Update on CO2 Laser Ablation of Polyoxymethylene

Abstract

Polyoxymethylene (POM) propellants have been studied since the 1970's, and perhaps represent the most promising match of a propellant to the CO2 laser for laser propulsion studies. Applications range from ground-launch of laser propulsion vehicles at atmospheric pressure to spacebased laser ablation propulsion microthrusters. In this paper we broadly update the state of understanding of CO2 laser ablation of POM based on new experiments conducted in Japan and Germany, with a focus on the basic physics of ablation of flat POM targets. Measurements using 10 J-class and 100 J-class lasers are compared to previous literature results for ablation of POM. Emphasis is placed on the influence of control parameters on ablation, especially the incident laser fluence and ambient pressure. New results highlight the influence of the ambient pressure on ablation physics from the vaporization threshold to the plasma regime, and clarify the role of the fluence in determining ablation behavior in air and vacuum environments. Imparted impulse and ablated mass were measured at the target using piezoelectric force sensors, impulse pendulums, and scientific balances. The new experimental investigations cover orders of magnitude in fluence (10E-2 to 10E3 J/cm2) and ambient pressure (10E-3 to 10E5 Pa).