Akihiro Sasoh

Bio: Akihiro Sasoh is an academic researcher from Nagoya University. The author has contributed to research in topics: Shock wave & Laser. The author has an hindex of 22, co-authored 295 publications receiving 2299 citations. Previous affiliations of Akihiro Sasoh include University of Tokyo & University of Washington.

Review: Laser-Ablation Propulsion

Abstract: LASER ablation propulsion (LAP) is a major new electric propulsion concept with a 35-year history. In LAP, an intense laser beam [pulsed or continuous wave (CW)] strikes a condensedmatter surface (solid or liquid) and produces a jet of vapor or plasma. Just as in a chemical rocket, thrust is produced by the resulting reaction force on the surface. Spacecraft and other objects can be propelled in this way. In some circumstances, there are advantages for this technique compared with other chemical and electric propulsion schemes. It is difficult to make a performance metric for LAP, because only a few of its applications are beyond the research phase and because it can be applied in widely different circumstances that would require entirely different metrics. These applications range from milliwatt-average-power satellite attitude-correction thrusters through kilowatt-average-power systems for reentering near-Earth space debris and megawatt-to-gigawatt systems for direct launch to lowEarth orbit (LEO). We assume an electric laser rather than a gas-dynamic or chemical laser driving the ablation, to emphasize the performance as an electric thruster. How is it possible for moderate laser electrical efficiency to givevery high electrical efficiency? Because laser energy can be used to drive an exothermic reaction in the target material controlled by the laser input, and electrical efficiency only measures the ratio of exhaust power to electrical power. This distinction may seem artificial, but electrical efficiency is a key parameter for space applications, in which electrical power is at a premium. The laser system involved in LAP may be remote from the propelled object (on another spacecraft or planet-based), for example, in laser-induced space-debris reentry or payload launch to low planetary orbit. In other applications (e.g., the laser–plasma microthruster that we will describe), a lightweight laser is part of the propulsion engine onboard the spacecraft.

Technology and Application Aspects of Applied Field Magnetoplasmadynamic Propulsion

Abstract: Currently available or realizable applied e eld magnetoplasmadynamic (AF‐MPD) thrusters operating in the power range 5‐100 kW appear to be excellently suited for orbit change and stationkeeping (drag compensation) of large satellites because of their high specie c impulse, sufe cient thrust, and compact geometry They were developed to considerable maturity almost 20 years ago, but have not yet been used in space because of the lack of missions, appropriate power, and qualie cation There is evidence that these engines cannot be operated realistically in the laboratory, mainly because of the high vacuum needed to exclude unknown environmental interaction with the plume, even at very low vacua A space experiment is needed to provide proof of Isp and efe ciency The International Space Station now provides the opportunity to qualify the engine in space This paper describes the application potential, performance characteristics, and technological status of the AF‐MPD thruster, remaining application issues to be resolved, and a space experiment proposed to operate and investigate the engine under space-e ight conditions

Electromagnetic effects in an applied-field magnetoplasmadynamic thruster

Abstract: Experimental and analytical studies have been conducted on the performance and thrust production mechanisms of an applied-field magnetoplasmadynamic thruster. The thruster was able to run with a high-thruster performance due to large electromagnetic effects related to the applied magnetic field. Using hydrogen, helium, and argon as the propellant, over 20 percent thrust efficiency was obtained over a wide specific impulse range from 1000 to 7000 s at input power levels between 2.2 and 15.9 kW. From the measurements of performance characteristics and current densities in the acceleration region, and by a theoretical analysis, it is found that the thruster operation is characterized by a parameter, B-squared/m (B: applied magnetic field strength, m: propellant mass flow rate). 9 refs.

Laser-driven in-tube accelerator

Abstract: A device of accelerating a projectile using laser power, “laser-driven in-tube accelerator,” has been developed. It is characterized by accelerating the projectile in a tube and by supplying the laser beam from the direction opposite to the projectile motion. The laser beam is incident on the nose of the projectile, reflected first on the nose and second on the inner wall of the projectile shroud, then focused behind. Operation performance is measured using a CO2 transversely excited atmospheric laser of a nominal output energy of 5 J/pulse. A coupling coefficient of 73 N/MW is obtained using the atmospheric air as the working fluid.

Similarity and Dimensional Methods in Mechanics

Abstract: By L I Sedov London: Cleaver-Hume Press Ltd Pp xvi + 363 Price 105s This is really two separate books within the same pair of covers First of all Chapters 1-3, some 145 pages, are devoted to the discussion of similarity and dimensional, methods and their application to a variety of problems in mechanics and fluid mechanics

A Flux Splitting Scheme with High-Resolution and Robustness for Discontinuities(Proceedings of the 12th NAL Symposium on Aircraft Computational Aerodynamics)

Abstract: A flux splitting scheme is proposed for the general nonequilibrium flow equations with an aim at removing numerical dissipation of Van-Leer-type flux-vector splittings on a contact discontinuity. The scheme obtained is also recognized as an improved Advection Upwind Splitting Method (AUSM) where a slight numerical overshoot immediately behind the shock is eliminated. The proposed scheme has favorable properties: high-resolution for contact discontinuities; conservation of enthalpy for steady flows; numerical efficiency; applicability to chemically reacting flows. In fact, for a single contact discontinuity, even if it is moving, this scheme gives the numerical flux of the exact solution of the Riemann problem. Various numerical experiments including that of a thermo-chemical nonequilibrium flow were performed, which indicate no oscillation and robustness of the scheme for shock/expansion waves. A cure for carbuncle phenomenon is discussed as well.

Spacecraft Electric Propulsion—An Overview

Abstract: A short review of the status of electric propulsion (EP) is presented to serve as an introduction to the more specialized technical papers also appearing in this Special Issue (Journal of Propulsion and Power, Vol. 14, No. 5, Sept. –Oct. 1998). The principles of operation and the several types of thrusters that are either operational or in advanced development are discussed Ž rst, followed by some considerations on the necessary power sources. A few prototypical missions are then described to highlight the operational peculiarities of EP, including spacecraft interactions. We conclude with a historical summary of the accumulated  ight experience using this technology.

Pulsed Plasma Thruster

Abstract: The 35-year history of the development and application of the pulsed plasma thruster (PPT) is reviewed. The PPT operates by creating a pulsed, high-current discharge across the exposed surface of a solid insulator, such as a Tee on t bar. The arc discharge ablates material from this surface, thereby providing propellant that is ionized, heated, and accelerated to high speed. Typically, the current pulse lasts for a few microseconds, driven by a capacitor that is charged and discharged approximately once per second. Exhaust speeds range from 3 to 50 km/s, depending on the details of the PPT design. We review the basic physics and types of PPTs, and discuss the performance of e ight and laboratory versions, with special attention to velocity and plume measurements. We also present the status of PPT theory and modeling, with emphasis on mass evolution and plasma acceleration, and describe recent variations on PPT operation, laboratory thrust measurement techniques, and the separate components of PPT efe ciency.

Electric propulsion for satellites and spacecraft: established technologies and novel approaches

Abstract: This contribution presents a short review of electric propulsion (EP) technologies for satellites and spacecraft. Electric thrusters, also termed ion or plasma thrusters, deliver a low thrust level compared to their chemical counterparts, but they offer significant advantages for in-space propulsion as energy is uncoupled to the propellant, therefore allowing for large energy densities. Although the development of EP goes back to the 1960s, the technology potential has just begun to be fully exploited because of the increase in the available power aboard spacecraft, as demonstrated by the very recent appearance of all-electric communication satellites. This article first describes the fundamentals of EP: momentum conservation and the ideal rocket equation, specific impulse and thrust, figures of merit and a comparison with chemical propulsion. Subsequently, the influence of the power source type and characteristics on the mission profile is discussed. Plasma thrusters are classically grouped into three categories according to the thrust generation process: electrothermal, electrostatic and electromagnetic devices. The three groups, along with the associated plasma discharge and energy transfer mechanisms, are presented via a discussion of long-standing technologies like arcjet thrusters, magnetoplasmadynamic thrusters, pulsed plasma thrusters and ion engines, as well as Hall thrusters and variants. More advanced concepts and new approaches for performance improvement are discussed afterwards: magnetic shielding and wall-less configurations, negative ion thrusters and plasma acceleration with a magnetic nozzle. Finally, various alternative propellant options are analyzed and possible research paths for the near future are examined.