Masakatsu Nakano

Dual Propulsive Mode Microthruster Using a Diode Laser

Introduction M ICROSPACECRAFT have increasingly attracted the interest of researchers in recent years. The research is motivated by the need to reduce in the cost of developing and launching spacecraft and to improve in the mission capability and redundancy using microspacecraft constellations. Although several laboratory and flight models of 1–10 kg class microspacecraft have been developed, most of them do not have propulsion systems.1−3 To enable future microspacecraft missions, such as formation flying, a small propulsion system suitable for microspacecraft, namely, a microthruster, is needed.4 One of the most important requirements in the microthruster is the capability to generate both lower range thrust and higher range thrust. For instance, microspacecraft require lower thrust for attitude controls and higher thrust for slew maneuvers. In the case of formation flying,4 microspacecraft need lower thrust for the constellation controls and higher thrust for the rearrangement of their formation patterns. In particular, formation flying inevitably requires propulsive capability, although attitude control is accomplished by passive systems such as momentum wheels and magnetic torqueres. To limit the weight and size of microspacecraft, it is essential to satisfy the requirement of lower and higher range thrusts with the same propulsion system. To our knowledge, there is as yet no single propulsion system that can supply such a wide range of thrust for the 1–10 kg class microspacecraft. A diode laser ablation microthruster and digital microthruster array seem to be promising candidates for the 1–10 kg class microspacecraft. The diode laser ablation microthruster5 uses laser beams to irradiate the surface of a polymer propellant, and the heated

Alumina reduction by laser sustained plasma for aluminum-based renewable energy cycling

A novel alumina (Al2O3) reduction technique for a renewable energy cycling system based on aluminum is proposed. Al2O3 powder was fed into laser-sustained plasma and thermally dissociated. The produced Al was expanded to supersonic speeds through a nozzle. From the Al and argon line distributions in the flow direction, it was found that Al remained in the dissociated state. A water-cooled copper tube was inserted in the flow to collect Al. X-ray analysis indicated that elemental Al was observed on the surface of the tube. The maximum value of the estimated reduction efficiency was 5%.

LE-NET and Multi-Purpose Laser Propulsion System

The concept of the Laser Energy NETwork (LE-NET) and the multi-purpose laser propulsion system being studied at NAL are overviewed. The LE-NET can provide abundant energy supplies on earth acting as the effective and long lasting measures against global warming and will cover wide variety of transportation needs by the laser power. The LE-NET needs a Solar Excited Laser (SEL) that directly converts a solar light into a laser beam. The SEL is expected to minimize the SPS weight considerably, leading low-cost realization of the LE-NET.

Fundamental Experiments on Glycerin Propellant Laser Thruster

Impulse generation experiments of a liquid propellant laser thruster were conducted using glycerin propellants in the energy range of 60 mJ ∼ 60 J. Momentum coupling coefficients and specific impulses were obtained from momentum impulse and propellant mass measurements. The maximum specific impulse was 18 s at the laser beam energy of 55 J. Experimental data were scaled in terms of the laser beam energy and the diameter of the glycerin droplet to extrapolate laser thruster performance. The results indicate that the diameter of the glycerin droplet must be less than 0.24 mm in these experiments to achieve specific impulse more than 1,000 s that will be required to compete with other space propulsion systems.

Numerical simulation of full-aperture-pair ion optics in a miniature ion thruster

The 211-aperture-pair two-grid ion optics of a miniature ion thruster is numerically simulated. Since the plasma in the miniature ion thruster is too inhomogeneous to introduce mirror or translational boundary conditions between apertures, all the apertures of the grid system are considered. The simulation is self-consistent, the ion current profile in the discharge chamber plasma is given by the particle-in-cell with Monte Carlo collision algorithm calculations, and all the ion beams extracted from the full-aperture-pair array were tracked including charge-exchange ions. A scheme for the construction of the full-aperture-pair simulation domain is proposed based on the array of a six-fold hexagonal single-aperture-pair simulation domain, which can be extended to other numbers of aperture pairs. Numerical results on accel impingement current and ion-beam profile are compared to experimental data and shown to be in reasonable agreement. Furthermore, the full-aperture-pair ion-optics model is compared with t...

Impulse Generation Mechanism in Glycerin Propellant Laser Thruster

A sequential process from pulsed laser irradiation onto a spherical liquid propellant to impulse generation is discussed toward higher specific impulse performance of the thruster. A Q‐switched 10‐ns Nd: YAG laser pulse with 1 μm wavelength was focused in a 2‐mm diameter glycerin droplet in vacuum condition (∼10 Pa). Visible image of the droplet shot with the laser pulse, laser energy transmitted through the droplet, emission spectrum in visible to near infrared region, and temporal impulse behavior measured with piezoelectric devices were obtained. It is found that the impulse generation mechanism can be divided into energy deposition on the surface and inside of the droplet, and subsequent explosion of the droplet, depending on laser irradiation conditions.

Fundamental Experiments on Liquid Propellant Laser Thruster

Impulse generation experiments of a liquid propellant laser thruster were conducted using glycerin propellants in the energy range of 60mJ–60J. Momentum coupling coefficients and specific impulses were obtained from impulse and propellant mass measurements. The maximum specific impulse was 18s at the laser beam energy of 55J. Experimental data were scaled in terms of energy and the radius of the glycerin droplet to extrapolate laser thruster performance. The results indicate that the radius of the glycerin droplet must be less than 0.24 mm in these experiments to achieve specific impulse more than 1,000s that will be required to compete with other space propulsion systems.