15 October 2018

1. Validating the NASA Standard Breakup Model:A comparison against recorded on-orbit fragmentation events Samuel Diserens (s.d.diserens@soton.ac.uk) Hugh Lewis JörgFliege 15 October 2018

2. My Research Debris Models and the Activities of NewSpace How the changing utilisation of space will impact the use of debris models • Student in the Next Generation Computational Modelling (NGCM) Centre for Doctoral Training at the University of Southampton • A member of the Astronautics research group within the School of Engineering Funded by grant from the Engineering and Physical Sciences Research Council (EPSRC)

3. What is NewSpace? • Rise of the private sector in the space industry • Significant changes including: • Smaller spacecraft, • CubeSats • Differences in spacecraft construction: • Composite materials, • Additive manufacturing • Novel mission concepts: • Mega-constellations, • On-orbit servicing, • Active Debris Removal (ADR), • Reusable rockets

4. NewSpace &The Space Environment • Requirement to regulate and licence industry to control liability • Open questions on how this will impact the debris environment • New questions regarding space debris, such as: • ADR: Which objects to remove? When? • What is the impact of material and density on fragment production?

5. Challenges for Debris Modelling • Debris models are expected to provide answers to these questions • Debris modelling requires a range of assumptions to be made based on previous observations and knowledge • Models and assumptions must be challenged and tested in the face of changing behaviour

6. The NASA Standard Breakup Model • The first model to be tested • Current version developed in 1998 (Reynolds et al., 1998; Johnson et al., 2001; Krisko, 2011) • Has become the de facto breakup model, used in (almost) every space debris model currently in use • Simulates the breakup of on orbit objects • Due to explosion; or • Due to collision of two objects • Generates fragments by characteristic length • Distributed according to a power law

7. Limits & Assumptions NASA Breakup Model NewSpace Spacecraft More spacecraft at size extremes, large and small Lower densitymaterials Novel approaches to manufacturing, to materials and to debris shielding. Complex structures • Explosion model valid for 600-1000kg spacecraft. • Explosion distribution is independent of mass • Catastrophic collisions occurs for impact energy >40J/g of target mass • Mass of spacecraft concentrated in a single body

8. Comparison to IADC Study Collision Scenario Explosion Scenario (Data Source:NASABreakupModelImplementation Comparisonofresults, A. Rossi, 24th IADC Meeting April 2006)

9. Verifying the Model

10. Test Cases • Unfortunately (or perhaps fortunately) there are few major breakups to use as reference data • Comparing simulation results against the values recorded by SSN (on Space-Track) for small (>0.1 m), medium (> 0.4 m) and large (> 1.3 m) fragments • Both collision events and explosions are examined including both rocket-bodies and payloads

11. Rocket Body Explosion Scenarios • Four major explosions of rocket bodies were chosen for replication and comparison. • These were selected from the list of the top 10 largest contributors to the space debris population.(ANZ-MEADOR, 2016)

12. Rocket Body Explosion Scenarios

13. Payload Explosion Scenarios • Three examples were chosen for the explosion of payloads. • These were chosen as some of the most recent and significant contributions to the debris environment from the breakup of satellites.

14. Payload Explosion Scenarios

15. Collision Scenarios • Three scenarios were chosen for collision events • Breakup of Fengyun-1C following the 2007 Chinese ASAT test. • Breakups of Iridium-33 and Cosmos-2251 after the two accidentally collided in 2009. • These Scenarios were replicated for comparison

16. Collision Scenarios

17. Comparing Results • Explosions: • Close fit for most rocket bodies • Worse fit for small rocket body (Pegasus) • For payloads there appear to be fewer medium and large fragments and more small objects than predicted • Collisions: • Results for each of the fragmentations indicate a steeper relationship between number and size than predicted • Fewer larger fragments and more smallerfragments are observed than are predicted • Extrapolation suggests this may represent a significant under-prediction of objects under 10cm

18. What Does This Mean? • Implication that size and construction have an impact on fragmentation • Greater certainty requires more resolution and more examples • Ongoing NASA study into the fragmentation of DebriSat & DebrisLv • This will still only be 2 new data sets • If the advent of NewSpace changes what constitutes a ‘normal’ spacecraft then breakup models need to be recalibrated

19. Additional Challenges • How are the predicted area-to-mass ratios of fragments expected to change? • What does this imply for the evolution of the environment? • Fewer larger objects suggests fewer catastrophic collisions • If the advent of NewSpace lowers the threshold then may result in more catastrophic collisions • Next Steps: Review collision algorithms • Identify key algorithms in use • Test their suitability for use with different scenarios • Investigate potential refinements

20. Summary • ‘NewSpace’ changes some of the assumptions that can be made when modelling space debris impacting the results of these models • This may change the distribution of fragments generated by the NASA Standard Breakup Model • May also impact the threshold for catastrophic breakup • Results of the NASA model were compared with observed breakup events in order to test these assumptions • Model is a good fit for traditional objects (large upper stages) • Non-traditional objects may generate fewer large fragments and more smaller fragments • Further study is required to investigate the impact on the overall debris environment

21. References I acknowledge financial support from the EPSRC Centre for Doctoral Training in Next Generation Computational Modelling grant EP/L015382/1 N. L. Johnson, P. H. Krisko, J. C. Liou, and P. D. Anz-Meador. NASA’s new breakup model of EVOLVE 4.0. Advances in Space Research, 28(9):1377–1384, 2001. ISSN 02731177. doi: 10.1016/S0273-1177(01)00423-9. P. H. Krisko. Proper Implementation of the 1998 NASA Breakup Model. Orbital Debris Quarterly News, 15(4):4–5, 2011. ISSN 1364-503X. doi: 10.1016/0273-1177(93)90600-G. Alessandro Rossi. NASA Breakup Model Implementation Comparison of results. Technical report, IADC Working Group 2, 2006. Thanks to participants of the 2006 IADC study, reference to DISCOS and Space-Track databases

22. The Space Debris Problem • The utilisation of space is important to modern life • E.g. Telecommunications; GNSS; Earth Observation • Space debris poses a threat to this • Collision of small objects (>1g) with a satellite at orbital velocities can have catastrophic consequences • Over 750,000 objects with diameter 1cm or greater • Debris models exist to study this problem • Simulate the debris environment • Significant challenges are present • Computationally expensive • Relatively little data

23. Verifying the model

24. Comparison to NASA results

25. Comparison to IADC Study Fragment Lengths

26. Comparison to IADC Study Fragments Masses

27. Comparison to IADC Study Fragment Velocities

28. Validation Results

29. Collision Scenarios • Three scenarios were chosen for collision events • Breakup of Fengyun-1C following the 2007 Chinese ASAT test. • Breakups of Iridium-33 and Cosmos-2251 after the two accidentally collided in 2009. • These Scenarios were replicated for comparison

30. Collision Results

31. Rocket Body Explosion Scenarios • Four major explosions of rocket bodies were chosen for replication and comparison. • These were selected from the list of the top 10 largest contributors to the space debris population.(ANZMEADOR, 2016)

32. Rocket Body Explosion Results

33. Payload Explosion Scenarios • Three examples were chosen for the explosion of payloads. • These were chosen as some of the most recent and significant contributions to the debris environment from the breakup of satellites.

34. Payload Explosion Results