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- 1. Space Environment Lecture 32 – Space Debris (Vol. 3) Large constellations (part 1) Professor Hugh Lewis SESA3038 Space Environment
- 2. Overview of lecture 32 • In this lecture we look back (very briefly) to remind ourselves why constellations of satellites in LEO are useful and why they might present problems for the space environment, before we focus on a simulation study conducted for ESA: – Aiming to understand the sensitivity of the debris environment to key satellite and constellation parameters – Can we use this information to design and build better constellations? • Here, we just focus on the simulation objectives and the baseline parameters and assumptions • The results from this study will be included in the next lecture Space Environment – Space Debris (Vol. 3)
- 3. Space debris Space Environment – Space Debris (Vol. 3) • The space debris environment: update • Space surveillance/measurement of space debris • Impacts on space operations • Modelling of space debris • Environment/evolutionary modelling • Impact modelling • Breakup modelling • Re-entry modelling • On-ground risk modelling • Clean Space Volume 3 (Week 7)
- 4. Why use a constellation? Space Environment – Space Debris (Vol. 3) (From SESA3041/6079) Typical drivers for constellations: Global coverage Temporal coverage In combination with other requirements, e.g.: High spatial resolution Low latency User experience E.g. In communications missions, trend is towards low orbit constellation systems principally because of the low power requirement of the user terminal (a hand-held phone has an isotropic, low radiated power transmitter for physiological reasons)
- 5. Latency Space Environment – Space Debris (Vol. 3) (From SESA3041/6079) Latency for difference communications orbits: E.g. SpaceX Starlink & OneWeb constellations latency is close to fibre-optic Orbit Altitude Latency (one- way/hop) Latency (four- way/full-hop) LEO 1000 km 0.003 s 0.013 s MEO 16000 km 0.053 s 0.213 s GEO 36000 km 0.12 s 0.48 s
- 6. Starlink, OneWeb and Kuiper in LEO Space Environment – Space Debris (Vol. 3) (Updated from SESA3041/6079) OneWeb Starlink Kuiper
- 7. Starlink Space Environment – Space Debris (Vol. 3) Data from SOCRATES (note that these are predictions for a 7-day period) • Proportion of all conjunctions in the SOCRATES report (excluding Starlink-on- Starlink): • ~11% of all conjunctions < 5 km (1-in-9) and ~9% of all conjunctions < 1 km (1-in-11) • Also ~ 11% of conjunctions< 1 km affecting ACTIVE spacecraft
- 8. A study for ESA Space Environment – Space Debris (Vol. 3) • Cohen et al. 2016*: • “A positive and creative vision for sustainability focuses on building something new and clean rather than defeating something old and dirty.” *Cohen, S.A., DeFrancia, K.L., and Martinez, H.J., 2016, J Environ. Stud. Sci., 6, 231-238, DOI: 10.1007/s13412-016-0368-7
- 9. A study for ESA Space Environment – Space Debris (Vol. 3) • Review historical and proposed future small satellite activities and associated technologies; • Perform long-term projections using three evolutionary codes; and • Conduct a detailed analysis of the results of the first two activities, to understand the sensitivity of the debris environment to key satellite and constellation parameters. Results from the simulations were presented @IAC in 2016 and at the European Conference on Space Debris in 2017
- 10. Space Environment – Space Debris (Vol. 3) Debris models Three evolutionary debris models: • DAMAGE (University of Southampton) • LUCA (Technische Universität Braunschweig) • SDM (IFAC-CNR) All evolutionary models: • Have full 3D capability • Use the NASA breakup model (different implementations) • Have different orbital propagators and collision prediction algorithms • Have been cross-validated (in previous IADC/ESA studies) – LUCA was an exception
- 11. Space Environment – Space Debris (Vol. 3) Reference case • Initial population: all objects ≥ 10 cm with perigee < 2000 km in orbit on 1 Jan 2013 (data from MASTER) • Future launch traffic: repeat 2005-2012 launch cycle (data from MASTER) • Projection period: 1 Jan 2013 to 1 Jan 2213 • Post-mission disposal (PMD) of 90% of spacecraft and rocket bodies to a 25- year orbit • No explosions • 50 Monte Carlo runs
- 12. Space Environment – Space Debris (Vol. 3) Baseline constellation case • Reference case for background traffic • Walker-delta constellation comprising 1080 satellites in 20 orbital planes at 1100 km altitude and inclined at 85° • Satellite design lifetime of 5 years, 200 kg and 1 sq. metre • Build-up phase from 1 Jan 2018 to 1 Jan 2021 • Replenishment phase from 1 Jan 2021 to 1 Jan 2070 (50 years) • PMD of 90% of constellation spacecraft to a 400 × 1100 km orbit • Immediate de-orbit of rocket bodies used to launch constellation • No explosions in constellation
- 13. Overview of lecture 32 • In this lecture we looked back to previous lectures to remind ourselves why constellations of satellites in LEO are useful and why they might present problems for the space environment • We then focused on a simulation study conducted for ESA: – Aiming to understand the sensitivity of the debris environment to key satellite and constellation parameters and to determine whether we can use this information to design and build better constellations • The results from this study will be included in the next lecture Space Environment – Space Debris (Vol. 3)
- 14. Activities • Revisit SESA3041/6079 lectures on orbit design/constellations: – Design drivers (especially latency) – Constellation designs (e.g. Walker- Star v Walker-Delta) – Constellation maintenance (e.g. Iridium) – Constellation disposal (e.g. Iridium v Globalstar) • The ESA simulation study is reported in a paper that is available to you on the Blackboard site. You can read to gain a further insight into the work Space Environment – Space Debris (Vol. 3)