Mechanism And Experiment Investigation Of Laser Micro-Propulsion

Spatial thruster is an important component for attitude control and orbital maneuver and maintenance of a satellite. As the rapid development of micro-satellite technology and the micro-satellite formation flying, the precision requirement for micro-thruster is more strict. With the recent development, laser micro-propulsion is becoming one of the chosen proposals for micro-satellite's driving. This dissertation is to study the mechanism and application of laser micro-propulsion through experimental investigation and the development of the parts of a laser micro-thruster model.In order to conduct the study experimentally, we designed and built a multi-scale test platform in the lab for measuring the impulses induced by the laser ablation accurately. The plateform includes the laser loading system, the vacuum chambers and the impulsive test equipment. The loading system includes the high power YAG laser, the W magnitude output LD Laser and the relevant optics. The vacuum chamber can simulate the atmosphere pressure from 0-50km above the sea level and can be filled with other different gases for testing. The impulse measurement range of the system is from 10^-8N. s to 10^-3N. s, and the maximum relative error is less than 15% for the smallest impulse of 10^-8N. s.The first attitude control laser micro-thruster prototype model developed in this lab is reported. The model includs the LD light source,micro-lens,target propellant supply device and signal receiving and controlling device. The model size is 8. 5X3. 6cm, and weights only 100g. Black ink paper and double base propellant are used as the ablation target materials under the static test of the model. The black ink paper under transmmission mode gets the highest specific impulse Isp=170s, and the double base propellant under reflection mode gets the highest momentum coupling coefficient Cm=1.9dyne/w. The ratio n. of the jet kinetic energy over laser energy is 0. 77%, and the impulse bit of the model ranges from3. 35×10^-8N. s to 1.6×10^-6N. s.After analyzing the test results of the first model, it is concluded that enhancing the focusing power intensity I on the laser spot and developing suitable target material can improve the propulsion performance. After upgrading, I of the new LD lens is 32 times higher than the original LD Lens. 4 targets of PMMA, double base propellant, celluloid and black paint sheets are made ourselves in the lab. The experimental results show that Isp of PMMA target increases to 1543.7s, Cm of double base propellant increases to 18dyne/W, andηof PMMA, double base propellant, celluloid and black paint have increased to 40%, 44%,10% and4. 8%, respectively. From the results we can see that the enchantment of I and the suitable ablated targets have improved the propulsion performance greatly. PMMA can be used as the target candidate for the attitude control laser micro-thruster because of its higher Isp, and the double base propellant can be used for the target of orbit maintenance laser micro-thruster because of its higher Cm. Comparing the experimental results of targets with same propelleant but different thickness, it can be found the thinner target gets better propulsion performance. The above results can be applied in the development of new laser mcro-thruster model.Using a parabolic reflector as a main laser thruster's model for micro- satellite. With a high power TEA-CO₂ pulsed laser (20J/pulse, 66-150Hz), both single- and multi- pulse propulsion experiments are conducted for three kinds of the parabolic model. The experimental results show that the Cm increases with the increase of half open angle of the model, and the Cm of multi pulse experiments is much lower than the single pulse case. The PVDF stress gauges and the infrared CCD camera are used to measure the pressure and temperature distribution and evolution on the wall of the model. The experiments not only check the test method, but also suggest the thermo-mechanical impact effect should be taken into account in the laser thruster study.