Cleaning space debris with laser is a hot topic in the field of space security research. Impulse characteristics are the basis of cleaning space debris with laser. In order to study the impulse characteristics of rotating irregular space debris irradiated by multi-pulse laser, the impulse calculation method of rotating space debris irradiated by multi-pulse laser is established based on the area matrix method. The calculation method of impulse and impulsive moment under multi-pulse irradiation is given. The calculation process of total impulse under multi-pulse irradiation is analyzed. With a typical non-planar space debris (cube) as example, the impulse characteristics of space debris irradiated by multi-pulse laser are simulated and analyzed. The effects of initial angular velocity, spot size and pulse frequency on impulse characteristics are investigated.
With much more attention and utilizing paying to space resource, the detection and removal of space debris, the biggest threatened to the orbiting spacecraft, has become a research hotspot in recent years. In order to protect the important space assets, such as the international space station, it has been realized of simulation and system parameters’ design, which contained debris’ detection and removal by space-based pulse laser. Simulation results show that the determine time of detection laser and removal laser should be considered after judging weather debris is in the “clear window”. As the increasing of detection pulse and removal pulse, the orbit element of space debris has a regular change, with the decreasing of single pulse velocity increment. The system of detection and removal of space debris designed as: detection laser power 50W, removal laser power 150kW, laser wavelength 1064nm, pulse width 10ns, frequency 100Hz. The research has a great significance of detection and removal of debris by space-based laser and engineering application.
Laser ablation micro-propulsion technology is the most promising field in laser propulsion. The specific impulse is the important evaluate indicator of the micro propulsion performance. It represents the impulse generation by consuming unit weight of the working medium. Its accurate measurement can not only help to analyze the mechanism of laser ablation matter, but also help the design of micro laser ablation thruster. This paper presents a measurement method, which can not only obtain the impulse by single pulsed laser ablation the working medium, but also measure the ablation mass, which can directly measure the specific impulse. The method is based on the model of torsion pendulum in vertical direction movement, which is the direction of impulse by pulsed laser ablation and the gravitation direction caused by the loss of the ablation mass, to obtain the corresponding impulse and ablative weight. The paper deduced the measuring principle, pointed out the error and analysed the design principle of the torsion balance, the results show that, according to the torsion angle change due to the impulse by pulsed laser ablation and the mass loss by laser ablation, the maximum angle can be used to calculate the impulse and the stable rotation angle can be used to calculate the loss weight when the torsion period is much greater than four times the width of a single pulse.
A threat to spacecraft in long-term low earth orbits is the high probability of impacts with small particles of man-made space debris in 1-cm to 10-cm size range. One possible solution for 1-10 cm size debris is to de-orbit the particles with a ground or space based laser. A modified torsional impulse balance system has been developed as a diagnostic tool to study fundamental laser ablative process on different material such as aluminum, titanium, magnesium and carbon fiber composite that are frequently used in spacecraft. Of particular interest is the force due to process of laser ablation as well as the impulse coupling coefficient. It can be concluded from the experimental result that for the experimental materials, with the increasing laser intensity, the coupling coefficient increase firstly and then decrease and it reaches the maximum at some value when the laser intensity varies around 10<sup>9</sup> W/cm<sup>2</sup>. And the experimental data compares well with the calculation result according to Phipps' scaling law. As we extend the previous research, it will provide a reference for the study in cleaning man-made space debris by laser.
Plume generation and expansion performance measurements have been performed with ns-shadowgraphy time resolved method on laser micro ablation. The optical display method of micro jet plume characteristics is discussed and the plume character is measured and analyzed to research the relationship between coupling mechanics and plume dynamics. The micro laser ablation properties of different commercial ploymers are compared to find out the ideal micro laser thruster fuel to achieve propulsion performance improvement. The plume generation and expansion character is analyzed by the shock wave and ablation product evolution. Shock wave and ablation product jet could be formed in the air condition, and the velocity is different. Normally, the shock wave is faster than the jet, but the inverse situation is still observed that could be taken as signal of the higher specific impulse. Nine common polymers were tested and compared, the results show that: polyvinyl chloride ( PVC ) material is the best choice of commonly used polymer material. A velocity of 820m/s of shock wave formed by PVC ablation could be obtained, which is highest in the chosen polymers, while the velocity is 844m/s for Al, and there are more ablation product could be found for PVC. The result indicates that ablation efficiency of PVC is the best, and PVC is the priority fuel material for the better propulsion performance, easy machining and storage.
Ablaiton of solid target with high power energy can induce laser vapor plasma, which would impart reverse impulse to the target. The physical processes include target heating, melting, vaporization and formation of plasma plume. In this paper, we presented a new numerical model, which described target heating, melting and evaporation. Meanwhile, the ejection of material formed a plasma plume above the surface and expanded into the ambient vacuum. The formed plasma absorbed the laser energy passing through it. The heating of the target was described with a heat conduction equation, which led to the temperature distribution inside the target, as a function of time. When the temperature rises further, vaporization would appear. The vapor velocity and temperature at the surface were used as input for the boundary conditions of plasma plume, which was described with Navier–Stokes equations, for conservation of total vapor mass density, momentum and energy. We considered two dominant absorption mechanisms in the process of plasma shielding, which were electron–ion and electron–neutral inverse Bremsstrahlung. Based on above assumptions, the left laser energy because of plasma shielding was calculated. Results for an aluminum target with Gaussian profile laser pulse with duration of nanosecond were obtained, including the plasma plume temperature, ionization degree, densities of neutral, ions and electrons and laser absorption energy. Results showed that the energy absorption by plasma plume played an important role in the coupling of laser energy and target.