Wholesale debris removal from LEO

Recent advances in electrodynamic propulsion make it possible to seriously consider wholesale removal of large debris from LEO for the first time since the beginning of the space era. Cumulative ranking of large groups of the LEO debris population and general limitations of passive drag devices and rocket-based removal systems are analyzed. A candidate electrodynamic debris removal system is discussed that can affordably remove all debris objects over 2 kg from LEO in 7 years. That means removing more than 99% of the collision-generated debris potential in LEO. Removal is performed by a dozen 100-kg propellantless vehicles that react against the Earth's magnetic field. The debris objects are dragged down and released into short-lived orbits below ISS. As an alternative to deorbit, some of them can be collected for storage and possible in-orbit recycling. The estimated cost per kilogram of debris removed is a small fraction of typical launch costs per kilogram. These rates are low enough to open commercial opportunities and create a governing framework for wholesale removal of large debris objects from LEO.     

Optical orbital debris spotter

The number of man-made debris objects orbiting the Earth, or orbital debris, is alarmingly increasing, resulting in the increased probability of degradation, damage, or destruction of operating spacecraft. In part, small objects (<10 cm) in Low Earth Orbit (LEO) are of concern because they are abundant and difficult to track or even to detect on a routine basis. Due to the increasing debris population it is reasonable to assume that improved capabilities for on-orbit damage attribution, in addition to increased capabilities to detect and track small objects are needed. Here we present a sensor concept to detect small debris with sizes between approximately 1.0 and 0.01 cm in the vicinity of a host spacecraft for near real time damage attribution and characterization of dense debris fields and potentially to provide additional data to existing debris models.     

A laser-optical system to re-enter or lower low Earth orbit space debris

Collisions among existing Low Earth Orbit (LEO) debris are now a main source of new debris, threatening future use of LEO space. Due to their greater number, small (1–10 cm) debris are the main threat, while large (>10 cm) objects are the main source of new debris. Flying up and interacting with each large object is inefficient due to the energy cost of orbit plane changes, and quite expensive per object removed. Strategically, it is imperative to remove both small and large debris. Laser-Orbital-Debris-Removal (LODR), is the only solution that can address both large and small debris. In this paper, we briefly review ground-based LODR, and discuss how a polar location can dramatically increase its effectiveness for the important class of sun-synchronous orbit (SSO) objects. With 20% clear weather, a laser-optical system at either pole could lower the 8-ton ENVISAT by 40 km in about 8 weeks, reducing the hazard it represents by a factor of four. We also discuss the advantages and disadvantages of a space-based LODR system. We estimate cost per object removed for these systems. International cooperation is essential for designing, building and operating any such system.     

Overview of the legal and policy challenges of orbital debris removal

Much attention has been paid recently to the issue of removing human-generated space debris from Earth orbit, especially following conclusions reached by both NASA and ESA that mitigating debris is not sufficient, that debris-on-debris and debris-on-active-satellite collisions will continue to generate new debris even without additional launches, and that some sort of active debris removal (ADR) is needed. Several techniques for ADR are technically plausible enough to merit further research and eventually operational testing. However, all ADR technologies present significant legal and policy challenges which will need to be addressed for debris removal to become viable. This paper summarizes the most promising techniques for removing space debris in both LEO and GEO, including electrodynamic tethers and ground- and space-based lasers. It then discusses several of the legal and policy challenges posed, including: lack of separate legal definitions for functional operational spacecraft and non-functional space debris; lack of international consensus on which types of space debris objects should be removed; sovereignty issues related to who is legally authorized to remove pieces of space debris; the need for transparency and confidence-building measures to reduce misperceptions of ADR as anti-satellite weapons; and intellectual property rights and liability with regard to ADR operations. Significant work on these issues must take place in parallel to the technical research and development of ADR techniques, and debris removal needs to be done in an environment of international collaboration and cooperation.     

L׳ADROIT – A spaceborne ultraviolet laser system for space debris clearing

Small (1–10 cm) debris in low Earth orbit (LEO) are extremely dangerous, because they spread the breakup cascade. Pulsed laser active debris removal using laser ablation jets on target is the most cost-effective way to re-enter the small debris. No other solutions address the whole problem of large (~100 cm, 1 t) as well as small debris. Physical removal of small debris (by nets, tethers and so on) is uneconomical because of the energy cost of matching orbits. In this paper, we present a completely new proposal relative to our earlier work. This new approach uses rapid, head-on interaction in 10–40 s rather than 4 minutes, using 20–40 kW bursts of 100 ps, 355 nm UV pulses from a 1.5 m diameter aperture on a space-based station in LEO. The station employs “heat-capacity” laser mode with low duty cycle to create an adaptable, robust, dual-mode system which can lower or raise large derelict objects into less dangerous orbits, as well as clear out the small debris in a 400-km thick LEO band. Time-average laser optical power is less than 15 kW. The combination of short pulses and UV wavelength gives lower required fluence on target as well as higher momentum coupling coefficient. An orbiting system can have short range because of high interaction rate deriving from its velocity through the debris field. This leads to much smaller mirrors and lower average power than the ground-based systems we have considered previously. Our system also permits strong defense of specific assets. Analysis gives an estimated cost less than $1 k each to re-enter most small debris in a few months, and about 280 k$ each to raise or lower 1-ton objects by 40 km. We believe it can do this for 2000 such large objects in about four years. Laser ablation is one of the few interactions in nature that propel a distant object without any significant reaction on the source.     

低地轨道空间碎片环境建模与分析

根据“箱中粒子”（PIB）的模型和气体分子运动学理论，建立了估算低地轨道（LEO）上空间碎片总数的微分方程，参考国外文献提供的有关空间碎片统计数据和初始条件，求解方程，并分析了空间碎片环境的短期和长期变化趋势。     

A sensitivity study of the effectiveness of active debris removal in LEO

The near-Earth orbital debris population will continue to increase in the future due to ongoing space activities, on-orbit explosions, and accidental collisions among resident space objects. Commonly adopted mitigation measures, such as limiting postmission orbital lifetimes of satellites to less than 25 years, will slow down the population growth, but will be insufficient to stabilize the environment. To better limit the growth of the future debris population, the remediation option, i.e., removing existing large and massive objects from orbit, needs to be considered. This paper does not intend to address the technical or economical issues for active debris removal. Rather, the objective is to provide a sensitivity study to illustrate and quantify the effectiveness of various remediation options. An effective removal criterion based upon mass and collision probability is developed. This study includes simulations with removal rates ranging from 5 to 20 objects per year, starting in the year 2020. The outcome of each simulation is analyzed and compared with others. The summary of the study serves as a general guideline for future debris removal consideration.     

Investigation of national policy shifts to impact orbital debris environments

Low earth orbit has become increasingly congested as the satellite population has grown over the past few decades, making orbital debris a major concern for the operational stability of space assets. This congestion was highlighted by the collision of the Iridium 33 and Cosmos 2251 satellites in 2009. This paper addresses the current state of orbital debris regulation in the United States and asks what might be done through policy change to mitigate risks in the orbital debris environment. A brief discussion of the nature of orbital debris addresses the major contributing factors including size classes, locations of population concentrations, projected satellite populations, and current challenges presented in using post-mission active debris removal to mitigate orbital debris. An overview of the current orbital debris regulatory structure of the United States reveals the fragmented nature of having six regulating bodies providing varying levels of oversight to their markets. A closer look into the regulatory policy of these agencies shows that, while they all take direction from The U.S. Government Orbital Debris Mitigation Standard Practices, this policy is a guideline with no real penalty for non-compliance. Various policy solutions to the orbital debris problem are presented, ranging from a business as usual approach to a consolidated regulation system which would encourage spacecraft operator compliance. The positive aspects of these options are presented as themes that would comprise an effective policy shift towards successful LEO conservation. Potential economic and physical limitations to this policy approach are also addressed.     

SDEEM2015空间碎片环境工程模型

文章介绍了哈尔滨工业大学空间碎片高速撞击研究中心"十二五"期间发布的空间碎片环境工程模型(SDEEM 2015)。该模型可实现LEO空间碎片环境描述,空间碎片撞击风险评估以及地基探测结果仿真,还可输出LEO航天器不同轨道位置处空间碎片撞击通量随撞击方位角、撞击速度及碎片尺寸的分布规律,地基探测设备探测区域内空间碎片空间密度及通量的分布情况等信息。SDEEM 2015适用轨道高度范围为200~2000 km,时间范围为1959年—2050年,所考虑的空间碎片来源包括解体碎片、Na K液滴、固体火箭发动机喷射物、溅射物和剥落物。     

Beam-Park-Experiment-1/2000 with TIRA

A monostatic 24-h debris observation campaign (BPE-1/2000) has been prepared and conducted using FGAN's TIRA L-Band system. Based on experiences from previous Beam-park experiments a similar largely automated data processing is applied on an extended range window of 300–2000km. More than 1500 detections are encountered, 471 of them are verified as being real objects in Low-Earth-Orbit (LEO). PROOF's observation forecasting of catalogued objects is evaluated against the observed objects, and the difficulties obtaining radar cross-sections (RCSs) and object sizes from Beam-park experiments are discussed. Sidelobe detections are identified by using background information like two-line element (TLE) sets and/or catalogued RCSs.In comparison with previous experiments, the statistics show similarities confirming the concept of Beam-park experiments for space debris observations, despite the snapshot character of 24-h experiments. The comparison with MASTER/PROOF'99 and ORDEM2000 leads to a reasonable agreement between models and observations.     

低地轨道空间碎片环境建模与分析

根据“箱中粒子”(PIB-Particles In a Box)的模型和气体分子运动学理论,建立了估算低地轨道上空间碎片总数的微分方程,参考国外文献有关空间碎片统计数据和初始条件,求解方程,并分析了空间碎片环境的短期和长期变化趋势.     

Modelling of Ejecta as a Space Debris Source

When a micro-debris or a micrometeoroid impacts a spacecraft surface, a large number of secondary particles, called ejecta, are produced. These particles can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the components of complex and large space structures, or at great distance by the formation of a population of small orbital debris. This paper describes firstly, the ejecta overall production, and secondly, the lifetime and the orbital evolution of the particles. Finally the repartition of ejecta in LEO is computed. Some results describing the population as a function of size and altitude are presented.     

System engineering analysis of derelict collision prevention options

Sensitivities to the future growth of orbital debris and the resulting hazard to operational satellites due to collisional breakups of large derelict objects are being studied extensively. However, little work has been done to quantify the technical and operational tradeoffs between options for minimizing future derelict fragmentations that act as the primary source for future debris hazard growth. The two general categories of debris mitigation examined for prevention of collisions involving large derelict objects (rocket bodies and payloads) are active debris removal (ADR) and just-in-time collision avoidance (JCA). Timing, cost, and effectiveness are compared for ADR and JCA solutions highlighting the required enhancements in uncooperative element set accuracy, rapid ballistic launch, despin/grappling systems, removal technologies, and remote impulsive devices. The primary metrics are (1) the number of derelict objects moved/removed per the number of catastrophic collisions prevented and (2) cost per collision event prevented. A response strategy that contains five different activities, including selective JCA and ADR, is proposed as the best approach going forward.     

天基照相跟踪空间碎片批处理轨道确定研究

随着国内外天基观测空间碎片研究的展开,文章提出了利用跟踪卫星的CCD(Charge
Coupled Device)相机对空间碎片进行轨道探测的方法,首先建立了CCD照相观测模型和基于 照相观测 的空间碎片批处理轨道确定模型。通过对CCD相机底片归算方法的分析可知,利用
CCD相机所获得的观测数据与跟踪卫星的姿态无关,且其精度只与测量和坐标转换计算的精 度有关,在测量和计算中可获得较高的精度。分别对分布密度较高的低轨道和地球同步 轨道区域的空间碎片进行了定轨分析。仿真结果表明,定轨时采用两个跟踪弧段的照相数据 定轨精度大大高于一个弧段照相数据的定轨精度;跟踪卫星距离空间碎片越近,定轨精度越 高;低轨道空间碎片的定轨精度高于地球同步轨道上的空间碎片定轨精度。
     

Enhancement and Validation of the IDES Orbital Debris Environment Model

Orbital debris environment models are essential in predicting the characteristics of the entire debris environment, especially for altitude and size regimes where measurement data is sparse. Most models are also used to assess mission collision risk. The IDES (Integrated Debris Evolution Suite) simulation model has recently been upgraded by including a new sodium–potassium liquid coolant droplet source model and a new historical launch database. These and other features of IDES are described in detail. The accuracy of the IDES model is evaluated over a wide range of debris sizes by comparing model predictions to three major types of debris measurement data in low Earth orbit. For the large-size debris population, the model is compared with the spatial density distribution of the United States (US) Space Command Catalog. A radar simulation model is employed to predict the detection rates of mid-size debris in the field of view of the US Haystack radar. Finally, the small-size impact flux relative to a surface of the retrieved Long Duration Exposure Facility (LDEF) spacecraft is predicted. At sub-millimetre sizes, the model currently under-predicts the debris environment encountered at low altitudes by approximately an order of magnitude. This is because other small-size debris sources, such as paint flakes have not yet been characterised. Due to the model enhancements, IDES exhibits good accuracy when predicting the debris environment at decimetre and centimetre sizes. Therefore, the validated initial conditions and the high fidelity future traffic model enables IDES to make long-term debris environment projections with more confidence.     

A model for the evolution of the on-orbit man-made debris environment

A model for the evolution of the low Earth orbit man-made debris population is presented and the results of several test cases discussed. Debris sources include normal operations in space, explosions occurring on spacecraft in orbit, and collisions between objects in orbit; the stochastic occurrence of these deposition events is modeled using Monte Carlo techniques. A technique for discriminating between objects populating long-life vs rapid-decay orbits is discussed and applied to the analysis of debris contributions from collisions of comparable sized objects. In varying degrees, each of the cases presented indicate there is cause for concern for spacecraft and space operations from the 1990s onward-man-made debris will play a role which may vary from presenting a considerable hazard to certain operations or certain spacecraft to effectively prohibiting the use of certain spaceccraft or space operations.     

Continuum Model for Space Debris Evolution with Account of Collisions and Orbital Breakups

The paper discusses the mathematical modeling of long-term orbital debris evolution taking into account mutual collisions of space debris particles of different sizes. Investigations and long-term forecasts of orbital debris environment evolution in low Earth orbits are essential for future space mission hazard evaluation and for adopting rational space policies and mitigation measures. The paper introduces a new approach to space debris evolution mathematical modeling based on continuum mechanics incorporating partial differential equations. This is an alternative to the traditional approaches of celestial mechanics incorporating ordinary differential equations to model fragments evolution. The continuum approach to orbital debris evolution modeling has essential advantages for describing the evolution of a large number of particles, because it replaces the traditional tracking of space objects by modeling the evolution of their density of distribution.     

Analysis of the Micrometeoroid and Debris Hazard Posed to an Orbiting Parabolic Mirror

Many concepts of future space systems involve the use of parabolic mirrors for optical applications. The need for a highly reflective finish means that performance of such systems will be particularly vulnerable to space debris and micrometeoroids. A case study was performed to examine the micrometeoroid and debris hazard posed to an orbiting parabolic mirror. The mirror considered was nominally Earth-pointed in a circular orbit with two candidate altitudes in low Earth orbit (LEO), well within the region inhabited by man-made debris. The timeframes of interest for the two missions were 2002–2004 and 2005–2015. Microgram and larger particles were considered.To perform this study, it was necessary to determine the debris and meteoroid flux across the parabolic surface. To assess sensitivity of results to uncertainity in available data, two approaches were taken. The first approach was an analytical procedure based on use of long duration exposure facility (LDEF) data and published theoretical results. The second approach used two readily available computer models: the ESA MASTER model and NASA's ORDEM96. In addition, an in-house implementation of the Grün meteoroid model was used. While multiple results were available for the total flux and flux distributed over azimuth, only the MASTER model was available for generating the desired elevation data to obtain the flux distribution over the parabolic mirror. In an attempt to bound the uncertainty in the knowledge of the elevation distribution, the results from both the MASTER and ORDEM96 models were processed together to form a separate, hybrid prediction. In addition, results were used in the preliminary design of a protective skirt.This case study elucidated the practical obstacles and considerations in performing a sufficiently accurate debris and meteoroid analysis using data and tools that are readily available to the broad space sector. The resulting procedures are useful in the assessment of the risk posed to optics by the meteoroid and debris environment and in the design of protection.     

New insights on the orbital debris collision hazard at GEO

An analysis is performed of the orbital debris collision hazard to operational spacecraft at geosynchronous orbit (GEO). As part of the examination, the contribution of individual components of the population are considered and presented to provide a clearer linkage between object characteristic and resulting risk. Our examination of GEO collision risk reveals several critical new insights: (1) the current probability of collision in GEO is relatively low, yet the future is difficult to predict due to our limited ability to observe objects in GEO and the uncertainty in past and future debris-generating events in GEO; (2) the probability of collision in GEO is not uniform by longitude — it is seven times greater in regions centered about the geopotential wells; (3) the probability of a mission-terminating collision is greatly dependent upon the approximately 2200 objects in the 10 cm–1 m range observed in GEO but not yet cataloged; (4) hardware relocated to GEO “graveyard” disposal orbits pose a potential additional, but not fully understood, collision hazard to operational GEO satellites; and (5) the collision hazard throughout the course of a day or year is highly episodic (i.e. non-uniform).     

低轨星座多波束相控阵天线研究进展与发展趋势

多波束相控阵天线是一种利用波束形成网络,同时实现多个独立的高增益波束的多波束天线,具有高灵活性和宽角度扫描等优点,是低轨通信卫星系统的核心载荷之一。旨在针对应用于低轨星座的星载多波束相控阵天线进行归纳和分析。对低轨星座多波束相控阵天线的发展历程、波束形成技术、关键技术进行了介绍,并对低轨星座多波束相控阵天线的未来发展趋势进行了分析,为我国未来低轨卫星星座建设提供技术参考。