Katsuto Kisara

Feasibility Study of FGM Technology in Space Solar Power Systems (SSPS)

In this paper, we introduce research and development in SSPS (aimed at global energy supply) in Japan. To build SSPS, we must develop ultra lightweight materials and high efficiency energy conversion materials. Feasibility of adapting FGM concept for those new demands and advanced research theme for future FGM research are also introduced in this paper.

Wide field-of-view single-mode-fiber coupled laser communication terminal

This paper describes the design of a wide field-of-view single-mode-fiber coupled free space laser communication terminal which has mutual beacon tracking system using a commercially available fast steering mirror. Using the terminals, we tried a low power laser beam transmission experiment over 500-m distance using a 1064 nm wavelength. This paper also reports the experimental results of terminal performance as well as propagation characteristics.

Structural design of laser-photovoltaic power converter

As part of research and development into the Laser Based Space Solar Power System (L-SSPS), a laser-photovoltaic power converter for 1.07 μm laser light has been researched at the Japan Aerospace Exploration Agency (JAXA). To improve conversion efficiency of the InGaAs laser-photovoltaic power converter, photovoltaic properties under 1.07 μm laser illumination were calculated in this study with varying the structural parameters such as In/Ga ratio, layer thickness, p/n-junction depth and carrier concentration of the InGaAs cell. The conversion efficiency of 42.6 % at 0.3 W/cm2 laser irradiance and 300 K cell temperature was obtained by optimizing all the structural parameters, indication that the thickness and carrier concentration optimization leads remarkable improvements in conversion efficiency.

Overview of Studies on Space Solar Power Systems and Elemental Technology Development

Japan Aerospace Exploration Agency (JAXA) has studied Space Solar Power Systems (SSPS) using laser and microwave beams for years since 1998. Current SSPS study undertaken by JAXA consists of three main subjects, SSPS concepts and architectures study, technology demonstration and elemental technology development. In current research of Laser based SSPS (L-SSPS), we have studied some elemental technologies such as ultralight film mirror, wavelength selective mirror, laser generator based on direct solar pumping solid-state laser diode, laser transmission property in atmosphere, photovoltaic generation converting laser energy to electricity and photocatalytic hydrogen generation. This paper presents the introduction of SSPS concepts and architectures study and elemental technology development of L-SSPS.

Technology of Low Cost Production of FGMs

In this paper, we introduced research and development of technology of low cost production of FGMs. This research is designated for development of mass production technology for production of ceramic wares with induction heating (IH) function. Slurry lamination method has advantage in forming graded layers due to its simplicity and easiness. However, this method has a disadvantage to generate cracks during drying process. Therefore, freeze-dry in vacuum was introduced in drying process of slurry lamination. By doing so, mass production could be achieved. In this trial production, we adopted SPS sintering method to production technique. In the future, we will further develop other applications of FGMs into industrial products.

LE-NET and Multi-Purpose Laser Propulsion System

The concept of the Laser Energy NETwork (LE-NET) and the multi-purpose laser propulsion system being studied at NAL are overviewed. The LE-NET can provide abundant energy supplies on earth acting as the effective and long lasting measures against global warming and will cover wide variety of transportation needs by the laser power. The LE-NET needs a Solar Excited Laser (SEL) that directly converts a solar light into a laser beam. The SEL is expected to minimize the SPS weight considerably, leading low-cost realization of the LE-NET.

Prototype Design and Evaluation of Lightweight Mirror and Wavelength Selective Filter for Space Solar Power Systems

The large scale SSPS (Space Solar Power System) needs large reflection mirrors for sunlight concentration. To use film mirror in space, the mirror must have lightweight structures and resistive to harsh space environment. The wavelength selective filter to avoid heat is a dielectric multilayer film which has FGM structure. In this article, we will report the development of a lightweight wavelength selective mirror and wavelength selection on the solar light excitation laser.

Prospect of YAG Laser Medium for Laser Space Solar Power System and Possible Application of Graded Structure for Efficient Cooling System

Laser medium for solar-pumped solid laser of 10MW-1GW power is a key to realize Laser Space Solar Power System (L-SSPS). Since it is an ultrahigh power system operated in space, the laser medium must satisfy the conditions such as high efficiency, high power per weight or volume, excellent durability and maintainability, thermal equilibrium operation, and excellent long-range propagation of oscillated laser. YAG (Y3Al5O12) ceramics doped doubly with Nd and Cr is considered to be a suitable laser medium for L-SSPS at present. There are the following important points for L-SSPS application: 1) Optimization of the doping amount, 2) Process, 3) Temperature control. Feasibility of YAG ceramics is discussed from a view point of material science and proposed a YAG ceramics structure with graded distribution of dopants.

Report on FY 2007 Functionally Graded Materials Database

Functionally Graded Materials Database (hereinafter referred to as FGMs Database) has been run by Japan Aerospace Exploration Agency (JAXA) since October, 2002. So far, the database contains 1,815 research paper information including 12,790 figures and tables, 2,632 author information, 904 PDFs, and 563 university, research institution and company information. The database had been used by 34,968 users from 113 countries in FY2007, where the effective total visits counted to 73,072. Approx. 20% of users had repeatedly visited the website. In FY 2007 users from Japan were significantly increased. Additionally, the interest of Europe and Middle east/Africa region was remarkable.

Investigation and Research on the Applicability of FGM Technology for Advancement of the Space Solar Power System (SSPS)

The objective of this research is to enhance the economics of the Space Solar Power System (SSPS) which is to supply a large quantity of energy from space to the ground, and which is expected to become operational in 20–30 years. Weight reduction and improvement of the life span of SSPS are needed to reduce transportation and life cycle costs. Related to the SSPS research that has been conducted by JAXA, the present report suggests a new vision for material development applying the FGMs concept, and proposes some concepts of innovative materials in which the advantages of FGMs are fully utilized.