著者

Takahiro SASAKI Hiroyuki OKAMOTO Yu NAKAJIMA Ryo NAKAMURA Toru YAMAMOTO

出版者

International Symposium on Space Technology and Science

雑誌

Journal of Evolving Space Activities (ISSN:27581802)

巻号頁・発行日

vol.1, pp.52, 2023 (Released:2023-06-30)

参考文献数

17

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Considerable research is being directed toward active debris removal (ADR) in space, especially by small, cost-effective satellites. In the descent phase, thrust vector control (TVC) is often utilized to maintain the satellite’s trajectory and thrust vector by gimbaling the thrust vector. A common challenge in performing TVC is that its effectiveness depends on the mass, moment of inertia and location of the thrusting point with respect to the center of mass. Since these properties change with fuel consumed during a mission, a designer needs to consider such parameters as they strongly affect the resulting dynamics. This paper introduces spacecraft dynamics with a gimbaled thruster and proposes an adaptive controller for TVC with model uncertainties. Through numerical examples, the effectiveness of the proposed controller is demonstrated for improved control performance.

著者

Minghui Tang Toru Yamamoto

出版者

Japanese Society for Magnetic Resonance in Medicine

雑誌

Magnetic Resonance in Medical Sciences (ISSN:13473182)

巻号頁・発行日

pp.rev.2021-0047, (Released:2022-02-26)

参考文献数

161

被引用文献数

1

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RF electromagnetic wave exposure during MRI scans induces heat and occasionally causes burn injuries to patients. Among all the types of physical injuries that have occurred during MRI examinations, RF burn injuries are the most common ones. The number of RF burn injuries increases as the static magnetic field of MRI systems increases because higher RFs lead to higher heating. The commonly believed mechanisms of RF burn injuries are the formation of a conductive loop by the patient’s posture or cables, such as an electrocardiogram lead; however, the mechanisms of RF burn injuries that occur at the contact points, such as the bore wall and the elbow, remain unclear. A comprehensive understanding of RF heating is needed to address effective countermeasures against all RF burn injuries for safe MRI examinations. In this review, we summarize the occurrence of RF burn injury cases by categorizing RF burn injuries reported worldwide in recent decades. Safety standards and regulations governing RF heating that occurs during MRI examinations are presented, along with their theoretical and physiological backgrounds. The experimental assessment techniques for RF heating are then reviewed, and the development of numerical simulation techniques is explained. In addition, a comprehensive theoretical interpretation of RF burn injuries is presented. By including the results of recent experimental and numerical simulation studies on RF heating, this review describes the progress achieved in understanding RF heating from the standpoint of MRI burn injury prevention.

著者

Takahiro SASAKI Yu NAKAJIMA Toru YAMAMOTO

出版者

THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES

雑誌

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES (ISSN:05493811)

巻号頁・発行日

vol.64, no.3, pp.136-146, 2021 (Released:2021-05-04)

参考文献数

25

被引用文献数

1

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As the amount of debris in orbit increases, so does the risk of collisions and their seriousness. All nations involved with space operations acknowledge this growing threat. One solution receiving increased attention is active debris removal. The first step in a debris removal mission would be to approach the debris. In this phase, it is important to ensure passive abort safety and to guarantee the robustness against collisions in the case of off-nominal thruster burns, that may be caused by spacecraft anomalies such as navigation sensor or actuator failures. This paper compares two types of passive abort safe trajectories –the V-bar hopping and spiral approaches– considering the ΔV budget, the duration of operations, and variation in the line-of-sight vector to the target. This paper also proposes design strategies for determining the parameters in the two candidate trajectories, considering passive abort safety. The robustness of the trajectories against collisions due to off-nominal thruster burns is also demonstrated through Monte Carlo simulations. The paper investigates which trajectories are suitable for an active debris removal mission to a non-cooperative target.