Propulsion by Absorption of Laser Radiation

The results of an experimental study of the physics of propulsion by absorption of radiation from a remotely stationed high-power laser are presented. Both pulsed and steady-state simulation experiments were performed utilizing a megawatt peak power pulsed CO2 laser. The steady-state simulation experiments were carried out in a vacuum chamber with graphite, Lucite and lithium fluoride as solid propellants. The pulsed experiments consisted of ballistic pendulum measurements of thrust, wall pressure traces, and streak camera records of plasma velocity to deduce the efficiency of a laser powered pulsejet, where air is utilized as fuel. Results indicate that for steady-state propulsion a high ratio of thrust to laser power (~ 10-100 dynes/w) can be obtained by using the laser to simply vaporize a suitable solid propellant. However, for high specific impulse (~1000 sec) it is necessary to add energy to the vapor in a stable manner. This may require gaseous propellants with external control over the absorption characteristics for stable heating in a throatless nozzle. The pulsejet experiments resulted in a ratio of thrust to laser power ~ 25 dynes/w. In order to increase the efficiency of propellant mass utilization, shorter laser pulses with higher power are desirable.