Realities and Myths of Small Satellite Collision Risk Dan Oltrogge 3-5 November 2016

Transcription

1 Realities and Myths of Small Satellite Collision Risk Dan Oltrogge 3-5 November

2 Topics in this briefing Explore common misconceptions and realities associated with small satellites and collision risk Discuss sources of increasing LEO collision risk Assess average rate of LEO encounters Typical collision probability metrics not relevant Collisions, warnings, avoidance maneuvers LEO collision likelihood vs risk Concluding Remarks 2

3 Small S/C Collision Risk: Myth vs Reality Myth Reality Perception Why? Small S/C = high % of catalog Small satellite operators act irresponsibly compared to large S/C operators Only 0.7% of current RSO catalog, and only 0.07% of 2 cm catalog. As of 2011, half of CubeSats were placed in > 25 yr orbits. Responsible CubeSat operators + ISS deployments are now improving that ratio. Oltrogge and Leveque, An Evaluation of CubeSat Orbital Decay, SmallSat Conference, SSC11-VII-2, Logan UT Meanwhile, 40% of large satellite space actors violated UN COPUOS & IADC guidelines from * Morand, V., et al, Mitigation Rules Compliance in Low Earth Orbit, Intl. Assoc. for the Adv. of Space Safety, JSSC Vol. 1 No. 2, Dec Small S/C have small collision risk due to small size Small S/C don t impinge on others Collision probability a function of combined hardbody radius; infinitesimally-small S/C still have collision risk Any space object (regardless of size), impinges on other space operators 3

4 Small S/C Collision Risk: Myth vs Reality (cont.) Myth Reality Perception Why? CubeSats like a bullet w/orbit lifetimes much longer than big S/C For equivalent-density shapes, drag is inversely proportional to lineal dimension, such that CubeSat orbit lifetime is relatively shorter CubeSats are inexpensive Can be inexpensive to manufacture, though on a per-kilogram basis, some (i.e. 1 st builds) can be as much as $100K/kg - - on par with large satellites. And even if flight units were inexpensive, can still be expensive to fly using best practices. Collisions with very small S/C can yield as much debris as large S/C Large S/C have much more mass & are likely to generate much more debris if hit. This is genesis for Active Debris Removal (ADR) concept Collision risk is low ( Big Sky ) While true in some low-population orbit regimes, space population increased by as much as 100 X in last decade. Operator perception of safety typically exceeds reality. Collisions are more frequent now. 4

5 Small S/C Collision Risk: Myth vs Reality (cont.) Myth Reality Perception We would know if/when collisions occur, because operators routinely and transparently share such collision/anomaly info Is the small satellite community leaning forward? They don't know about SDA, or [best practices]". Dr George Nield, Space Symposium 2016 Adhering to 25-year lifetime is sufficient. Why? Insurance rates, stock holders, cultural inhibitions, customer confidence, competition can all contribute to a lack of transparency Several (Planet Labs & Terra Bella) are members of SDA. Also, small satellite operators working with SSA entities (e.g. JSpOC). Good if the small satellite community could be still more forwardleaning Best practice: Reenter as soon as is practical upon mission completion. Our international orbital debris mitigation efforts depend upon this. 5

6 Reality: Small S/C inherit a legacy of LEO debris Source: NASA 6

7 3D Spatial Density shows debris population increase Although perhaps not yet a dire situation, we have in just 10 years increased spatial density in select orbit regimes by up to two orders of magnitude X per decade!

8 Resulting in increased collision risk Feng Yun 1C intercept generated 3800 fragments, leading to 14,691 JSpOC-issued emergency-reportable CDMs for FY-1C debris from 2010 to May 2016, corresponding to 5,000 unique conjunction events* Iridium/Cosmos collision generated 2500 fragments, leading to numerous conjunctions & CDMs since 2009* Collisions cannot be undone Multiple Iridium fragmentation events since * Source: JSpOC, Sept

9 Myth: Laws prevent collisions and debris creation Article 6 of Outer Space Treaty (1967) requires authorization and continuing oversight of non-traditional services ( States Parties to the Treaty shall bear international responsibility for national activities in outer space, including the Moon and other celestial bodies, whether such activities are carried on by governmental agencies or by non-governmental entities, and for assuring that national activities are carried out in conformity with the provisions set forth in the present Treaty. The activities of non-governmental entities in outer space, including the Moon and other celestial bodies, shall require authorization and continuing supervision by the appropriate State Party to the Treaty. When activities are carried on in outer space, including the Moon and other celestial bodies, by an international organization, responsibility for compliance with this Treaty shall be borne both by the international organization and by the States Parties to the Treaty participating in such organization. In principle, launching country liable - - but enforcement is not the norm Some State Parties gain commercial launch advantage by being loose w/ these obligations Liability assigned to states ultimately, but you d have to prove such liability + treaty doesn t cover clean-up Space Code of Conduct an international Transparency and Confidence-Building Measure Subscription to this Code is open to all States, on a voluntary basis. This Code is not legally binding, and is without prejudice to applicable international and national law. Bringing the Code under the umbrella of the UN has invited procedural complications that have placed it in bureaucratic limbo - Space Code of Conduct is dead opinion of legal colleague Locally, some State Parties mandate adherence to ISO, CCSDS and ECSS standards Still the Wild West in space; regulators have no tools in their regulatory toolbox 9

10 LEO collision risk increasing for 5 primary reasons 1. Increased crowding in the LEO regime 2. Increasingly cheaper and easier launch access 3. Increasing quantities of satellites produced & flown 4. Plans for mega-constellations 5. Increased collision risk from past collisions that leave a lasting legacy (the gift that keeps giving) 10

11 What s the LEO RSO population? 11

12 Increasingly cheaper and easier launch access # S/C launched may increase dramatically as conventional launch platforms offer inexpensive space access (ULA, Vega, SpaceX, Nammo) Cheaper launch concepts may come to fruition Launch brokers (ISIS, ESA, NASA, Spaceflight) CubeCab wants to fire microsatellites into orbit from F-104 fighter jets DARPA small satellite launch concept Nammo Virgin Galactic 12

13 Increasing quantities of satellites Proliferation of CubeSats projected Modern 3D printing techniques, CNC machining and satellite kits make it easier to manufacture, mass produce and operate satellites of modest capability *Used by permission of author, Dr. Michael Swartwout, St. Louis University *Used by permission of author, Mr. Bill Doncaster of SpaceWorks 13

14 Mega-Constellations Large constellations planned, joining existing ones Some have even secured financing We ll analyze planned, existing and hypothetical constellations contained in this table to estimate LEO encounter rates Collisions, warnings (3km miss distance) and avoidance manoeuvres (1km miss distance) Caution: S/C and constellation characteristics from public sources # Operator # S/C Altitude (km) Inclination (deg) S/C Hardbody SIZE (full dimension in m) Secondary's Hardbody SIZE (full dimension in m) Combined Hardbody Radius (m) 1a Boeing V-band * b Boeing V-band * c Boeing V-band * CubeSat CubeSat 600 ( Planet) Hypothetical CubeSat Globalstar a Hawkeye b Hawkeye c Hawkeye Iridium LeoSat OneWeb Orbcomm SpaceX Spire Terra Bella

15 Assessing LEO collision and close approach risk Several ways to assess LEO conjunction encounter rates (for both warnings & actual collisions): Method 1: Surveys & anecdotal accounts of suspected collisions Method 2: Generate stats from SDC CA reports Method 3: Generate stats from JSpOC CDMs Method 4: Parametric AdvCAT of all LEO orbits Method 5: Encounter volumetric assessment Patent application filed 2015, Alfano & Oltrogge In higher-density, non-synodic (LEO) regimes: 2 Demonstrated that# encounters R encounter Method 6: Spatial density-based estimates Selected for its suitability, efficiency, generality and accuracy 15

16 Spatial density softens (misrepresents) actual risk 1D 1D and 2D spatial density portrayals deemphasize risk Even 3D representation misses synodic motion Previous studies failed to address these concerns 2D > 2 cm 2D > 2 cm post-collision 3D 2D Today 16

17 How often do space objects encounter each other? Volumetric incursion detection and encounter tool *,** : Detects if encounter can occur Counts incursions (N ENCOUNTER ) *Alfano, S. & Oltrogge, D., Volumetric Assessment of Encounter Probability, AAS , 2014 Astro Specialist Conf, San Diego CA Don t want M 1 bounding limits Want M 1 encounter limits **Alfano, S. & Oltrogge, D., Volumetric Encounter Analysis Enhancements, AAS , 2015 Astro Specialst Conf, Vail, CO 17

18 Sample: Iridium Volumetric Encounter Rates Increasing variability & deviation due to undersampling; Monte Carlo and spot-check methods become unstable Sweet Spot for y=mx+b fit in log-log space Increasing encounter rate variability & deviation due to spatial density altitude striation 18

19 Encounter rates stable in high-density LEO 19

20 2 What s driving R enc encounter rate relationship? 1. Increasing R enc linearly admits more RSOs having encounter potential from neighboring altitude bands 2. When encounter potential already exists, increasing R enc linearly increases encounter rate

21 Can also estimate average collision rate! Note: R enc 2 power law applies to LEO (homogeneous, dense, non-synodic) orbits. At GEO, power law still applies, but typically has smaller exponent) 21

22 Encounter rate similarities w/molecular gas dynamics Analogous to molecular Mean Free Path (λ) in gas dynamics On average, molecules travel distance of λ between collisions as f(density ρ = n = P ) V RT Δt molecular collision = λ 1 = v rms 2 π d 2 ρ v rms Average collision rate cannot indicate if, or when, a particular molecule (or satellite) will collide with another But does yield avg. collision risk α Radius 2! 22

23 Encounters in 10 years of non-intervention ops # Operator # S/C Current RSO Catalogue: Avg # Collisions in 10 yrs Current RSO Catalogue: Avg # 3km Warnings in 10 yrs Current RSO Catalogue: Avg # 1km Mnvrs in 10 yrs K-RSO 2 cm Catalogue: Avg # Collisions in 10 yrs 200K-RSO 2 cm Catalogue: Avg # 3km Warnings in 10 yrs 200K-RSO 2 cm Catalogue: Avg # 1km Mnvrs in 10 yrs 1a Boeing V-band ,426 43, ,392, ,515 1b Boeing V-band ,630 33, ,640, ,783 1c Boeing V-band ,931, , ,893,494 3,543,722 1 Boeing V-band ,631, , ,926,169 5,214,020 2 CubeSat ,687 3, ,532 28,836 3 CubeSat 600 ( Planet) ,376 18, ,556, ,096 4 CubeSat ,512 43, ,086, ,120 5 Globalstar ,871 2, ,527 56,503 6a HawkEye ,744 1, ,271 20,475 6b HawkEye ,739 1, ,239 13,471 6c HawkEye ,807 1, ,954 15,550 6 Hawkeye ,289 3, ,464 49,496 7 Iridium ,385 41, ,843, ,081 8 LeoSat ,405 11, ,281, ,497 9 OneWeb ,613 32, ,633, , Orbcomm ,602 10, , , SpaceX ,971, , ,177,201 8,019, Spire ,348 21, ,070, , Terra Bella ,878 3, ,144 71,794

24 Encounters in 10 years of non-intervention ops # Operator # S/C Current RSO Catalogue: Avg # Collisions in 10 yrs Current RSO Catalogue: Avg # 3km Warnings in 10 yrs Current RSO Catalogue: Avg # 1km Mnvrs in 10 yrs K-RSO 2 cm Catalogue: Avg # Collisions in 10 yrs 200K-RSO 2 cm Catalogue: Avg # 3km Warnings in 10 yrs 200K-RSO 2 cm Catalogue: Avg # 1km Mnvrs in 10 yrs 1a Boeing V-band ,426 43, ,392, ,515 1b Boeing V-band ,630 33, ,640, ,783 1c Boeing V-band ,931, , ,893,494 3,543,722 1 Boeing V-band ,631, , ,926,169 5,214,020 2 CubeSat ,687 3, ,532 28,836 3 CubeSat 600 ( Planet) ,376 18, ,556, ,096 4 CubeSat ,512 43, ,086, ,120 5 Globalstar ,871 2, ,527 56,503 6a HawkEye ,744 1, ,271 20,475 6b HawkEye ,739 1, ,239 13,471 6c HawkEye ,807 1, ,954 15,550 6 Hawkeye ,289 3, ,464 49,496 7 Iridium ,385 41, ,843, ,081 8 LeoSat ,405 11, ,281, ,497 9 OneWeb ,613 32, ,633, , Orbcomm ,602 10, , , SpaceX ,971, , ,177,201 8,019, Spire ,348 21, ,070, , Terra Bella ,878 3, ,144 71,794

25 Public RSOs: Who is at greatest collision risk? 25

26 Public RSOs: Who generates most warnings? 26

27 > 2 cm RSOs: Who is at greatest collision risk? 27

28 How can operators help prevent collisions? JSpOC SSA Data Sharing Agreement (free service) Commercial services exist to refine tracking & SoF Space Data Association (SoF & RFI mitigation) Small satellite-leaning membership fee structure AGI Commercial Space Operations Center (ComSpOC) is the first commercial multi-phenomenology SSA service; merges state-of-art processing w/data fusion, sensors Extensive optical, radar and passive RF sensor network Phased-Array Radar Fusion of operator ranging & optical obs Passive RF Optical Telescope 28

29 Concluding Remarks LEO will continue to get increasingly crowded CubeSats dominating newly-deployed objects due to their ease, low cost and rapidity of manufacture/launch/deploy/dispersion Mega constellations pose serious challenges & collision risk Imperative to seek authoritative, actionable SSA, CA and RFI analysis Automation of CA and RFI mitigation processes an absolute must have. CubeSats generally NOT the collision risk some portray; But: many CubeSat CA warnings in highly-populated orbits CA warnings warrant intense satellite operator scrutiny CA warnings can lead to avoidance maneuvers CubeSat ISS deploy minimizes post-mission lifetime AND ISS collision risk 29

30 Thank you and Questions 30 Dan Oltrogge