Laser-ablative propulsion using polyacetal at low ambient pressures

Experimental studies about impulse generation mechanisms and performance of polyacetal with TEA carbon dioxide laser pulse(s) were conducted. The time variation of the laser-ablative pressure was measured using the Velocity Interferometer System for Any Reflector (VISAR). Unlike an aluminum target, the ablative pressure became enhanced at an ambient pressure of 10^-2 Pa, whereas at the atmospheric pressure the laser plasma shielded the target against the laser power in the later portion of a laser pulse. The integrated impulse performance from multiple laser pulses was measured using a ballistic pendulum that had a long oscillation time of 27 seconds at a maximum. Up to about ten laser pulses, the impulse stayed low due to the target surface condition. Then, the impulse rose up to a higher level, kept increasing slightly. These impulse characteristics were not significantly affected by the laser pulse repetition frequency, while its magnitude strongly depended on the ambient pressure. The vertical launch of a 6.7-gram projectile using only POM ablation through an evacuated launch tube was successfully demonstrated, and the impulse performance was analyzed.