With the development of space station technologies, irradiation of space debris by space-based high-power lasers, can locally generate high-temperature plasmas and micro momentum, which may achieve the removal of debris through tracking down. Considered typical square-shaped space debris of material Ti with 5cm×5cm size, whose thermal conductivity, density, specific heat capacity and emissivity are 7.62W/(m·°C), 4500kg/m<sup>3</sup>, 0.52J/(kg·°C) and 0.3,respectively, based on the finite element analysis of ANSYS, each irradiation of space debris by high-power lasers with power density 10<sup>6</sup>W/m<sup>2</sup> and weapons-grade lasers with power density 3000W/m<sup>2</sup> are simulated under space environment, and the temperature curves due to laser thermal irradiation are obtained and compared. Results show only 2s is needed for high-power lasers to make the debris temperature reach to about 10000K, which is the threshold temperature for plasmas-state conversion. While for weapons-grade lasers, it is 13min needed. Using two line elements (TLE), and combined with the coordinate transformation from celestial coordinate system to site coordinate system, the visible period of space debris is calculated as 5-10min. That is, in order to remove space debris by laser plasmas, the laser power density should be further improved. The article provides an intuitive and visual feasibility analysis method of space debris removal, and the debris material and shape, laser power density and spot characteristics are adjustable. This finite element analysis method is low-cost, repeatable and adaptable, which has an engineering-prospective applications.
Ranging ability valuation for high-repetition laser ranging system (High-repetition LRS) is essential in space debris measurement. Traditional approaches are usually based on system parameters, such as laser transmission frequency, single pulse energy, transmission aperture, etc. However, precision is not properly evaluated when system conditions varies from ideal conditions. In this paper, a degradation model with a new decrement process based on precision curves is proposed. First, the equation of detection probability and ranging distance is derived. Then, a degradation model to get detection-probability-dependent precision curves is established——a decrement process of data sparsity is simulated, by gradually decreasing effective data while keeping all the noisy data remained. From the curve, a detection probability “threshold” can be seen, from which the ranging ability of the LRS system can be evaluated. In this degradation model, the demanded ranging precision is satisfied automatically. The novel method is reliable and simple with only the detection-probability-dependent precision curve needed. Degradation modeling based on high-repetition ranging experiments for space debris——NORAD 10861, 11574, 16182, 25530 shows an improvement by about 20% in ranging ability evaluation without sacrificing the ranging precision.
The classical Mean shift algorithm for target tracking, when it is used to track window in a complex background, appears too vulnerable to avoid window jitter, which leads to a failure of accurately tracking the target; while in tracking the target of fast-moving video sequences, the loss of tracking targets can not be avoid. As an improvement based on the classical Mean shift algorithm, the proposed algorithm with characteristic of combining tracking differentiator (TD) can eliminate window jitter and predict the target location with the help of TD. Experiments demonstrate that the proposed algorithm is capable of getting over deficiency of the original algorithm and holding improved stability and robustness.
Measurement for spin velocity is an important method for identification of space debris from functioning crafts as the
obtained light curve shows periodic signatures, which helps to identify the debris from functioning space craft. In this paper,
space debris of different spin velocities, different altitudes, and different surface materials (Al2O3, TiO2) are both
theoretically analyzed and simulated with a ray tracing method by Tracepro. In the ray tracing simulation, light is presented
by a visible way as light rays, and only some basic laws of geometrical optics are needed. Simulation results show light
curves have periodic signatures which can be used for spin velocity measurement. And spin velocities obtained from active
illumination and passive illumination are different, which may have some reference value in the practical engineering.