Composition of debris object classes in space as of October 2012
Composition of debris object classes in space as of October 2012

Analysis and prediction

The consolidation of knowledge on all known objects in space is a fundamental aspect  of the operational support activities of ESA's Space Debris Office. 

This knowledge is maintained and kept up-to-date through the DISCOS database (Database and Information System Characterising Objects in Space). DISCOS serves as a single-source reference for information on launch details, orbit histories, physical properties and mission descriptions for about 38 700 objects tracked since Sputnik-1, including nearly 10 million orbit records in total. The US Space Surveillance Network provides a continuous flow of orbit data for all tracked, unclassified objects.

Today, DISCOS constitutes a recognised, reliable and dependable source of space object data that is regularly used by almost 40 customers worldwide. Apart from its use for standard database queries, DISCOS generates several automated products, which include a log of upcoming re-entries, and publication-quality status reports.

MASTERing debris densities

ESA’s most prominent debris and meteoroid risk assessment tool is the MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) model covering all debris and meteoroid sizes larger than 1 micrometre, and predictions of the space debris environment until 2050.

ESA maintains and distributes a number of models for the characterisation of the space debris environment and its evolution. The Agency's most prominent debris and meteoroid risk assessment tool is called MASTER (Meteoroid and Space Debris Terrestrial Environment Reference).

It was first issued in 1995 and has been continuously improved; the current release is MASTER-2009. MASTER uses sophisticated mathematical techniques to determine impact flux (number of impacts per square meter of satellite area and per year) information with high spatial resolution for an object population derived from all known, historic debris-generation events.

These comprise more than 250 in-orbit fragmentation events, more than 1000 solid rocket motor firings, and 16 reactor core ejections from RORSAT satellites. The model can be used to assess the debris and meteoroid impact flux that a spacecraft would encounter on any arbitrary Earth orbit. The MASTER model covers all debris and meteoroid sizes larger than 1 micrometre.

At small (sub-millimetre) particle sizes, natural meteoroids can prevail over space debris in some orbital regions, in particular during intense seasonal meteoroid streams, with peak activities close to perihelion passes of the related source comets (e.g. the Leonids in 1966 and 1999). The ESA Interplanetary Meteoroid Model (IMEM) describes the resulting meteoroid environment, also outside Earth-bound orbits.

DELTA: Assessing mitigation effectiveness

ESA's MASTER software tool
ESA's MASTER software tool

In order to study the effectiveness of debris mitigation measures on the debris population stability, long-term forecasts are required to determine future trends as a function of individual mitigation actions. This kind of analysis can be performed with ESA's DELTA tool (Debris Environment Long-Term Analysis).

DELTA is a 2- to 3-dimensional, time-dependent, dynamic debris model, with detailed traffic model and release event data, and with statistically generated collision events, based on local object densities and collision probabilities. It is built on the mathematical principles of MASTER. Starting from a current MASTER population, DELTA analyses the effects of traffic variations and different debris mitigation measures (e.g. explosion prevention, re-orbiting at end of mission, de-orbiting at end of mission, lifetime reduction) on the future evolution and stability of the space debris environment up to beyond-GEO altitudes.

The time spans covered in such projections are typically 100 to 200 years. The particle sizes considered by DELTA are larger than 1 mm (as compared to 1 micrometre for MASTER), since only these are relevant for risk assessments. DELTA uses a corresponding MASTER debris population as a starting point for its projections. An underlying traffic model statistically distributes the contributions of launches, explosions and solid rocket motor firing events into different orbit regimes of the Earth environment.

The resulting collision risk is dynamically determined from the actual status of the environment at each epoch, and in each altitude regime. Collision events are statistically triggered - and fragments are added to the environment - if a given kinetic energy threshold is exceeded. The so-called 'business-as-usual' scenario (i.e. if today’s operational practises remain unchanged) forms the baseline for comparisons with alternative approaches in which mitigation measures are applied.

It can be shown that business-as-usual space activities lead to a progressive, uncontrolled increase of object numbers, with collisions becoming the primary debris source within less than 50 years. The removal of mass from orbit turns out to be the most effective way of preventing this collisional cascading process from setting in.

To make their analyses more accessible by mission planners, spacecraft designers, and manufacturers, ESA has published a "Space Debris Mitigation Handbook." {{LINK TO PDF}} This comprehensive document provides an overview of all major space debris research disciplines, with a large number of tables and charts to characterise the space debris environment, to determine related risks, and to outline effective protection and mitigation measures. 

Last update: 19 April 2013

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