THE ORBITAL DEBRIS HAZARD FACT OR FICTION

Transcription

1 THE ORBITAL DEBRIS HAZARD FACT OR FICTION DR. DARREN MCKNIGHT MIT ALUMNI CLUB APRIL 8,

2 Good News and Bad News On Gravity Good News Sorry to ruin your fun but The exact sequence of events portrayed in Gravity has zero probability of occurring Wrong orbits for several objects altitudes and inclinations The general sequence of events portrayed in Gravity has a very near zero probability of occurring (~1/100,000,000) Will calculate probabilities for one breakup directly hitting the ISS once The Gravity-depicted chain reaction is many orders of magnitude less likely Bad News Over 200 explosions and collisions that have occurred in space have produced an impact hazard from orbital debris in many regions The hazard will continue to increase if current mitigation practices are not followed closely and then followed with derelict collision prevention operations 2

3 SATELLITE BOX SCORE [~16,900] 12MAR2014 ALL COUNTRIES WITH > 100 OBJECTS Rest of the World ROW USA China Japan India Payloads Rocket Bodies Debris France Russia

4 SPACE DEBRIS GROWTH TWO LARGE EVENTS HAVE DRIVEN GROWTH OVER LAST 10 YEARS Figure: Compliments of NASA/JSC, Nick Johnson 4

5 Cross-sectional Flux of a Given Size and Larger [Number/m 2 - Yr] 1.0E+6 1.0E+5 1.0E+4 1.0E+3 1.0E+2 1.0E+1 1.0E+0 1.0E-1 1.0E-2 1.0E-3 1.0E-4 1.0E-5 1.0E-6 1.0E-7 1.0E-8 NATURAL VS ARTIFICIAL SPACE DEBRIS SIZE, FLUX, DENSITY, AND VELOCITY ARE ALL DIFFERENT Orbital Debris Environment Meteoroids: smaller, less dense, faster, less populous in LEO except in the 100 micron size range; in GEO persistent meteoroids have caused several failures Meteoroids, 400 km Haystack flux, km HAX Flux km Catalog Flux km LDEF IDE, km SMM impacts LDEF craters (Humes) HST Impacts (Drolshagen), 500 km Space Flyer Unit, 480 km Goldstone radar, km SMM holes SMM craters, km LDEF craters (Horz) EuReCa Impacts (Drolshagen), 500 km Diameter [cm] Figure: Provided by NASA/JSC, appeared in Technical Report on Space Debris to UN,

6 LNT. Potential Encounters Flight Safety Instability LEO: VR ~ 10 km/s Trackable Fragments II Destroy Derelict II 10,000 2,000 III Derelict Objects OBSERVATION Cascading effect known as Kessler Syndrome will take decades to manifest itself, not hours even though mathematically we have surpassed the critical density in some parts of LEO. One Derelict Object? I I III Two Derelicts Destroyed Operational Satellites Degrade or Terminate Mission 6 Source: McKnight and Di Pentino, Controlling the Future Growth of Orbital Debris, ISU Space Sustainability Conference, Strasbourg, France, February 2012

7 Mapping of Space Debris Iridium and C km in Feb 2009 Major collision event (80% still in orbit; 20% will remain in orbit 6E-8 past 2040) Chinese breakup event Fengyun-1C 860km in Jan 2007 Major intentional collision (91% still in orbit; 33% will remain in orbit past 2040) Trackable (Catalog) Spatial Density (#/km 3 ) 5E-8 4E-8 3E-8 2E-8 Hubble 1E-8 Tiangong Data plot courtesy of NASA/JSC 0 ISS Altitude (km) 7

8 Fengyun-1C vs Gravity Fengyun-1C (Reality) 860km/750kg 3,000 cataloged pieces Altitude range of initial debris spread km but ± 150km for about 75% Potential targets are many operational satellites whose aggregate collision crosssection exceeds ISS No collisions between resulting trackable debris and other cataloged objects over last six years Gravity 420km/750kg 3,000 cataloged pieces Altitude range of initial debris spread ± 150km from 2,500 of them Same spread of debris would put half onto reentry trajectories within 2 weeks Two collisions occurred within several hours ISS shown getting struck multiple times 8

9 Debris is Distributed In Altitude Gabbard Diagram for Fengyun-1C Source: Pardini, C. and Anselmo, L., Evolution of the Debris Cloud Generated by the Fengyun-1C Fragmentation Event Debris distributed across wide range of altitudes Reentry to 4000km Majority of debris stayed within ± 150km Collisions spread debris significantly This is both good and bad 9

10 LEO Breakup Evolution Fengyun-1C Cloud Depending on orbit Cloud Torus Clam shell Truncated shell Pinch point remains for weeks Evolution rate in LEO depends on inclination and magnitude of breakup One Month Six Months One Year Figure compliments of NASA/JSC 10

11 Probability of Collision (PC) PC = VR * SPD * AC * T PC = probability of collision VR = relative velocity SPD = spatial density = number of objects per km 3 AC = collision cross-section T = time over which PC is determined Gravity Scenario VR = 10 km/s AC = 900 m 2 (ISS only) or 7500m 2 w/solar arrays 11 V AC MI V SPD

12 Collision Hazard Evaluation/Evolution Worst Case: Used high-end ISS size and debris cloud counts Probability of one strike >>> probability of two or more impacts (as shown in the movie) Cloud of debris is a large undulating ellipsoid that dismantles over time Total PC = Probability of Encountering Cloud * Probability of Collision While in the Cloud Time After Fragmentation Total PC Probability of Encountering Cloud PC Within Cloud Number of Fragments Used (Out of 3000) Time in Cloud 10 sec 75 min (3/4 orbit) 6 months 4x10-11 One pass 4x10-8 One pass 4x10-6 Per orbit ~5x10-11 ~0.75 ~3000 ~0.1 sec ~9x10-5 ~4x10-4 ~2500 ~30 sec ~1 ~4x10-6 ~1500 ~90 min Debris will rapidly decay at this altitude so hazard will diminish quickly over time 12

13 Alternative Context for Gravity To Increase Physical Validity of Plot Proposed by Don Kessler Scenario could have been set up with: The orbits of major assets were different than they are now... plus, not only did no one follow the 25-year rule, the usage of satellites in LEO had significantly increased. NASA stopped using TDRS in GEO and switched to something like Iridium for communication. At great expense, NASA changed the orbital inclination of Hubble to match that of the ISS so that Hubble could be easily serviced by the ISS. China liked that approach and launched as planned in 2020, but into a near-by orbit. Hubble had proven so successful that not only was servicing it a matter of national pride, the Space Shuttle was put back into service so that when Hubble was finally retired, it could safely be returned to Earth to go into the Smithsonian. All these events provided a perfect target for some adversary to conduct an anti-satellite test that would create debris specifically to disable these three systems to (re)establish their leadership in space... as the result of an "accident". For this scenario to have been effective, it still would have required a significant antisatellite system and a lot of luck. 13

14 Gravity - Epilogue Go and get Gravity on DVD and enjoy over and over Do not base funding decisions or engineering options on the portrayal of events in Gravity Orbital debris is a growing hazard that needs to be addressed soon to prevent a measurable degradation in operational lifetimes of LEO satellites in the future Hazard growth is uncertain due to lack of empirical collision data and the large range of potential collision events Watch for massive collision analysis in Fall of 2014 Active Debris Removal (ADR) seen as necessity to manage future growth of debris hazard 14

15 ADR NOT CONSIDERED URGENT BUT MAYBE SHOULD BE USG National Space Policy (June 2010) called for NASA and DoD to pursue R&D on ADR, reducing hazards, and increasing understanding of debris environment. NASA Centralized funding and policy implementation through NASA/HQ. Johnson Space Center is center of excellence for orbital debris mitigation. Several other centers and Office of Chief Technologist have unique contributions. Space Technology Program applying resources for concept exploration and technology development. DoD ADR activities performed largely in labs (NRL, APL, AFRL, etc.) and the Defense Advanced Research Programs Agency (DARPA). Regular (at least annual) NASA/DoD OD Working Group meetings cover a full range of OD efforts to include ADR. 15

16 FOUR MAINSTREAM AREAS LIKELY TO BE FIELDED IN NEXT DECADE EDDE (ElectroDynamic Debris Eliminator) E-tether uses Earth s magnetic field to create propulsive force Use force to both rendezvous for grappling and to move derelict Some partially successful component testing in the past GOLD (Gossamer Orbit Lowering Device) Inflatable Simple, effective Better long-term collision risk than any ADR system except for propulsive tug Solar Sail Uses solar photon pressure to move derelicts Similar systems deployed previously but not for operational ADR applications Fragile system & slow deorbit process Propulsive Tug Traditional propulsion system still the most mature capability High impulse and controllability for reentry risk mitigation Exemplar for several satellite servicing initiatives 16

17 THREE NICHE EFFORTS NOT LIKELY TO EVER BE FIELDED Laser Removal from ground or space No need to detumble or even go to space for groundbased version Physics of dwell time and laser interaction are unproven Feasibility for ADR unclear Tungsten Dust Remove derelicts by depositing tons of dust in space to wash out medium-large debris Significant effects on operational spacecraft Feasible only for start over mode Geosynchronous Large Debris Reorbiter (GLiDeR) Contactless-coupling plus ion thrusters in GEO only No need to detumble Unproven, limited applications Deposit in GEO graveyard, not deorbit 17

18 ADR-RELATED OBSERVATIONS KEY ISSUES NOT BEING ADDRESSED 1. Need to examine metric for success for ADR of large derelict objects Environmental stability is the common factor discussed but reduction in satellite operational lifetimes from collisions with nontrackable/lethal debris fragments might be more relevant (i.e. flight safety) 2. Detumbling of derelicts is often overlooked May be significant component of solution 3. Include Just-in-Time Collision Avoidance (JCA) with ADR for derelict collision prevention mission space 18 SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63 rd International Astronautical Congress, Naples, IT; October 2012.

19 JCA Operations: Prevent imminent JCA orbital Operation collision w/o going into orbit 1. Identify: Ground and orbital systems detect imminent collision. 2. React: Air-launch system is mobilized with JCA system on board. 3. Deflect: JCA system is deployed to induce a slight change in the orbit of one of the objects involved by deploying cloud of high density gas. 4. Prevent: If the object s orbit is changed enough the collision will be prevented. Original Orbit Ground Detection Aircraft Trajectory Launch Vehicle Trajectory New Orbit 3. Deflect 4. Prevent 1. Identify 2. React 19 SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63 rd International Astronautical Congress, Naples, IT; October 2012.

20 SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63 rd International Astronautical Congress, Naples, IT; October PREVENTING DERELICT COLLISIONS (PDC) ADR AND JCA Removal Active Debris Removal (ADR) -Requires many launches -Requires grapple/detumble -Execute over decades -Manage reentry risk STRATEGIC - Statistical Avoidance Just-In-Time CA (JCA) -Want low false alarms -Need enhanced el set accuracy -Hourly/daily response -No reentry risk TACTICAL - Deterministic 20

21 SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63 rd International Astronautical Congress, Naples, IT; October ADR AND JCA (PDC) BOTH ARE DIFFICULT AND EXPENSIVE ADR JCA Number of objects moved/removed per collision prevented ~30-50 ~5-3,000 Costs per collision prevented Game Changer(s) Needed ~$100M s-$b s 10s-100s of derelicts removed per launch ~$10M s-$10b s Improve el set accuracy by 25x (250m 10m) and ballistic launch less than $1M 21

22 Timing for PDC PDC REALITIES PAY ME NOW OR PAY ME MORE LATER 1) research and development; 2) demonstrations; 3) industry scale-up; 4) legal/policy evolution and codification; 5) operations and maintenance; and 6) accrued benefits are uncertain. Tradeoff between acting too soon or acting too late needs to be examined. 22

23 LEO vs GEO Low Earth Orbit (LEO) km i = ,000,000 km 3 ~ 450 <<< 20,000x Volume = Operational Satellites Geosynchronous Orbit (GEO) 35,785 ± 200km i = ,000,000,000 km 3 ~ 450 ~ 12,000 Randomly distributed by longitude and latitude but clustered by altitude 4x > Objects > 10cm Orbital Distribution ~ 3,000 Synchronized in time and clustered by altitude and longitude 6-14 km/s 20x > Collision Velocity m/s 23

24 Contrasting LEO and GEO Average Spatial Density (SPD): Number of objects per km 3 LEO Peaks ~ 5E-8 > 55x > GEO Peaks ~ 9E-10 1.E-07 Spatial Density (number/km 3 ) 1.E-08 1.E-09 1.E-10 1.E-11 1.E-12 1.E Altitude (km) Data plot courtesy of NASA/JSC The mean is often meaningless

25 Gravity Wells in GEO Period of Oscillation 6 yrs 4 yrs circular 2-3yrs 2-3yrs circular 10 days 2 yrs Longitude (deg) Earth s deformities (relative to a perfect sphere) create geostationary longitudinal gravity wells Long-term stable positions at 75 E and 105 W (255 E) 25

26 Objects in the Wells Characteristic Payload: Radugas (29), Gorizonts (9), Ekrans (8), etc. 75 East Well 105 West Well Trapped in Both Wells (Left at hills ) Rocket Body: Largely Proton- K Fourth Stages Debris: 2006 Feng Yun and 1978 Ekran 2 Total 105 (75% Russian) (2/3 US) 16 (75% Russian) 26

27 Probability of Collision at GEO Longitudinally-Dependent Note: Peak hazard at center of wells is only 10x below much of LEO. 27

28 GEO Video: Inertial 24hr Larger Simulation 28

29 GEO Video: Earth-Centered DEC

30 GEO Video: Inertial Excel Simulation of Only Derelicts 30

31 Proton Rocket Body Explosion in GEO Simulation by University of Colorado >Breakup at 83.7 E >Near center of eastern well >All six trackable fragments remained trapped in the Eastern well 31

32 Hazard Understanding in GEO 32

33 Trends in GEO Rocket bodies still being abandoned near GEO 36 left over the last decade Mostly Russian not Chinese Non-zero inclination no longer means it is abandoned Complicates hazard calculations and characterization algorithms Low-thrust, high-efficiency constant thrusting operations makes SSA difficult GEO graveyard continues to be a concern potential source of future debris In late 2011, old GOES-10 in graveyard orbit (a full 355km above GEO) was jolted 20 km closer to GEO arc Most likely due to a collision from another graveyard object Hazard is low but no drag so any mistake will linger 33

34 SUMMARY Gravity is cool but not real accurate ADR will happen eventually to control debris growth in LEO JCA should be developed in tandem LEO GEO in many ways Lower collision velocities Lack of secular removal mechanisms in GEO GEO hazard will just gradually increase (never decrease) 34