ESA UNCLASSIFIED - Releasable to the Public

ESA ESOC
Robert-Bosch-Strasse 5
D-64293 Darmstadt
Germany

ESA’S ANNUAL SPACE ENVIRONMENT REPORT

Prepared by

ESA Space Debris Office

Document Type

LOG

Reference

GEN-DB-LOG-00288-OPS-SD

Issue/Revision

8.0

Date of Issue

19 July 2024

StatusFinal

ESA UNCLASSIFIED - Releasable to the Public

Table of contents
Executive summary ............................................................................................................................... 3
1. Introduction ...................................................................................................................................... 9
1.1. Definitions .................................................................................................................................... 10
1.2. Data sources ............................................................................................................................... 121.3. Methodology ................................................................................................................................ 13
1.4. Notable changes .......................................................................................................................... 14
1.5. Acknowledgements ..................................................................................................................... 16
1.6. Disclaimer .................................................................................................................................... 16
2. Space Environmental History in Numbers ...................................................................................... 17
2.1. Overall Space Environment ......................................................................................................... 18
2.2. Evolution of Environment in LEO ................................................................................................. 222.3. Evolution of Environment in GEO ................................................................................................ 24
2.4. Non-catalogued and modelled objects ......................................................................................... 26
2.5. Usage of the Protected Regions .................................................................................................. 27
2.6. Constellations in the LEO protected region .................................................................................. 39
2.7. Active payloads in the LEO protected region ............................................................................... 40
2.8. New Catalogued Objects in the Space Environment.................................................................... 43
2.9. Objects Removed from the Space Environment .......................................................................... 45
2.10.Nuclear Power Sources ............................................................................................................... 50
2.11.Registration of Objects Launched in Outer Space ....................................................................... 51
3. Environmental Status 2023 ............................................................................................................ 53
3.1. Status of the Environment in LEO ................................................................................................ 56
3.2. Status of the Environment in GEO ............................................................................................... 62
3.3. Fragmentations in 2023 ............................................................................................................... 64
3.4. Changes to the Environment in 2023 ........................................................................................... 65
3.5. Conjunction statistics in LEO in 2023........................................................................................... 69
4. Intentional object release ............................................................................................................... 74
4.1. Mission Related Objects .............................................................................................................. 74
4.2. Solid Rocket Motor Firings ........................................................................................................... 78
5. Fragmentation History .................................................................................................................... 79
5.1. All fragmentation events .............................................................................................................. 81
5.2. Non-system related fragmentation events ................................................................................... 88
6. End-Of-Life Operations History ...................................................................................................... 90
6.1. End-Of-Life Operations in Low Earth Orbit .................................................................................. 90
6.2. End-Of-Life Operations in Geostationary Orbit .......................................................................... 107
6.3. End-Of-Life Operations in MEO ................................................................................................. 112
7. Environment metrics .................................................................................................................... 114
7.1. Environmental Index in 2023 ..................................................................................................... 114
7.2. Environment evolution ............................................................................................................... 116
References ....................................................................................................................................... 121

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EXECUTIVE SUMMARY
Ever since the start of the space age there has been more space debris in orbit than operational satellites. As spacedebris poses a problem for the near Earth environment on a global scale, only a globally supported solution can be
the answer. This creates the need for a set of internationally accepted space debris mitigation measures. A major
step in this direction was taken in 2002, when the Inter-Agency Debris Committee (IADC) published its first Space
Debris Mitigation Guidelines. This document, and subsequent updates, has since served as a baseline for nonbinding policy documents, national legislation, and as a starting point for the derivation of technical standards. The
standardisation of mitigation measures is important in order to achieve a common understanding of the required
tasks leading to transparent and comparable processes. Even if having a consistent set of measures is paramountto tackle the global problem of space debris, it is still up to the individual nations, operators, and manufacturers to
implement them.
In order to have an overview of the ongoing global debris mitigation efforts and to raise awareness of space
activities in general, the European Space Agency, ESA, has been publishing a Space Environment Report since2017. The document is updated yearly, it is publicly available, and it supports the awareness raising guideline
laid out in United Nations Committee on the Peaceful Uses of Outer Space’s (UNCOPUOS) Guidelines for theLong-Term Sustainability of Outer Space Activities published in 2019. The purpose of this report is to:• Provide a transparent overview of global space activities;• Estimate the impact of these activities on the space environment;• Quantify the effect of internationally endorsed mitigation measures aimed at improving the sustainability ofspace flight.
In this report, the status of the space environment is presented in various facets, focusing on the time evolution of
catalogued and asserted objects in terms of number, mass, and area, as well as addressing the global adherence
to space debris mitigation measures. Most internationally accepted space debris mitigation measures can betraced back to the following objectives:• The limitation of space debris released during normal operations;• The minimisation of the potential for on-orbit break-ups;• Post mission disposal;• Prevention of on-orbit collisions.
These objectives are translated in design and operation guidelines that can be measured and the consequences
can be assessed. Aspirationally, these objectives lead to future in which space debris is not an issue.
Whereas the presentation of numerical values associated to launch and re-entry activities are essentially absolute, it is important to point out that metrics dealing with the adherence to space debris mitigation measures are
estimates. These estimates depend on complex physical problems such as estimating orbital lifetime and require
under-determined interpretations of observational quantities. As such, the conclusions on the state of the spaceenvironment presented hereafter need to be taken with appropriate care and can vary between yearly releases of
the report. Notwithstanding such caveats, all care is taken in the design of the methodologies to minimise suchvariability and some summarising statements can be derived from the presented data.

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The amount of objects, their combined mass, and their combined area has been steadily rising since thebeginning of the space age, leading to the appearance of involuntary collisions between operational payloads andspace debris. Ever increasing improvements in space surveillance sensor capabilities during the last decades
have brought down the size limits where debris can be reliably tracked and catalogued. This, in turn, implies that
we know about significant amounts of space debris, but not all their originating events. The space traffic itself isalso undergoing notable changes since 2015, particularly in Low Earth Orbits, fuelled by the miniaturisation of
space systems and deployment of large constellations, with a shift towards commercial operators. In 2023,
the launch traffic in all mass and type classes is still at the highest rate seen thus far. These three elements (i.e.
volume of traffic, type of spacecraft, type of operators) are all of relevance when one considers the adequacy of
space debris mitigation guidelines and possible ways for sustainable space operations, especially when looking
at the Earth’s orbital environment as a finite resource, in line with the UN Long-Term Sustainability Guidelines[1].

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Figure 1: Evolution of number of objects in geocentric orbit by object class. Please consult Section 1.1 for thedefinitions.

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Figure 2: Evolution of the launch traffic near LEOIADC per mission type (left) and mass category (right).

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Figure 3: Historical trend of fragmentation events per event cause. The last bin covers until the end of 2023.
On average over the last two decades, 10.6 non-deliberate fragmentations continue to occur in the space environment every year. This number is stable, however the impact of each event is variable. This number drops
significantly to 1.8 per year when the lifetime of the generated fragments is considered a factor of importance,and even 0.4 per year when systematic and unexplained events are excluded from the analysis. This suggeststhat non-collisional events with a large environmental impact are still taking place partly due to re-use of a design
with known issues. Further details are presented in Table 5.1 and Table 5.2. Fragmentations other than collision
are currently the dominant source of space debris as can be seen from Figures 5.6 and 5.5. The increase in launchtraffic and permanence of space debris events in Low Earth orbit results in a significant conjunction risk in themost congested Earth orbits. Detailed information is given in Section 3.5.
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Figure 4: Conjunction events (i.e. events that could trigger an operator response but not necessarily an avoidance
manoeuvre nor a collision) and corresponding chaser classification for a set of representative missions over 2023.

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Between 98% and 78% of payloads below 1000.0 kg in mass, reaching the end of their mission since 2020 andinjected into the LEO protected region, operate in orbits that naturally adhere to the space debris mitigation
measures. For the payloads with masses between 100.0 kg and 1000.0 kg in mass, this is dominated by the
behaviour of constellations. Currently, natural adherence is measured against 25 years of remaining orbital lifetime.
However, it is becoming increasingly clear that this threshold is not sufficient for achieving a sustainable spaceenvironment long-term [2]. The majority of larger payloads reaching the end of their mission since 2020 did
so in orbits where they did not successfully remove themselves from.
Between 40 and 70% of all payload mass, excluding human spaceflight, estimated as reaching end-of-life during
the last decade in the LEO protected region does so in orbits that are estimated to adhere to the space debris
mitigation measures, as shown in Fig. 6.4. The noted increase in small payloads reaching end-of-life in compliant orbit implies a rising share, as does an increasing share of objects with manoeuvre capabilities such as
constellations. Between 60 and 90% of all rocket body mass reaching end-of-life during the last decade does soin orbits that are estimated to adhere to the space debris mitigation measures on protecting LEO as shown in
6.6. A significant amount of this is due to controlled re-entries after launch, a practice which increased from 10%
to over 60% over the last decade.

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Figure 5: Breakdown of the 2020 decade of observed behavioural classes for payloads per mass category. Please
consult Section 6.1 for the definitions.

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One of the core principles of the space debris mitigation guidelines is to remove objects from the LEO and GEO
protected regions with a high success rate for those orbits where a natural disposal mechanism is absent [2]. In
practice, a common target for this success rate set at 90% based on space traffic condition corresponding to first
decade of the millennium and with a goal to slow down the rate of space debris creation. It is thus a valuable
first step towards space sustainability, but will by itself not reduce the amount of debris in orbit, and will needto increase to near 100% in the near future. Between 20 and 65% of payloads, excluding human spaceflight,
reaching end-of-life during the last decade in the LEO protected region in a non-compliant orbit attempt tocomply with space debris mitigation measures, with peaks in 2018 and 2020 respectively due to the de-orbitingof a constellation and a low amount of satellite reaching end of life in a non-compliant orbit. The difference inbehaviour between constellation and non-constellation objects can be significant as shown in Fig. 6.3. Between
5% and 60%, again with peaks in 2018 and 2020 for the same reasons as before, do so successfully and a rising
trend is evident. Between 50 and 95% of rocket bodies reaching end-of-life during the current decade in the LEO
protected region in a non-compliant orbit attempt to comply with space debris mitigation measures. Between 40%
and 90% do so successfully, with the compliance trend linearly increasing. Between 25% and 55% of the rocket
bodies delivering payloads in or near the GEO protected region during the last decade are in compliancewith space debris mitigation measures. Between 85% and 100% of all payloads reaching end-of-life during thelast decade in the GEO protected region attempt to comply with space debris mitigation measures. Between
70% and 95% do so successfully, with the compliance trend asymptotically increasing, but notable exceptions in2015 and 2022.
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Figure 6: Trend of adherence to clearance of the protected region over time in terms of numbers, excluding naturally
compliant objects where no action was needed or taken.

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Whereas adoption of, and compliance to, space debris mitigation practices at a global level is noted as slowly
increasing, it is of importance to note that the successful implementation is still at a too low level to ensure asustainable environment in the long-run. Notably, some of the increase in uptake of mitigation measures as
analysed by the metrics above, such as controlled re-entries of rocket bodies or post mission disposal success rates
for payloads in LEO, are linked with the deployment and retirement of large constellations. Other effects, suchas a shift in usage of operational mission orbits in Low Earth Orbit as show in Fig. 2.20, are however independentof the category of the payload.

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The extrapolation of the current changing use of orbits and launch traffic, combined with continued fragmentations
and limited post mission disposal success rate could lead to a cascade of collision events over the next centuries.
Even in case of no further launches into orbit, it is expected that collisions among the space debris objects alreadypresent will lead to a further growth in space debris population in Low Earth Orbit. Based on these findings, among
others, there is a growing consensus that stricter space debris mitigation practices need to be implemented globally,
and, eventually, remediation might need to be considered. In line with this, the early twenty-twenties saw somesignificant policy shifts come into force across major launching states across the globe, including ESA’s own Zero
Debris Policy and updated Space Debris Mitigation Standard [3], whose effects, it is hoped, will be seen in future
editions of this report.

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Figure 7: Number of cumulative collisions in LEOIADC in the simulated scenarios of long-term evolution of theenvironment.

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1. INTRODUCTION
Ever since the start of the space age on the 4th of October 1957 there has been more space debris in orbit thanoperational satellites. Space debris poses a problem for the near Earth environment on a global scale, to which
all spacefaring nations have contributed and for which only a globally supported solution can be the answer. The
first awareness of the problem came about in the early 1960s, based on initial research activities undertaken in the
United States of America, but it took some time to reach the international community. It eventually did by the mid
1970s via conferences organised by the International Astronautical Federation. The effect whereby the generationof space debris via collisions and explosions in orbit could lead to an exponential increase in the amount of artificial
objects in space, in a chain reaction which would render spaceflight too hazardous to conduct, was first postulated
by Donald Kessler in 1978 [4]. The first dedicated conference on space debris was held in 1982, organised by the
National Aeronautics and Space Administration (NASA), followed by the first workshop on the re-entry of spacedebris in 1983, organised by the European Space Agency (ESA), in response to the re-entries of Skylab andCosmos-1402.
The technical expertise on space debris, from re-entries to on-orbit break-up and hypervelocity impact testing, wasgathered on agency and national level for much of the 1970s and 1980s. However, the global dimension of theissue called for bilateral knowledge transfer, which started on the initiative of NASA. These exchanges between
experts resulted in multi-lateral meetings and lead to the creation of the Inter-Agency Space Debris Coordination
Committee (IADC) in 1993, founded by ESA (Europe), NASA (USA), NASDA (now JAXA, Japan), and RSA (nowRoscosmos, Russian Federation). Nine more agencies have joined the IADC since: ASI (Italy), CNES (France),
CNSA (China), CSA (Canada), DLR (Germany), KARI (South Korea), ISRO (India), NSAU (Ukraine), and UKSA
(United Kingdom). The IADC was founded as a forum for technical exchange and coordination on space debris
matters, and can today be regarded as the leading international technical body in the field of space debris. Space
debris has also been a recurring agenda item for the Scientific & Technical Subcommittee of the United Nations’Committee on the Peaceful Uses of Outer Space (UNCOPUOS) since 1994.
The threat of space debris to the future of spaceflight combined with the nearly universal adoption of the Liability
Convention [5] created the need for a set of internationally accepted space debris mitigation measures. A major
step was taken in 2002, when the IADC published the IADC Space Debris Mitigation Guidelines [6] and presented
them to the UNCOPUOS Scientific & Technical Subcommittee. This document has since served as baseline fornon-binding policy documents, national legislation, and as starting point for the derivation of technical standards.
A consistent set of measures is paramount to tackle the global problem of space debris, but it is up to the individual
nations, operators, and manufacturers to implement them, which can lead to variations on a case by case basis. As
such, nations around the world have developed safety standards and specific guidelines building on the work of the
IADC. However, standardisation of mitigation measures is important in order to achieve a common understandingof the required tasks leading to transparent and comparable processes. This is the task of normative international
standardisation bodies such as the International Standards Organisation (ISO) [7].
In order to address the issues posed by space debris on spaceflight activities UNCOPUOS has taken the initiative
to create a set of internationally agreed guidelines for the long-term sustainability of outer space activities [1].
These guidelines contain recommendations on the policy and regulatory frameworks for space activities, the safetyof space operations, rules of engagement for international cooperation, capacity-building and awareness, andscientific and technical research and development.

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The content of this document is written in response to those guidelines by raising awareness of space activities,
and aims to:• Provide a transparent overview of global space activities,• Estimate the impact of these activities on the space environment,• And quantify the effect of internationally endorsed mitigation measures aimed at sustainability of the environment.
The document is structured as follows: Section 1 contains the definitions, data sources, and methodologies used
to compile this document. Section 2 contains the history of the space environment since the beginning of the spaceage. Section 3 contains a snapshot of the space environment for a specific year analysed. The content of Sections
2 and 3 are further analysed in depth in Sections 4, 5, and 6 where respectively the intentional release of objects,
fragmentation events, and end-of-life operations of space missions are covered. Section 7 summarises the space
activities in Low Earth Orbit up until the year of analysis into an environment index. Furthermore, an executive
summary containing the main space environment trends identified is added to the beginning of this report.

1.1. Definitions
This document aims to describe the space environment. This environment is understood to contain all artificial
objects, including fragments and elements thereof, which currently, or previously did, reside in an Earth boundorbit.
The space environment will be described since the beginning of the space age, understood to start with the launchof Sputnik 1 on the 4th of October 1957, unless explicitly stated otherwise.
Space debris is defined as all artificial objects including fragments and elements thereof, in Earth orbit or re-entering
the atmosphere, that are non-functional [6].
Objects in the space environment can be categorised in two broad categories: The ones which can be traced backto a launch event and for which the nature can be identified, and the ones for which this is impossible. The laterones will be identified as Unidentified, whereas the former can be further categorised in:• Payloads, space object designed to perform a specific function in space excluding launch functionality. This
includes operational satellites as well as calibration objects.
• Payload mission related objects, space objects released as space debris which served a purpose for thefunctioning of a payload. Common examples include covers for optical instruments or astronaut tools.
• Payload fragmentation debris, space objects fragmented or unintentionally released from a payload as spacedebris for which their genesis can be traced back to a unique event. This class includes objects created whena payload explodes or when it collides with another object.
• Payload debris, space objects fragmented or unintentionally released from a payload as space debris forwhich the genesis is unclear but orbital or physical properties enable a correlation with a source.
• Rocket body, space object designed to perform launch related functionality; This includes the various orbital
stages of launch vehicles, but not payloads which release smaller payloads themselves.
• Rocket mission related objects, space objects intentionally released as space debris which served a purpose
for the function of a rocket body. Common examples include shrouds and engines.
• Rocket fragmentation debris, space objects fragmented or unintentionally released from a rocket body as

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space debris for which their genesis can be traced back to a unique event. This class includes objects
created when a launch vehicle explodes.
• Rocket debris, space objects fragmented or unintentionally released from a rocket body as space debris forwhich the genesis is unclear but orbital or physical properties enable a correlation with a source.
A fragmentation is thus loosely defined as an event on-orbit that creates space debris without purpose, including
but not limited to collisions, explosive break-ups, and tear and wear. With this definition of a fragmentation event in
mind, the distinction between mission related objects and fragmentations debris is clear. Objects that are classified
as general payloads or rocket debris can be reclassified when more information becomes available. An overview
of this object type classification and the abbreviations used in the rest of the document is given in Table 1.1.
The taxonomy of objects in the space environment can be done based on type as defined previously, but also
via the orbital regime in which they reside. A catalogued object will refer to an object whose orbital elements aremaintained for prolonged periods of time in a catalogue created by a space surveillance system. An asserted
object will refer to an object which has not been reported by a space surveillance system but is known to exist in
the space environment by design. Asserted objects include, for example, rocket bodies that perform a re-entry
burn after inserting a payload into orbit prior to repeated detections by a space surveillance system. As such,catalogued and asserted objects are not mutually exclusive and neither one is strictly contained within the other.
Further objects exists in the space environment that are not catalogued for prolonged periods of time, for example
as unpredictable orbit motion prohibits the correlation of observations, and can neither be asserted from a design
point of view. These objects are beyond the scope of this report.
Catalogued and asserted objects can be categorised in terms of their orbital elements for a given epoch. Orbital
regimes in this report will be identified based on semi-major axis, eccentricity, inclination, perigee height andapogee height. The orbital regimes that shall be used are defined in Table 1.2. Two regions are often identified
as so-called protected regions by international standards, guidelines, and national legislation; they are specificallydefined in Table 1.3 and will be referred to as such. It is important to note that all these definitions are inherent to thisdocument and can change between issues. In addition to the orbital regions defined in Table 1.2, the report also
refers to Sun-Synchronous orbits, i.e. orbits for which the secular variation of the right ascension of the ascending
node, due the Earth’s oblateness, matches the Earth’s rotation rate around the Sun. As a result, the orbital planeremains approximately fixed with respect to the Sun and a satellite in those orbits passes over a point on the Earthwith the same local solar time and this makes Sun-Synchronous orbits particularly used for Earth Observation
missions. This report will also make use of Destination Orbits for Payloads and Rocket Bodies. This single orbit
per object is defined by an analyst to be representative for orbits used during its normal operations.
Table 1.1: Object Classifications.
Type

Description

PL

PayloadPF

Payload Fragmentation Debris

PD

Payload Debris

PM

Payload Mission Related Object

RB

Rocket Body

RF

Rocket Fragmentation Debris

RD

Rocket Debris

RM

Rocket Mission Related Object

UI

Unidentified

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Table 1.2: Ranges defining each orbital class, with semi-major axis a, eccentricity e, inclination i, perigee height
hp and apogee height ha . The units are km and degrees.
Orbit Description

Definition

GEO Geostationary Orbiti ∈ [0, 25]

hp ∈ [35586, 35986]

ha ∈ [35586, 35986]

IGO

Inclined Geosynchronous Orbita ∈ [37948, 46380]

e ∈ [0.00, 0.25]

i ∈ [25, 180]

EGO Extended Geostationary Orbita ∈ [37948, 46380]

e ∈ [0.00, 0.25]

i ∈ [0, 25]

NSO Navigation Satellites Orbiti ∈ [50, 70]

hp ∈ [18100, 24300]ha ∈ [18100, 24300]

GTO GEO Transfer Orbiti ∈ [0, 90]

hp ∈ [0, 2000]

ha ∈ [31570, 40002]

MEO Medium Earth Orbit

hp ∈ [2000, 31570]

ha ∈ [2000, 31570]

GHO GEO-superGEO Crossing Orbits hp ∈ [31570, 40002]

ha > 40002

LEO Low Earth Orbit

hp ∈ [0, 2000]

ha ∈ [0, 2000]

HAO High Altitude Earth Orbit

hp > 40002

ha > 40002

MGO MEO-GEO Crossing Orbits

hp ∈ [2000, 31570]

ha ∈ [31570, 40002]

HEO Highly Eccentric Earth Orbit

hp ∈ [0, 31570]

ha > 40002

LMO LEO-MEO Crossing Orbits

hp ∈ [0, 2000]

ha ∈ [2000, 31570]

UFO Undefined Orbit
ESO Escape Orbits
Table 1.3: Ranges defining each protected region, with altitude h and declination δ. The units are km and degrees.
Orbit

Description

Definition

LEOIADC IADC LEO Protected Regionh ∈ [0, 2000]

GEOIADC IADC GEO Protected Regionh ∈ [35586, 35986]

δ ∈ [−15, 15]At various moments during the space age, payloads based on a limited amount of platforms have been deployedon-orbit with the intent to create a single larger system by operating in a coordinated manner. Well known examples
include space segments of satellite navigation systems or systems dedicated to global data information coverage.
Colloquially, such systems of payloads are known as constellations. For the purpose of this report, a constellationis understood as a set of at least 20 individual Payloads objects, released into orbits over more than 2 events andcovering more than 1 year in time from first to last event, sharing the same objective as a combined system, andwith the orbits in which they are deployed directly related to the systems’ objective. A constellation is considered
active, i.e. functional, as long as at least one of its constituting Payloads is functional. For the current analysis,
constellations are identified only in LEOIADC and MEO, resulting in a total of 26 constellations.

1.2. Data sources
Orbital information for catalogued objects is obtained from the USSTRATCOM Two-Line Elements data set, theVimpel data set maintained by the JSC Vimpel Interstate Corporation and Keldysh Institute of Applied Mathematics(KIAM), and the Royal Aircraft Establishment (RAE) Tables of artificial satellites. Orbital information on asserted
objects, as well as the justification for their assertion, is taken from the DISCOS Database (Database and Information System Characterising Objects in Space) [8]. Orbital information on catalogued and asserted objects arecorrelated among the various sources to avoid duplication.
Physical properties for the objects, and the mission classification for Payloads, used in this report are taken fromDISCOS. Shape properties such as area are derived from design values and not estimated from space surveillance

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systems, which implies that the debris and unidentified object types have no mass nor area indicated as part ofthis report. From the area and mass values so defined, the object area-to-mass ratio (A/m) is computed and it
is used in the characterisation of Payloads (Section 2.7) and, more in general, for the propagation of the object
trajectories for compliance analysis (Section 6) and in the simulation of the long-term evolution of the environment(Section 7.2). For orbital lifetime assessments, data derived from space surveillance systems can be used forthese objects for the determination of the Ballistic Coefficient (BC), as explained in Section 6. Further informationon the individual objects which is not directly physical in nature, e.g. ownership, is deliberately not reported on inthis document.
The classification of whether a Payload is considered active is based on the data available at [9], which is used fordata from 2019 onwards, and from the Union of Concerned Scientists (UCS) database [10], for earlier data since2005. This classification by activity level is not used for the end-of-life analyses, where the activity of an object isinstead estimated from space surveillance data.

1.3. Methodology
The first aim of this report is to describe the space environment based on observable facts. This takes the form ofanalysing trends in the various physical characteristics of the objects within the space environment, both covering
the history since the beginning of the space age as well as a single year of analysis. The report focusses on theamount of mass, area, and object count passing through the different orbital regimes, with specific emphasis on
the protected regions. Furthermore, the usage of the protected regions by payloads is documented.
Secondly, metrics are identified that serve as proxies for the global adherence to space debris mitigation guidelines,
which have been put in place to protect the space environment from adverse effects such as the Kessler syndrome.
The evolution of these metrics is described. Most internationally accepted space debris mitigation measures canbe traced back to the following objectives:• The limitation of space debris released during normal operations; i.e. in all operational orbit regimes, payloads and rocket bodies should be designed not to release space debris during normal operations. Where
this is not feasible, any release of debris should be minimised in number, area and orbital lifetime.
• The minimisation of the potential for on-orbit break-ups; i.e. in all operational regimes one should minimise
the potential for break-ups during operational phases, e.g. by thorough analysis of the failure trees, increase(sub)system reliability, etc., minimise the potential for post-mission break-ups resulting from stored energy,
e.g. stored in tanks, batteries, flywheels, etc., and the avoidance of intentional destruction and other harmful
activities, e.g. intentional break-ups should avoided at all cost but if need be they should be conducted at
sufficiently low altitudes so that orbital fragments are short-lived.
• Post mission disposal; i.e. two protected regimes, Low Earth Orbit (LEOIADC ) and Geostationary Orbit(GEOIADC ), have been identified and should be cleared from permanent or (quasi-) periodic presence of
non-functional artificial objects. Payloads or rocket bodies that are terminating their operational phases inother orbital regions should be manoeuvred to reduce their orbital lifetime, commensurate with LEO lifetime
limitations, or relocated if they cause interference with highly utilised orbit regions.
• Prevention of on-orbit collisions; i.e. in developing the design and mission profile of a space object, a project
should estimate and limit the probability of accidental collision with known objects during the payload orrocket body’s orbital lifetime. If reliable orbital data is available, avoidance manoeuvres and co-ordination oflaunch windows may be considered if the collision risk is not considered negligible.
Even though the goals of the mitigation measures as identified above are intuitively clear, their technical implementation is less straightforward. The proposed metrics to observe adherence to these objectives are described

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ESA UNCLASSIFIED - Releasable to the Publicin the corresponding sections and follow as close as possible [7]. In case of orbital lifetime predictions, the corresponding international standard is followed [11]. Details on the data gathered or methods used corresponding toresults presented in the individual sections of in this report are covered in those sections.
Not all aspects of space debris mitigation can, currently, be reliably derived from observational data. For example
a collision avoidance manoeuvre can look similar to an orbit control manoeuvre to maintain a specific ground-track.
In the same way, the observed behaviour due to passivation of fluids at the end of life of a mission does not need
to be different from the effects of an orbit control manoeuvre. The philosophy behind this document is to accept
these limitations and not to risk over-interpreting the available data.
Thirdly, metrics are identified to estimate the impact of global space activities on the space environment. Historically, such metrics have often been formulated in terms of the outcomes of long-term, i.e. centuries, spaceenvironment evolution models that serve to extrapolate a set of space traffic condition into the future and derive
the expected amount of space debris and collision events. As of recent, also the establishment of dedicated risk
metrics for the purpose of impact assessments has become more commonplace. Both metrics are included in thisreport.

1.4. Notable changes
1.4.1. Edition 4
Significant changes have taken place when it comes to the usage of the space environment since the first issue of
this report in 2016. As can be observed in Section 2, there has been a significant increase in the ability of spacesurveillance networks to reliably catalogue objects in orbits near the Geostationary Orbit, and launch traffic to Low
Earth Orbit increased to previously unseen levels. With the improvements in capabilities of observation systems
and the rapid miniaturisation and innovation for space system designs, it is likely that those developments willcontinue in the future.
As a consequence, also international documents dealing with space debris mitigation have been updated in 2019,with most notably the ISO space debris mitigation requirements [7] and the IADC space debris mitigation guidelines [2]. This is also reflected in the content of this report by means of some noticeable changes. Prior to edition 4,
attempts to relocate Payloads above Low Earth Orbit were seen as a positive space debris mitigation effort, eventhough this was not endorsed by the IADC space debris mitigation guidelines. This is no longer the case. Furthermore, given the uncertainties associated with orbital lifetime predictions, the thresholds used to categorise Payload
or Rocket Body as (non-)compliant w.r.t. space debris mitigation guidelines are now addressed stochastically for
those cases near the threshold.
A major event visible in this edition of the report is the de-orbiting of a telecommunication constellation in Low Earth
Orbit which started in 2018. Just as the insertion of this constellation is visible in the launch traffic increase, it now
stands out as an increase in successful post mission de-orbiting when it comes to compliance to the guidelines.
Furthermore, with the coming into operations of a newer generation of launchers, the release of mission related
objects as part of their operations is going down. However, releasing large mission related objects altogether isunfortunately not a relic of the past (yet).

1.4.2. Edition 5
Starting with edition 5 of this report, an increased emphasis is put on the consequence of the global level of adherence to space debris mitigation guidelines. To capture these consequences in relation to the dynamic evolution of
the actors in orbit and measures to achieve space debris mitigation, it became necessary to estimate automaticallythe average properties of objects and the orbital usage alike. Based on these properties, short-term consequences

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such as the risk of collision faced by operators in the LEO protected region as well as the long term risk of triggering
the Kessler syndrome in the LEO protected region can be estimated.
Notable events visible in this edition of the report are the completion of the de-orbiting of a telecommunication
constellation from Low Earth orbit in 2019 and the start of on-orbit deployment of two new ones during 2020. To acertain extent, 2020 marks the beginning of a new era in spaceflight with the maturation of large and medium-sized
constellations being deployed on orbit and the availability on ground of the derived service, the increased use of
so-called ride-share missions, and the continuation of miniaturisation of space system. This is in contrast with theperiod between the mid 1990’ies and ending mid 2010’s, which saw the slow but steady roll-out and demonstrationof the new technologies that are becoming commonplace today.
The start of solar cycle 25 marks a change for the regularly updated orbital lifetimes used in this report. Thechange in cycle behaviour has an impact on the estimated compliance rates as show in Fig. 6.16. In the uncertainty
analysis, the values for the last year are affected by the low number of cases for Rocket Bodies due to the increased
usage for controlled re-entry as disposal strategy. This is not an issue, as Payload data is accounted for with one
year delay, and the uncertainties have generally a limited impact in this case.

1.4.3. Edition 6
The space environment continued to change rapidly in 2021 with the accelerated deployment of large constellations
in LEOIADC , increasing demand for the deployment of small Payloads, but reduction of launch traffic to GEOIADC .
For the first time, launching more than one payload per launch has become the most common way of getting into
orbit. To put this into perspective, the analyses introduced in Edition 5 of this report were extended to cover different
epochs from the recent space age, i.e. addressing how collision avoidance risk has evolved (Fig. 3.12) and what
would be the outcome of extrapolating various long-term evolution scenarios (Fig. 7.5-7.6). The combination ofchanging launch traffic patterns in general, and the dichotomy between constellation-related objects and otherintact objects specifically, has a noticeable impact on both short and long-term risk indicators.
With the increased awareness of space sustainability in the community at large, a new emphasis is placed on
space debris mitigation aspects that were previously less noticeable or are gaining in prominence. As such, newanalyses have been added to this version of the report to highlight the risks posed by Rocket Bodies crossing the
GEOIADC Protected Region (Fig. 6.20), show the variability in disposal orbit strategies in the MEO region (Fig. 6.21),
and focus on the space surveillance issues associated with the release of large amounts of Payloads by various
services (Fig. 2.17). In addition, a review of the United Nation Register of Objects Launched into Outer Space isadded to show the diversification of space actors (Section 2.11).

1.4.4. Edition 7
The accelerated use of space over the last years continued unabated in 2022, leading to launch and re-entry
traffic rates to see new records and challenges in keeping accurate track of the state of the environment. The
metrics presented in this report were further refined to give an overview of the impacts on space debris mitigation
aspects, and to prepare for the trend in calling for stricter guidelines. Notably, forecasting methodologies havebeen updated and a greater emphasis on understanding the space debris environment at smaller length scales
has been introduced. Furthermore, it is worth mentioning that the observed spike in 2022 concerning re-entering
space debris is due to the Kosmos 1408 anti-satellite missile test.

1.4.5. Edition 8
In 2023, the space environment continued to experience substantial growth, with launch traffic once again reachingrecord levels. In LEOIADC , large constellations, which have outpaced other payloads not only in number but also
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ESA UNCLASSIFIED - Releasable to the Publicmass and area, now drive many of the global statistics. While this is leading to increased congestion and challenges
for space traffic coordination in certain orbits, it is also accompanied by an increased usage of controlled re-entry as
a disposal strategy for rocket bodies and new levels of compliance with space debris mitigation guidelines.
In this edition of the report, methodologies for modelling the future evolution of the space environment have beenfurther refined, specifically for forecasting the growing contribution from constellations, leading to new and updated
results for the analysed years 2022 and 2023. It should be noted that current levels of compliance still result inan unsustainable environment in the long-term. Consequently, there is a growing trend advocating for stricter
guidelines, with new measures introduced in 2023 as a part of ESA’s Zero Debris Policy and updated Space
Debris Mitigation Standard [3]. These developments imply that notable changes may be anticipated in the next
edition of this report in terms of methodologies and assessed thresholds, reflecting ongoing efforts to address thechallenges of space sustainability.

1.5. Acknowledgements
The authors take the opportunity to thank the team at the European Space Agency’s Space Debris Office for providing technical support and all data quality work. Furthermore, we thank the international space debris community
at large for the received comments and suggestions for improvements.

1.6. Disclaimer
The contents of this document are intended for the personal and non-commercial use of their users. Permission is
granted to users to reprint or copy information for personal non-commercial use when providing appropriate creditby citing the source plus date of issue. For commercial use, authorisation need to be sought. Users may notmodify, publish, transmit, participate in the transfer or sale of, reproduce, translate into other languages, create
derivative works from, distribute, perform, display or in any way exploit any of the content, material or images, inwhole or in part, without obtaining prior written authorisation.
The analysis presented in this document is derived from a continuously evolving database. Mistakes can unavoidably happen during the preparation process and we are thus ready to take feedback. If you detect any error or if
you have any comment or question please contact:

Emma Stevenson

Francesca Letizia

European Space Agency

European Space Agency

Space Debris Office (OPS-SD)

Independent Safety Office (TEC-QI)

Keplerlaan 1

Keplerlaan 1

2201 AZ Noordwijk, Netherlands 2201 AZ Noordwijk, Netherlands
emma.stevenson@esa.int
Stijn Lemmens
European Space Agency
Space Debris Office (OPS-SD)
Keplerlaan 1
2201 AZ Noordwijk, Netherlands
stijn.lemmens@esa.int

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francesca.letizia@esa.int

ESA UNCLASSIFIED - Releasable to the Public

2. SPACE ENVIRONMENTAL HISTORY IN NUMBERS
This section reports on the evolution of the space environment since the beginning of the space age. The evolutionof catalogued objects in orbit is graphically represented for count, mass, and area. This data is further subdivided
based on object and orbit classification. A catalogued object is only taken into account for a given year if it appeared
in a space surveillance system during that year. This implies that reported evolutions do scale with the quality ofthe space surveillance systems at a given epoch. In case of the evolution of payloads and rocket bodies thereported numbers are close to values one would obtain when only considering asserted objects. In all other object
classifications the amount of catalogued objects are almost certainly an underestimation and hence lower limit for
the true space environment.
Concerning the LEO and GEO protected regions, the absolute and equivalent number of objects, mass, and areainterfering with these regions are graphically represented. To obtain the equivalent object penetrating the protected
regions, the physical property of the absolute object, i.e. count, mass, and area, is multiplied with an equivalence
factor. This factor is computed as the ratio of the time spent in the protected region per orbit to the orbital period
for each orbit. This indicates per orbital class how many objects are interfering with the protected regions without
being permanently present. Even though the LEO and GEO regions are defined as protected regions as a whole,most of the traffic takes place in narrow bands.
The evolution of the catalogued and asserted objects appearing in or re-entering the Earth atmosphere from thespace environment is graphically represented for count, mass, and area. This data is further subdivided basedon object and orbit classification. In case of incomplete orbital data, the orbit classification may be affected. Thisis the case, for example, of a group of objects for which the last available orbital data is such to classify themas MEO, but the re-entry epochs are several months later. Objects that are both asserted and catalogued are
only counted once for a given year. In case of minor inconsistencies between the asserted and catalogued object
information for the same object, the ’N/A’ tag is applied. Objects associated with human spaceflight include crew
vehicles or parts thereof as well as payloads dedicated to cargo transfer, but not the rocket bodies associated tothese missions. For the vast majority of cases, there is no reliable mass or area estimate for objects in the Debris
or Unidentified categories and hence they are equated to 0.
In all figures within Sections 2.1, 2.2, and 2.3, the environment parameters are presented as they are at the 1stof January of the indicated year. In all figures within Sections 2.5, 2.8, and 2.9, the environment parameters arepresented as aggregated data within the indicated year. All data used to generate the analysis in this section isavailable online [8].

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ESA UNCLASSIFIED - Releasable to the Public2.1. Overall Space Environment
Fig. 2.1 captures the evolution of the space environment in terms of number of objects, mass, and area in geocentric
orbit by object class. This data is limited to catalogued and asserted objects, and hence at any given epoch limited
to the capability of the space surveillance system in use at the time. A secondary effect hereof is that when new
objects are detected due to increased sensor performance, they can generally not be traced back to an event orsource and become classified as Unidentified. In Figures 2.2 the same data is presented by orbit class instead ofobject class. In Figures 2.3 the same data is presented in relation to the cumulative values for those properties incase they would not have been removed from orbit.

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Figure 2.5: Evolution of equivalent number of objects, mass and area residing in or penetrating LEOIADC .

Page 23/121

ESA UNCLASSIFIED - Releasable to the Public

2.3. Evolution of Environment in GEO
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Figure 2.6: Evolution of absolute number of objects, mass and area residing in or penetrating GEOIADC .

Page 24/121

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Figure 2.7: Evolution of equivalent number of objects, mass and area residing in or penetrating GEOIADC .

Page 25/121

ESA UNCLASSIFIED - Releasable to the Public

2.4. Non-catalogued and modelled objects
According to ESA’s space debris environment model MASTER, at the most recent reference epoch November 1st
2016, the estimated number of debris objects in orbit in the different size ranges is the following:• 34.000 objects greater than 10 cm,• 900.000 objects from 1 cm to 10 cm,• 128 million objects from 1 mm to 1 cm.

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The distribution of the number of objects as a function of their size is shown in Fig. 2.8: the plot shows the numberof objects larger than the threshold size indicated in x-axis, considering space debris objects in all Earth orbits.
Fig. 2.9 shows the density profiles with altitude corresponding to different minimum debris sizes (respectively 10
cm in dark blue and 1 cm in red), considering only the LEO region. The logarithmic scale is used in the y-axis totake into account the different orders of magnitude corresponding to the two populations.
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Figure 2.9: Density profiles in LEO for different space debris size ranges.

Page 26/121

ESA UNCLASSIFIED - Releasable to the Public

2.5. Usage of the Protected Regions
This section aims to provide an overview of the usage of the protected regions in terms of launch traffic as represented by object count and mass, given that the stability of the space environment is dependent on them.
From a historical point of view, the launch traffic of Payloads can be categorised in terms of the main funding
source (Civil, Defence, Commercial, Amateur) or in terms of the main missions type (Communication, Imaging,
Navigation, etc.). The Amateur category includes those Payloads associated by academic institutions when noneof the other entities are the driving contributor. Payloads that are deployed from the International Space Station(ISS) are identified with a separate label as part of the launch traffic.
In case of Rocket Bodies, it is of importance which launcher family is generating the traffic to orbit, given that theadherence level to space debris mitigation guidelines correlates with this family identifier. These families are to
be understood as major stable design versions of a launcher, e.g. covering performance improvements but notengine changes. New families can appear sporadically and in this report the most regularly used ones over recent
years are identified. Earlier families of launchers are grouped under Used earlier.
Of increasing importance in a changing space traffic landscape are also the so-called ride-share launch opportunities, where a single launch vehicle carries a multitude of Payloads from different entities into orbit. For the purposeof this report, ride-share launches are defined as those launches that carry Payloads with at least three different
mission domains and at least ten Payloads in total. A mission domain is defined by the combination of mission
type, funding, and operator.
For Payload objects in LEOIADC , it is instructive to analyse not only where they reside now, but also how thedestination orbits that enable their operations evolve over time. In particular, as space debris mitigation measures
focus on limiting orbital lifetimes, adoption of these practice leaves a noticeable imprint on the data. This imprint
can distinctively visible as a function of the mission domain, in particular when distinguishing between constellationand non constellation objects.

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Figure 2.10: Evolution of the launch traffic near LEOIADC per mission funding (top) and type (bottom).

Page 28/121

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Figure 2.11: Evolution of the launch traffic near LEOIADC per launcher family expressed in terms of number ofobjects (top) and mass (bottom).

Page 29/121

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Figure 2.12: Evolution of the launch traffic near GEOIADC per mission funding (top) and type (bottom).

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 2.13: Evolution of the launch traffic near GEOIADC per launcher family expressed in terms of number ofobjects (top) and mass (bottom).

Page 31/121

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Figure 2.14: Evolution of the launch traffic outside LEOIADC and GEOIADC per launcher family expressed in termsof number of objects (top) and mass (bottom).

Page 32/121

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Figure 2.15: Evolution of the launch traffic per mass category in terms of number of objects in LEOIADC (top) and
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Page 33/121

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Page 34/121

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Unidentified Payload objects form a collision risk for active operators as potential avoidance scenarios cannot
be coordinated effectively. In particular, ride-share launches can form an issue for timely identification by spacesurveillance networks when deployment is not coordinated with the operators on-board. Fig. 2.17 plot represents
the rate of identification for Payloads on ride-share launches since 2018, applying the definition introduced above.
The x-axis indicates the launch epoch and the y-axis lists some of the crucial timings between launch and identification. Per ride-share launch event, the grey lines indicate the time interval between the epoch when 10% and
90% of the Payloads in the launch were identified with a cut-off after 12 months (some Payload might never beidentified). If the 90% has not (yet) been reached, the interval is indicated with a dashed line. The location of
the circular marker indicates the time when 50% of the Payloads are identified, the size is proportional to the total
number of Payloads in the ride-share launch, and the colour indicates which fraction of the Payloads belong to a
constellation. The latter makes a practical distinction in terms of amount of Payloads that can be coordinated witha space surveillance operators.

Page 35/121

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Figure 2.18: Evolution of the launch traffic: mass injected.

Page 36/121

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Figure 2.20: Estimated lifetime for the Payload destination orbits by launch year: share of mass.

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ESA UNCLASSIFIED - Releasable to the Public

2.6. Constellations in the LEO protected region
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Figure 2.21: Evolution of number of objects, mass, and area in LEOIADC distinguishing constellations and nonconstellation payloads.

Page 39/121

ESA UNCLASSIFIED - Releasable to the Public

2.7. Active payloads in the LEO protected region








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
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

1XPEHURIDFWLYHSD\ORDGV


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

         
h>NP@

Figure 2.22: Distribution of active payloads in LEO by year and mean altitude.










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1XPEHURIDFWLYHSD\ORDGV





         
h>NP@

Figure 2.23: Distribution of active payloads not belonging to constellations in LEO by year and mean altitude.

Page 40/121

ESA UNCLASSIFIED - Releasable to the Public









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


1XPEHURIDFWLYHSD\ORDGV




         
h>NP@

Figure 2.24: Distribution of active payloads belonging to constellations in LEO by year and mean altitude.

0DQRHXYUDEOHSD\ORDGV$FWLYHQRQPDQRHXYUDEOHSD\ORDGV
,QDFWLYHSD\ORDGV
2WKHUREMHFWV1XPEHURIREMHFWV

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




    
3HULJHHDOWLWXGH>NP@

Figure 2.25: Number of manoeuvrable and active objects as a function of the perigee altitude.

Page 41/121

ESA UNCLASSIFIED - Releasable to the Public

$FWLYHSD\ORDGVWRFDWDORJXHGREMHFWVGHVWLQDWLRQRUELWV

$FWLYHSD\ORDGV
&RQVWHOODWLRQV

5DWLR

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



Figure 2.26: Ratio of active and constellation objects over the total number of catalogued objects.

0DVV>NJ@

0HDQDFWLYHSD\ORDGSURSHUWLHV

$UHD>P2@





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1RFRQVWHOODWLRQV
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&RPELQHG

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

Figure 2.27: Payload parameters for active payloads in LEO over time.

Page 42/121

ESA UNCLASSIFIED - Releasable to the Public

2.8. New Catalogued Objects in the Space Environment1HZO\$GGHG2EMHFWV
8,
50
5'
5)
5%

2EMHFW&RXQW>@

30
3'
3)
3/













<HDU













(a) Evolution of newly added object by count.

1HZO\$GGHG2EMHFWV

8,
50
5'
5)
5%

2EMHFW0DVV>WRQV@

30
3'
3)
3/








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(b) Evolution of newly added mass.

1HZO\$GGHG2EMHFWV

2EMHFW$UHD>P2@

8,
50
5'
5)
5%

30
3'
3)
3/










<HDU

(c) Evolution of newly added area.

Figure 2.28: Evolution of newly added objects in each year by object type.

Page 43/121

ESA UNCLASSIFIED - Releasable to the Public1HZO\$GGHG2EMHFWV1$
2WKHU
+(20*2
/020(2

2EMHFW&RXQW>@

162*72(*2*(2
/(2

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(a) Evolution of newly added object by count.

1HZO\$GGHG2EMHFWV1$
2WKHU
+(20*2
/020(2

2EMHFW0DVV>WRQV@


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/(2





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(b) Evolution of newly added mass.

1HZO\$GGHG2EMHFWV

2EMHFW$UHD>P2@

1$
2WKHU
+(20*2
/020(2

162*72(*2*(2
/(2








<HDU

(c) Evolution of newly added area.

Figure 2.29: Evolution of newly added objects in each year by orbit type.

Page 44/121

ESA UNCLASSIFIED - Releasable to the Public

2.9. Objects Removed from the Space Environment5HHQWHULQJ2EMHFWV

8,
50
5'
5)
5%

2EMHFW&RXQW>@

30
3'
3)
3/

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
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(a) Evolution of re-entered numbers.

5HHQWHULQJ2EMHFWV
8,
50
5'
5)
5%

2EMHFW0DVV>WRQV@


30
3'
3)
3/






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(b) Evolution of re-entered mass.

5HHQWHULQJ2EMHFWV

8,
50
5'
5)
5%


2EMHFW$UHD>P2@

30
3'
3)
3/



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







<HDU





(c) Evolution of re-entered area.

Figure 2.30: Evolution of re-entering objects in each year by object type without human spaceflight.

Page 45/121

ESA UNCLASSIFIED - Releasable to the Public5HHQWHULQJ2EMHFWV

2WKHU
+(2
/02

2EMHFW&RXQW>@

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/(2
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(a) Evolution of re-entered numbers.

5HHQWHULQJ2EMHFWV

2WKHU
+(2
/02

2EMHFW0DVV>WRQV@

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/(2
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(b) Evolution of re-entered mass.

5HHQWHULQJ2EMHFWV

2WKHU
+(2
/02

0(2*72
/(2

2EMHFW$UHD>P2@
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

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(c) Evolution of re-entered area.

Figure 2.31: Evolution of re-entering objects in each year by orbit type without human spaceflight.

Page 46/121

2EMHFW&RXQW>@ESA UNCLASSIFIED - Releasable to the Public5HHQWHULQJ2EMHFWV












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

30

3/



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(a) Evolution of re-entered numbers.

5HHQWHULQJ2EMHFWV30

3/

2EMHFW0DVV>WRQV@


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(b) Evolution of re-entered mass.



5HHQWHULQJ2EMHFWV
30

3/

2EMHFW$UHD>P2@





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(c) Evolution of re-entered area.

Figure 2.32: Evolution of re-entering human spaceflight objects in each year by object type.

Page 47/121

2EMHFW&RXQW>@ESA UNCLASSIFIED - Releasable to the Public5HHQWHULQJ2EMHFWV















2WKHU
+(2

/02
/(2



<HDU



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(a) Evolution of re-entered numbers.

5HHQWHULQJ2EMHFWV
2WKHU
+(2

/02
/(2

2EMHFW0DVV>WRQV@


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

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(b) Evolution of re-entered mass.



5HHQWHULQJ2EMHFWV
2WKHU
+(2

/02
/(2

2EMHFW$UHD>P2@


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





<HDU

(c) Evolution of re-entered area.

Figure 2.33: Evolution of re-entering human spaceflight objects by orbit type.

Page 48/121

ESA UNCLASSIFIED - Releasable to the Public
&RQWUROOHG

7RWDOPDVV>W@

1XPEHURIREMHFWV







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



      
5HHQWU\\HDU      
5HHQWU\\HDU(a) Payloads: Count(b) Payloads: Mass

&RQWUROOHG8QFRQWUROOHG&RQWUROOHG8QFRQWUROOHG


7RWDOPDVV>W@

1XPEHURIREMHFWV




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

&RQWUROOHG8QFRQWUROOHG8QFRQWUROOHG

      
5HHQWU\\HDU(c) Rocket Bodies: Count      
5HHQWU\\HDU(d) Rocket Bodies: Mass

Figure 2.34: Controlled and uncontrolled re-entries for Payloads (top) and Rocket Bodies (bottom).

Page 49/121

ESA UNCLASSIFIED - Releasable to the Public

2.10. Nuclear Power Sources
Nuclear power sources (NPS) have been used in outer space as an efficient way of producing larger quantities ofenergy or heat, commonly implemented as small fission reactors or radioisotope thermoelectric generators. Since
early during the space age such power systems were used in Earth orbit but they have been largely phased out
after the 1980s due to safety concerns. The notable exception is the use of NPSs for interplanetary Payloads andplanetary exploration.

































,QFOLQDWLRQ>GHJ@/LIHWLPH>\HDUV@The safety concerns related to NPSs in Earth orbit related to risks implied when they would re-enter the atmosphereand break-up. To mitigate this risk, the reactor cores were generally injected into orbits with long orbital lifetimes
after the end of operations of the Payload. There are 61 objects related to NPSs known to have entered Earthorbit, out of which 3 are asserted but not catalogued. A total of 3 out of those 61 have re-entered, and the orbital
distribution on the remainder is presented in Figure 2.35.








0HDQDOWLWXGH>NP@

Figure 2.35: Distribution of space objects with nuclear power sources with mean altitude, orbital lifetime, andinclination.

Page 50/121

ESA UNCLASSIFIED - Releasable to the Public

2.11. Registration of Objects Launched in Outer SpaceThe United Nations Register of Objects Launched into Outer Space [12] and its implementation was established
as consequence of the Convention on Registration of Objects Launched into Outer Space [13]. State parties to thetreaty are required to establish their own national registries and provide information on their space objects, which
in turn creates transparency on space operations. The increasing amount of launching states of time serves as areminder for the need to coordinate space debris mitigation measures across all those actors, as one failure to do
so will affect many others. Notwithstanding the increase in actors, positive trends are the retro-active registrationof objects and the reducing time between launch and registration.

&XPXODWLYHQXPEHURIODXQFKLQJVWDWHV

7RWDO
$PDWHXU
&LYLO
&RPPHUFLDO
'HIHQVH




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


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<HDU





Figure 2.36: Launching states with at least one registered space object over time by category.

Page 51/121

ESA UNCLASSIFIED - Releasable to the Public

6KDUHRIUHJLVWHUHG3D\ORDGV>@













/DXQFK\HDU



Figure 2.37: Share of registered payloads over the total of launched payloads by launch year.

0HGLDQWK3HUFHQWLOH

$YHUDJHUHJLVWUDWLRQGHOD\>\HDUV@


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



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
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




/DXQFK\HDU

Figure 2.38: Delay between launch and registration by launch year.

Page 52/121



ESA UNCLASSIFIED - Releasable to the Public

3. ENVIRONMENTAL STATUS 2023
In this section, the status of the environment as of end of 2023 is listed and illustrated.
Table 3.1: Number of objects orbiting Earth. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

10136

5747

115

227

953

3274

40

579

83

21154

GEO

800

3

3

9

64

0

0

0

33

912

EGO

521

1

1

49

203

82

3

4

1889

2753

GTO

51

28

1

10

235

202

12

51

626

1216

NSO

282

0

0

1

96

0

0

2

38

419

MEO

77

0

4

49

25

42

1

4

415

617

LMO

83

138

5

46

246

590

22

215

955

2300

MGO

68

65

1

3

177

1968

4

0

1178

3464

HEO

29

13

0

1

54

113

0

0

1101

1311

Other

45

0

0

5

5

0

0

0

97

152

Total

12092

5995

130

400

2058

6271

82

855

6415

34298

Table 3.2: Absolute and equivalent number of objects intersecting with the protected regions.
PLboth (abs)

PF

PD

PM

RB

RF

RD

RM

UI

Total

22

19

1

1

77

127

1

19

309

576

LEOIADC (abs)

10287

5926

121

284

1472

4118

74

845

1810

24937

LEOIADC (eqv)

10167

5835

119

238

1006

3439

46

613

246

21709

GEOIADC (abs)

969

57

5

51

310

814

3

20

3376

5605

GEOIADC (eqv)

842

5

3

19

104

39

1

1

233

1247

none (abs)

858

31

5

66

353

1466

6

9

1538

4332

Page 53/121

ESA UNCLASSIFIED - Releasable to the Public

Table 3.3: Mass in tons orbiting Earth. Objects of unknown mass do not contribute to the figures presented. Other:
IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

LEO

3810.9

0.0

0.0

13.2

1439.60.0

GEO

2628.6

0.0

0.0

1.0

132.4

0.0

EGO

903.5

0.0

0.0

5.1

389.9

0.0

GTO

92.8

0.0

0.0

1.0

550.4

NSO

366.0

0.0

0.0

0.4

MEO

79.2

0.0

0.0

LMO

67.0

0.0

MGO

91.7

HEO

RD

RM

UI

Total

0.0

9.3

0.0

5273.0

0.0

0.0

0.0

2762.0

0.0

0.3

0.0

1298.8

0.0

0.0

23.4

0.0

667.5

215.7

0.0

0.0

0.0

0.0

582.1

0.3

41.6

0.0

0.0

4.2

0.0

125.4

0.0

6.9

470.2

0.0

0.0

88.1

0.0

632.1

0.0

0.0

1.9

292.1

0.0

0.0

0.0

0.0

385.7

41.3

0.0

0.0

0.1

131.8

0.0

0.0

0.0

0.0

173.2

Other

74.5

0.0

0.0

0.1

8.4

0.0

0.0

0.0

0.0

83.0

Total

8155.5

0.0

0.0

29.9

3672.1

0.0

0.0

125.3

0.0

11982.7

Table 3.4: Absolute and equivalent mass in tons intersecting with the protected regions.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

23.5

0.0

0.0

0.1

169.4

0.0

0.0

6.6

0.0

199.6

LEOIADC (abs)3989.5

0.0

0.0

21.1

2559.0

0.0

0.0

120.8

0.0

6690.4LEOIADC (eqv)3834.7

0.0

0.0

14.8

1521.6

0.0

0.0

20.2

0.0

5391.4

GEOIADC (abs)2943.1

0.0

0.0

6.4

609.8

0.0

0.0

6.8

0.0

3566.0

GEOIADC (eqv)2725.4

0.0

0.0

2.1

208.5

0.0

0.0

0.4

0.0

2936.5none (abs)1246.5

0.0

0.0

2.5

672.6

0.0

0.0

4.4

0.0

1926.0both (abs)Page 54/121

ESA UNCLASSIFIED - Releasable to the Public

Table 3.5: Area in m2 orbiting Earth. Objects of unknown area do not contribute to the figures presented. Other:
IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

LEO

102598.2

GEO25782.0

0.0

0.0

95.3

11286.3

0.0

23.6

8.4

1439.3

EGO

11599.3

0.0

0.6

38.5

4411.1

GTO

704.0

0.0

0.0

8.8

NSO

3098.3

0.0

0.0

MEO

1121.8

0.0

LMO

642.0

MGO

RF

RD

RM

UI

Total

1.3

4.7

0.0

0.0

323.7

0.0

114309.7

0.0

0.027253.4

0.0

0.0

9.7

0.0

16059.2

5457.5

0.0

0.0

664.3

0.0

6834.6

0.8

1852.4

0.0

0.0

0.0

0.0

4951.5

0.0

11.2

435.8

0.0

0.0

21.6

0.0

1590.5

0.0

0.0

22.7

5047.50.6

0.0

1604.10.0

7316.9

862.3

0.0

0.0

14.7

3147.2

0.0

0.0

0.0

0.0

4024.2

HEO

610.8

0.0

0.0

0.1

1331.0

0.0

0.0

0.0

0.0

1941.9

Other

475.9

0.0

0.0

0.5

71.4

0.0

0.0

0.0

0.0

547.8

Total

147494.7

0.0

24.2

201.1

34479.6

1.9

4.7

2623.40.0

184829.8

Table 3.6: Absolute and equivalent area in m2 intersecting with the protected regions.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

335.1

0.0

0.0

0.1

1988.4

0.0

0.0

321.7

0.0

2645.3LEOIADC (abs)104283.9

0.0

0.0

127.0

22847.6

1.9

4.7

2592.10.0129857.3

LEOIADC (eqv)102759.2

0.0

0.0

102.0

12175.2

1.4

4.7

528.2

0.0

115570.8

GEOIADC (abs)29111.9

0.0

23.6

50.4

6603.0

0.0

0.0

322.3

0.0

36111.2

GEOIADC (eqv)26772.6

0.0

23.6

17.7

2268.7

0.0

0.0

21.4

0.0

29104.0

none (abs)14433.9

0.0

0.6

24.0

7017.4

0.0

0.0

30.7

0.0

21506.5

both (abs)Page 55/121

ESA UNCLASSIFIED - Releasable to the Public

3.1. Status of the Environment in LEO
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Figure 3.1: Distribution of mass and area of payloads in LEO.

Page 56/121

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Figure 3.2: Distribution of mass and area of rocket bodies in LEO.

Page 57/121

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Figure 3.3: Distribution of number of objects in LEO as a function of inclination and perigee altitude.

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Figure 3.4: Distribution of mass in LEO as a function of inclination and perigee altitude.

Page 58/121

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Figure 3.5: Distribution of area in LEO as a function of inclination and perigee altitude.

Page 59/121

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Figure 3.6: Launch traffic in 2023 (top) and distribution of active payloads (bottom) in LEOIADC by mean altitude.

Page 60/121
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Figure 3.7: Distribution of active payloads in LEO by mean altitude and inclination.

Page 61/121

ESA UNCLASSIFIED - Releasable to the Public

3.2. Status of the Environment in GEO
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Figure 3.8: Distribution of mass and area of payloads in GEO.

Page 62/121

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Figure 3.9: Distribution of mass and area of rocket bodies in GEO.

Page 63/121



ESA UNCLASSIFIED - Releasable to the Public

3.3. Fragmentations in 2023
In Table 3.7 all established fragmentation events of the year 2023 are shown. For a description of the event
categories, please consult Section 5. In case no credible source is available on the amount of Asserted Objects
associated with a fragmentation event, it is indicated with None. Those Asserted Object are reported by spacesurveillance networks which can have variable detection limits. A more in-depth overview of the consequences of
those events can be accessed online [14].
Table 3.7: Fragmentation events in 2023.
Event
epoch

Object
type

Mass
[kg]

Catalogued
objects

2023-01-04

Payload45

58

2023-02-10

Rocket Body

1500

5

2023-03-11

Payload4482023-06-29

Payload223

62023-07-31

Rocket Mission
Related Object

100

7

1912

84

Total

Page 64/121

Asserted
objects

Orbit

Event
cause

LEO

Unknown

LEO

Unknown

LEO

Unknown

6

LEO

Electrical

11

LEO

Small Impactor

5

ESA UNCLASSIFIED - Releasable to the Public

3.4. Changes to the Environment in 2023
In this section, the change to the environment during 2023 is listed. The last state of the year is used to classify
the object orbit. If no state is available, a destination orbit defined by an analyst is used instead.
Table 3.8: Number of newly added objects orbiting Earth. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

2835

50

15

17

90

13

26

124

13

3183

GEO

28

0

0

0

0

0

0

0

2

30

EGO

5

0

0

1

10

0

0

2

304

322

GTO

1

0

0

0

8

0

0

2

120

131

NSO

4

0

0

0

2

0

0

0

10

16

MEO

6

0

0

0

4

0

0

1

108

119

LMO

0

0

0

0

9

0

5

0

147

161

MGO

0

0

0

0

1

0

0

0

257

258

HEO

3

0

0

0

5

0

0

0

215

223

Other

2

0

0

0

1

0

0

0

14

17

N/A

9

0

0

0

5

0

0

2

0

16

2884

50

15

18

130

13

31

129

1190

4460

Total

Table 3.9: Absolute and equivalent number of newly added objects intersecting with the protected regions.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

2

0

0

0

3

0

0

0

57

62

LEOIADC (abs)

2839

50

15

17

112

13

31

126

305

3508

LEOIADC (eqv)

2836

50

15

17

91

13

29

124

40

3215

GEOIADC (abs)

32

0

0

0

4

0

0

0

624

660

GEOIADC (eqv)

28

0

0

0

0

0

0

0

35

63

none (abs)

15

0

0

1

17

0

0

3

318

354

both (abs)Page 65/121

ESA UNCLASSIFIED - Releasable to the Public

Table 3.10: Newly added mass in tons orbiting Earth. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

1286.6

0.0

0.0

18.9

182.2

0.0

GEO

101.6

0.0

0.0

0.0

0.0

0.0

0.0

4.9

0.0

1492.6

0.0

0.0

0.0

101.6

EGO

3.6

0.0

0.0

0.2

27.3

0.0

0.0

0.2

0.0

31.3

GTO

2.2

0.0

0.0

0.0

34.6

0.0

0.0

1.4

0.0

38.2

NSO

8.0

0.0

0.0

0.0

6.0

0.0

0.0

0.0

0.0

14.0

MEO

9.1

0.0

0.0

0.0

11.6

0.0

0.0

2.2

0.0

22.9

LMO

0.0

0.0

0.0

0.0

27.6

0.0

0.0

0.0

0.0

27.6

MGO

0.0

0.0

0.0

0.0

3.2

0.0

0.0

0.0

0.0

3.2

HEO

7.6

0.0

0.0

0.0

20.2

0.0

0.0

0.0

0.0

27.9

Other

3.9

0.0

0.0

0.0

1.0

0.0

0.0

0.0

0.0

4.9

N/A

17.0

0.0

0.0

0.0

22.2

0.0

0.0

0.0

0.0

39.2

Total

1422.7

0.0

0.0

19.1

313.7

0.0

0.0

8.8

0.0

1764.3

Table 3.11: Absolute and equivalent newly added mass in tons intersecting with the protected regions.

both (abs)

PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

2.2

0.0

0.0

0.0

12.9

0.0

0.0

0.0

0.0

15.1

LEOIADC (abs)1292.8

0.0

0.0

18.9

264.6

0.0

0.0

6.4

0.0

1582.6LEOIADC (eqv)1288.0

0.0

0.0

18.9

187.0

0.0

0.0

5.0

0.0

1498.8

GEOIADC (abs)

112.9

0.0

0.0

0.0

15.3

0.0

0.0

0.0

0.0

128.1

GEOIADC (eqv)

101.2

0.0

0.0

0.0

0.8

0.0

0.0

0.0

0.0

101.9

none (abs)

19.3

0.0

0.0

0.2

46.8

0.0

0.0

2.4

0.0

68.6

Page 66/121

ESA UNCLASSIFIED - Releasable to the Public

Table 3.12: Newly added area in m2 orbiting Earth. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

45276.1

0.0

0.0

149.3

1537.2

0.0

4.7

91.4

0.1

47058.8

GEO

860.6

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

860.6

EGO

35.1

0.0

0.0

1.5

402.1

0.0

0.0

9.0

0.0

447.7

GTO

14.3

0.0

0.0

0.0

232.6

0.0

0.0

35.6

0.0

282.5

NSO

40.6

0.0

0.0

0.0

14.2

0.0

0.0

0.0

0.0

54.8

MEO

145.1

0.0

0.0

0.0

120.6

0.0

0.0

6.4

0.0

272.1

LMO

0.0

0.0

0.0

0.0

289.6

0.0

0.0

0.0

0.0

289.6

MGO

0.0

0.0

0.0

0.0

49.8

0.0

0.0

0.0

0.0

49.8

HEO

58.9

0.0

0.0

0.0

195.1

0.0

0.0

0.0

0.0

254.0

Other

33.3

0.0

0.0

0.0

8.4

0.0

0.0

0.0

0.0

41.6

N/A

144.3

0.0

0.0

0.0

201.5

0.0

0.0

0.0

0.0

345.9

Total

46463.8

0.0

0.0

150.8

2849.6

0.0

4.7

142.4

0.1

49611.5

Table 3.13: Absolute and equivalent newly added area in m2 intersecting with the protected regions.
PLboth (abs)

PF

PD

PM

RB

RF

RD

RM

UI

Total

11.5

0.0

0.0

0.0

119.9

0.0

0.0

0.0

0.0

131.4

LEOIADC (abs)45318.4

0.0

0.0

149.3

2254.5

0.0

4.7

127.0

0.1

47854.0

LEOIADC (eqv)45288.6

0.0

0.0

149.3

1580.2

0.0

4.7

93.0

0.1

47115.9

GEOIADC (abs)

953.5

0.0

0.0

0.0

119.9

0.0

0.0

0.0

0.0

1073.4

GEOIADC (eqv)

859.3

0.0

0.0

0.0

0.5

0.0

0.0

0.0

0.0

859.8

none (abs)

203.5

0.0

0.0

1.5

595.1

0.0

0.0

15.4

0.0

815.5

Page 67/121

ESA UNCLASSIFIED - Releasable to the Public

Table 3.14: Number of re-entered objects. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

653

781

13

23

93

185

10

166

12

1936

LMO

0

1

0

0

2

2

0

0

0

5

Other

1

0

0

0

0

0

0

0

0

1

N/A

2

1

0

0

8

0

0

0

0

11

Total

654

782

13

23

95

187

10

166

12

1942

Table 3.15: Re-entered mass in tons. Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

75.1

0.0

0.0

18.1

180.0

0.0

0.0

8.5

0.0

281.7

LMO

0.0

0.0

0.0

0.0

7.3

0.0

0.0

0.0

0.0

7.3

Other

1.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1.1

N/A

0.1

0.0

0.0

0.0

29.1

0.0

0.0

0.0

0.0

29.2

Total

76.2

0.0

0.0

18.1

187.3

0.0

0.0

8.5

0.0

290.1

Table 3.16: Re-entered area in m2 . Other: IGO, GHO, HAO, UFO, ESO.
PL

PF

PD

PM

RB

RF

RD

RM

UI

Total

LEO

1911.8

0.0

0.0

129.7

1661.6

1.3

0.0

197.7

0.1

3902.2

LMO

0.0

0.0

0.0

0.0

86.3

0.0

0.0

0.0

0.0

86.3

Other

9.4

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

9.4

N/A

0.2

0.0

0.0

0.0

289.7

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ESA UNCLASSIFIED - Releasable to the Public

3.5. Conjunction statistics in LEO in 2023
This section aims to provide an assessment of the short-term risk related to space debris, quantified in terms ofthe number of conjunctions expected in different orbital regions, distinguishing also the type of secondary object
involved in the conjunction. For the purpose of this report, a conjunction is understood as a geometric close approach between two objects, irrespective of their activity status, triggering an operator analysis but not necessarily
an avoidance manoeuvre nor implying a collision.
The first step of the analysis is to define some representative target (or primary) objects in the conjunctions. The
physical characteristics of the objects are derived from the average parameters of active payloads in LEOIADC ,reported in Fig. 2.27. In particular, a mass value of 355 kg and a cross-sectional area of 6 m2 were used forthe analysis based on the averages for 2020 and applied also to 2023 considering the consistent trend in theproperties shown in Fig. 2.27, especially when considering non-constellation payloads. For what concerns theorbital parameters of the targets, two approaches are used here. The first set of representative targets is definedby looking at the distribution of active payloads in LEOIADC in semi-major axis and inclination as shown in Fig. 3.7,
and a total of seven targets were defined for this analysis. The second approach is to define a set of targets in the
Sun-Synchronous region; in particular, seven targets are defined to cover the region between 400 and 1000 km
in altitude. In both cases, twelve values of the initial longitude of ascending nodes are considered and the resultspresented in the following are the mean across the simulated cases for each target.
In both cases, the trajectory of the targets is propagated for one year (from 1st January 2023 to 31st December2023) and for each day of the year an analysis is run to detect potential conjunctions with catalogued objects, byusing ESA CRASS (Collision Risk ASsessment Software) [15]. For the analysis shown here, General Perturbations(GP) data is retrieved to define the orbits of the secondary objects involved in the conjunctions [16]. The data in
DISCOS is used to further characterise the secondary object, for example in terms of its size and its category. In
addition to the object categories defined in Section 1.1, the following subcategories are introduced:• Payloads is further distinguished in:– Constellation objects, payloads belonging to a constellation,– Small satellites, payloads with a mass smaller than 15 kg,– Other Payloads, all the other payloads.
• Payload fragmentation debris, four subcategories were defined to collect objects belonging to the fragmentation events with the highest number of catalogued objects.
– Fengyun 1C Fragmentation Debris, objects generated by the fragmentation of Fengyun 1C (1999-25A),
with mass 958.0, on the 11/01/2007 at an altitude between 843.3 and 863.3 km and inclination of 98.6
degrees.
– Cosmos-2251 Fragmentation Debris, objects generated by the fragmentation of Cosmos-2251 (199336A), with mass 892.0, on the 10/02/2009 at an altitude between 776.1 and 791.1 km and inclination of
86.4 degrees.
– Iridium 33 Fragmentation Debris, objects generated by the fragmentation of Iridium 33 (1997-51C),
with mass 661.0, on the 10/02/2009 at an altitude between 776.2 and 779.4 km and inclination of 86.4
degrees.
– Cosmos-1408 Fragmentation Debris, objects generated by the fragmentation of Cosmos-1408 (198292A), with mass 2180.4, on the 15/11/2021 at an altitude between 465.0 and 490.5 km and inclinationof 82.6 degrees.

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ESA UNCLASSIFIED - Releasable to the Public– Other Payload fragmentation debris, all the other payload fragmentation debris.
• Rocket fragmentation debris, five subcategories were defined to collect objects belonging to the fragmentation events with the highest number of catalogued objects.
– Centaur-5 SEC Fragmentation Debris, objects generated by the fragmentation of Centaur-5 SEC (201879B), with mass 2020.0, on the 06/04/2019 at an altitude between 8526.3 and 35092.8 km and inclination of 12.0 degrees.
– HAPS Fragmentation Debris, objects generated by the fragmentation of HAPS (1994-29B), with mass
96.1, on the 03/06/1996 at an altitude between 584.1 and 818.9 km and inclination of 82.0 degrees.
– Centaur-5 SEC Fragmentation Debris, objects generated by the fragmentation of Centaur-5 SEC (200947B), with mass 2020.0, on the 25/03/2019 at an altitude between 6673.4 and 34706.6 km and inclination of 23.3 degrees.
– L-15 (YF115) Fragmentation Debris, objects generated by the fragmentation of L-15 (YF115) (2022151B), with mass 1850.0, on the 12/11/2022 at an altitude between 813.5 and 847.1 km and inclinationof 98.8 degrees.
– Other Rocket fragmentation debris, all the other rocket fragmentation debris.
Additional information on the fragmentation events can be found in ESA Fragmentation Database [14].
For each conjunction, the encounter geometry (i.e. the relative orientation of the orbits and time of closest approach) is retrieved from CRASS, whereas the computation of the collision probability is performed using AlfriendAkella’s method [17]. The values of positional uncertainty required for the collision probability calculation are obtained with the methodology in [18], where the covariance for an object is dependent on its size, orbit (i.e. perigee
altitude, eccentricity, inclination) and time between the assessment and the Time of Close Approach (TCA).
In the results in the following, the conjunctions are grouped in events, where an event is defined by a pair of primaryand secondary objects and a given TCA. The number of conjunction events with collision probability above 10−6
within three days to TCA is shown in Fig. 3.10 and Fig. 3.11, which refer, respectively, to targets defined basedon the distribution of payload objects and to targets defined along the Sun-Synchronous region. The threshold at
10−6 is usually well below the reaction threshold for payloads in LEOIADC (i.e. the events in Fig. 3.10 and Fig. 3.11
will not all results in collision avoidance manoeuvres), but this threshold could be already representative of events
where increased monitoring of the conjunction is activated.
In addition to the yearly statistics, the analysis has been systematically repeated yearly since 2015. This shows,particularly in the lower LEOIADC regime, the increase of conjunction events that require coordination between
active operators due to the change in space traffic, whereas higher orbits remain dominated by space debris
related events.

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ESA UNCLASSIFIED - Releasable to the Public

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ESA UNCLASSIFIED - Releasable to the Public

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ESA UNCLASSIFIED - Releasable to the Public

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ESA UNCLASSIFIED - Releasable to the Public

4. INTENTIONAL OBJECT RELEASE
A major part of the space debris mitigation measures are dedicated to the avoidance of intentionally releasing
space debris of a rocket body or payload as part of the mission. This type of mission related objects can generally
be sub-categorised into functional parts that are designed to be released after they are no longer required, e.g.
covers protecting instruments during launch, or combustion related products that support the main mission, e.g.
slag from solid rocket motors, or pyrotechnics. Objects from both subcategories can generally be avoided bydesign changes on the rocket bodies or payloads. For example, camera covers can be opened and folded away
instead, or pyrotechnically expelled and solid rocket motor slag can be avoided by using on-board chemical orelectrical propulsion systems. Small, i.e. sub millimetre, combustion related particles do contribute to the spacedebris environment but are not considered a threat. Most pyrotechnic devices fall under this case.
In this section, the evolution in terms of occurrence of this type of space debris is illustrated.

4.1. Mission Related Objects
As metric for the adherence to space debris mitigations guidelines, the release of catalogued mission related
objects can be used. For every single payload and rocket body, the amount of released and catalogued mission
related objects are counted. Furthermore, the fraction of payloads and rocket bodies releasing mission related
objects to the total amount of payloads and rocket bodies launched in given year is presented.

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ESA UNCLASSIFIED - Releasable to the Public

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bodies injected into the space environment during that year.

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ESA UNCLASSIFIED - Releasable to the Public

4.2. Solid Rocket Motor Firings

3URSHOODQWPDVV>NJ@As a metric of the adherence to space debris mitigations guidelines the amount of solid rocket motor firings for
asserted objects can be used. The propellant mass associated with each firing is given versus the date of thefiring. Not all solid rocket motor firings are equally damaging for the space environment, i.e. solid rocket motor
fuels which do not create large slag particles have been developed. However, such an identification is not madein this section.

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ESA UNCLASSIFIED - Releasable to the Public

5. FRAGMENTATION HISTORY
Since the beginning of the space age until the end of 2023, there have been 645 confirmed on-orbit fragmentation
events. In Fig. 5.2, the historical trend of the amount of fragmentation events per year is shown, as a function of
the event date and the launch date, respectively. Fragmentation events are currently being categorised in mainand sub-classes according to the assessed break-up cause. In the first list of classes, the break-up cause is fairly
well known:
Accidental: Subsystems that showed design flaws ultimately leading to breakups in some cases. This includes,for example, the breakup of Hitomi (Astro-H) in 2016 or the sub-class of Oko satellites.
Cosmos 862 Class (Explosive Charge): The Oko missile early warning satellites were launched into Molniya orbits. Each satellite carried an explosive charge in order to destroy it in case of a malfunction.
Reportedly, the control of this mechanism was unreliable.
Aerodynamics: A breakup most often caused by an overpressure due to atmospheric drag.
Collision: There have been several collisions observed between objects. A sub-class are so-called small impactors.
Small Impactor: Caused by a collision, but without explicit evidence for an impactor. Changes in the angularmomentum, attitude and subsystem failures are, however, indirect indications of an impact.
Deliberate: All intentional breakup events.
ASAT: Anti-satellite tests.
Cosmos 2031 Class: The Orlets reconnaissance satellites were introduced in 1989 and employed detonation as a standard procedure after the nominal mission.
Payload Recovery Failure: Some satellites were designed such that they exploded as soon as a nonnominal re-entry was detected.
RORSAT Reactor Core Ejection Class: Between 1980 and 1988, the Soviet Union re-orbited their Radar
Ocean Reconnaissance Satellites (RORSAT) after a successful mission to a sufficiently high orbit around
900 km altitude. The manoeuvre was followed by a reactor core ejection, which resulted in an opening of
the primary coolant loop (Sodium-Potassium or NaK alloy) and an associated release of NaK droplets.
Electrical: Most of the events in this category occurred due to an overcharging and subsequent explosion ofbatteries. A sub-class is defined based on the satellite bus.
Battery: Battery-related explosions may occur due to over-charging, over-temperature, short-circuits, overdischarging, structural issues or damage, in each cases leading to a thermal run-away and subsequent
breakup.
DMSP/NOAA Class: Based on the Television and InfraRed Observation Satellite (TIROS-N) satellite bus,
some of the satellites in this series suffered from battery explosions.
Propulsion: Stored energy for non-passivated propulsion-related subsystems might lead to an explosion, forexample due to thermal stress. Several sub-classes are defined for rocket stages that showed repeatedbreakup events.
Ariane Upper Stage: Breakups for the H8 and H10 cryogenic stages were observed, most likely due tooverpressure and subsequent bulkhead rupture. Passivation was introduced in 1990.

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ESA UNCLASSIFIED - Releasable to the Public

Briz-M: The fourth stage of the Proton rocket which is used to insert satellites into higher orbits.
Delta Upper Stage: There were several events for Delta second stages due to residual propellants until
depletion burns were introduced in 1981.
Proton Ullage Motor: The Blok D/DM upper stages of the Proton rocket used two ullage motors to support
the main engine. They were released as the main engine performed its final burn.
Titan Transtage: The upper stage of the Titan 3A rocket used a hypergolic fuel oxidizer combination.
Tsyklon Upper Stage: The third stage of the Tsyklon-3 launcher used a hypergolic fuel oxidizer combination.
Zenit-2 Upper Stage: The second stage of the Zenit 2 launcher used an RP-1/Liquid oxygen propellant.
A second list of classes relates to break-ups where the cause has not been well established. Events or sub-classes
within these classes could be reclassified in the future:
Anomalous: Defined as the unplanned separation, usually at low velocity, of one or more detectable objects from asatellite that remains essentially intact. This may include debris shedding due to material deterioration, which
includes insulation material or solar panels all of which have been observed from ground in the past. Eventswith sufficient evidence for an impact of debris or micrometeroids are classified under Small Impactor. Subclasses for anomalous events are defined, as soon as events occur multiple times for the same spacecraft
or bus type.
Cosmos-3 Class: Soviet/Russian launcher for small satellites.
Delta 4 Class: Events with several catalogued objects for the Delta Cryogenic Second Stages (DCSS).
ERS/SPOT Class: Both the ERS-1 and -2 satellites, as well as the SPOT-4 satellite had confirmed anomalies and fragments were catalogued.
Meteor Class: Russian meteorological satellite family.
Scout Class: Refers to the Altair upper stage of the Scout rocket family.
TOPAZ Leakage Class: There are two known events for TOPAZ satellites where NaK droplets have been
observed in the vicinity of the parent object presumably due to leakage [19].
Transit Class: Satellites of the U.S. Navy’s first satellite navigation system operational between 1964 and1996.
Vostok Class: Refers to the upper stage of the Vostok rocket (Blok E).
Assumed: Introduced for the MASTER model. Currently the only assumed events are in the GEO region, backed
by information obtained during survey campaigns [20].
Unconfirmed: A provisional status until an event is confirmed and classified accordingly.
Unknown: Is assigned whenever there is lacking evidence to support a more specific classification.
Cosmos 699 Class (EORSAT): For many of the ELINT Ocean Reconnaissance Satellites (EORSAT) a
breakup was observed during the orbital decay.
H-IIA Class: The second stage of the H-IIA launcher used a cryogenic propellant.
L-14B Class: The third stage of the Long March 4B (CZ-4B) launcher used a hypergolic propellant.

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5.1. All fragmentation events
A summary of the statistics on the recorded fragmentation events is reported in Table 5.1, where Assumed andUnconfirmed were excluded from the aggregation. A breakdown of the observed fragmentation events groupedby the main classes in terms of frequency and resulting catalogued debris is given in Fig. 5.3 and Fig. 5.4, respectively.
Table 5.1: Statistics on fragmentation events.
All history Last 20 years

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(b) Relative number of fragmentation events per event cause.

Figure 5.3: Historical trend of fragmentation events per event cause.

Page 84/121

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Figure 5.4: Historical trend of numbers of fragments produced by fragmentation events.

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 5.5: Elapsed time between fragmentation and launch by category. The bubble size indicates the numberof generated fragments.

Page 86/121

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 5.8: Cumulative distribution function (CDF) for the elapsed time between fragmentation and launch for nonsystem related fragmentation events, with different cut-off values on the launch year.

5.2. Non-system related fragmentation events
As also described when introducing the classes for fragmentation events, not all events are similar in nature andhence the consequences on the environment and for mitigation measures can vary. In particular, events caused
by a technical flaw in the design of a (sub-)system that is re-used for many Rocket Bodies or Payload platforms,
so-called system related events as for battery-related classes, are not representative for the space environment
as a whole and need targeted counter measures, e.g. it as was done for certain launch vehicle related classes.
To understand the likelihood of fragmentation events occurring in the environment as single stochastic events, i.e.
a background risk for any intact space object, it is instructive to analyses the non-system related fragmentation
events in isolation. In this sense, we can group the data from the fragmentation classes Unknown, Accidental,
Propulsion, Electrical, Battery, excluding their sub-classes.
A relation between the time to a fragmentation event and the launch epoch can be observed for non-system relatedclasses in Fig. 5.8. A causal relationship with the orbital region in which these object resided at the time of thefragmentation event could not be derived, as shown in Fig. 5.9. The derived statistics for the non-system related
fragmentations are significantly lower than those for the entire population as observed in the previous sub-section,and reported in Table 5.2. Based on the recent trend analysis, a value of 18 years is adopted as time limit after
which the explosion probability for a recently launched space object, due to non-systematic design flaws, can beconsidered as effectively 0.

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 5.9: Distribution of non-system related fragmentation events in mean altitude, inclination, and time to fragmentation.

Table 5.2: Statistics on non-system related fragmentation events.
All history Last 18 years

Page 89/121

Number of events

170

47

Non-deliberate events per year

2.7

2.5

Yearly rate of events where 50% of the generated
fragments have a lifetime of greater than 10 years

0.7

0.4

Yearly rate of events where 50% of the generated
fragments have a lifetime of greater than 25 years

0.5

0.3

Mean time (years) between launch and fragmentation

5.4

10.0

Median time (years) between launch and fragmentation

1.3

4.5

ESA UNCLASSIFIED - Releasable to the Public

6. END-OF-LIFE OPERATIONS HISTORY
Post mission disposal mitigation measures are specifically aimed at reducing the long term interference an object
in the space environment could have on the two protected regions, LEOIADC and GEOIADC . These mitigation
measures are associated with time criteria, i.e. so-called orbital lifetimes or clearance of orbital regions, and hence
require evaluating the long term evolution of orbits. For both protected regions, different mitigation measures imply
different end-of life operations. The reported years for payload clearance of LEOIADC goes up to 2022, for rocket
body clearance of LEOIADC goes up to 2023, and for payload clearance of GEOIADC goes up to 2023.

6.1. End-Of-Life Operations in Low Earth Orbit
Due to the presence of atmospheric drag in the lower levels of the LEO region, a natural cleansing of spacedebris from these regions occurs. A payload or rocket body operating in the LEO Protected region, with either apermanent or periodic presence, shall limit its post-mission presence in the LEO Protected region to a maximumof 25 years from the end of mission [7]. This limit by itself will not lead to a long-term reduction in the amount of
space debris, as will be show in Section 7.2, but is an important step towards limiting the space debris growth rate
in LEOIADC [2]. The mitigation measure itself, i.e. the so-called 25-year rule, does not indicate how it has to beachieved, but various standards provide an order of preference for various methodologies, i.e. controlled re-entry,
accelerated natural orbital decay, etc.
For catalogued objects, the orbital activity of a payload or rocket body can be derived and the orbital lifetime
estimated. This method is preferred over direct investigation, intelligence, of communication with the owners of a
payload or a rocket body, which could increase the accuracy of the prediction, but it might be unbalanced as therequest for such data might not be answered nor can all owners be clearly identified and approached. As somerocket bodies have been found to perform direct re-entries before they can be considered catalogued objects,
additional asserted objects are used as to make sure that such positive cases are correctly considered in the
resulting statistics. The methodology to determine the end of the operational phase of an object in LEO employed
here is described in depth in [21].
For satellites without orbit control capacity (OCC), i.e. no propulsion system, or for satellites that never exhibitedany orbit manoeuvre otherwise, the assessment of the mission end is not possible from orbit information alone.
Therefore, a statistical approach is pursued for those objects. The source of the statistics for mission lifetimes are
the measurable missions with orbit control capacity. Observed mission lifetimes are processed into histograms by
mission category, e.g. science, communications, military, etc. They are then applied to generate missions lifetime
estimations for the objects without orbit control capacity of the same category.
The boundaries between having an orbital control capacity or not is not always clearly defined by the underlying
technology. This is because the effects observed by the space surveillance system may not be reliably discernedin all cases. Impulsive manoeuvres, multi-revolutions use of electrical propulsion, and large drag sail deployments
are reliably picked up and hence objects exhibiting those features are categorised as having OCC.
On the other hand, smaller orbital changes, such as drag sailing, where the change in ballistic coefficient is smaller
than the error margin or the orbit determination capacity of the space surveillance system, are not picked up.
However, the most important metric w.r.t. the implementation is to remove an object from LEOIADC within 25 years,
or shortly thereafter, which is measured independently of the OCC categorisation.
In order to estimate the orbital lifetime of an object after reaching its end of life, the general processes as laid out instandard [11] are followed. To apply these processes to all catalogued objects, a Ballistic Coefficient (BC) needs
to be estimated for each of them. The BC estimation is based on least root-mean-square orbit fitting during thelongest periods free from estimated manoeuvres, generally after end of life is reached in case of OCC classified

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ESA UNCLASSIFIED - Releasable to the Public

objects. In case this can’t be achieved, the BC is defined based in the available physical properties in DISCOS.
The estimated BC is used to extrapolate the last recorded orbital state in 2023 until re-entry in combination with along term space weather forecast [22]. The used values and obtained results are stored in DISCOS and distributedon request [8]. The process itself is subject to a significant amount of stochastic assumptions which are describedin [23]. Hence, the reported orbital lifetimes are procedurally defined and need to be understood as a current
best-estimate that can vary between different versions of this report, as discussed in Section 6.1.3.
In case of payload objects, at least one calendar year without orbit control actions needs to pass for an object to beclassified as reaching end-of-life unless it performs a controlled re-entry. This is done to mitigate the implications of
the detection algorithm described above, and to avoid a potentially large amount of reclassifications in subsequent
editions of this report as some operators implement less frequent actions near the end-of-life. In practice, thismeans that the reported years for the payload clearance of LEOIADC goes up to 2022 instead of 2023.
It is important to note that for this report, where conformance to a time-limitation guidelines is to be evaluated,the categorisation of each object becomes fixed after 25 years. Unpredicted events, such as increased solar
activities or missions which actively remove large pieces of space debris, will thus be accounted for only when
they materialise.
Relocations from LEOIADC into orbits with a perigee altitude above 2000 kilometres are no longer viable end-of-life
debris mitigation practices [7]. While such relocations where relatively rare for Payload objects and only a minor
historical entry in the dataset of this section, they have been more commonly used to raise the perigee of Rocket
Bodies when, e.g. eccentric destination orbits such as GTO were targeted.
Human spaceflight (HS) related missions are analysed separately, as they skew results in terms of mass and countaffected. These missions include crew vehicles as well as cargo payloads, but not the rocket bodies that bringthem into orbit. Throughout this section, Stage is used as synonym for Rocket Body. The end-of-life behaviour of
space objects can be categorised in seven behavioural classes to illustrate disposal success rates:• NCWO: (Not Compliant WithOut attempt) the 25-year rule is not met by the mission orbit and no disposal
action has been taken;• NCWFB: (Not Compliant With attempt False Before) the 25-year rule is not met by the mission orbit, a disposal
action has been attempted but it was unsuccessful or insufficient;• NCWTB: (Not Compliant With attempt True Before) the 25-year rule was met by the initial mission orbit, adisposal action has been attempted but it was unsuccessful or the mission orbit was otherwise altered, andthe new orbit is not compliant;• CWFB: (Compliant With attempt False Before) the 25-year rule is not met by the mission orbit, but a disposal
action has been taken and was successful;• CWTB: (Compliant With attempt True Before) the mission orbit allowed to meet the 25-year guideline, but adisposal action has been taken nonetheless;• CWO: (Compliant WithOut attempt) the mission orbit allowed to meet the 25-year guideline, no action was
taken (nor needed);• CD: (Compliant With Direct Re-entry) a controlled re-entry has been performed.
In summary, clearance of the LEO protected region by payloads and rocket bodies will be presented as Naturally
Compliant if injected into an orbit that fulfils the 25-year lifetime measure, Successful Attempt when compliant after
an attempt to reduce its orbital lifetime, Insufficient Attempt when not compliant but having attempted to reduce its
orbital lifetime or No Attempt when not compliant with no attempt at all. It should therefore be noted that ‘disposal’
here is defined according to lifetime and does not include passivation aspects, which, as discussed in Section 1.3,
Page 91/121

ESA UNCLASSIFIED - Releasable to the Publiccannot currently be reliably derived from observational data.

6.1.1. Evolution of compliance shares
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Figure 6.1: Share of payloads and rocket bodies in terms of mass and number (top) and compliance in terms ofclearing the LEO protected region (bottom). The reported years for payload clearance of LEOIADC goes up to 2022,
for rocket body clearance of LEOIADC goes up to 2023.

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.2: Share of compliance in terms of clearing the LEO protected region by mission type.

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Figure 6.3: Compliance in terms of clearing the LEO protected region for constellation and non-constellation objects, in absolute numbers and in relative share.

Page 93/121

ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.4: Relative share of disposal behaviour classes over time in terms of number (top) and mass (bottom) for
payloads in LEO, excluding objects associated with human spaceflight by end-of-life year.

Page 94/121

ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.5: Relative share of disposal behaviour classes over time in terms of number (top) and mass (bottom) for
payloads in LEO, excluding objects associated with human spaceflight by launch year.

Page 95/121

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Figure 6.6: Relative share of disposal behaviour classes over time in terms of number (top) and mass (bottom) for
Rocket Bodies in LEO by end-of-life, i.e. launch year.

Page 96/121

ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.7: Relative shares of success w.r.t. compliance (top) and non-compliance (bottom) over time, excluding
objects associated with human spaceflight.

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Figure 6.8: Trend of adherence to clearance of LEOIADC over time in terms of numbers.

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Figure 6.9: Trend of adherence to clearance of LEOIADC over time in terms of mass.

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.10: Trend of adherence to clearance of LEOIADC over time in terms of numbers, excluding naturally
compliant objects where no action was needed or taken.

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ESA UNCLASSIFIED - Releasable to the Public

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Figure 6.11: Trend of adherence to clearance of LEOIADC over time in terms of numbers, considering payloads
and rocket bodies together.

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6.1.2. Evolution of behavioural classes per mass breakdown
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Figure 6.12: Breakdown per decade of observed behavioural classes for payloads with a mass below 10.0 kg.

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Figure 6.13: Breakdown per decade of observed behavioural classes for payloads with a mass between 10.0 and
100.0 kg.

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Figure 6.14: Breakdown per decade of observed behavioural classes for payloads with a mass between 100.0
and 1000.0 kg.

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Figure 6.15: Breakdown per decade of observed behavioural classes for payloads with a mass above 1000.0 kg.

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6.1.3. Robustness of the evaluation of compliance shares in LEO

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The following analysis shows how the compliance classification has changed over the different editions of thereport, considering that each edition is based on a current best-estimate of the residual orbital lifetime and reclassification can take place. Fig. 6.16 shows the share of successful re-/de-orbit attempts for payloads according to
the different report editions. As mentioned in Section 6.1, in case of payload objects, as in the case in Fig. 6.16,
at least one calendar year without orbit control actions needs to pass for an object to be classified as reaching
end-of-life, so the report issued in a given year covers up to the end of two years before the release year (e.g.
the report issued 2017 covers until the end of 2015). Note that for this visualisation (and for the purpose of thecomparison), re-orbits are still considered as successful attempts.

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Figure 6.16: Successful re-/de-orbit attempts for payloads according to the different report editions.

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6.2. End-Of-Life Operations in Geostationary Orbit
Unlike in LEO, no natural sink mechanism is available for the GEO protected region by which objects could leave.
The solar radiation pressure on the objects will also make long term predictions subject to non-negligible uncertainties. A payload or rocket body operating in the GEO Protected Region, with either a permanent or periodic
presence, shall be manoeuvred in a controlled manner during the disposal phase to an orbit that lies entirely outside the GEO Protected Region. There are different ways of ensuring that this condition is met. For example, thelaunch procedure for Rocket Bodies can be adapted to ensure that the release of the payloads no longer takes
place directly within the geostationary orbit but below. In this case, the payload has to climb the last part into
GEOIADC but the launcher remains on a GTO trajectory that does not intersect the GEO protected region. For
payloads within the GEO protected region, the mitigation measure has been refined, i.e. the so called IADC formulation [6], to ensure that a disposal occurs in a graveyard orbit with minimal interference. At least one of thefollowing two conditions should be met:
• The orbit has an initial eccentricity less than 0.003 and a minimum perigee altitude ∆H (in km) above thegeostationary altitude, in accordance with equation:
1.

∆H = 235 + (1000Cr A/m);2.

where Cr is the solar radiation pressure coefficient (dimensionless);3.

A/m is the ratio of the cross-section area (in m2 ) to dry mass (in kg) of the payload.

• The orbit has a perigee altitude sufficiently above the geostationary altitude that long-term perturbation forces
do not cause the payload to enter the GEO Protected Region within 100 years.
In summary, clearance of the GEO protected region by payloads will be presented as Successful Attempt, i.e.
the payload clears GEOIADC in-line with the formulation above, Insufficient Attempt when the payloads attempt toclear the GEOIADC but does not reach the criteria in the IADC formulation, and No Attempt otherwise. An in-depth
overview of the status of objects in GEOIADC and description of the summarised results shown here is available
via [24].
For the rocket bodies delivering payloads in or near the GEO protected region, the long-term disposal orbits are
influenced by a variety of perturbations potentially including Luni-Solar, solar radiation pressure, gravitational resonances, and atmospheric drag. This implies that long-term, i.e. over 100 years [7], clearance of both protected
regions by these rocket bodies is only predictable as a stochastic estimate. To assess the adherence by rocket
bodies to the disposal guidelines in a first approximation, we list the amount of rocket bodies predicted to cross one
or both of the protected regions within the next 100 years after launch, as a function of the total number of rocket
bodies that launch payload objects with a destination orbit in GEO. In addition, for those objects crossing the LEO
protected region, an object is marked as LEO-crossing if it crosses LEO and the permanence time in the LEO
region is longer than 25 years. Objects for which no orbital data is available are marked as Not classified.

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Figure 6.17: Orbital evolution status of payloads near the Geostationary orbit during 2023.

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Figure 6.18: Trend of adherence to the disposal guideline in GEOIADC .

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Figure 6.19: Mass trend of adherence to the disposal guideline in GEOIADC .

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Figure 6.20: Trend of adherence to the disposal guideline for rocket bodies used to insert satellites in GEOIADC .

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6.3. End-Of-Life Operations in MEO
Compared to the LEOIADC and GEOIADC regions, MEO contains relatively fewer objects in a larger volume of space.
Notwithstanding the resulting lower space debris density, the region is of importance for global navigation andcommunication constellations, and crossed by space objects with large eccentricity and semi-major axis orbits.
Space debris mitigation guidelines call for the avoidance of space debris dense regions by means of targeted
disposals, even outside the protected regions [2]. With this perspective in mind, it is instructive to show the orbital
disposal behaviour of Payload objects in this region.

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Figure 6.21: Distribution of payloads in MEO in mean altitude and inclination, distinguishing by activity status(symbols) and constellation (colour).

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7. ENVIRONMENT METRICS
7.1. Environmental Index in 2023
The effect of adherence to space debris mitigation guidelines and regulations on a global level has a direct influenceon the avoidance of the Kessler syndrome in Low Earth Orbit. In order to quantify the relation between them,the concept of an environment index is introduced via a general risk metric. The risk associated to an event istraditionally computed as Risk = Probability × Severity.
This definition can be applied to space objects to measure the fragmentation risk associated to them and use thisas a metric of their potential contribution to the space debris environment. The term probability represents theprobability of a catastrophic collision, which is dependent on the flux of debris able to trigger a collision and thecross-sectional area of the object. The flux values are obtained from MASTER-8 [25] considering for each object
the last available orbit in DISCOS. The physical properties and the activity status of the objects are also retrieved
from DISCOS. The term severity measures the effect of such a fragmentation on operational spacecraft. This isdone by simulating the generation of the cloud with the NASA breakup model [26] and modelling the evolutionof its density over time under the effect of atmospheric drag. A representative set of target spacecraft is definedas proxy of the population of operational satellites. For each of these target spacecraft, the resulting cumulative
collision probability over 25 years due to the fragment cloud is computed and their sum is used as a severity
measure.
The risk is evaluated along the mission profile of an object, simulating its orbit evolution over 100 years. For active
and manoeuvrable objects, the implementation of a Post-Mission Disposal (PMD) manoeuvre and its estimatedsuccess rate are considered when computing the trajectory evolution. More details on the approach can be foundin [27]. The risk metric can be used to compare objects or missions against each other, and the cumulated risktaken by all objects in space at a given time, and their behaviour in the future, thus introduces the notion of capacityof the environment.
Fig. 7.1 shows the distribution, in mean altitude and inclination, of the analysed objects in LEO. The colour of themarker indicates the category of the objects, i.e. whether it is a rocket body, an inactive payload, an active one
or a constellation. The size of the marker indicates the debris index value and an aggregated score is shown for
constellations. The values are obtained assuming a 90% PMD success rate for active objects. Areas with high risk
concentration can be observed around 850 km of mean altitude and 70-80 degrees in inclination. Fig. 7.2 shows
the distribution of the total index among object categories: By far, most of the risk is associated to inactive objects(97%), with the largest contribution coming from spent rocket bodies.

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or constellation.

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Figure 7.2: Distribution of the total index among object categories.

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7.2. Environment evolution
The simulation of the future evolution of the debris population can be used to assess the efficacy of proposed
mitigation actions and of current behaviours. In particular, two scenarios are presented in this section:• A defined extrapolation (Extr) of the current behaviour in terms of launch traffic, explosion rates, and disposal
success rates;• No future launches (NFL), where it is assumed that no launch takes place after 2023.
The definition of trends in launch traffic, explosion rates, and disposal success rates is based on the data available
in DISCOS and on the analysis contained in this report. DELTA-4 [28] was used to simulate the evolution of theenvironment over 200 years, performing 100 Monte Carlo runs per scenario. The parameters for the scenario
definition are summarised hereafter.
For both scenarios, the reference population used for the analysis is an extraction of the DISCOS population at thereference epoch (1st January 2024). For each object, physical characteristics such as mass, cross-sectional area,
and orbital parameters are retrieved, while for Rocket Bodies and Payloads, launch information is also stored.
For Payloads specifically, it is also stored in which orbital region they are active and whether they belong to a
constellation, following the definitions in Section 1.1.
The annual explosion rate is taken from statistics on non-system related fragmentations over the last 18 years(Table 5.2). In the No future launches scenario, we assume a linear decline in the explosion rate, reaching zeroafter the first 18 years. No explosion event is simulated after this period, as Fig. 5.8 shows that 95% of non-systemrelated fragmentation events occur within 18 years of launch, as described in Section 5.2.
For the extrapolation scenario, a launch traffic model is also needed as input for the simulations. This was obtainedby repeating the launch traffic between 2017 and 2023, discounting the contribution from constellations. For
each constellation, in-orbit or planned (according to the definition given in Section 1.1), a model of deployment
and replenishment was defined using publicly available data. For these constellation Payloads, a capability tosuccessfully perform collision avoidance manoeuvres is assumed for objects with propulsion for as long as they
are active in the simulation.
A fixed operational lifetime of eight years is assumed for Payloads not belonging to a constellation instead of thevalues derived in this report, in line with current long-term space debris environment modelling practices. Specificvalues are used for Payloads belonging to constellations, based on the available information on the current constellation designs where possible. Post-mission disposal success rates are derived from the observed values reported
in Section 6, considering the performance of objects with End-Of-Life equal or later than 2017. In particular, thepost-mission disposal success rate is set to 60% for rocket bodies and 15% for payloads, to reflect the slow but
upwards trend in compliance in combination with the shifting traffic towards destination orbits with lifetimes below
25 years. For constellation Payloads, specific values for the post-mission disposal success rate and lifetime areagain taken depending on currently available information, else are assumed to be 90% and 25 years respectively.
These baseline values reflect the bare minimum identified in [2], whereas in practice, far higher rates of compliancewould need to be observed over time to limit the long-term growth of the space debris population.
The evolution of the number of objects larger than 10 cm and the cumulative number of catastrophic collisions, i.e.
collisions leading to the complete destruction of target and impactor, are shown in Fig. 7.3 and Fig. 7.4: the boldline for each scenario represents the mean value over all the Monte Carlo runs, while the lighter-coloured lines
indicate the outcome of each individual run. This representation was selected to visualise the variability across the
single runs without introducing standard deviation bands as they may be not representative of the result distribution[29].

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The results from the evaluation of the scenario indicated that even when spaceflight is completely halted today,
the amount of space debris objects in Low Earth Orbit is likely to increase. The extrapolation of our current
behaviour, which assumes the continuation of explosion in orbits at current rates, adherence by constellations toat least the minimum desirable post-mission disposal success rates, and continuation of the currently estimatedpost-mission disposal success rates for all other objects, leads to an unstable environment with collision rates
increasing exponentially. While a shift in launch traffic to orbits with low orbital decay as observed in Section 2.7
improves the situation [30], the implementation of all space debris mitigation strategies are necessary to avoid anadverse future.
Establishing the space debris growth rates based on the status of annual environment snapshots provides anestimate for the consequences of the current levels of global space debris mitigation. To analyse trends in the predicted environment evolution, additional scenarios can be simulated using different starting epochs, while adopting
the logic laid out above for what concerns deriving space traffic settings for the model.
In particular, in addition to the starting points generated from past and current editions of the report, other two
reference epochs (at 2014 and 2005) were defined, for which the corresponding launch traffic, explosion rate, anddisposal rates were extracted from the data in DISCOS. The years 2014 and 2005 are not chosen arbitrarily, but
respectively correspond to the last year before the fundamental change in launch traffic (due to the increase inusage of small satellites) and the adoption of the IADC mitigation guidelines in national practices.
The number of objects larger than 10 cm in the final population and the final cumulative number of catastrophic
collisions at the end of the simulation are shown in Fig. 7.5 and Fig. 7.6, where red is used for the extrapolation
scenarios and dark blue for no further launches. For each simulation, this end date is 200 years after the starting
point.
Boxplots are used to visualise the spread of results over the runs: the box covers the range between the first andthe third quartile, with the horizontal line within the box indicating the median; the whiskers indicate the distanceof 1.5 the interquartile range in both directions and any datapoint outside this range is considered an outlier andindicated with a small dot. For Fig. 7.5, the number of objects at each starting epoch is further denoted by a grey
triangle. It is important to note that in all extrapolation scenarios the simulated space debris environment continues
to deteriorate. Under the current extrapolation conditions, the amount of catastrophic collision could rise quickly.
Even under the no further launches scenarios, the amount of space debris objects is observed to increase in allcases.

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Figure 7.3: Number of objects in LEOIADC in the simulated scenarios of long-term evolution of the environment.

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Figure 7.4: Number of cumulative collisions in LEOIADC in the simulated scenarios of long-term evolution of theenvironment.

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Figure 7.5: Number of objects in LEOIADC in the simulated scenarios of long-term evolution of the environment.

Figure 7.6: Number of cumulative collisions in LEOIADC in the simulated scenarios of long-term evolution of theenvironment.

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ESA UNCLASSIFIED - Releasable to the Public

References[1] United Nations. Guidelines for the long-term sustainability of outer space activities (A/AC.105/C.1/L.366),
2019.
[2] Inter-Agency Space Debris Coordination Committee. Space Debris Mitigation Guidelines, IADC-02-01,
Revision 3, 2021.
[3] European Space Agency. ESA Space Debris Mitigation Requirements, ESSB-ST-U-007, Issue 1, 2023.
[4] D. J. Kessler and B. G. Cour-Palais. Collision frequency of artificial satellites: The creation of a debris belt.
Journal of Geophysical Research, page 2637–2646, 1978.
[5] United Nations. Convention on International Liability for Damage Caused by Space Objects, 1972.
[6] Inter-Agency Space Debris Coordination Committee. Space Debris Mitigation Guidelines, 2002.
[7] International Standards Organisation. Space systems - Space debris mitigation requirements, ISO TC
20/SC 14 24113:2019, 2019.
[8] European Space Agency. Database and information system characterising objects in space.
https://discosweb.esoc.esa.int/, 2021. Accessed: 2024-06-01.
[9] T.S. Kelso. CelesTrak. https://celestrak.com/.
[10] Union of Concerned Scientists. Satellite Database.
https://www.ucsusa.org/resources/satellite-database.
[11] International Standards Organisation. Space systems - Estimation of orbit lifetimes, ISO TC 20/SC 14
27852:2016, 2016.
[12] United Nations Office for Outer Space Affairs. United Nations Register of Objects Launched into Outer
Space. http://www.unoosa.org/oosa/en/spaceobjectregister/index.html.
[13] United Nations. Convention on Registration of Objects Launched into Outer Space, 1974.
[14] European Space Agency. ESA’s Fragmentation Database. https://fragmentation.esoc.esa.int/, 2020.
Accessed: 2024-06-01.
[15] K. Merz, B. Bastida Virgili, V. Braun, T. Flohrer, Q. Funke, H. Krag, S. Lemmens, and J. Siminski. Current
collision avoidance service by ESA’s space debris office. 7th European Conference on Space Debris,
Proceedings of the conference, 2017.
[16] United States Space Force’s 18th Space Control Squadron. Space-track.
https://www.space-track.org/, 2021. Accessed: 2024-06-01.
[17] K. T. Alfriend, M. R. Akella, J. Frisbee, J. L. Foster, D. J. Lee, and M. Wilkins. Probability of collision error
analysis. Space Debris, 1(1):21–35, 1999.
[18] ESA Space Debris Office. Assessment of Risk Event Statistics (ARES).
https://sdup.esoc.esa.int/drama/downloads/documentation/Technical-Note-ARES.pdf, 2019.
[19] C. Wiedemann, E. Gamper, A. Horstmann, V. Braun, and E. Stoll. Release of liquid metal droplets from
Cosmos 1818 and 1867. 67th International Astronautical Congress, Proceedings of the conference, 2016.
[20] S. Flegel, J. Gelhaus, M. Möckel, C. Wiedemann, and D Kempf. Maintenance of the ESA MASTER Model.

Page 120/121

ESA UNCLASSIFIED - Releasable to the Public

Final Report of ESA contract 21705/D/HK, 2010.
[21] S. Lemmens and H. Krag. Two-line-elements-based maneuver detection methods for satellites in low earth
orbit. Journal of Guidance, Control, and Dynamics, 37(3):860–868, 2014.
[22] R. Mugellesi-Dow, D. J. Kerridge, T. D. G. Clark, and A. W. P. Thompson. Solmag: an operational system forprediction of solar and geomagnetic activity indices. 1st European Conference on Space Debris,
Proceedings of the conference, 1993.
[23] S. Lemmens, B. Bastida Virgili, V. Braun, T. Flohrer, Q. Funke, H. Krag, F. Mclean, and K. Merz. From
End-of-Life to Impact on Ground: An Overview of ESA’s Tools and Techniques to Predict Re-entries from theOperational Orbit to the Earth’s Surface. 6th International Conference on Astrodynamics Tools andTechniques, Proceedings of the conference, 2016.
[24] ESA Space Debris Office. Classification of Geosynchronous Objects. Issue 26.
GEN-DB-LOG-00290-OPS-SD, ESA/ESOC, Darmstadt, Germany, 2024.
[25] C. Wiedemann, A. Horstmann, S. Hesselbach, V. Braun, H. Krag, S. Flegel, M. Oswald, and E. Stoll.
Particle flux analysis with the updated MASTER model. 67th International Astronautical Congres,Proceedings of the conference, 2018.
[26] N. L. Johnson and P. H. Krisko. NASA’s new breakup model of EVOLVE 4.0. Advances in Space Research,
28(9):1377–1384, 2001.
[27] F. Letizia, S. Lemmens, B. Bastida Virgili, and H. Krag. Application of a debris index for global evaluation of
mitigation strategies. Acta Astronautica, 161:348–362, 2019.
[28] A. Horstmann, S. Hesselbach, C. Wiedemann, S. Flegel, and M. Oswald. Enhancement of S/C
Fragmentation and Environment Evolution Models. Final Report of ESA contract 4000115973/15/D/SR,
2020.
[29] A. A. Lidtke, H. G. Lewis, and R. Armellin. Statistical analysis of the inherent variability in the results ofevolutionary debris models. Advances in Space Research, 59(7):1698–1714, 2017.
[30] H.G Lewis. Evaluation of debris mitigation options for a large constellation. Journal of Space Safety
Engineering, 7:192–197, 2020.

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