田中 孝治

© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This work presents digital retrodirective method to do microwave power transfer (MPT) for solar power satellite (SPS). Due to space environment, there is concern of antenna deformation, which will affect beam forming. Size of SPS is large and synchronization among antenna modules is difficult. Flexibility regarding frequency selection for MPT is also a requirement for SPS. Digital Retrodirective method determines phase of pilot signal and power signal is transmitted with conjugate phase. Digital Signal Processing (DSP) circuit is used for digital retrodirective method. Experiment is performed without antenna deformation and with antenna deformation cases. Digital retrodirective method performs beam forming without synchronization among antenna modules and corrects effect of antenna deformation successfully. Flexibility for frequency selection is also achieved by the DSP circuit. The presented results confirm that digital retrodirective method is a good candidate for power transfer from SPS.

We are studying and developing a hybrid system combined with thin film and bulk structure to realize a solar power satellite (SPS). One of the problems of realization for SPS is the number of space transportation. Therefore, to reduce the number of space transportation, we're considering replacing some functions from a bulk structure with by lightweight and thin flexible structure. Also, to meet temperature requirements, thermal design of hybrid structure for the SPS should be considered. In this study, we found thermal structural conditions of hybrid system combined with thin film and bulk structure for SPS.

This paper discusses the near-field measurement results of deployable seven-panel parallel plate slot-array antenna system compatible with 100kg class satellite. This antenna system will be used for SAR image acquisition on-board Synspective Inc.'s first demonstration satellite Strix-Alpha, scheduled to be launched in 2020.

<p>Ejecta from hypervelocity impact includes not only fragments but also luminous vapor cloud with plasma. The plasma (i.e. plasma density) is an important parameter for estimating the risk of discharge on solar array paddle or power harness of spacecraft. We carried out hypervelocity impact experiments using a two-stage light gas gun to analyze luminous vapor cloud and plasma from impacts of the different projectile and target materials. We measured luminous vapor cloud and plasma by using a high-speed video camera and a streak camera spectroscopy, which gives time-resolved spectra and a plasma probe. From the time-resolved spectra, the temperature of the luminous vapor cloud was calculated by fitting the black body radiation from a continuous spectrum of the luminous vapor cloud. Also, we compared and investigated the temporal change of each emission line spectrum from impacts of different target and projectile materials. </p>

© 2008-2012 IEEE. This article shows development and performance evaluation of a MicroX-SAR demonstration satellite, scheduled to be launched in 2020 for synthetic aperture radar (SAR) application. This compact SAR system and its instruments are briefly described. The SAR antenna consists of deployable seven panels with a slot array and the antenna size is 4.9 × 0.7 m. This article proposes a simple evaluation method of the SAR antenna. The seven-panel antenna array performance is estimated from isolated single-panel antenna measurement results and synthesized scattering matrix. It is validated by comparing with near-field measurement of a seven-panel antenna array. The on-board SAR system is combined with a single-point source simulator and the point source SAR image is evaluated. The ambiguity to the signal ratio is computed for the bandwidth-integrated seven-panel antenna radiation patterns, and finally the pulse repetition frequency selection is computed along with noise equivalent sigma zero to estimate the SAR image quality based on various requirements of swath-width and ground-range resolution as per the application of interest. The prototype system is capable of 1-m ground-range resolution SAR image acquisition for 28-km swath-width within acceptable limits of signal-to-noise ratio and ambiguity levels.

© 2019 Antenna Branch of Chinese Institute of Electronics. Wireless power transmission (WPT) is one of the significant technologies towards Solar Power Satellite (SPS). Software Retrodirective method, consisting direction finding and beam forming is proposed for performing WPT. Tethered SPS has power generation and transmission panel to transmit 1 GW power. Required accuracy of WPT is 0.0005 degrees for Tethered SPS. Due to space environment, there is a concern of antenna deformation which will affect accuracy of WPT. We performed basic experiment for antenna deformation of λ/20 and λ/10. Effect of the deformation was analyzed for direction finding by measuring error of angle of arrival. Estimation was done to obtain allowable limit of position error for achieving the required accuracy.

© 2019 IEEE. This paper presents the proto-flight model test results of X band synthetic aperture radar for small satellites with 130kg mass. The specification of SAR performance is single polarization SAR with 3m ground resolution for strip map mode. Optional 1 m ground resolution can be achieved with sliding spot light mode under condition of limited valus of NESZ. The paper describes the unique antenna system, the RF power amplifier, high speed data storage/transmission system, and the ground SAR response test results.

© 2018 IEICE Japan Space Systems (J-spacesystems) has been studying wireless power transmission (WPT) for the realization of Space Solar Power Systems(SSPS). We have been working for the essential technologies to realize SSPS. They are the improvement of total DC-RF conversion efficiency at the transmission section, RF-DC conversion efficiency at the receiving section and light weight thinner transmission panel. In order to apply microwave power technology to our daily life before space application, we have started discussion with members from Industry, Academia and Government Agencies. We believe application to the daily life can lead us to the cost effective microwave power transmission technology.

© 2018 IEICE Direction finding (DF) is important technology to perform wireless power transmission (WPT) for solar power satellite (SPS). For Tethered SPS, required accuracy of DF is 0.0005 degrees and high uplink power is necessary with restraint of noise level for DF system. This paper proposes use of array antennas to detect pilot signal from rectenna to SPS. Effect of wider baseline is also considered for accuracy of DF by using 1m and 5m baselines for array antennas. Error of angle of arrival (AOA) of 0.00137 degrees is obtained for 48 dB of signal to noise ratio (SNR). Estimations of uplink power are presented to achieve the needed accuracy for Tethered SPS.

© 2018 IEICE To promote the research of Solar Power Satellite (SPS), it is necessary to show feasibility early and for that purpose, strategic development of critical issues is important. Required technology for the SPS that were studied past research were evaluated. Issues to be promptly conducted research and development were considered based on the tethered SPS study in Japan.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Japan Space Systems (J-spacesystems) has been studying wireless power transmission (WPT) from the beginning of 2000. In this study, we have focused on the microwave power transmission as a key technology for the realization of future Space Solar Power System (SSPS). J-spacesystems group have been kept on developing high-efficient microwave transmission and receive system. We have reviewed “Technology Road Map for SSPS development.” We have been discussing with technology experts of the various fields and make it reliable and feasible plan for the development of SSPS. We have been conducting development of Wireless Power Transmission (WPT) technology. Improvement of total DC-RF conversion efficiency at the transmission section and RF-DC conversion efficiency at the receiving section, development of light weight thinner transmission panel are the essential technologies to realize solar space power system. In order to apply microwave power technology to our daily life before space application, we have started discussion with members from Industry, Academia and Government Agencies. We believe application to the daily life can lead us to the cost-effective microwave power transmission technology. Updated information has been added to this paper. Steady state progress has been expected in this area.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. This paper presents the proto-flight model results of X band synthetic aperture radar for 100ok class satellites including the RF power amplifier, the high speed data storage/transmission system, and the SAR response test results on ground. The specifications of SAR performance are single polarization SAR with 3m ground resolution for strip map mode. 1 m ground resolution can be achieved with sliding spot light mode under condition of limited value of NESZ. The data down link is high speed X band down link with max.2.65Gbps. We will launch the first demonstration SAR satellite in 2020 as collaboration with a private company.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. We proposed a new wireless power transmission system for UAV. WPT system that we are developing with around 160W output adopting a phased array antenna with a frequency of 5.8 GHz was used for the experiments. The phased array antenna with the size of around 50 cm squares consists of 64 sub array antenna elements. This system detects the position of the target UAV by the onboard GNSS system and forms microwave beams. Appropriate multi-beam forming was confirmed by our proposed method experimentally.

© 2016 Institute of Electrical and Electronics Engineers Inc.. All rights reserved. Space debris are traveling at a velocity of 7-8km/s in a low Earth orbit and has been an urgent problem in human space activity. Space debris impacts induce not only mechanical phenomena such as cratering but also electrical ones such as radiofrequency (RF) emission, plasma generation, and generation of luminous cloud. In particular, it is confirmed that RF with a wide band frequency from several kHz to dozens of GHz emits from the debris impact (ie. hypervelocity impact), but the mechanism has not been clarified. To simulate the debris impact, the ground-based experiments using the two-stage light gas gun installed at ISAS/JAXA were carried out. We selected a pure aluminum and various aluminum alloy plates which are commonly used for the metal of spacecraft structure as targets. We measured microwave emissions using the receiver with a frequency band of 300MHz, heterodyne receivers with frequency bands of 2.1GHz and 5.8GHz, and the receiver for a wide-band frequency from 850MHz to 6GHz. In addition, generations of plasma and luminous cloud were simultaneously measured by using plasma probes, high-speed video camera and photo detector. In this paper, characteristics of microwave emissions from hypervelocity impacts on aluminium plates are described.

Copyright © 2018 by the International Astronautical Federation (IAF). All rights reserved. An engineering model (EM) of 1 kW class X band high power pulsed amplifier (XPA) for Synthetic Aperture Radar (SAR) system that aims to install in a 100 kg class small satellite was developed. We performed verification tests and evaluated resistance against launch conditions and space environments of the XPA. In this paper, we describe a concept of the XPA and results of the verifications tests.

© 2017 The Authors. Published by Elsevier Ltd. Impacts of space debris smaller than 1 mm can cause fatal damage to a satellite's power system through impact-induced, permanent sustained discharge (PSD). This study re-examines the risk of electrical failure on the bundle of satellite power harnesses using more realistic experimental configurations than in previous studies. In the two-stage light gas gun experiment, the simulated debris particles made of stainless steel (0.3 mm and 0.5 mm in diameter) were impacted at 4 km/s and 7 km/s on a three-layered harness specimen composed of hot and return lines. As a result, PSD did not occur in a typical satellite's power configuration in low Earth orbit. However, the power condition of 100 V/3.0 A was found to be a threshold for PSD. It was also suggested that a critical range of impact strength, which could control the distance between discharge electrodes, exists for PSD on the satellite power harnesses.

Copyright © 2017 by the International Astronautical Federation (IAF). All rights reserved. We carried out the wireless power transmission (WPT) experiments on direction finding using the array antenna for receiving the pilot signals and on on-board calibration of phase error caused by temperature change of the microwave circuit. WPT from space to the ground is one of the significant technologies toward the solar power satellite (SPS). Tethered-SPS consists of power generation and transmission panels that generates electricity and transmits energy using microwave. High gain antenna for the receiving of the pilot signals is necessary in order to decrease the up link power of the pilot signals. We measured the errors for phase measurement, deformation and baseline for direction findings. Also, Rotating element electric field vector method (REV) is a candidate of the calibration of the phase error for WPT system of the SPS, but it takes long time. We are developing the fast REV method utilizing the on-board near field REV. Basic properties of the near field REV using bread board model for the WPT experiments are measured. Evaluation of the on-board REV will be presented.

© 2015 IEEE. This paper describes thermal design and analysis of a hybrid photovoltaic module for the conversion of sunlight into microwave that is used in Tethered-Solar Power Satellite. A practical configuration of the hybrid module was designed and the relationship between module structure and temperature profile under the operation in geostationary orbit was investigated by simulation in comparison with the conventional space photovoltaic module. To obtain realistic analysis model in which practical thermal resistance is considered, thermal-vacuum test using a prototype hybrid module was conducted. The simulation result shows that contact thermal resistance of the hybrid module is small and hybrid structure can reduce the thermal stress risk.

A space craft as a solar power sail requires lightweight and large scale power generation system. Thus, we are developing an ultra lightweight flexible power generation system with thin film photovoltaic cells. Each layer of a thin film solar cell on the polyimide film will bend with changes in temperature, because it has different material characteristic values. For use a thin-film solar cell as a power generation system, it should be flat in a space environment. We built a model formula for maintaining of the shape. Next, we studied about shape control by sputtering utilizing metal oxide materials and durability against space environment. We describe the experimental results of the calculation the internal stress and coefficient of thermal expansion of the coating layer. And we confirm the durability against the space environment of thin film solar cell.

We carried out the experiments of direction finding and wireless power transmitting for clarification of design requirement toward the Tethered-SPS. The Tethered-SPS's microwave transmitting antenna will have position error and phase error that is expected. These errors are caused by automatically assembling by robots. But their effects are not clarified yet. In the result of the experiments, we discovered controllability of the position error of the microwave transmitting antenna by the phase of the excitation microwave. And we clarified design requirements of direction finding system on the Tethered-SPS. In this paper, we describe something to clarify about the wireless power transmitting system.

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.

A lithium-ion battery was developed using off-the-shelf pouch cells and launched with a small scientific satellite "REIMEI." The cells were potted with polyurethane or epoxy resin to protect the battery from vacuum in space. Preliminary experimental test results of pouch cells potted in a soft aluminum cap suggested that the cells tended to swell in vacuum, although they had been reinforced with the resins. Bread board models (BBMs), in which pouch cells were potted with resins in a hard aluminum case, were fabricated for cycle life performance tests in the laboratory. The test results indicated that the performance of epoxy-potted BBM was superior to that of the polyurethane-potted BBM. The measured cell resistance implied that the electrolyte solution leaked through the polyurethane resin, resulting in premature deterioration. The epoxy resin was used for the flight battery. The end-of-discharge-voltage (EoDV) trend of the flight battery on orbit was compared with the laboratory test results corrected based on a post-launch cycle test using a fresh cell. The corrected EoDV trend in the laboratory was in good agreement with the on-orbit trend for the early cycle period, indicating that the on-orbit battery was not inadvertently affected by conditions in space. (C) 2011 Elsevier B.V. All rights reserved.

Solar Power Satellite (SPS) is an energy system which collects solar energy in space and transmits it to the ground. It has been believed as a promising infrastructure to resolve global environmental and energy problems for human beings. One of the most important technologies for the SPS is the wireless power transmission from the geostationary orbit to the ground. Microwave power transmission has been investigated and demonstrated for more than 40 years, but still requires further research regarding high-efficiency power conversion and high-accuracy beam control for SPS application. This paper introduces the concept of SPS, and presents microwave power transmission technologies necessary for SPS, their demonstration experiments both on the ground and in space in the near future, and future prospects towards commercial SPS. © 2011 IEEE.

We have carried out the experiments for the research on the oblique hyper velocity impact experiment using several materials in order to confirm an effect of the stone skipping on the surface of the target. The two stage light gas gun and the rail gun accelerator were used. Nylon sphere with a diameter of around 7 mm and a weight of around 0.21 g was used as a projectile for the gas gun. Ejectors were monitored by the high speed video camera and captured using a shielding plate. Velocities of the projectile for our experiments were from 2 km/s to 5 km/s. CFRP, Aluminium and Titanium target was set on the target holder that could make an adjustment of the impact angle. We confirmed recoiled conditions of the projectile, and observed destruction phenomena of the CFRP and Aluminium plate for the several incident angles. Results of the CFRP plate and metal plates were compared. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

The technologies for the Solar Power Satellite (SPS) have been well studied on the ground and now it is highly required to make demonstration experiments in space as the next logical step. One of the important subjects to be verified in space is the microwave power transmission pointing at the rectenna site on the ground. It includes verification of high-power microwave power transmission through the ionosphere and demonstration of the retro-directive phase control technology for the microwave beaming. These studies can be conducted by the "Small Satellite" that is currently promoted as one of the near future space programs in Japan. The conceptual study for the demonstration experiment has shown that 1 kW class microwave power transmission experiment at 5.8 GHz in the low earth orbit is worthwhile and feasible under constraints of current concept of the "Small Satellite" program.

Tethered solar power satellite (Tethered-SPS) consisting of a large panel with a capability of power generation/transmission and a bus system which are connected by multi-wires is proposed as an innovative solar power satellite (SPS). The power generation/transmission panel is composed of a huge number of perfectly equivalent power modules. The electric power generated by the solar cells at the surface of each module is converted to the microwave power in the same module. Since the modules are controlled by the bus system using wireless LAN, no wired signal/power interfaces are required between the modules. The attitude in which the microwave transmission antenna is directed to the ground is maintained by the gravity gradient force. The tethered panel is composed of individual tethered subpanels which are loosely connected to each other. This configuration enables an evolutional construction in which the function of the SPS grows as the construction proceeds. A scale model of the tethered subpanel can be used for the first step demonstration experiment of the SPS in the near future. © 2006 Elsevier Ltd. All rights reserved.

This paper describes the on-orbit results and lessons-learned of the small scientific satellite "INDEX" (REIMEI) for aurora observation and demonstration of advanced satellite technologies. INDEX is a small satellite with 72kg mass, and is provided with three-axis attitude controll capabilities for aurora observation. INDEX was launched into a nearly sun synchronous polar orbit on Aug. 23rd, 2005 (UT) from Baikonur, Kazakhstan by Dnepr rocket. INDEX satellite has been satisfactorily working on the orbit for 24 months at present of August,2007. Three axis control is achieved with accuracy of 0.1 deg(3 σ). Multi-spectrum images of aurora are taken with 8Hz rate and 2 km spatial resolution to investigate the aurora physics. INDEX is performing the simultaneous observation of aurora images and particle measurements. INDEX indicates that even a small satellite launched as a piggy-back can successfully perform unique scientific mission purposes. Copyright IAF/IAA. All rights reserved.

This paper describes the initial on-orbit results of the small scientific satellite "INDEX" (REIMEI) for aurora observation and demonstration of advanced satellite technologies. REIMEI is a small satellite with 72kg mass, and is provided with three-axis attitude controlled capabilities for aurora observation. REIMEI was launched into a nearly sun synchronous polar orbit on Aug. 23rd, 2005 (UT) from Baikonur, Kazakhstan by Dnepr rocket. After REIMEI was separated from the Dnepr rocket, REIMEI successfully performed a sun-pointing acquisition with spinning motion. A week later REIMEI switched into three-axis attitude control mode. REIMEI satellite functions works satisfactorily in the orbit. The first imaging observations of aurora were successfully performed above the southern polar region in Sep. 16th, 2005. Multi-spectrum images of aurora were taken with 8Hz rate and 2 km spatial resolution.