船木 一幸

A coupled cylindrical rotating detonation engine (RDE) with two cylindrical RDEs (both combustors had a combustor inner diameter of 23 mm and an axial length of 30 mm) placed next to each other was tested for rocket clustering application. The objective of the experiment was to achieve two-engine synchronized initiation with a single igniter. Experiments were conducted on the inner wall of the combustors with different connecting-hole diameters and wall heights to evaluate the ignition delay time, combustion mode, and propulsion performance. The propellants were gaseous ethylene and oxygen, and experiments were conducted under constant conditions of mass flow rate ([Formula: see text]), equivalence ratio ([Formula: see text]), and backpressure (approximately 10 kPa). When the two combustion chambers were completely separated by a wall, ignition occurred with a time delay of 260 ms in the chamber without an igniter. However, when a large hole ([Formula: see text] diameter) was placed in the wall separating the two combustion chambers, synchronous initiation was successful. Synchronous initiation was also successful when the wall height was lowered (7-mm height). Under both conditions, the same level of specific impulse was achieved as for RDEs operating at the same mass flux.

There are few experimental studies on rotating detonation engines (RDEs) with liquid propellants. This study reveals the static thrust performance of a cylindrical RDE with ethanol and liquid nitrous oxide as propellants under atmospheric pressure. This RDE had an inner diameter of 40 mm, a maximum combustor length of 230 mm, a nozzle contraction ratio of 1.7, and a nozzle expansion ratio of 9.1. Nineteen experiments were conducted at total mass flow rates of [Formula: see text], mixture ratios of 3.6–5.9, and combustion pressures of 0.35–0.46 MPa, resulting in a maximum detonation velocity of [Formula: see text] (approximately 80% of the theoretical detonation velocity, [Formula: see text]), maximum thrust at sea level of 294 N, and maximum specific impulse at sea level of 148 s. In addition, the maximum characteristic exhaust velocity, [Formula: see text], was [Formula: see text], which was 99% of the theoretical value. The characteristic length of the combustion chamber at this time was 0.15 m. Since conventional rocket combustion requires 1.57 m to achieve the same [Formula: see text] efficiency, this study shows that detonation combustion can reduce the combustor size by 88%.

Rotating detonation engines (RDEs) have been actively researched around the world for application to next-generation aerospace propulsion systems because detonation combustion has theoretically higher thermal efficiency than conventional combustion. Moreover, because cylindrical RDEs have simpler combustors, further miniaturization of conventional combustors is expected. Therefore, in this study, with the aim of applying RDEs to space propulsion systems, a cylindrical RDE with a converging–diverging nozzle was manufactured; the combustor length [Formula: see text] was changed to 0, 10, 30, 50, and 200 mm; and the thrust performance and combustion mode with the different combustor lengths were compared. As a result, four combustion modes were confirmed. Detonation combustion occurred with a combustor length of [Formula: see text]: that is, a converging rotating detonation engine. The thrust performance of this engine was 94 to 100% of the theoretical rocket thrust performance, which is equivalent to the thrust performance of conventional rocket combustion generated at [Formula: see text]. This study shows that detonation combustion can significantly reduce engine weight while maintaining thrust performance.

Abstract This paper presents a control algorithm for ensuring the stable operation of a 6 kW Hall thruster. The Japan Aerospace Exploration Agency is developing a “wide-range” power processing unit (PPU) to power a 6 kW Hall thruster system, a candidate for all-electric satellites. The PPU provides discharge oscillation, power, and discharge current control. The increments in the control loop are fixed, so the PPU digital controller does not need to calculate them, and the algorithm’s computational complexity is minimal. Results of integration tests on the 6 kW Hall thruster and the PPU breadboard model showed that the three control functions run correctly. The total controlled PPU power was adjusted in the range of 3.45–3.55 kW under constant power control with a target of 3.5 kW. Oscillations of ± 0.05 kW around the target power are acceptable. 70% of the peaks in the discharge current acquired for 100 ms exceeded the limit of 1.5A. Discharge oscillation control varied the coil magnetic field and reduced them to 0%. The PPU successfully controlled the coil current, reducing the discharge current from 13.7 A to 13 A. The propulsion efficiency increased from 59% to 60.5%.

2021年7月27日早朝5：30，JAXA内之浦宇宙空間観測所からデトネーションエンジンシステムを搭載した観測ロケットS-520-31号機が打ち上げられた．高度約200kmにてメタン–酸素推進剤による回転デトネーションエンジン（RDE）の6秒間作動およびパルスデトネーションエンジン（PDE）の2Hz作動を実施した．取得されたフライトデータから，RDE作動で時間平均推力518N，比推力290±18sおよび速度増速量8.0m/sを達成した．PDE作動では1サイクル当たりの圧力時間積分値が5％以内の高精度での繰り返しインパルス生成およびロケット機軸周りのスピンレート減少が確認された．本結果は，地上燃焼試験データとよく一致し，宇宙空間でのデトネーションエンジン作動が実証された．デトネーション波の判定に用いた圧力・加速度センサの高速サンプリングデータおよびRDEプルーム撮影用のデジタルカメラ画像は，JAXA/ISASで開発された再突入データ回収システムRATSにて回収することに成功した．

<p>The ion energy angle distribution and its relationship to plasma parameters for spot and plume modes are elucidated for a LaB₆ hollow cathode with a radiative heater. Measurements were conducted using a retarding potential analyzer (RPA) and a single Langmuir probe. The ion energy distribution function (IEDF) characteristics showed different tendencies in the current density and mass flow-rate dependence under different plasma modes. The IEDF peak potential for the spot mode varied from 16 to 23 V with increasing current density, and the IEDF peak potential for the plume mode varied from 16 to 32 V with decreasing mass flow rate. Considering angle dependency of ion energy, when the observation angle was changed from the radial direction to the axial direction, the IEDF peak potential increased from 29 to 40 V for the plume mode (10 A, 10 sccm) and increased slightly from 16 to 18 V for the spot mode (20 A, 30 sccm). The probe measurement analysis revealed that the IEDF peak energies are the same as, or exceed, the plasma potential and have a qualitative correlation with the electron temperature spatial distribution.</p>

<p>In order to improve ion engine's performance, the neutralization performance with two field emission cathodes in an ion engine is investigated. The neutralization performance is evaluated by the potential difference between cathode and ground, using a 100μN class ion thruster developed at Kyushu University and two 50×50mm² field emission cathodes with carbon nanotube emitter. The potential difference between cathode and ground is not only determined by cathode electron supply capacity and the position of the cathodes but also foot print of the neutralizers, it would be due to the space charge limitation. That is, the potential difference between cathode and ground is improved with increase in total emission current, and that with a single field emission cathode at emission current of 6mA is -20V, on the contrary, that with two field emission cathodes is -12V. </p>

<p> 電気推進を用いた軌道間輸送機（OTV）の開発における技術的挑戦と克服に関するパネルディスカッションが行われた．太陽発電衛星の輸送では，ペイロードの太陽電池をOTVで利用できる場合，電気推進は特に有効な推進システムとなる．電気推進の推進剤として有力な候補はアルゴンであり，大出力のアルゴン推進機を開発する上での技術的課題が議論され共有された．また太陽発電衛星の実現には打ち上げ機との連携や，OTV全体でのシステム最適化が必要不可欠であり，分野を横断した研究者間の協調と，共通で意識すべき事業戦略（ロードマップ）の策定が重要であると再認識された.</p>

<p> 宇宙太陽光発電においては大量の物資輸送が求められ，そのためには膨大な推進剤が消費される．現在の主流となっているキセノンは高価であるため，現実的ではない．そこで我々は，常温常圧で固体であり昇華性を持つ物質を推進剤として使用することを提案する．固体推進剤を使用することにより，高圧タンクやシステム全体の大幅な削減も期待でき，より低価格の軌道間輸送システムが構築可能となる．昇華性推進剤が代替燃料となり得るのか，イオンエンジンを用いて性能を評価した結果を報告する．</p>