Pulsed Laser Propulsion Performance of 11-cm Parabolic 'Bell' Engines: CO2 TEA vs. EDL

Single pulse laboratory experiments were carried out with a high-power CO2 Transversely-Excited Atmospheric (TEA) laser using three laser pulsejet engines, shaped as parabolic bells, measuring 11-cm in diameter. Assuming the vertex is set at the parabola's focus, the "calibration bell" engines had three different total divergence angles of 60, 87.2, and 120 degrees (i.e., viewing outward towards the 11-cm nozzle exit plane). The objective was to quantify and calibrate the effects of laser pulse duration upon the momentum coupling coefficient (Cm) performance from the two CO2 lasers, using laser pulse energy as the parametric variable. Bell engine performance data from the TEA laser are contrasted with former results from the PLVTS CO2 electron discharge laser (EDL). The single-pulse PLVTS tests were conducted in Sept. 2000 and Sept. 2001, revealing that the impulse and Cm performance of the 60 deg bell generally exceeded the 87.2 deg engine, which in turn outperformed the 120 deg bell. With PLVTS, the maximum single-pulse Cm varied from 275 to 375 Nsec/MJ. In contrast, the 2 microsecond TEA laser tests generated results that were distinctively different from that of the EDL. Both tests used a standard ballistic pendulum to measure airbreathing engine performance at a pressure of one atmosphere.