1015/cm2 (1 MeV electron equivalent fluences)), (2) redundant tether wires (tape tether) of more than 15 mm wide, and (3) modularized structure for the power generation/transmission panel with a module size of 0.5m × 0.5m, beyond that the impact damage does not propagate. In the end of life scenario, new units of SPS are transported to the geostationary orbit from the ground and are exchanged for degraded units, and then the degraded units are transported to the ground for refurbishment. The replacement operation starts near the end of life and is completed in a year in the same way as the initial construction. The replacement operation does not generate any junk in the orbit. This scenario is heavily dependent on the space transportation system between the ground and the orbit, consisting of reusable launch vehicle (RLV) and orbit transfer vehicle (OTV). Copyright © 2013 by the International Astronautical Federation. All rights reserved.

A terahertz (THz) beam steering method is demonstrated by applying the characteristic of grating lobe (GL) radiation from a linear array antenna and the interference of femtosecond optical pulses. A photoconductive device is illuminated by two femtosecond laser beams combined at an angle of less than 0.5 degrees. Considering the interference pattern as a THz point source array, THz GL radiation is generated through the superposition of radiation emitted from all point sources and steered by varying the interval of the interference pattern. The THz beam direction could be changed by 20 degrees at 0.93THz by varying the relative incidence angle of the pump beams by 0.033 degrees. (C) 2012 Optical Society of America