田中 孝治

我々は、小型科学衛星を用いた太陽発電衛星のための実証実験計画を検討している。主目的は以下の二項目である。(1)電離層を介し軌道上でのアンテナダイナミクスを考慮したマイクロ波ビーム制御能力の実証、(2)マイクロ波の電離層通過実験による非線形現象の評価である。また、本実証実験に基づき、実用太陽発電衛星の電力システムとしての総合電力効率の評価及び運用性の評価、既存の通信インフラに与える影響の評価を行うとともに、次フェーズの軌道上実証実験、実証プラントへ至る技術的な課題を明らかにする.

将来の新たな発電システムとして研究している太陽発電衛星の軌道上実証を目指して、その事前実験を実施するための送電装置のブレッドボードモデルの開発状況と技術実証について報告する。太陽発電衛星において、地上への送電手段であるマイクロ波を介した遠距離無線電力伝送に要求される技術の一つに、受電アンテナへ向けた送電ビームの精密指向制御があり、本モデルによって送電アンテナの指向性を実験的に評価する。このモデルは、256素子のフェーズドアレーアンテナで構成されており、マイクロ波の増幅・位相制御素子を含む回路基板と2層の薄型構造を成していることが特徴である。本報告では、各出力ポートにおける相対位相の誤差が送電ビーム指向性に与える影響を実験的に明らかにし、位相の補正を適用することによる送電性能に対する効果を検証する。

本報告では,H22年5月に打ち上げられたソーラー電力セイル実証機IKAROSに搭載された薄膜発電システムの軌道上実験に関して述べる.ソーラーセイルの膜面上にa-Si太陽電池を用いた薄膜太陽電池アレイを搭載し,軌道上での展開及び発電実験を行った.太陽電池アレイは8個の発電ブロックに分けて搭載し,各発電ブロック間のばらつきは少なく,製造管理,収納及び軌道上での展開の影響評価が実施できた.ただし,打ち上げ前にフレキシブルハーネスの一部が不具合を起こしており,ハーネスの構造,管理には課題がある.発電特性は,初期特性は地上検証データと近い値を示しているが,時間変化の特性は若干劣化が大きくなる傾向が得られている.発電特性の継続的取得により,惑星探査機用薄膜超軽量発電システム開発のための知見を得る.

Light-weight thin plate structure is expected to play an important role in space development in the near future. Thin film solar array, solar sail, planar antenna, and inflatable structure are the typical examples. We have carried out hyper-velocity impact experiments on thin plate targets using a light gas gun, to study propagation of the impact plasma associated with an interference with electrical parts on the planar plate. Propagation of the luminous cloud and generated plasma were observed by a high-speed video camera and an array of plasma probes, respectively. It was found there existed a high-dense plasma propagating along the surface of the plate at a high-speed more than the projectile velocity. The characteristic behaviors of the plasma propagation were explained by the half-range Maxwellian plasma uniformly ejected from the collision area.

The experiment of charged particle collection experiment by bare electrodynamic tape tether was performed by using JAXA's sounding rocket S-520-25 on August 31, 2010. This was the first experiment of bare tether in space in the world. This paper shows the outline of the experimental apparatus and the initial experimental results of the verification of bare electrodynamic tether operation and the charged particle collection theory. As experimental results, Valuable data of electron collection by the induced electromotive force and ion collection by a space potential probe in space were obtained, although charged particle collection data by tether and boom were not obtained by a trouble of high voltage power source.

本稿では,小型ソーラー電力セイル実証機IKAROSのセイル展開方式として採用した,遠心力展開方式について, JAXAにて著者らが行ってきた研究開発を概説する. IKAROSは世界に先駆けてJAXAが実施したソーラー電力セイル技術の宇宙技術実証であり,宇宙機全体のスピンによる遠心力を利用してセイルの展開・展張をするという独特な方式を採用している.著者らは,軽量かつスケーラブルなセイル展開システムとして遠心力展開方式を採用し,研究開発を行ってきた.本活動は, 2002年にJAXA内に発足したソーラーセイルワーキンググループが中心となり,全国の多数の大学研究機関とともに行ってきたものである.最終的な目標はφ50m級のソーラー電力セイルを実現することにあり,φ20m級のセイルを搭載したIKAROSはその最終段階の宇宙技術実証試験と位置付けられたものである.ここでは,本研究開発活動の主要な柱である遠心力展開技術について紹介し, IKAROSプロジェクト発足以前に著者らが行ってきた主要な試験プロセスと数値シミュレーション技術について概説する.

Series connections of energy-storage modules such as electric double-layer capacitors (EDLCs) and lithium-ion batteries result in voltage imbalance because of the nonuniform properties of individual modules. Conventional voltage equalizers based on traditional dc-dc converters require numerous switches and/or transformers, and therefore, their costs and complexity tend to increase. This paper proposes a novel single-switch equalization charger using multiple stacked buck-boost converters. The single-switch operation not only reduces the circuit complexity but also contributes to increasing the reliability. The fundamental operating principles and design procedures of key components are presented in detail. An experimental charge test using a 25W prototype of the proposed equalization charger was performed for four series-connected EDLC modules whose initial voltages were intentionally imbalanced. Experimental results demonstrated that the proposed equalization charger could charge the series-connected modules preferentially in the order of increasing module voltage and that all the modules could be charged up to a uniform voltage level.

Electric double-layer capacitors (EDLCs) offer several advantages over traditional batteries, such as long cycle life, high power capability, good low-temperature performance, etc. However, their major drawbacks, such as low specific energy and large voltage variation due to charge/discharge cycling, necessitate the use of high-efficiency power conversion electronics that can be used to efficiently discharge EDLCs and thus completely utilize the precious stored energy. In this study, we propose a novel discharger for EDLCs; this discharger uses cascaded switched capacitor converters (SCCs) and selectable intermediate taps. Although the voltage conversion ratio of SCCs is fixed, the load voltage can be maintained within a desired voltage range by the selectable intermediate taps. The circuit configuration, operating principle, and procedure for designing SCCs and selectable intermediate taps are presented. Experimental tests were performed using an EDLC module and a 200W prototype of the discharger. The obtained results showed that the 60V EDLC could be discharged to 30V with an average efficiency of 96% when the load voltage was maintained within the range 30-40V.

When electric double-layer capacitors (EDLCs) are connected in series, cell voltage imbalance that results due to non-uniform cell properties is observed. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energy of cells. In this study, we propose a series-parallel reconfigurable cell voltage equalizer that is considered suitable for energy-storage systems using EDLCs instead of traditional secondary batteries as main energy-storage sources. The proposed equalizer requires only EDLCs and switches as its main circuit elements, and it utilizes EDLCs not only for energy storage but also for equalization. An equivalent circuit model using equivalent resistors that can be regarded as an index of equalization speed is developed. Current distribution and cell voltage imbalance during operation are quantitatively generalized. Experimental charge-discharge tests were performed for EDLC modules to demonstrate the performance of the cell voltage equalizer. All the cells in the modules could be charged/discharged uniformly even when a degradation-mimicking cell was intentionally included in the module. The resultant cell voltage imbalances and current distributions were in good agreement with those predicted by mathematical analyses.

Power conversion electronics for photovoltaic (PV) systems are desired to operate as efficiently as possible to exploit the power generated by PV modules. This paper proposes a novel PV system in which a dc-dc converter is partially connected to series-connected PV modules. The proposed system achieves high power-conversion efficiency by reducing the passing power and input/output voltages of the converter. The theoretical operating principle was experimentally validated. Resultant efficiency performances of the proposed and conventional systems demonstrated that the proposed system was more efficient in terms of power conversion though the identical converter was used for the both systems.

月周回衛星SELENEは,主衛星「かぐや」と,2機の子衛星であるリレー衛星「おきな」,VRAD衛星「おうな」から構成され,2007年9月の打上げから2009年6月まで運用が行われた.運用に際して使用された地上局は,JAXAのGN局,臼田宇宙空間観測所(UDSC),及び海外局等である.とりわけ臼田局64mアンテナでは,「かぐや」ミッションデータのダウンリンク,及び「おきな」を用いた世界で初となる月周回衛星の4ウェイドプラ計測が実施された.これらの運用の概要と,4ウェイ中継を実現するための改良点を述ペる.

DC-DCコンバータやインバータ等の電力変換装置は動作周波数ならびに商用周波数に応じたリップル電流を発生する.燃料電池を電力変換装置と接続して使用する場合,燃料電池には平均直流電流にリップル成分が重畳した電流が流れるため,燃料電池の電位は高周波で変動することになる.固体高分子形燃料電池(PEMFC)の主な劣化要因の一つとしてPt/C触媒の電気化学的表面積(ESA)の低下が挙げられるが,この劣化モードは電位変動時に顕著に進行することが知られている.本稿では電力変換装置との相互作用により発生する高周波の電位変動がPEMFCのPt/C触媒劣化に及ぼす影響の定性的評価を目的とし,発電ならびに非発電状態のPEMFCを高周波の電位変動環境に晒し,ESAの劣化傾向を観察した.電位変動周波数が低周波の場合は顕著なESA劣化傾向を示す一方,100Hz以上の高周波域では直流条件時と同等の低い劣化率を示した.本稿で得られた知見は電力変換装置の動作周波数の決定ならびにリップル周波数を規制する際に有用になるものと期待できる.

高効率を目指す固体高分子形燃料電池(PEMFC)システムでは,燃料電池出口から排出される未反応の水素ガスを入口へと循環させるために,主に機械式ポンプが用いられている.しかし,ポンプは動作時に振動・騒音を発生するのに加えて電力を消費するため,高効率・静寂性・無振動等の燃料電池の長所を定性的に相殺してしまう.本稿では電気-流体間のアナロジーに基づき電気回路で汎用的に用いられるスイッチトキャパシタ回路を起源としたポンプレス循環システムの導出を行う。アナロジーより得られたポンプレスガス循環システムに対して各種実験を行い,スイッチトキャパシタ回路のシミュレーション結果と動作特性を比較することによりアナロジーの妥当性検証を行った.また,ポンプレスガス循環システムを用いて単セルのPEMFCを10時間に渡り運転を行った結果,セル電圧は低下することなく安定な特性が得られた.

Conventional cell/module voltage equalizers or equalization chargers based on traditional dc-dc converters require numerous switches or transformers as the number of series connections increases; therefore, their cost and complexity tend to increase and their reliability decreases as the number of connections increases. This paper proposes a novel voltage equalization charger that consists only of passive components such as capacitors, diodes, and a transformer. The fundamental operating principle, major features, and derivation of equivalent dc circuits are presented. A symmetrical configuration is also proposed to mitigate the RMS current flowing through energy storage cells in the charging process. Simulations and experimental charging and cycle tests were performed on series-connected electric double-layer capacitor modules to demonstrate the equalization performance. The experimental and simulation results were in good agreement, and the voltage imbalances were gradually eliminated as time elapsed even during charge-discharge cycling.

Conventional voltage equalizers or equalization chargers, which are used for series-connected energy storage cells to eliminate cell voltage imbalance, consisting of a number of switches or transformers tend to be complex with the number of series connection of the energy storage cells. A novel voltage equalization charger consisting only of capacitors, diodes, and an ac power source is proposed, and its dc equivalent circuit expressed by resistors and a dc power source is derived in this paper. Experimental charge tests demonstrated that series-connected EDLCs could be charged up to the uniform voltage by the proposed equalization charger.

Series-connected energy storage cells require cell equalizers in order to mitigate cell voltage imbalance. Conventional cell equalizers, however, consist of a number of switches or transformers that are considered not preferable in the viewpoint of circuit complexity and reliability. This paper proposes an equalization charger that consists of a single switch and passive components. Experimental performance tests showed that series-connected EDLCs could be charged up to the uniform voltage level by the proposed equalization charger though the initial voltages of the EDLCs were imbalanced.

ソーラーセイルWG では,太陽の光子の圧力を受けて進む光子セイルに,薄膜太陽電池を貼り付けて大電力を発生し高比推力のイオンエンジンを駆動する推進システム,ソーラー電力セイルの検討を進めている.このシステムの確立において重要な技術課題である大型膜面の展開機能を検証するため,大気球を用いた大型膜面の展開総合実験を計画し,展開システムの開発を行った.あいにく実験場の天候不良により平成20 年度に続き,放球を実施できなかったが,本論文では,この実験の内容および位置付けについて紹介する.

The primary objectives of the sounding rocket experiment, S-520-25, are to deploy an electro-conductive bare tape tether in space and to study the electron current-collection by the tape tether when biased positively. Before the space experiment, we have carried out laboratory experiments on the plasma collection by the tape tether in a large space science chamber at ISAS/JAXA. This paper presents the major results on the currentvoltage characteristics of the tape tether in the plasma environment which simulates the ionospheric plasma It was found that the tether current approached to the prediction by the Orbit Motion Limit (OML) theory as the tether voltage was increased up to 500 V. In the high voltage region more than 200 V, we often observed the discharge at the surface of the tether that damaged the tether material.

Unreacted fuel expelled from the outlet of fuel cells should be recirculated back to the inlet if wastage of the fuel must be minimized. Conventional recirculation systems employ mechanical pumps that consume electrical power and generate vibration and noise. This paper derives the pump-less recirculation system based on the analogy between electrical and fluid circuits. Concept of a switched capacitor circuit which is commonly used in electrical circuits was applied for recirculation in the fluid circuit. Operating characteristics and long-term stability of the proposed fuel cell system were experimentally demonstrated.

SELENE (Selenological and Engineering Explorer) is a Japan's lunar probe which was launched and injected into the lunar polar orbit in 2007. The Main Orbiter of SELENE named Kaguya has separated the Relay Satellite: Rstar (Okina). We have executed four-way Doppler measurements which determined the orbit of Kaguya aviating above the lunar far side. The ground station up-links ranging signals, and the relay satellite transponder on Rstar (RSAT-1) relays the carrier waves to Kaguya. Then the transponder on Kaguya (RSAT-2) receives the signals and returns to Rstar, and down-linked to UDSC. Thus, our system has achieved the first case to track two fully moving links between the lunar orbiters and carried out Doppler measurements.

The Japanese lunar explorer SELENE (KAGUYA), which has been launched on Sep. 14th, 2007, utilizes VLBI observations in lunar gravimetry investigations. This can particularly improve the accuracy of the low degree gravitational harmonics. Combination of ground based VLBI observations and Doppler measurements of the spacecrafts enable three dimensional orbit determinations and it can improve the knowledge of the gravity field near the limb. Differential VLBI Radio sources called VRAD experiment involves two on-board sub-satellites, Rstar (Okina) and Vstar (Ouna). These will be observed using differential VLBI to measure the trajectories of the satellites with the Japanese network named VERA (VLBI Exploration of Radio Astrometry) and an international VLBI network.<BR>Two new techniques, a multi-frequency VLBI method and the same-beam VLBI method, are used to precisely measure the angular distance between the two sub-satellite radio sources Okina and Ouna. The observations are at three frequencies in S-band, 2212, 2218 and 2287 MHz, and one in X-band, 8456 MHz. We have succeeded in making VLBI observations of Okina/Ouna with VERA and the international network, and have also succeeded in correlating of signals from Okina/Ouna, and obtained phase delays with an accuracy of several pico-seconds in S-band.

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. 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. 23^<rd>, 2005 (UT) from Baikonur, Kazakhstan by Dnepr rocket. REIMEI satellite functions satisfactorily on the orbit. Three axis control is achieved with accuracy of 0.05 deg. Multi-spectrum images of aurora are taken with 8Hz rate and 2 km spatial resolution to investigate the aurora physics. REIMEI is a small scientific satellite for aurora observation and advanced satellite technologies, and was launched into a nearly sun synchronous polar orbit on Aug. 23^<rd>, 2005 (UTC) from Baikonur, Kazakhstan by Dnepr rocket. REIMEI satellite functions satisfactorily on the orbit. The three-axis attitude control is achieved with accuracy of 0.05deg. REIMEI is performing the simultaneous observation of aurora images as well as particle measurements. REIMEI indicates that even a small satellite launched as a piggy-back can successfully perform the unique scientific mission purposes.

資料番号: AA0063585018レポート番号: JAXA-SP-06-035

The current-voltage characteristics of the array electrodes on the dielectric material in laboratory plasma have been studied in association with the interaction of high-voltage solar array with the ambient space plasma. It has been found that the charging effect and secondary electrons of the dielectric material surrounding the electrodes play an important role in collection of the electrode current. The charging effect suppresses the electrode current, while the secondary electrons enhance the electron current to the electrode. In the electrode array (3 × 3 electrodes separated by 0.5~10 cm) , the current of each electrode was generally smaller than that of single electrode, but a rapid enhancement of the electrode current was observed when spacing of the electrodes was less than 1.5 cm. These results indicate a possibility that we can reduce the risk of electric discharge if we use the dielectric material with a low secondary-emission yield and select the distribution of the solar array voltage minimizing the high voltage-plasma interaction.

資料番号: AA0049213013レポート番号: JAXA-SP-05-020

小型科学衛星INDEX(れいめい)の打上げと初期成果

資料番号: AA0049206030レポート番号: JAXA-SP-05-001E

A laboratory experiment on the interaction between the high voltage solar array and the ambient plasma has been conducted.In the experiment, an array of electrodes distributed on the honeycomb structure CFRP panel was used to simulate the inter-connectors of the solar array. One of major concerns in the usage of the high voltage solar array in space is the arc discharge on the array. Based on the plasma sheath theories, there is a possibility to control or to prevent the discharge by selecting a potential distribution of the electrode array. As the first step to find the potential distribution which tolerates the discharge, we measured the distribution of space potential surrounding an array of electrodes and measured the current to the electrodes. This paper presents the preliminary results of the experiment suggesting that we can control the discharge by selecting a proper potential distribution of the high voltage solar array.

本報告では、太陽発電衛星送電アンテナ部への適用を目的とした小型積層アクティブ集積アンテナアレーの試作、検討について報告する。はじめに、出力を2ポートとしたPush-Pull増幅器の設計、試作を行った。その結果、それぞれの出力から180°位相差のある出力が得られた。また、そのPush-Pull増幅器をパッチアンテナと積層化した2素子アクティブ集積アンテナアレーを試作した。これらの実測より良好な結果が得られた。

本報告では、太陽発電衛星搭載を目的とした、原型レトロディレクティブアクティブ集積アンテナについ述べる。レトロディレクティブ機能の基本原理を示し、本研究では並列帰還形発振器とバッチアンテナを用いた、ヘテロダインミキシング方式によるレトロディレクティブアクティブ集積アンテナについて検討を行った。レトロディレクティブ機能の基本動作を確認するために、位相差の異なる電力分配器を用いて外部から信号を入力することにより、到来信号を擬似的に作り出せる回路の試作・測定を行った。さらに、これらの結果を元に送信・受信アンテナを付加し、積層構造としたレトロディレクティブアクティブ集積アンテナの試作・測定結果について報告する。

太陽発電衛星実現のために衛星軌道上から地上へのマイクロ波による無線送電技術は、最初に確立、実証されるべき重要な技術課題ある.また、世論へのデモンストレーション効果も少なくないと考えられる.我々は、この無線送電を中心とした試験衛星計画を検討しており、実施期間を5年程度とし、かつ大型ロケット一機で実現可能であることを前提条件とした.特に、地上で電力システムとしての評価を可能にするために、400kW程度の大電力マイクロ波が放射可能な大型アンテナの電気的特性、機械的及び熱構造特性の検討を行った.

SPS2000は西暦2000年の技術レベルで実現可能な宇宙太陽発電システムとして概念構想がまとめられたが，また，その構想書の中でSPS2000実現に向けて全体計画の予備段階として先行する研究開発プロジェクトの必要性も検討されている．無線送電もその１つである．SPS2000実現に向けての先行実験として，5年程度で実施可能であり，また，大型ロケット一機で実現可能な，宇宙送電を中心とした周回衛星による実証実験の検討を行った．資料番号: SA0200087000

太陽発電衛星実現のために衛星軌道上から地上へのマイクロ波による無線送電技術は、最初に確立、実証されるべき重要な技術課題ある.また、世論へのデモンストレーション効果も少なくないと考えられる.我々は、この無線送電を中心とした試験衛星計画を検討しており、実施期間を5年程度とし、かつ大型ロケット一機で実現可能であることを前提条件とした.特に、地上で電力システムとしての評価を可能にするために、400kW程度の大電力マイクロ波が放射可能な大型アンテナの電気的特性、機械的及び熱構造特性の検討を行った.

大電力後進波発振器に関して、円殻状電子ビーム仮定した場合の準TEモードの線形分散関係を数値的に解析し、TMモードの解析結果と比較を行った。π-モードから離れた動作条件に関して、数値解析に基づき発振実験を行い、準TE_<11>モードとTM_<01>モードの発振を確認した。実験結果は、数値解析結果と良く一致し、特に2π-モードの動作領域では、準TE_<11>モードの発振が主となることがわかった。準TEモード発振に関する研究は、BWOの最適な設計を行う上で、広い動作条件の範囲で単一モード放射を実現するために重要である。