Ikkoh Funaki

Magsail is a space propulsion system using the interactions between the solar wind and the magnetic field generated by the onboard coils. Magnetoplasma sail is a propulsion system that increases thrust by expanding the magnetosphere through plasma injection from the spacecraft. There are two mechanisms on the magnetospheric inflation: method using frozen-in of magnetic field to carry magnetic field lines by high dynamic pressure plasma and method using the diamagnetic current by thermal plasma, which is called the ring current. We investigated the effect of the dynamic pressure and thermal pressure on the MPS thrust performance used electromagnetic hydrodynamic simulation. It was shown that the ring current is enhanced by adding dynamic pressure to the thermal plasma and increases thrust gain. The high thrust gain over 2.25 was obtained at β_th = 0.5 - 2 and β_k = 4 - 8. However, the thrust is reduced because the super magneto acoustic wave region is generated in the magnetosphere, which prevents the propagation of thrust in large β conditions. The wide parameter survey reveals injection plasma parameter regions where thrust reduction is restrained and high thrust gain is obtained.

Abstract This review deals with the selection of the electric propulsion system (EPS) for the internationally developed and designed, primary nuclear-electric space tug International Nuclear Power and Propulsion System (INPPS). INPPS is scheduled for interplanetary missions to Mars and Jupiter moon Europa missions by the end of decade 2020. Regarding specific technical and mission parameters preselected electric thruster (ET) types, developed by international companies and institutions, are analysed, evaluated and investigated for a possible application as propulsion system (PS), the so-called CET (Cluster of Electric Thrusters). It is analysed whether solely electric thrusters, combined in an adequate CET, enable the envisaged interplanetary missions—robotic and astronautic/crewed with the INPPS flagship. Thruster clusters with strategic consortium considerations are analysed as a feasible PS of the INPPS. The studied CET consists of the following: (a) only European ETs, (b) combination of German and European ETs, (c) Japanese and European ETs or at least (d) Japanese, European and US thrusters. The main results are (1) Robotic and crewed INPPS mission to Mars/Europa are realizable with EPS only (no chemical propulsion is needed), (2) that every CET, except (c) of only Japanese and part of European thrusters, is capable to perform the main part of envisaged INPPS flagship mission orbit to Mars, back to Earth and to Jupiter/Europa moon.

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.

This paper reports on our study to develop a magnetic circuit with a discrete outer coil and test its performance in a Hall thruster. The results were compared to those of a Hall thruster on board the Engineering Test Satellite-9 (ETS-9), which used a cylindrical outer coil. At the normalized magnetic field strength of 0.58 for the 6 kW operation using a six poles discrete outer coil, the thrust, discharge current, Isp, thrust-to-power ratio, thrust efficiency, and discharge oscillation were 386.7 mN, 19.0 A, 1890 s, 66.9%, 62.0%, and 13.5% respectively. The Hall thruster with the new magnetic circuit achieved equivalent performance (including discharge stability) to the Hall thruster on board the ETS-9. Further, the study investigated the effect of the number of poles on the performance of the Hall thruster: the performance with the three pole coil was lower than that with the six poles coil. This paper also reports on the effect of pole numbers on utilization efficiency. Mass and current utilization efficiency were more affected by the magnetic field generated by the three poles outer coil.

To create a new flyable detonation propulsion system, a detonation engine system (DES) that can be stowed in sounding rocket S-520-31 has been developed. This paper focused on the first flight demonstration in the space environment of a DES-integrated rotating detonation engine (RDE) using S-520-31. The flight result was compared with ground-test data to validate its performance. In the flight experiment, the stable combustion of the annulus RDE with a plug-shaped inner nozzle was observed by onboard digital and analog cameras. With a time-averaged mass flow of [Formula: see text] and an equivalence ratio of [Formula: see text], the RDE generated a time-averaged thrust of 518 N and a specific impulse of [Formula: see text], which is almost identical to the ideal value of constant pressure combustion. Due to the RDE combustion, the angular velocity increased by [Formula: see text] in total, and the time-averaged torque from the rotational component of the exhaust during 6 s of operation was [Formula: see text]. The high-frequency sampling data identified the detonation frequency during the recorded time as 20 kHz in the flight, which was confirmed by the DES ground test through high-frequency sampling data analysis and high-speed video imaging.

This paper presents the results of an S-shaped pulse detonation engine (PDE) ground firing test in the form of a detonation engine system. The world's first technology demonstration of PDE in space using a sounding rocket is planned, and the aim is to control the rocket spin rate in the axial direction using pulsed detonation. The PDE operation at full sequence was successful. The despin rate change of the rocket between continuous oxygen supply and successful PDE operation is expected to be 0.95 deg/s per run. This change in despin rate can be measured by an onboard gyro sensor, making the system flyable. The test results were compared with data from thrust measurement tests conducted in a laboratory, the results of which confirmed the thrust generation under an ambient pressure of 0.5 & PLUSMN;0.1 kPa. The average thrust values in the thrust measurement experiments showed good agreement of 101 & PLUSMN;3% with a quasi-steady-state model introduced to predict the PDE thrust. These results demonstrate the feasibility of the newly developed PDE and its system as the world's first technology demonstration of detonation propulsion in space.

<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>

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. An engine cooling concept for cylindrical rotating detonation engine which had an injector surface on the combustor side wall has been tested with three combustor length of 21, 30, and 6 mm. Thrust measurement of the cylindrical RDE (24-mm-diameter) was conducted with monitoring K-type thermocouples inserted in combustor wall. Single rotating detonation wave was observed with the combustor length of 30 and 69 mm in this study. Cooling effect due to the propellant injection was confirmed as the nearly saturated temperature response in the combustor side wall. when the chamber length is more than 30 mm, the specific impulse maintained more than 80% of theoretical value assuming sonic condition at the chamber exit. The result indicated that modest combustor length as an efficient thruster exists in the range of 30 to 69 mm.