JAXA Repository / AIREX 未来へ続く、宙(そら)への英知
Other TitleDevelopment of Ultra-small Imaging Device, PHOENIX, for Plasmaspheric EUV Radiation
Author(jpn)桑原, 正輝; 吉岡, 和夫; 疋田, 伶奈; 村上, 豪; 荒尾, 昇吾; 吉川, 一朗
Author(eng)Kuwabara, Masaki; Yoshioka, Kazuo; Hikida, Reina; Murakami, Go; Arao, Shogo; Yoshikawa, Ichiro
Author Affiliation(jpn)宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS); 東京大学; 東京大学; 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS); 東京大学; 東京大学
Author Affiliation(eng)Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS); The University of Tokyo; The University of Tokyo; Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS); The University of Tokyo; The University of Tokyo
Issue Date2019-03-08
Japan Aerospace Exploration Agency (JAXA)
Publication title宇宙航空研究開発機構研究開発報告
JAXA Research and Development Report
Start page1
End page16
Publication date2019-03-08
AbstractNASAの有人ロケットSLS (Space Launch System)試作機の相乗り衛星としてJAXAの超小型深宇宙探査機EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft)の打ち上げが予定されている.この探査機は太陽や月の重力を利用することによりリソース制約の厳しいCubeSatでも実現可能な軌道変換能力で地球-月のラグランジュ点へ効率的に航行することを目指す.我々はこのEQUULEUS探査機に搭載される極端紫外光(EUV)撮像装置PHOENIX(Plasmaspheric Helium ion Observation byEnhanced New Imager in eXtreme ultraviolet)の開発を行っている.PHOENIXは地球プラズマ圏に広がるヘリウムイオンの発光(波長30.4 nm)を地球-月のラグランジュ点から1つのフレームに収める.連続的かつ長期間の撮像を行うことで,プラズマ圏の動的描像の大局的な理解を目指す.PHOENIXは多層膜反射鏡,金属薄膜フィルタおよび2次元位置検出器からなる光学系を有しており,それぞれの性能が観測の成否を左右する.探査機のサイズが6U (10×20×30 cm)と非常に小型であり,それ故観測器に与えられる包絡域も極めて狭小(7×10×10 cm)なものとなる.超小型探査機にEUV撮像器を搭載する際に特に問題となるのが,主鏡の小型化に伴う集光能力の低下である.また,EUV領域の光を透過する窓材は存在しないため光学系は反射型である必要がある.従って,小型化のためには光軸上に検出器を配置しなければならず,開口面積の縮小も避けられない.本研究では,従来の大型探査機に用いられてきた実績のある光学系の設計を基に,超小型探査機に搭載可能なEUV撮像装置の光学系の最適化を図った.特に,上記問題を解決するため,集光能力を担う多層膜反射鏡の高効率化に重点をおいて研究を行った.従来の大型探査計画では,波長30.4 nmの光の撮像のためにMoとSiの組み合わせから成る多層膜コーティングが用いられており,その反射率は18%程度であった.本研究ではMo/Si多層膜コーティングより約2倍高い反射率を達成可能なMgとSiCの多層膜コーティングを搭載品に採用した.さらに, 2次元位置検出器に用いられているレジスティブアノードエンコーダー(RAE)を従来の四角形から三角形に改良することで開口面積の拡大を図った.本論文では上記のMg/SiC多層膜反射鏡,C/Al/C薄膜フィルタ及び2次元位置検出器それぞれの性能を実験的に評価した結果を述べる.実験結果からPHOENIXの検出効率を評価し,観測の実現可能性を検証した.その結果,PHOENIXはプラズマ圏界面を空間分解能0.1 Re,1時間以下の露出時間で観測可能な性能を有していることを確認した.これはプラズマ圏の動的描像を議論するに十分な性能である.
EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft), which is a JAXA's ultra-small deep space explorer, will be launched by the prototype of NASA's manned rocket, SLS (Space Launch System), as a piggy-back satellite. By using gravity of the sun and the moon, the explorer aims to navigate efficiently to the Earth-moon Lagrangian point with orbital transformation ability that can be realized even in CubeSat which is strictly limited by resources. We are developing the Extreme Ultra Violet (EUV) imaging device, which is named PHOENIX (Plasmaspheric Helium ion Observation by Enhanced New Imager in eXtreme ultraviolet) and will be installed in EQUULEUS. From the Earth-Moon Lagrangian point, PHOENIX will obtain the distribution of emission from He ions (at a wavelength of 30.4 nm) spreading in the Earth's plasmasphere in one flame. By continuous and long-term imaging, we aim for a comprehensive understanding of dynamic picture of the plasmasphere. PHOENIX has an optical system composed of a multilayer reflecting mirror, a metallic thin filter and a two-dimensional position detector, and each performance affects the possibility of its succeeding in the observation. The size of the spacecraft is 6U (10 × 20 × 30 cm) which is extremely small, so the enveloping area given to the instrument is also very narrow (7 × 10 × 10 cm). The reduction in the light collection efficiency due to the miniaturization of the main mirror would be highly important problem when installing the EUV imager in the ultra-small explorer. Also, since there is no window material that effectively transmits light in the EUV range, the optical system must be reflective. Therefore, in order to reduce the size, disposing a detector on the optical axis is needed and reducing the opening area is inevitable. In this research, we have optimized the optical system of the EUV imaging device which can be mounted in the ultra-small spacecraft based on the design of the optical systems used for the conventional large spacecraft. In particular, we have focused on making highly efficient the multilayer reflecting mirror, which is responsible for convergence of light, in order to solve the above problem. In the conventional large-scale exploration plan, multilayer coating consisting of a combination of Mo and Si has been used for imaging of light at a wavelength of 30.4 nm, and its reflectance is about 18%. In this study, multilayer coating of Mg and SiC which can attain reflectivity about 2 times higher than Mo/Si multilayer coating has been adopted. In addition, the opening area has been expanded by improving the resistive anode encoder (RAE), used for the two-dimensional position detector, from the conventional rectangular shape to the triangular shape. In this research, each performance of the Mg/SiC multilayer reflecting mirror, C/Al/C thin filter and two-dimensional position detector has been experimentally evaluated. From the experimental results, we have evaluated the detection efficiency and verified the feasibility of observation by PHOENIX. As a result, we have confirmed that PHOENIX has enough performance to detect the plasmapause with a spatial resolution of 0.1 Re and exposure time of less than 1 hour. This value is sufficient to discuss the behavior of plasma in the Earth's plasmasphere.
Description形態: カラー図版あり
Physical characteristics: Original contains color illustrations
KeywordsEUV; Plasmasphere; He ion; 30.4 nm
Document TypeTechnical Report
JAXA Category研究開発報告
NASA Subject CategoryLunar and Planetary Science and Exploration
Report NoJAXA-RR-18-010

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