Kazuhisa Fujita

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.

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.