| Laser propulsion is a revolutionary new form of rocket propulsion in which a remote high-power laser is used to heat hydrogen propellant to extremely high temperatures. This approach has important advantages over existing propulsion systems, and is being explored for use in advanced orbital transfer vehicles.; The key problem encountered is how to efficiently convert the laser energy into the thermal energy of the propellant. At this time, high-temperature laser-sustained plasmas appear to be the most efficient conversion mechanism.; A comprehensive study of argon laser-sustained plasmas has been conducted using the University's 110 kW CO(,2) laser facility. It has been found that the plasmas are stable phenomena which will adjust to variations in laser power or flow velocity. Calorimetric studies have shown that the plasma can absorb up to 80 percent of the incident laser energy in extremely short distances. The dependence of absorption on power, pressure, flow rate, and beam optics has been examined.; The fraction of the laser energy retained by the gas as thermal energy has also been measured under a range of flow and power conditions; efficiencies as high as 40 percent have been demonstrated. A laser-induced fluorescence diagnostic system using atomic seedants has been developed to obtain more acurate efficiency measurements.; A two-dimensional numerical model of the plasma has also been developed, which includes real argon properties and accurate absorption and emission coefficients. Excellent agreement with the experimental results has been demonstrated, specifically with regard to plasma size, peak temperatures, absorption fractions, minimum maintenance powers, blowout velocities, and conversion efficiencies. The model also predicts that efficiencies as high as 75 percent should be achievable at high f numbers, a prediction now being tested experimentally. |
