Debris Population Research Articles

The influence of solid rocket motor retro-burns on the space debris environment

The ESA space debris population model MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) considers firings of solid rocket motors (SRM) as a debris source with the associated generation of slag and dust particles. The resulting slag and dust population is a major contribution to the sub-millimetre size debris environment in Earth orbit. The current model version, MASTER-2005, is based on the simulation of 1076 orbital SRM firings which contributed to the long-term debris environment. A comparison of the modelled flux with impact data from returned surfaces shows that the shape and quantity of the modelled SRM dust distribution matches that of recent Hubble Space Telescope (HST) solar array measurements very well. However, the absolute flux level for dust is under-predicted for some of the analysed Long Duration Exposure Facility (LDEF) surfaces. This points into the direction of some past SRM firings not included in the current event database. The most suitable candidates for these firings are the large number of SRM retro-burns of return capsules. Objects released by those firings have highly eccentric orbits with perigees in the lower regions of the atmosphere. Thus, they produce no long-term effect on the debris environment. However, a large number of those firings during the on-orbit time frame of LDEF might lead to an increase of the dust population for some of the LDEF surfaces. In this paper, the influence of SRM retro-burns on the short- and long-term debris environment is analysed. The existing firing database is updated with gathered information of some 800 Russian retro-firings. Each firing is simulated with the MASTER population generation module. The resulting population is compared against the existing background population of SRM slag and dust particles in terms of spatial density and flux predictions.

Collision risk against space debris in Earth orbits

Opik’s formulae for the probability of collision are applied to the analysis of the collision risk against space debris in Low-Earth Orbit (LEO) and Medium Earth Orbit. The simple analytical formulation of Opik’s theory makes it applicable to complex dynamical systems, such as the interaction of the ISS with the whole debris population in LEO The effect of a fragmentation within a multiplane constellation can also be addressed. The analysis of the evolution of the collision risk in Earth orbit shows the need of effective mitigation measures to limit the growth of the collision risk and of the fragmentation debris in the next century.

Introduction of a nozzle throat diameter dependency into the SRM dust size distribution

The ESA space debris population model MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) considers 1032 firings of solid rocket motors (SRM) with the associated generation of SRM slag and dust particles in its current version. The resulting dust population is a major contribution to the sub-millimetre size space debris environment in Earth orbit. For the modelling of each SRM dust release event a detailed knowledge of the particle size distribution is essential. However, the knowledge of the particle sizes after passing the nozzle throat is poor. The current dust implementation in the MASTER model assumes a fixed size distribution which is identically used for both large upper stages and small apogee motors. This assumption can lead to an over-representation of large dust particles in regions, where mainly apogee motors are used (i.e., Geostationary Earth Orbit) and an under-representation in lower altitudes, where large stages predominate. In this paper, a concept for the improvement of SRM dust size modelling is discussed. It will be shown that an introduction of a nozzle throat diameter dependency into the dust size distribution enables a more precise modelling of SRM dust release events. The improved SRM dust size distribution is going to be used by the MASTER-2005 space debris model which is currently under development by the Institute of Aerospace Systems and QinetiQ (UK) under ESA contract.

Orbital Evolution of Cloud Particles from Explosions of Geosynchronous Objects

Current orbital debris search strategies for telescopes observing in geosynchronous Earth orbit are designed around the known orbital distributions of cataloged objects. However, the majority of cataloged objects are believed to be intact spacecraft and rocket bodies, not the debris particles the searches are intended to locate. If there have been breakups in geosynchronous Earth orbit, the explosions may have put the debris into orbits that are significantly different from those in the catalog. Consequently, observation plans optimized for the catalog population may not be optimized for any unseen debris populations. Some hypothetical cases and a real near-synchronous U.S. Titan IIIC transtage explosion will be presented to demonstrate this effect. Perturbing accelerations to be considered for orbital evolution are the nonspherical part of the Earth’s gravitational attraction and gravitational attractions due to the sun and moon. Solar radiation pressure effects are omitted in this analysis, not because they are unimportant for this type of analysis, but to concentrate on the primary orbit perturbations.

Collision activities in the future orbital debris environment

We have analyzed potential collision activities among orbiting objects for the next 100 years from the low Earth orbit (LEO), medium Earth orbit (MEO), to geosynchronous orbit (GEO) regions. The analysis was based on results from the NASA orbital debris evolutionary model, LEGEND. A total of 30 Monte-Carlo simulations were performed. The 1996-to-2003 launch cycle was repeated in the future projection. No postmission disposal options were applied to satellites and rocket bodies. All collisions among objects 10 cm and larger were identified for the analysis. One of the new features of LEGEND is its ability to identify objects involved in collisions individually. This allows the user to better quantify the characteristics of future collision events, for example, by orbit type (e.g., LEO/GTO/GEO, inclination, right ascension of the ascending node), by object type (satellite, rocket body, breakup fragment), by breakup time, by location, and by mass. Our analysis shows that almost all future collisions occur in LEO. Intact–intact catastrophic collisions contribute the most to the generation of future debris populations. The majority of intacts involved in collisions come from future launches. This underlines the importance of postmission disposal of satellites and rocket bodies to reduce future collision activities. More than half of the “projectile fragments” involved in intact–fragment collisions originated from future collisions, indicating the nature of the feedback process in future collisions. Most LEO collisions occur in regions of high spatial density, around 800 and 1000 km altitudes. Although there is a wide spread in impact speed, about half of the collisions occur with impact speeds greater than 14 km/s. Since collisions are likely to produce more fragments than explosions in the future, it is critical to have a high fidelity model to analyze future collision activities to ensure reliable environment predictions. With the new capabilities of LEGEND we are able to examine the process in great detail and have a better understanding of the nature of collisions.

The earth orbiting space debris

The space debris population is similar to the asteroid belt, since it is subject to a process of high-velocity mutual collisions that affects the long-term evolution of its size distribution. Presently, more than 10 000 artificial debris particles with diameters larger than 10 cm (and more than 300 000 with diameters larger than 1 cm) are orbiting the Earth, and are monitored and studied by a large network of sensors around the Earth. Many objects of different kind compose the space debris population, produced by different source mechanisms ranging from high energy fragmentation of large spacecraft to slow diffusion of liquid metal. The impact against a space debris is a serious risk that every spacecraft must face now and it can be evaluated with ad-hoc algorithms. The long term evolution of the whole debris population is studied with computer models allowing the simulation of all the known source and sink mechanisms. One of these codes is described in this paper and the evolution of the debris environment over the next 100 years, under different traffic scenarios, is shown, pointing out the possible measures to mitigate the growth of the orbital debris population. .

Space debris mitigation strategies and practices in geosynchronous transfer orbits

Missions to geosynchronous orbits remain one of the most important elements of space launch traffic, accounting for 40% of all missions to Earth orbit and beyond during the four-year period 2000–2003. The vast majority of these missions leave one or more objects in geosynchronous transfer orbits (GTOs), contributing on a short-term or long-term basis to the space debris population. National and international space debris mitigation guidelines seek to curtail the accumulation of debris in orbits which penetrate the regions of low Earth orbit and of geosynchronous orbit. The orbital lifetime of objects in GTO can be greatly influenced by the initial values of perigee, inclination, and right ascension of the orbital plane, leading to orbital lifetimes of from less than one month to more than 100 years. An examination of the characteristic GTOs employed by launch vehicles from around the world has been conducted. The consequences of using perigees above 300 km and super-synchronous apogees, typically above 40,000 km, have been identified. In addition, the differences in orbital behavior of launch vehicle stages and mission-related debris in GTOs have been investigated. Greater coordination and cooperation between space launch service providers and spacecraft designers and owners could significantly improve overall compliance with guidelines to mitigate the accumulation of debris in Earth orbit.

Hypervelocity impacts on HST solar arrays and the debris and meteoroids population

Accurate debris and meteoroid flux models are crucial for the design of manned and unmanned space missions. For the most abundant particle sizes smaller than a few millimetres, knowledge of the populations can only be gained from in situ detectors or the analysis of retrieved space hardware. The measurement of impact flux from exposed surfaces improves with increased surface area and exposure time. A post-flight impact investigation was initiated by the European Space Agency to record and analyse the impact fluxes and any potential resulting damage on the two flexible solar arrays of the Hubble Space Telescope. The arrays were deployed during the first Hubble Space Telescope servicing mission in December 1993 and retrieved in March 2002. They have a total exposed surface area of roughly 120 m 2, including 42 m 2 covered with solar cells. This new Hubble post-flight impact study follows a similar activity undertaken after the retrieval of one of the first solar arrays, in 1993. The earlier study provided the first opportunity for a numerical survey of damage to exposed surfaces from more than 600 km altitude, and of impacts from particles larger than 1 mm. The results have proven very valuable in validation of important flux model regimes. The second set of Hubble solar arrays has again provided an unrivalled opportunity to measure the meteoroid and debris environment, now sampled during a long interval in low Earth orbit, and to identify changes in the space debris environment since the previous survey. The retrieved solar array wings exhibit thousands of craters, many of which are visible to the naked eye. A few hundred impacts have completely penetrated the 0.7 mm thick array. The largest impact features are about 7–8 mm in diameter. The cover glass of the solar cells is particularly well suited to the recognition of small impact features by optical and electron microscopy. In this paper, we present the first results of the impact survey. Data upon the abundance of craters of specific measured size ranges are plotted as cumulative flux curves, and compared to the results of model predictions. The most significant change to the particle flux since 1993 is a decrease in the small debris population.

The effect of simulated hypervelocity space debris on polymers

Space debris population in low Earth orbit has been increasing constantly with the increase in spacecraft missions. Hypervelocity space debris impacts limit the functionality of polymeric outer surfaces and, in extreme cases, might cause a total loss of a spacecraft. In this work, the fracture of Kapton films by ultrahigh velocity impacts was studied. A laser-driven flyer ground simulation system was used to accelerate aluminum flyers to impact velocities as high as 2.9 km/s against polymer films with different thicknesses. Scanning electron microscopy was used to characterize the fracture morphology. Impact effects on the internal structure of the polymer were studied by means of X-ray microtomography. It was found that with an increase in debris velocity, a ductile-to-brittle transition occurred. However, fractures created by impacts at velocities above 1.7 km/s showed central impacts regions, which experienced the highest strain rate and were of ductile-type fracture, while the outer regions, which experienced a lower strain rate, failed through brittle cracking. A model explaining this phenomenon, based on the temperature gradient developed within the impacted region during collision, is presented.

Population models of space debris

More than 300 000 artificial debris particles with diameter larger than 1 cm are orbiting the Earth. The space debris population is similar to the asteroid belt, since it is subject to a process of high-velocity mutual collisions that affects the long-term evolution of its size distribution. The near–Earth space can be divided in three major regions where orbital debris is of concern: Low Earth Orbits (LEOs), below about 2000 km, Geosynchronous Orbits (GEOs), at an altitude of about 36000 km and the Medium Earth Orbits (MEOs) in between. The issues are in principle the same in the three regions, nevertheless they require different approaches and solutions. The space debris are composed by several different populations according to their source and their orbital region. A description of the nature and dynamics of the different populations in the low, medium and high orbital regimes is given. The impact risk posed by these debris is then briefly outlined.The long term evolution of the whole debris population can be studied with computer models allowing the simulation of all the known source and sinks mechanisms. One of these codes is described and the evolution of the debris environment, over the next 100 years, under different traffic scenarios is shown, pointing out the possible measures to mitigate the growth of the orbital debris population.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Survey of past on-orbit fragmentation events

Following the first on-orbit fragmentation, the explosion of the Transit 4A rocket body on June 29, 1961, 165 breakups were recorded up until August 31, 2001. So far, only three collisional breakups have been reasonably confirmed, while the remaining 162 fragmentations resulted from explosions. The aim of this paper is to assess the contribution of these on-orbit fragmentation events to the catalogued and undetected orbital debris population. To do this, the largest pieces of fragmentation debris were extracted by the US Space Command catalog of August 31, 2001, and subsequently assembled for families or single events, then counted and graphically represented. The contribution to the undetected debris population was investigated using CLDSIM, a dedicated software system, in order to simulate and propagate the debris clouds produced by each fragmentation event. The characteristics and properties of the fragmentation debris population, obtained by merging the catalogued and undetected particles, were then analyzed.

Toward a comprehensive GEO debris measurement strategy

In recent years there has been increasing interest in the effects of orbital debris on the Geosynchronous Earth Orbit (GEO) environment. This region has great economic importance that is only expected to grow stronger in the foreseeable future. The lifetime of any debris created is very long, so that there is no effective sink to remove the debris in a timely manner. Considerable resources have been brought to bear to understand the current debris environment at GEO. A number of optical telescopes in different countries are now systematically making observations of this region specifically to understand the debris population. We are now at a stage where we can begin to answer specific questions about orbital debris in these orbits, but what are these questions? Are we asking the right questions? Are the observations we are pursuing answering the most important questions? Are there changes needed in the observation techniques to better address the most important issues? Are there changes needed in the types of instruments to answer the most important questions? This paper will outline the broad questions that GEO observations should be designed to answer. I will discuss how observations so far have begun to answer those questions and where they need to concentrate in the future. This will include discussions of the benefits and limitations of the statistical sampling methodology versus the cataloguing methodology. I hope to provide a framework for future observations that will be of benefit to all GEO users.

Beam-park experiments at FGAN

The space debris situation is highly dynamic due to some on orbit break-ups and other debris producing events per year. This necessitates frequent observation campaigns e.g. with ground based sensors. FGAN (Research Establishment for Applied Science) conducted in the framework of study contracts from ESA several observation campaigns during the last years. FGAN’s L-band monopulse radar of their TIRA System (Tracking and Imaging Radar) was used to detect space objects (larger than 2 cm at 1000 km range) in LEO (Low Earth Orbit) passing the parked radar beam (Beam-park experiment; BPE). During 24-h periods complete small circles in right ascension were observed at altitudes ranging from about 300–2000 km. This paper summarizes the most recent observation campaigns in October 2000, October 2001, and April 2002. The analysis results demonstrate the changes in the debris population over time. The results are also compared with predictions by ESA’s MASTER/PROOF’99 model. The radar cross section (RCS) of detected objects is determined and converted to object size using NASA’s Size Estimation Model (SEM). These data can be used to verify e.g. the orbital size distribution assessed by space debris environmental models. RCS data of some detected larger space objects are compared with data published in the US Space Command (USSPACECOM) RCS-catalogue. The comparability of these data is discussed. Using radars in BPEs side lobe detections might happen. Since they falsify the statistics their identification and treatment is discussed.

Contribution of secondary ejecta to the debris population

When a micro-debris or a micrometeoroid impacts a spacecraft surface, secondary particles, called ejecta, are produced. These ejecta 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 distances by the formation of a population of small orbital debris. This paper describes the ejecta production mechanism, and shows their orbital evolution. Then, the distribution of ejecta in low earth orbits is given. Some results are presented describing the number of ejecta as a function of size and altitude.

Cost-effective and robust mitigation of space debris in low earth orbit

For the wide acceptance of space debris mitigation measures throughout government agencies and industry, their cost-effectiveness must be demonstrated. The selected measures must not only be effective at controlling the future growth of the debris population, but they should also aim to minimise the collision risk to spacecraft at a minimal cost of implementation. Furthermore, the selected measures must be sufficiently robust to retain their effectiveness if unexpected increases in space activity were to occur. In this paper, clear criteria are established in order to assess numerous different Low Earth Orbit (LEO) debris mitigation scenarios for their cost-effectiveness and robustness. The ESA DELTA debris model is used to provide long-term debris environment projections for these scenarios as an input to the effectiveness/robustness element. Manoeuvre requirements for the different post-mission disposal scenarios are calculated in order to define the cost-related element. A 25-year post-mission lifetime de-orbit policy, combined with explosion prevention and mission-related object limitation, was found to be the most cost-effective solution to the space debris problem in LEO. This package would also be robust enough to retain its effectiveness even after a significant increase in future launch traffic. It was found that the re-orbiting of space systems above the LEO region would not lead to significant collision activity there over the next century. However, above-LEO disposal should be used sparingly because the disposal region could become unstable after a limited number of localised explosion or collision-induced breakup events due to a lack of air drag to remove the resulting fragments.

A proposed in situ debris measurement in GEO

In situ measurements are required to characterize the particle environment below the threshold of remote sensors. Ground-based geosynchronous Earth orbit (GEO) optical measurements in general have been limited to objects greater than about 15 cm. It is highly unlikely that any ground-based telescope can detect GEO debris smaller than 1 cm. Firsthand knowledge of the untrackable debris population is critical to GEO environment definition, if we are to control that environment. The current, general debris mitigation and protection measures may be applied to GEO satellites, but characterizing the GEO debris environment (flux, size distribution, orbit distribution, sources) will also allow measures tailored specifically for that environment. Two specific issues need to be addressed for any effective in situ measurements in GEO: detector type and potential contamination from interplanetary and interstellar dust. In this paper, we will discuss why the polyvinylidene fluoride (PVDF) material makes an ideal GEO debris detector. We will also show that impacts from debris, interplanetary dust, and interstellar dust are very different in many ways (size, impact speed, flux, etc.). Debris impacts can be easily distinguished from other impacts.

The MASTER-2001 model

Meteoroid and Space Debris Terrestrial Reference model (MASTER) is the European particulate environment and risk assessment model. It is based on quasi-deterministic principles, using comprehensive orbit propagation theories and volume discretisation techniques, to derive spatial density and velocity distributions in a three-dimensional control volume ranging from LEO to GEO altitudes. The new release, MASTER-2001, incorporates new modelling and validation approaches and enables the calculation of fluxes on targets operating between the year 1957 and 2050, using detailed simulation results. This could be achieved by using not only the POEM simulation tool for the past to present debris populations, but also applying the long term prediction tool DELTA to obtain future populations. The paper describes the features and results of the MASTER-2001 model, and the updated modelling approach (e.g., the use of a new fragmentation model). The historical and future evolution of the space debris environment in terms of spatial density and object fluxes as given by MASTER-2001 are presented and discussed.

Environmentally-induced debris sources

Resident spacecraft and rocket bodies are known to spontaneously produce large fragments (>10 cm), usually released at low velocities in small numbers and normally exhibiting large area-to-mass ratios. Potential causes of these anomalous events, which are not related to the more dramatic satellite breakups, include material degradation due to environmental stresses and impact by small natural or man-made particles. An examination of known and previously undocumented anomalous events was undertaken to gain better insight into the frequency of such events and the resultant consequences to the overall orbital debris environment. Some space vehicle types, e.g., US Transit spacecraft and former Soviet Vostok orbital stages, demonstrate a propensity for debris generation, while other satellite designs appear less vulnerable. Some satellites are known to produce numerous debris over a period of many years, and the debris exhibit wide-ranging characteristics. It is concluded that such debris currently account for a small portion of the large orbital debris population, but the number of smaller debris cannot yet be estimated. Better identification and analysis of anomalous events might indicate the degree to which small particle impacts are responsible and whether the frequency of anomalous events in given orbital regimes can be used to monitor changes in the small particle population. Modifications to some satellite designs might mitigate anomalous event debris generation.

Optical observations of space debris in GEO and in highly-eccentric orbits

The space debris population in low Earth orbits (LEO) has been extensively studied during the last decade and reasonable models covering all size ranges were produced. Information on the distribution of objects in the geostationary ring (GEO), however, is still comparatively sparse. Until quite recently the population of man-made objects in GEO had to be inferred solely from the about 900 continuously tracked objects and the modeling of the two explosions known to have occurred in GEO. Optical observations from the last two years performed with ESA's 1-m telescope at the Teide observatory in Tenerife changed the situation substantially. A hitherto unknown but significant population of small-size objects with diameters as small as ten centimeters has been detected in GEO. Objects in highly-eccentric orbits crossing the GEO region, in particular objects in geostationary transfer orbits (GTO), also contribute to the density of space debris in GEO. This family is even less well known than the GEO population, although many explosion events were reported in this orbital region. The paper will summarize recent results from the ESA GEO survey and describe the techniques and first results of a trial GTO survey.

Assessment of orbital debris size estimation from radar cross-section measurements

MIT Lincoln Laboratory has conducted a measurement program for man-made orbital debris since 1991 in response to NASA's need to characterize the orbital debris population and facilitate manned spaceflight activities. The primary sensors used in that effort are the Haystack and Haystack auxiliary (HAX) radars located at the Lincoln space surveillance complex (LSSC) in Westford, Massachusetts. This paper will describe the results from a new effort conducted at LSSC, the objective of which is to assess the variability in NASA's current procedure for determination of size from radar data. RCS data have been acquired on 39 NASA-selected resident space objects (RSO). Results are also compared to the size estimates from the FPS-85 radar, an asset of the Space Surveillance Network.