卫星解体碎片生成数值模拟

提出卫星解体碎片生成的数值模拟方法,对卫星模型解体实验问题进行了数值模拟研究。有限元重构方法是一种有限元与 SPH 方法的结合,能够模拟获得孤立碎片的特性数据。通过在 SPH 模拟结果中重构有限元单元,能够有效区分碎片云中的置信孤立碎片和非置信孤立碎片,结合图论方法能够获得每个孤立碎片的单元构成及其尺寸、速度矢量和质量等信息。进而通过数据统计能够获得碎片分布信息。解体碎片数值模拟数据与实验数据具有较好的一致性,表明了该方法的有效性。     

Improved orbit predictions using two-line elements

The density of orbital space debris constitutes an increasing environmental challenge. There are two ways to alleviate the problem: debris mitigation and debris removal. This paper addresses collision avoidance, a key aspect of debris mitigation. We describe a method that contributes to achieving a requisite increase in orbit prediction accuracy for objects in the publicly available two-line element (TLE) catalog. Batch least-squares differential correction is applied to the TLEs. Using a high-precision numerical propagator, we fit an orbit to state vectors derived from successive TLEs. We then propagate the fitted orbit further forward in time. These predictions are validated against precision ephemeris data derived from the international laser ranging service (ILRS) for several satellites, including objects in the congested sun-synchronous orbital region. The method leads to a predicted range error that increases at a typical rate of 100 m per day, approximately a 10-fold improvement over individual TLE’s propagated with their associated analytic propagator (SGP4). Corresponding improvements for debris trajectories could potentially provide conjunction analysis sufficiently accurate for an operationally viable collision avoidance system based on TLEs only.     

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.     

Debris Discs Around Stars: The 2004 ISO Legacy

Debris discs around stars were first discovered by the Infrared Astronomical Satellite (IRAS) in 1983. For the first time material orbiting another star than the Sun, but distinct from a circumstellar envelope, was observed through its far infrared emission. This major discovery motivated astronomers to investigate those discs by further analyzing the IRAS data, using ground-based telescopes for the hunting of exoplanets, developing several projects using the Infrared Space Observatory (ISO), and now exploiting the ISO Data Archive (IDA). This review presents the main ISO results, statistical as well as individual, on debris discs in orbit around pre-main-sequence and main-sequence stars. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

基于多项式近似的空间碎片群体轨道预报算法

快速准确地分析空间碎片群轨道演化行为对于其他在轨航天器碰撞规避至关重要。在各摄动力的作用下,空间碎片群演化运动呈现出复杂的非线性特征。空间碎片群体个体数量巨大,如果通过对空间碎片群中每个空间碎片进行轨道积分来分析群体预报的方法会导致计算量过大。针对该问题,提出一种基于多项式近似的轨道快速预报分析方法。该方法将空间碎片群分为少量的标称碎片和其他大量关联碎片。针对标称碎片的轨道预报采用数值积分求解保证预报精度;而针对其他大量的关联碎片轨道预报问题,采用多项式泰勒展开半解析方法求解,从而在保证预报精度的前提下有效减少空间碎片群轨道预报的计算量。为了验证方法的有效性,对不同空间碎片群进行了轨道预报仿真。仿真结果表明,当轨道预报精度设定在1m范围内时,多项式近似算法的计算量较蒙特卡洛方法计算效率提高了2.2~17.2倍,验证了所提出方法的有效性。     

Strategy to search fragments from breakups in GEO

This paper proposes a strategy to search fragments from breakups in the Geosynchronous Earth Orbit (GEO) region based upon population prediction and motion prediction by means of ground-based optical observations. Breakup fragments have uncertainties in the states such as their position and motion, or even in their existence. Population prediction and motion prediction resolve those uncertainties. Population prediction evaluates the time-averaged distribution of fragments, whose position at a given time is unknown, in the celestial sphere. Motion prediction evaluates the expected motion of fragments appeared in image series acquired by a telescope’s CCD camera. This paper logically describes procedures of the search strategy, and provides mathematical expressions of population prediction and motion prediction. This paper also validates the search strategy via actual observations, in which a confirmed breakup in the GEO region is selected as a target. It is concluded that the proposed strategy is valid even for searching uncataloged fragments from breakups in the GEO region.     

Shape and motion estimate of LEO debris using light curves

We have derived a tri-axial ellipsoidal model of an LEO object, a Cosmos 2082 rocket body, including its rotational axis direction, rotation period, precession, and a compositional parameter, using only light curve data from an optical telescope. The brightness of the object was monitored for two days and least-squares fitting was used to determine these values. The derived axial ratios are 100:18:18, the coordinates of the rotational axis direction on the celestial sphere are R.A. = 305.8° and Dec. = 2.6°, and its observed average rotation period is 41 s. When precession is considered, its amplitude and precession period are 30.5° and 29.4 min. These results show that optical light curve data are sufficient to determine the shapes and the motions of LEO objects.     

Object image linking of earth orbiting objects in the presence of cosmics

In survey series of unknown Earth orbiting objects, no a priori orbital elements are available. In surveys of wide field telescopes possibly many non-resolved object images are present on the single frames of the series. Reliable methods have to be found to associate the object images stemming from the same object with each other, so-called linking. The presence of cosmic ray events, so-called Cosmics, complicates reliable linking of non-resolved images. The tracklets of object images allow to extract exact positions for a first orbit determination.     

Bayesian linking of geosynchronous orbital debris tracks as seen by the Large Synoptic Survey Telescope

We describe a Bayesian sampling model for linking and constraining orbit models from angular observations of “streaks” in optical telescope images. Our algorithm is particularly suited to situations where the observation times are small fractions of the orbital periods of the observed objects or when there is significant confusion of objects in the observation field. We use Markov Chain Monte Carlo to sample from the joint posterior distribution of the parameters of multiple orbit models (up to the number of observed tracks) and parameters describing which tracks are linked with which orbit models. Using this algorithm, we forecast the constraints on geosynchronous (GEO) debris orbits achievable with the planned Large Synoptic Survey Telescope (LSST). Because of the short 15 s exposure times, preliminary orbit determinations of GEO objects from LSST will have large and degenerate errors on the orbital elements. Combined with the expected crowded fields of GEO debris it will be challenging to reliably link orbital tracks in LSST observations given the currently planned observing cadence.