An active debris removal parametric study for LEO environment remediation

Recent analyses on the instability of the orbital debris population in the low Earth orbit (LEO) region and the collision between Iridium 33 and Cosmos 2251 have reignited interest in using active debris removal (ADR) to remediate the environment. There are, however, monumental technical, resource, operational, legal, and political challenges in making economically viable ADR a reality. Before a consensus on the need for ADR can be reached, a careful analysis of its effectiveness must be conducted. The goal is to demonstrate the need and feasibility of using ADR to better preserve the future environment and to explore different operational options to maximize the benefit-to-cost ratio. This paper describes a new sensitivity study on using ADR to stabilize the future LEO debris environment. The NASA long-term orbital debris evolutionary model, LEGEND, is used to quantify the effects of several key parameters, including target selection criteria/constraints and the starting epoch of ADR implementation. Additional analyses on potential ADR targets among the existing satellites and the benefits of collision avoidance maneuvers are also included.     

Identification of a debris cloud from the nuclear powered SNAPSHOT satellite with haystack radar measurements

Data from the Massachusetts Institute of Technology Lincoln Laboratory Long Range Imaging Radar (known as the Haystack radar) have been used in the past to examine families of objects from individual satellite breakups or families of orbiting objects that can be isolated in altitude and inclination. This is possible because, for some time after a breakup, the debris cloud of particles can remain grouped together in similar orbit planes. This cloud will be visible to the radar, in fixed staring mode, for a short time twice each day, as the orbit plane moves through the field of view. There should be a unique three-dimensional pattern in observation time, range, and range rate which can identify the cloud. Eventually, through slightly differing precession rates of the right ascension of ascending node of the debris cloud, the observation time becomes distributed so that event identification becomes much more difficult.     

A study of the material density distribution of space debris

Material density is an important, yet often overlooked, property of orbital debris particles. Many models simply use a typical density to represent all breakup fragments. While adequate for modeling average characteristics in some applications, a single value material density may not be sufficient for reliable impact damage assessments. In an attempt to improve the next-generation NASA Orbital Debris Engineering Model, a study on the material density distribution of the breakup fragments has been conducted and summarized in this paper.     

SGP4/SDP4模型用于空间碎片轨道预测的精度分析

为保证航天任务的顺利完成 ,必须采用一定的模型 ,对可能威胁目标轨道的空间碎片进行跟踪预测。文中首先给出标称轨道的计算模型 ;接着介绍两行轨道根数 (TLE)和考虑了简化常规 /深空扰动的近似解析解模型 (SGP4/SDP4) ,并提供TLE使用的坐标系和惯性系之间的转换 ;然后以典型轨道为例 ,分析SGP4/SDP4与标称轨道的偏差。运算结果表明SGP4/SDP4运算速度快 ,满足一定精度 ,可以用于空间碎片的轨道预测和初步威胁评估。     

Sensitivity analysis for air temperature profile estimation methods around the tropopause using simulated Aqua/AIRS data

A sensitivity analysis is performed to investigate potential improvements to the accuracy of air temperature profile retrievals near the tropopause. A simple inversion method is employed to identify and remove redundant spectral channels from the retrievals using simulated data for the high-spectral resolution sounder AIRS (Atmospheric Infrared Sounder) on the Aqua satellite. Bayesian optimal theory and inverse technique are applied for the atmospheric temperature profile retrievals, and the 15 μm CO₂ absorption bands (620–750 cm⁻¹) are chosen for this study. Sequentially elimination of redundant channels is directly integrated into the inverse scheme for the temperature profile, in order to accurately retain the valuable channels and remove all the redundant channels, for accurate retrieval of the temperature profile. Also, the tropopause and troposphere are treated differently in the inverse scheme to improve the retrieval accuracy in the tropopause. Results of a sensitivity analysis based on this method, for the Tropical and Middle-Latitude Summer models simulated by MODTRAN4.0, show that the estimated accuracies are improved by 2 K around the tropopause, and are only changed by less than 0.2 K in the troposphere.     

小样本或单次仿真运行的统计分析方法

提出用Bayes方法对小样本或单次运行的仿真输出进行分析,给出了几种条件下的Bayes方法和伽玛分布置信区间的估计方法,提出了Bayes方法中先验分布的确定方法和准则。并用M/M/1排队系统对几种分析方法进行了实例研究。实验结果表明,Bayes方法有明显的优越性和应用前景。     

跟踪与数据中继卫星系统资源调度优化问题

现有跟踪与数据中继卫星资源调度研究常采取简化模型,它将天线的准备时间假定为固定值,由此成为工程应用中系统利用率提升的一个瓶颈。文章借鉴时间窗约束的车辆路径问题理论,提出天线准备时间变长的规划优化问题（LOPVAPT）模型,通过优化天线的扫描路径,实现天线准备时间的动态最优取值。采用STK模拟任务过程,基于Matlab实现蚁群算法,结果表明可将系统利用率从低于80%提高到90%以上。