Low Earth Orbit Debris Environment Research Articles

Density-based evolutionary model of the space debris environment in low-Earth orbit

Lethal untrackable debris objects pose the highest risk to the sustainability of the space environment, and thus, shall be included in the assessment of the long-term effect of mitigation and remediation measures to the space debris problem. The introduction of centimetre-sized particles in the debris evolutionary models represents a challenge from a computational cost point of view. To answer this need, this work proposes a novel probabilistic debris environment propagator. The method classifies the objects population into intact objects and fragmentation debris. The evolution of the former population is retrieved through an individual definition of each object’s mission profile. A continuum approach is adopted for the characterisation of the fragments, whose density distribution in orbital elements is propagated in time through the continuity equation. The intrinsic computational efficiency of the density-based fragments cloud models is leveraged to make the method agnostic to the lowest fragments size considered. A second classification of the population of intact objects into species, such as payloads, rocket bodies, mission related objects and constellations, ensures a faithful replication of their orbit evolution. Fragmentation debris caused by intact objects explosion and accidental fragments-intact object collision are included in a probabilistic fashion at the detected fragmentation epoch, to account for their feedback effect onto the environment. The model is applied to estimate the evolution of the space debris population in low-Earth orbit up to 200 years from the reference epoch, with and without the inclusion of a future launch traffic pattern, and considering a different fulfilment of the post-mission disposal phase.

First Optical Satellite Tracking Station (OSTS) at NRIAG-Egypt

In March 2019 the first dedicated of optical observation of space debris and artificial satellites (Optical Satellites Tracking Station (OSTS)) in Egypt has been performed by National Research Institute of Astronomy and Geophysics (NRIAG) at Kottamia Observatory. The 0.28 m Telescope is used for tracking and surveying debris and operational satellites at Low Earth Orbit (LEO), High ellipse orbit (HEO) and the Geosynchronous Earth Orbit (GEO). OSTS has also collaborated with International Scientific Optical Network (ISON) for optical observation. The necessary programs to control the telescope, camera and monitoring process are configured. Coordinate corrected metric data is provided with the time information. The system has validated and calibrated processing. The first results of the observations with image processing using Apex-2 software are presented. The optical observations using OSTS are being used to help characterize the debris environment in LEO, HEO and GEO to assist in the modeling projections for space debris database, real population and distribution, detection and orbital determination, and conjunction analysis between operational satellites and/or dangers debris.

Space debris collision probability analysis for proposed global broadband constellations

Fragmentation events, caused by the collision of two objects in space, have been a significant source of space debris objects over a cumulative five decades of space activity. Current proposals by different commercial entities aim to launch constellations comprising thousands of satellites in Low Earth Orbit (LEO), which would result in an increase of more than five times the number of currently active satellites in a region where debris objects are most concentrated. The Inter-Agency Space Debris Coordination Committee (IADC) has already recognized the potential influence of large constellations on the LEO environment and the subsequent need to assess whether current mitigation guidelines will be adequate moving forward. Given developments for such constellations are already underway, independent research efforts ahead of any revision to current IADC guidelines could be of great value not only to the organizations involved in their operation, but also to policymakers and existing space users. This paper evaluates the probability of collisions for mega-constellations operating in the current LEO debris environment under best and worst-case implementation of current mitigation guidelines. Simulation studies are performed using the European Space Agency's (ESA) MASTER-2009 debris evolutionary model, and the specifications of the proposed OneWeb and SpaceX constellations as example mega-constellations. Multiple scenarios are then tested to assess mitigation measures and their ability to minimize the probability of fragmentation events and the creation of new debris in LEO.

Simulation of the space debris environment in LEO using a simplified approach

Several numerical approaches exist to simulate the evolution of the space debris environment. These simulations usually rely on the propagation of a large population of objects in order to determine the collision probability for each object. Explosion and collision events are triggered randomly using a Monte-Carlo (MC) approach. So in many different scenarios different objects are fragmented and contribute to a different version of the space debris environment. The results of the single Monte-Carlo runs therefore represent the whole spectrum of possible evolutions of the space debris environment. For the comparison of different scenarios, in general the average of all MC runs together with its standard deviation is used. This method is computationally very expensive due to the propagation of thousands of objects over long timeframes and the application of the MC method.At the Institute of Space Systems (IRAS) a model capable of describing the evolution of the space debris environment has been developed and implemented. The model is based on source and sink mechanisms, where yearly launches as well as collisions and explosions are considered as sources. The natural decay and post mission disposal measures are the only sink mechanisms. This method reduces the computational costs tremendously. In order to achieve this benefit a few simplifications have been applied. The approach of the model partitions the Low Earth Orbit (LEO) region into altitude shells. Only two kinds of objects are considered, intact bodies and fragments, which are also divided into diameter bins. As an extension to a previously presented model the eccentricity has additionally been taken into account with 67 eccentricity bins. While a set of differential equations has been implemented in a generic manner, the Euler method was chosen to integrate the equations for a given time span. For this paper parameters have been derived so that the model is able to reflect the results of the numerical MC-based simulation Long-term Utility for Collision Analysis (LUCA), which is also being developed at the IRAS. The evolution of the population in LEO for a 200years time span is shown and compared for both approaches using step sizes of 1year. For selected objects in LEO the collision flux values are shown. Additionally a value called environmental criticality (EC) is derived. It describes the effect an object can have on the space debris environment. In conclusion the field of application for such a fast model is shown.

An adaptive strategy for active debris removal

Many parameters influence the evolution of the near-Earth debris population, including launch, solar, explosion and mitigation activities, as well as other future uncertainties such as advances in space technology or changes in social and economic drivers that effect the utilisation of space activities. These factors lead to uncertainty in the long-term debris population. This uncertainty makes it difficult to identify potential remediation strategies, involving active debris removal (ADR), that will perform effectively in all possible future cases. Strategies that cannot perform effectively, because of this uncertainty, risk either not achieving their intended purpose, or becoming a hindrance to the efforts of spacecraft manufactures and operators to address the challenges posed by space debris.One method to tackle this uncertainty is to create a strategy that can adapt and respond to the space debris population. This work explores the concept of an adaptive strategy, in terms of the number of objects required to be removed by ADR, to prevent the low Earth orbit (LEO) debris population from growing in size. This was demonstrated by utilising the University of Southampton’s Debris Analysis and Monitoring Architecture to the Geosynchronous Environment (DAMAGE) tool to investigate ADR rates (number of removals per year) that change over time in response to the current space environment, with the requirement of achieving zero growth of the LEO population.DAMAGE was used to generate multiple Monte Carlo projections of the future LEO debris environment. Within each future projection, the debris removal rate was derived at five-year intervals, by a new statistical debris evolutionary model called the Computational Adaptive Strategy to Control Accurately the Debris Environment (CASCADE) model. CASCADE predicted the long-term evolution of the current DAMAGE population with a variety of different ADR rates in order to identify a removal rate that produced a zero net growth for that particular projection after 200years.The results show that using an adaptive ADR rate generated by CASCADE, alongside good compliance with existing mitigation measures, increases the probability of achieving a constant LEO population of objects greater than 10cm. This was shown to be 12% greater compared with removing five objects per year, with the additional advantage of requiring only 3.1 removals per year, on average.

Synergy of debris mitigation and removal

Since the end of the 20th Century there has been considerable effort made to devise mitigation measures to limit the growth of the debris population. This activity has led to the implementation of a “25-year rule” by a number of space-faring nations for the post-mission disposal of spacecraft and orbital stages intersecting the Low Earth Orbit (LEO) region. Through the use of projections made by computer models, it was anticipated that this 25-year rule, together with passivation and suppression of mission-related debris, would be sufficient to prevent the unconstrained growth of the LEO debris population. In the last decade both the LEO debris environment and the debris modelling capability have seen significant changes. In particular, recent population growth has been driven by a number of major break-ups, including the intentional destruction of the Fengyun-1C spacecraft and the collision between Iridium 33 and Cosmos 2251. State-of-the-art evolutionary models indicate that the LEO debris population will continue to grow in spite of good compliance with the commonly adopted mitigation measures and even in the absence of new launches. Consequently, this has led to considerable interest in the development of remediation measures and, especially, in debris removal. In this paper, we present a new and large study of debris mitigation and removal using the University of Southampton's evolutionary model, DAMAGE, together with the latest MASTER model population of objects ≥10cm in LEO. Here, we have employed a concurrent approach to mitigation and remediation, whereby changes to the PMD rule and the inclusion of other mitigation measures have been considered together with multiple removal strategies. In this way, we have been able to demonstrate the synergy of these mitigation and remediation measures and to identify potential, aggregate solutions to the space debris problem. The results suggest that reducing the PMD rule offers benefits that include an increase in the effectiveness of debris removal and a corresponding increase in the confidence that these combined measures will lead to the stabilisation of the LEO debris population.

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.

The fast debris evolution model

The ‘particles-in-a-box’ (PIB) model introduced by Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508–513, 1992.] removed the need for computer-intensive Monte Carlo simulation to predict the gross characteristics of an evolving debris environment. The PIB model was described using a differential equation that allows the stability of the low Earth orbit (LEO) environment to be tested by a straightforward analysis of the equation’s coefficients. As part of an ongoing research effort to investigate more efficient approaches to evolutionary modelling and to develop a suite of educational tools, a new PIB model has been developed. The model, entitled Fast Debris Evolution (FADE), employs a first-order differential equation to describe the rate at which new objects ⩾10 cm are added and removed from the environment. Whilst Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508–513, 1992.] based the collision theory for the PIB approach on collisions between gas particles and adopted specific values for the parameters of the model from a number of references, the form and coefficients of the FADE model equations can be inferred from the outputs of future projections produced by high-fidelity models, such as the DAMAGE model. The FADE model has been implemented as a client-side, web-based service using JavaScript embedded within a HTML document. Due to the simple nature of the algorithm, FADE can deliver the results of future projections immediately in a graphical format, with complete user-control over key simulation parameters. Historical and future projections for the ⩾10 cm LEO debris environment under a variety of different scenarios are possible, including business as usual, no future launches, post-mission disposal and remediation. A selection of results is presented with comparisons with predictions made using the DAMAGE environment model. The results demonstrate that the FADE model is able to capture comparable time-series of collisions and number of objects as predicted by DAMAGE in several scenarios. Further, and perhaps more importantly, its speed and flexibility allows the user to explore and understand the evolution of the space debris environment.

Characterization of the cataloged Fengyun-1C fragments and their long-term effect on the LEO environment

The intentional breakup of Fengyun-1C on 11 January 2007 created the most severe orbital debris cloud in history. The altitude where the event occurred was probably the worst location for a major breakup in the low Earth orbit (LEO) region, since it was already highly populated with operational satellites and debris generated from previous breakups. The addition of so many fragments not only poses a realistic threat to operational satellites in the region, but also increases the instability (i.e., collision cascade effect) of the debris population there. Detailed analysis of the large Fengyun-1C fragments indicates that their size and area-to-mass ratio (A/M) distributions are very different from those of other known events. About half of the fragments appear to be composed of light-weight materials and more than 100 of them have A/M values exceeding 1 m 2/kg, consistent with thermal blanket and solar panel pieces. In addition, the orbital elements of the fragments suggest non-trivial velocity gain by the fragment cloud during the impact. These important characteristics were incorporated into numerical simulations to assess the long-term impact of the Fengyun-1C fragments to the LEO debris environment. The collision probabilities between the Fengyun-1C fragments and the rest of the catalog population and the population growth in the low Earth orbit region in the next 100 years are summarized in the paper.

Instability of the present LEO satellite populations

Several studies conducted during 1991–2001 demonstrated, with some assumed launch rates, the future unintended growth potential of the Earth satellite population, resulting from random, accidental collisions among resident space objects. In some low Earth orbit (LEO) altitude regimes where the number density of satellites is above a critical spatial density, the production rate of new breakup debris due to collisions would exceed the loss of objects due to orbital decay. A new study has been conducted in the Orbital Debris Program Office at the NASA Lyndon B. Johnson Space Center, using higher fidelity models to evaluate the current debris environment. The study assumed no satellites were launched after December 2005. A total of 150 Monte Carlo runs were carried out and analyzed. Each Monte Carlo run simulated the current debris environment and projected it 200 years into the future. The results indicate that the LEO debris environment has reached a point such that even if no further space launches were conducted, the Earth satellite population would remain relatively constant for only the next 50 years or so. Beyond that, the debris population would begin to increase noticeably, due to the production of collisional debris. Detailed analysis shows that this growth is primarily driven by high collision activities around 900–1000 km altitude – the region which has a very high concentration of debris at present. In reality, the satellite population growth in LEO will undoubtedly be worse than this study indicates, since spacecraft and their orbital stages will continue to be launched into space. Postmission disposal of vehicles (e.g., limiting postmission orbital lifetimes to less than 25 years) will help, but will be insufficient to constrain the Earth satellite population. To better preserve the near-Earth environment for future space activities, it might be necessary to remove existing large and massive objects from regions where high collision activities are expected.

Monitoring the low earth orbit debris environment over an 11-year solar cycle

Orbital debris is a concern for all space faring nations. Prior to 1990, there were no statistically significant measurements of the debris environment for debris sizes below 10 cm diameter. Late in that year, NASA/Johnson Space Center began using the Haystack long range imaging radar to statistically sample the low earth orbit (LEO) debris environment for debris sizes as small as 0.5 cm diameter. These measurements have continued since that date. Models of the LEO debris environment predict a change in the debris flux due to solar activity. High solar activity heats the earth's atmosphere causing it to expand creating an increased atmospheric drag which causes debris to reenter the earth's atmosphere at a higher rate thereby depleting the population at low altitudes. This paper will summarize the Haystack measurements over a complete 11-year solar cycle.

The optical orbital debris measurement program at NASA and AMOS

The National Aeronautics and Space Administration (NASA) has been making optical observations of the Low Earth Orbit (LEO) and the Geosynchronous Earth Orbit (GEO) orbital debris environment. NASA operates two telescopes located near Cloudcroft, NM that obtain these observations. The 3.0 m Liquid Mirror Telescope (LMT) is used for LEO observations and the 0.32 m Charged Coupled Device (CCD) Debris Telescope (CDT) is used for GEO observations. The optical observations are being used to help characterize the debris environment in LEO and GEO and to assist in the modeling projections generated by NASA. NASA is also collaborating with the Air Force Maui Optical and Supercomputing Site (AMOS), which is located at the 10,000 foot summit of Haleakala on the island of Maui. There are three main observational programs at AMOS. There is an imaging program utilizing the 3.67 m telescope adaptive optics system to image objects that have had anomalous events or breakups. There is a spectroscopic program utilizing spectrographs on the 3.67 and 1.6 m telescopes to determine surface materials. There is also a program utilizing instrumentation on the 3.67 m telescope to determine the albedo of objects based upon simultaneous visible and thermal IR photometry. AMOS is also obtaining statistical observations of the GEO debris environment supporting NASA and the Inter-Agency Space Debris Coordination Committee (IADC) activities using the Near-Earth Asteroid Tracking (NEAT) camera on the 1.2 m telescope, In addition, a renovated Baker-Nunn telescope is available for observations. Results from these observation programs will be presented, as well as future plans.

Effects of uncertainty in hypervelocity impact performance equations and other parameters on variance in spacecraft vulnerability predictions

The increasing man-made debris environment in low-earth orbit (LEO) has prompted NASA to develop new methods for quantifying (and reducing) the risks to spacecraft and crew following hypervelocity penetration by orbital debris. The Manned Spacecraft and Crew Survivability (MSCSurv) computer analysis tool computes the probability of occurrence for seven failure modes which may lead to crew or station loss. The probability of loss, P loss, of station or crew (i.e., its vulnerability) due to impact by one or more orbital debris particles is calculated using three major terms: (a) N imp, the number of impacts on the ISS manned modules, (b) P pen/imp, the probability of penetration given that an impact has occurred, and (c) P loss/pen, the probability of loss given that a penetration has occurred. MSCSurv was designed to calculate terms (b) and (c). Utilizing MSCSurv, the objective of this study is: (1) to describe briefly the structure of the Manned Spacecraft and Crew Survivability computer code, (2) to detail results from a P loss calculation using baseline penetration, damage, station, and crew-related parameters, and (3) to quantify the variance produced in P pen/impact and P loss/pen associated with each input and modeling parameter used in calculating them. In general, higher uncertainties within Penetration, Damage, Station, or Crew parametric models produced higher uncertainties within the P loss calculation; however, small variances within some models (such as those for hole size following a penetration) produced larger overall P loss variance than large variance within other models (such as the crew movement rate, for example).

Debris families observed by the haystack orbital debris radar

The Haystack radar provides a unique capability to observe and monitor the orbital debris environment in low-Earth orbit for debris sizes down to less than 1 cm in diameter. Recent changes in the observation geometry of the Haystack radar have greatly enhanced the capability of the radar in separating debris objects into orbit families. Using this capability, it is possible to identify specific families of debris based on inclination and altitude regimes. The radar measurements can then be used to obtain size distributions and polarization characteristics of the debris in the families. Using this method, one previously unrecognized debris family in 65° inclination circular orbits between 850 and 1000 km altitude has been tentatively identified as the leaking sodium–potassium coolant from Russian RORSAT reactors. Debris from specific breakups have also been identified, such as from the breakups of Cosmos 1275 and Cosmos 1484. This ability to assign some debris objects to specific sources opens up new possibilities in studying the nature and causes of breakup events.

The long-term implications of operating satellite constellations in the low earth orbit debris environment

DRA's Integrated Debris Evolution Suite (IDES) model is used in this study to predict the future evolution of the orbital debris environment for two distinct scenarios. For the first case, a pre-generated background debris population for 1995 and ‘business as usual’ future launch/explosion rates are used as input to the model. IDES then employs its collision event prediction algorithm to simulate evolution from 1996 to 2020 as a baseline. The second scenario uses the same initial conditions and future trends, but in addition, a large constellation is introduced into the simulation process from year 1998 onwards. The additional contribution of the constellation to the temporal variation of key environment/population parameters is presented; including enhancement from any long-term collision coupling effects.

Final activities and results of the long duration exposure facility meteoroid and debris special investigation group

The LDEF contained 57 individual experiment trays or tray portions specifically designed to characterize critical aspects of meteoroid and debris environment in low-Earth orbit (LEO). However, it was realized from the beginning that the most efficient use of the satellite would be to characterize impact features from the entire surface of LDEF. With this in mind, particular interest has focused on common materials facing in all 26 LDEF facing directions; among the most important of these materials has been the LDEF frame and tray clamps. Therefore, in an effort to better understand the nature and flux of particulates in LEO, and their effects on spacecraft hardware, we are locating all impact features on LDEF frame member intercostals and tray clamps, down to 40 μm in diameter, analyzing the bulk major-element composition of impactor residues when present. We also describe current efforts to characterize impactor residues recovered from the impact craters, and we have found that a low, but significant, fraction of these residues have survived in a largely unmelted state. These residues can be characterized sufficiently to permit resolution of the impactor origin. We have concentrated on the residue from chondritic interplanetary dust particles (micrometeoroids), as these represent the harshest test of our analytical capabilities. We describe the Meteoroid and Debris Database, into which we have placed all pertinent LDEF data, as well as similar results from inspection of the Solar Maximum and Palapa Satellites. Finally, we describe the contents of the Final Report of the LDEF Meteoroid and Debris Special Investigation Group, which is currently being prepared.

Advanced shield design for space station freedom

Due to the predicted increase in the severity of the orbital debris environment in low-Earth orbit, the baseline meteoroid/debris protection system for Space Station Freedom (S.S. Freedom) must be augmented on orbit. In response to this need, an advanced shield design effort is underway at NASA's Marshall Space Flight Center (MSFC). The results to date of this program are presented. A series of 18 hypervelocity impact tests were conducted at MSFC's Space Debris Simulation Facility. These tests consisted of launching aluminum projectiles at velocities up to 7 km/s to evaluate various design solution. Parameters investigated include shield material and geometric configuration (thickness, spacing, orietation, and arrangement) in relation to the baseline aluminum “Whipple” bumper. The results of the hypervelocity impact tests are presented. Comparison with protection offered by the baseline protection system is made. Evaluation of protection offered by candidate augmented systems and hydrocode simulations is performed. An assessment of the often-overlooked structural design onsiderations such as launch loads, on-orbit loads, extravehicular activity requirements, maintainability, etc., is presented. These analyses lead to identification of a candidate system to augmented the baseline meteoroid/debris protection system for the habitable modules of S.S. Freedom.

Review of current activities to model and measure the orbital debris environment in low-earth orbit

A very active orbital debris program is currently being pursued at the NASA/Johnson Space Center (JSC), with projects designed to better define the current environment, to project future environments, to model the processes contributing to or constraining the growth of debris in the environment, and to gather supporting data needed to improve the understanding of the orbital debris problem and the hazard it presents to spacecraft. This paper is a review of the activity being conducted at JSC, by NASA, Lockheed Engineering and Sciences Company, and other support contractors, and presents a review of current activity, results of current research, and a discussion of directions for future development.