Ballistic measurements of laser ablation generated impulse

The continuously growing number of micro and nanosatellites launched in recent years has stimulated research institutes and industries to find alternative and less expensive ways to reach Low Earth Orbits. Laser ablation propulsion is one of the most promising launching techniques, even though a dedicated and reliable testing system has not been discussed in literature. We present a simple and dependable apparatus for measurements of laser ablation generated impulse and ejected mass. Impulse measurements are performed by using a ballistic pendulum, specifically designed for µNs impulses, whose oscillations are accurately detected by means of a reflected probe laser with a long optical path, which leads to a measurement accuracy of around 1%. The apparatus provides fast and reliable measurements that take into account the variability in centre of mass and moment of inertia that occur by changing the target material on the pendulum. Ablated mass measurements exploit the programmable displacements of a dedicated target irradiated with a large number of laser shots to increase the resolution of the measurement. The apparatus is tested with a KrF excimer laser at 248 nm and pulse width of 20 ns onto an aluminum target: a highly reproducible series of measurements of momentum coupling coefficient (Cm) with a standard deviation of around 1% is presented, along with a specific impulse (Isp) in favourable accordance with the literature.