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The impact of long-term trends on the space debris population Dr Hugh Lewis Astronautics Research Group, Faculty of Engineering & the Environment

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2 In the movies

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3 In the news

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4 Image courtesy of ESA 18 cm 1.2 cm Impact at 6.8 km/s The space debris hazard 4

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5 Space debris sources

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6 Top 10 worst fragmentations

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7 Space debris population Softball size or larger ( 10 cm) ~22,000~500,000~100,000,000 Total mass: 6,300 tonnes (2,700 tonnes in LEO) Marble size or larger ( 1 cm) Ball-point pen tip ( 1 mm)

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8 Active satellites (Aug 2012) Union of Concerned Scientists Satellite Database seen in DAMAGE 999 active satellites

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9 10 cm population (May 2009) ESA MASTER 2009 population seen in DAMAGE 29,370 objects 10 cm (2 catastrophic collisions)

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10 UN space debris mitigation guidelines 1.Limit debris released during normal operations 2.Minimize the potential for break-ups during operational phases 3.Limit the probability of accidental collision in orbit 4.Avoid intentional destruction and other harmful activities 5.Minimize potential for post-mission break-ups resulting from stored energy 6.Limit the long-term presence of spacecraft and launch vehicle orbital stages in the low Earth orbit (LEO) region after the end of their mission 7.Limit the long-term interference of spacecraft and launch vehicle orbital stages with the geosynchronous (GEO) region after the end of their mission

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11 Remediation Even with good compliance with the commonly adopted mitigation guidelines, the space debris population is likely to grow: Active Debris Removal About 50 removals needed to prevent one collision $1 $3 billion per year

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12 LEO mitigation & remediation 30% compliance 90% compliance 90% compliance with 5 removals p.a.

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Use Monte Carlo simulation to generate reliable statistics 13 Evolutionary modelling 30% compliance

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Show the probability of a particular population outcome: 14 Evolutionary modelling 30% compliance Population plume:

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15 LEO mitigation & remediation 30% compliance 90% compliance 90% compliance & 5 removals p.a.

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16 LEO mitigation & remediation 30% compliance 90% compliance 90% compliance with 5 removals p.a. 81% of MC runs see an increase in the LEO population after 100 years 49% of MC runs see an increase in the LEO population after 100 years 99% of MC runs see an increase in the LEO population after 100 years

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17 The known unknowns Predictions of the future are inherently difficult: Launch traffic Launch rate Technology development Small satellites Programmes & missions Human spaceflight Explosions Security Anti-satellite tests Cybersecurity Conflict Mitigation & remediation Solar activity Modelling capabilities

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Many futures approach 18 Solar activity: Launch rate: Also: explosion rate, compliance with mitigation measures

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19 LEO mitigation Traditional approach: 90% compliance Many futures approach: 90% compliance

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20 LEO mitigation Traditional approach: 90% compliance Many futures approach: 90% compliance

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LEO mitigation & remediation 21 Traditional approach: 90% compliance & 5 removals p.a. Many futures approach: 90% compliance & 5 removals p.a.

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22 LEO mitigation & remediation Traditional approach: 90% compliance & 5 removals p.a. Many futures approach: 90% compliance & 5 removals p.a.

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Long-term changes Solar activity: Sun enters an extended period of low activity after 10% of Grand Solar Maxima Thermospheric mass density: secular decrease in thermospheric mass density in the range -2% to -5% per decade identified from TLE data (e.g. Emmert et al., Saunders et al.) 23

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24 DAMAGE: thermospheric density trend Derived from work by Saunders et al., (JGR, 2010). Density multiplier Decades since 1970 h = 300 km

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25 Effects on satellite decay Debris lifetimes extended by up to 25% ( Lewis et al., 2005) Debris population increases at a faster rate Collision risk increases Expected lifetime: 25 years Actual lifetime: 27 years

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26 90% PMD and no removals No TREND With TREND

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27 90% PMD and no removals 8,082 objects No TREND With TREND

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28 90% PMD and no ADR

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29 90% PMD and 5 removals p.a. No TREND With TREND

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30 90% PMD and 5 removals p.a. 6,437 objects No TREND With TREND

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31 90% PMD and 5 removals p.a.

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Solar activity assumptions Future F10.7 cm solar flux Cycle 24 Cycle 25Cycle 29 32

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Long-term decline in solar activity 33 5 removals p.a.

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Long-term decline in solar activity 34 No TREND With TREND

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Long-term decline in solar activity 35

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36 Summary Many factors/mechanisms influence the evolution of the debris population and are difficult to predict Large uncertainties in the predicted space debris population: Active debris removal may not be necessary or may not be sufficient Significant reduction in the debris population is difficult to achieve (floor effect) Evidence for long-term changes in solar activity and thermospheric mass density but these are not routinely modelled: Can lead to rapid (and potentially sustained) population growth Extended lifetimes counter the benefits of mitigation & remediation Add to uncertainties Unknown unknowns: Other sources of uncertainty? Extrapolation of density trend into the future Anomalous densities

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Acknowledgements: Financial and technical support from: Holger Krag and Heiner Klinkrad (ESA), Richard Crowther (UK Space Agency), Adam White, Aleksander Lidtke & the Project SHARP Team (University of Southampton) www.un.org/en/events/tenstories/08/spacedebris.shtml Contact me: hglewis@soton.ac.uk Ten Stories the World Should Hear More About: Space Debris

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Back-up slides

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Space debris population 39

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40 30% PMD and no removals No TREND With TREND

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41 30% PMD and no removals 12,948 objects No TREND With TREND

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42 30% PMD and no removals