Keita Nishii

Verified

Keita verified their affiliation via an institutional email.

Learn more

Verified

Keita verified their affiliation via an institutional email.

Learn more

• Ph.D (Engineering)
• Professor (Assistant) at Tokyo Metropolitan University

This study addresses a quasi-steady self-field magnetoplasma dynamic (SF-MPD) thruster with water propellant. Water has no toxicity nor reactivity to materials and necessitates no high-pressure tank. Accordingly, using water as a propellant lowers thruster size and the ground-test costs. Moreover, water is abundant on Earth and accessible in space...

This study used a direct simulation Monte Carlo approach to investigate the effects of facility pressure on micronozzles for the propulsion systems of microspacecraft. The simulations quantitatively evaluated the effect of background pressure on the micronozzle performance in nozzle flows ranging up to a throat Reynolds number of 220. The results s...

This study investigates the facility effects on gridded ion thrusters tested in ground vacuum chambers using a Multi-GPU PIC-DSMC solver, CHAOS. The research summarizes our recent work on contamination by backsputtered particles and the coupling between the electron source and chamber walls. These results indicate that different sputter models sign...

DC Arcjet thrusters have enormous potential for inter-orbit transportation because of their higher specific impulse comparable to chemical propulsion and relatively high thrust density among electric propulsion. We proposed to use water as a propellant , which is not toxic and highly available to be advantageous over hydrazine from the viewpoints o...

This study aimed to enhance the performance of a double-channel TAL-type Hall thruster by redesigning its structure. The redesigned thruster, TMU-D058, exhibited improved an-ode efficiency in both inner and outer channels compared to the previous model. The inner channel achieved a maximum anode efficiency of 43% at 491 W, and the outer channel ach...

Recently, Hall thruster using water propellants is attracting attention. Although a hollow cathode is conventionally used as a cathode, there is concern that the ceramic used for thermionic electron emission will be degraded by the oxygen contained in the water. Therefore, we focused on RF cathodes without ceramics, which have the potential to be a...

This study investigates the performance of liquid-water-fed magnetoplasma dynamic (MPD) thrusters, focusing on enhancing the thrust-to-power ratio by changing the propellant injection method. Two types of injector orifices and injection methods, single and multi-injection, were tested under varying discharge currents. Results indicate that a higher...

This paper deals with a performance evaluation of an anode-layer-type Hall thruster (TAL-type Hall thruster) using water propellant. TMU-034, a 600-W class TAL-type Hall thruster originally designed for xenon propellant, was tested using water propellant. An evaporator provided water vapor using vapor-liquid equilibrium provided water vapor at the...

Ground testing is necessary to understand carbon sputtering that occurs when thruster beam ions hit the ground chamber walls and back-sputtered carbons contaminate the thruster. This study utilizes kinetic simulations with a molecular dynamics based carbon sputter model to investigate the sputtered carbons inside the vacuum chamber and compares wit...

A combination of water and aluminum powder has been studied for space propulsion. These propellants are particularly suitable for chemical micropropulsion. However, development is being delayed due to many constraints, mainly: safety requirements and system restrictions. This study measured the combustion pressure and reacted aluminum fraction of p...

This study investigated the behavior and temperature of condensed combustion products (CCPs) in a magnesium–water vapor flame. The experiments were conducted using magnesium plates with a surface area of 5×5mm2 and an oxidizer pressure in the range of 10–100 kPa, in consideration of potential applications in microspacecraft. Compared with the air a...

In this paper, we discuss various aspects of the plasma plume that forms when testing a Gridded Ion Thruster (GIT) inside a vacuum chamber. We use fully kinetic simulations of an ion engine using the hybrid MPI-CUDA code CHAOS which uses the PIC-DSMC method. The GIT is modeled as a separated source ion engine, with the neutralizer placed outside th...

The electrical environment of a ground vacuum testing chamber creates facility effects for gridded ion thrusters. For example, it is well known that the plume from the thruster generates current paths that are very different from what occurs in space, and the neutralization of this plume is also different. For reasons such as this, it is important...

Gridded ion thrusters are tested in ground vacuum chambers to verify their performance when deployed in space. However, the presence of high background pressure and conductive walls in the chamber leads to facility effects that increase uncertainty in the performance of the thruster in space. To address this issue, this study utilizes a fully kinet...

The electrical environment of a ground vacuum testing chamber creates facility effects for gridded ion thrusters. For example, it is well known that the plume from the thruster generates current paths that are very different from what occurs in space, and the neutralization of this plume is also different. For reasons such as this, it is important...

This study focuses on investigating the impact of facility conditions on micronozzles, a common issue encountered when attempting to replicate the space environment in experimental setups. When the background pressure within the vacuum chamber is high during micronozzle performance testing, the measured performance tends to decrease compared to the...

Magnesium has attracted widespread attention as fuel. Previous studies have suggested that the state of the residue oxide changes with the oxidizer. This study investigated the magnesium combustion plume by changing the oxidizer and its pressure. An ignition system was developed to observe the self-ignition of magnesium in a fixed position. We obta...

Gridded ion thrusters are tested in ground vacuum chambers to verify their performance when deployed in space. However, the presence of high background pressure and conductive walls in the chamber leads to facility effects that increase uncertainty in the performance of the thruster in space. To address this issue, this study utilizes a fully kinet...

View Video Presentation: https://doi.org/10.2514/6.2022-3497.vid Carbon contamination of an electric propulsion (EP) facility as a result of backsputtering is a well-known problem in EP testing. As EP systems progress towards higher power capabilities (∼100 kW), the need to decouple facility contamination effects from the on-orbit performance and w...

Micronozzles have recently been used for micro-/nanosatellites to expand their role in space development. At low Reynolds numbers, there are inevitable degradations in nozzle performance because of the viscosity. Several studies have revealed and evaluated this phenomenon. Especially at Reynolds numbers under 1000, background pressure significantly...

Carbon contamination sputtered from graphite lined vacuum facilities obscures erosion and deposition measurements of carbon-based thruster components during electric propulsion wear tests. The uncertainty in lifetime analysis models associated with facility effects compounds as thrusters move towards higher powers and the associated rates of backsp...

Backsputtering causes carbon contamination in an electric propulsion (EP) facility, which is a well-known concern in EP testing. The need to isolate facility contamination effects from on-orbit performance and wear characteristics grows as EP systems evolve toward larger power levels (∼100 kW). Both physics-based modeling and fundamental experiment...

Metals, specifically magnesium, have attracted widespread attention as fuels. Most research has pointed out the safety of the reactants and products. Furthermore, in terms of performance, the theoretical volumetric specific impulse of a metal-water propellant is much higher than that of hydrazine. Most metal-water combustion studies have focused on...

The combustion of magnesium with water is an attractive power source because of the high combustion enthalpies and safety of the materials. For space propulsion, wire-shaped magnesium, which is easy to be fed to the combustion chamber, is considered to be used as a fuel. This study aims to obtain the combustion characteristics of magnesium wire wit...

The ratio between thrust generated by a micronozzle and the theoretical thrust under assumption of quasi-one-dimensional compressible fluid generally drops as the Reynolds number of fluid gets lower. Therefore many experiments have been done to measure and reveal the characteristic values in the micronozzle flow including density distribution. Howe...

There have been many studies on a propulsion system using water, which is an attractive propellant in space. During the process of vaporizing water, flow boiling is commonly used despite difficulties with vapor–liquid separation. Previous studies have proposed a vapor feeding system, which separates the water vapor from the liquid using surface ten...

This paper highlights the power system design of the equilibrium lunar–Earth point 6-unit spacecraft (EQUULEUS), which will fly to the second Earth–Moon Lagrange point and perform a variety of scientific and technological missions. The limited power generation and high uncertainties of power generation and consumption are major difficulties encount...

Magnesium-water combustion is one of the promising energy sources for small spacecraft in terms of safety and high energy density. For actual application to propulsion system, the physics of the steady state combustion of magnesium wires in water vapor should be clarified. In this study, a magnesium wire with a diameter of 0.8 mm is burned in the 1...

This study directly measures the performance of a thruster nozzle using water vapor as propellant in the Reynolds number below 1000. Because of its properties, water is suitable as a propellant for small satellites, often with a low-Reynolds-number flow using a micronozzle. The low Reynolds number of the flow and the phase changes in supersonic vap...

High thrust propulsion systems that can be used in small spacecraft are urgently needed to expand the use of small spacecraft. This study proposes a hybrid thruster for small spacecraft using wire-shaped magnesium as a fuel and water as an oxidizer. “Hybrid thruster” means that the in-space propulsion system generates thrust using a chemical reacti...

The combustion of aluminum and magnesium is an attractive power source. Many practical tests have been conducted as a composite propellant of metal powder and water. However, because the safety and the ease of handling are required for applying small spacecraft, it is desirable that nonpowder metal is used as fuel and stored separately from oxidize...

EQUULEUS is a 6U CubeSat developed by the University of Tokyo and JAXA, which will fly to a libration orbit around the second Earth-Moon Lagrange point (EML2) as a secondary payload of the Space Launch System (SLS). At the destination and on the way there, EQUULEUS will conduct three scientific missions such as the detection of lunar impact flashes...

This paper presents the development of a thrust stand to enable direct measurement of thrust and specific impulse for a CubeSat propulsion system during firing. The thrust stand is an inverted pendulum and incorporates a mass balance for direct in situ mass measurement. The proposed calibration procedure allows precise performance characterization...

EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) will be the world's smallest spacecraft to explore the Earth–Moon Lagrange point. It is being jointly developed by JAXA (Japan Aerospace Exploration Agency) and the University of Tokyo, and will be launched by NASA's Space Launch System Exploration Mission-1. The spacecraft will fly to a librat...

The University of Tokyo has proposed a water resistojet thruster with a high certainty of liquid–vapor separation and low power consumption. In this propulsion system, liquid water is periodically vaporized in a pulsating manner to generate thrust. A vaporization chamber with a labyrinth-shaped flow path catches droplets using their surface tension...

For the realization of the complicating missions by small spacecrafts, it is necessary to establish the micro-propulsion technology. AQUARIUS (AQUA ResIstojet propUlsion System) is a micro-propulsion system which is going to be installed on a 6U CubeSat EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) and launched in 2020. AQUARIUS uses water...

Storability at low pressure Safety as secondary payload Liquid-Vapor separation Droplets attached on the wall Reuse waste heat of satellites Conclusion EQUilibriUm Lunar-Earth point 6U Spacecraft EQUilibriUm Lunar-Earth point 6U Spacecraft Result-1: Propulsion system stand-alone test AQUA ResIstojet propUlsion System Total 2.5 kg 1.2 kg 46% 26% 10%...

As a propulsion system for micro/nanosatellites, water is one of the most suitable propellants. Water has the merits of storability and safety. However, the water also has a disadvantage of difficulty of liquid-vapor separation and large latent heat. In this study, a water thruster that has a high certainty of liquid-vapor separation and small powe...

This paper highlights the power system design of EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft), which will fly to the 2nd Earth-Moon Lagrange point and perform a variety of science and technological missions. The limited power generation and the high uncertainties of power generation and consumption are major difficulties for the electrica...

In this study, an Al/Fe2O3 thermite reaction is proposed as a new ignition system of hybrid rockets for CubeSats. The advantage is that the reactants are not recognized as gunpowder, and that it is the gasless combustion, which means it has a high possibility of reaction in vacuum. The two experiments were conducted to reveal the characteristics of...

This study proposes a micropropulsion system unifying ion thrusters and resistojet thrusters and assessing that propulsive capability. The remarkable features of the system are the usage of water propellant and unification of the two types of thrusters by the single propellant. Water has been regarded as an attractive propellant in the view points...

Flight model of a micro-water resistojet propulsion system, named AQUARIUS (AQUA ResIstojet propUlsion System) was designed for a deep space exploration by 6U Cubesat. Ultra green propellant: water was used as propellant, which allowed for low pressure feeding system and a safe and easy handling. In addition, water has been arousing interest as a p...

EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) will be the world's smallest spacecraft to explore the Earth-Moon Lagrange point. The spacecraft is being jointly developed by JAXA and the University of Tokyo and will be launched by NASA's SLS (Space Launch System) EM-1 (Exploration Mission-1). The spacecraft will fly to a libration orbit aro...

AQUARIUS (AQUA ResIstojet propUlsion System) is a resistojet propulsion system installed on EQUULEUS. AQUARIUS uses a storable, safe, and non-toxic propellant: water, which allows for the downsizing of the whole propulsion system to 2U while storing 1.2 kg of water. It is operated by a mechanism in which liquid water stored in a tank is heated and...

At the University of Tokyo, the water resistojet named AQUARIUS is now having been developed. Water has some merits; non-toxic, storability at low pressure and potential as the space resources. The difference from the previous studies is that water is vaporized at low pressure at vaporization chamber. Vaporization chamber can completely separate li...

In this study, a water resistojet propulsion system, named AQUARIUS, is proposed and the breadboard model (BBM) test results and the engineering model (EM) design are described. AQUARIUS will be on-boarded the SLS EM-1 CubeSat: EQUULEUS, which is scheduled to be launch in 2019. AQUARIUS uses a storable, safe and non-toxic propellant: water, which a...

Today, the need for micropropulsion systems for micro- and nanospacecraft is growing. Micro-nozzles generally lead to low Reynolds numbers nozzle flow. It has been reported that nozzle efficiency was decreased at low Reynolds numbers region. However, there were gaps of nozzle efficiencies at same Reynolds number in previous researches, and ambient...

In this study, the performance of the water micro-resistojet propulsion system (AQUARIUS) was estimated. The latter is to be installed on a 6U CubeSat EQUULEUS. AQUARIUS has a vaporization chamber to separate vapor from liquid water and to the get waste of heat of satellite. At this system, pressure before nozzle and Reynolds number at nozzle flow...

In this study, Water micro-propulsion system AQUARIUS (AQUA ResIstojet propUlsion System) is proposed for 6U CubeSat: EQUULEUS to explore the deep space. AQUARIUS uses storable, safe and non-toxic propellant: water, which allows for downsizing of whole propulsion system to 2U and storing 1.2 kg water. Liquid propellant storage allows design of all...

In this study, Water micro-propulsion system AQUARIUS (AQUA ResIstojet propUlsion System) is proposed for 6U CubeSat: EQUULEUS to explore the deep space. AQUARIUS uses storable, safe and non-toxic propellant: water, which allows for downsizing of whole propulsion system to 2U and storing 1.2 kg water. Liquid propellant storage allows design of all...

In this study, a water resistojet propulsion system, named AQUARIUS, is proposed and the breadboard test results and the engineering model design are described. AQUARIUS will be equipped with the SLS EM-1 CubeSat: EQUULEUS, which is scheduled to be launch in 2018. AQUARIUS uses a storable, safe and non-toxic propellant: water, which allows the desi...