MIT ALUMNI CLUB APRIL 8, 2014 THE ORBITAL DEBRIS HAZARD FACT OR FICTION DR. DARREN MCKNIGHT 1
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M I T AL U M N I C L U B AP R I L 8 , 2 0 1 4
THE ORBITAL DEBRIS HAZARDFACT OR FICTION
DR. DARREN MCKNIGHT
1
Good News and Bad NewsOn “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
SATELLITE BOX SCORE [~16,900] – 12MAR2014ALL COUNTRIES WITH > 100 OBJECTS
30 1000 2000 3000 4000 5000 6000 7000
Russia
France
India
Japan
China
USA
ROW
Payloads
Rocket Bodies
Debris
Rest ofthe World
SPACE DEBRIS GROWTHTWO LARGE EVENTS HAVE DRIVEN GROWTH OVER LAST 10 YEARS
4Figure: Compliments of NASA/JSC, Nick Johnson
NATURAL VS ARTIFICIAL SPACE DEBRISSIZE, FLUX, DENSITY, AND VELOCITY ARE ALL DIFFERENT
5
Figure: Provided by NASA/JSC, appeared in Technical Report on Space Debris to UN, 1999
Orbital Debris Environm ent
1.0E-8
1.0E-7
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
0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000
Diameter [cm]
Cro
ss-s
ectio
nal F
lux
of a
Giv
en S
ize
and
Larg
er [N
umbe
r/m2 - Y
r]
Meteoroids, 400 km
Haystack flux, 350-600 km
HAX Flux 450-600 km
Catalog Flux 450-600 km
LDEF IDE, 300-400 km
SMM im pacts
LDEF craters (Hum es)
HST Impacts (Drolshagen),500 kmSpace Flyer Unit, 480 km
Goldstone radar, 300-600 km
SMM holes
SMM craters, 500-570 km
LDEF craters (Horz)
EuReCa Impacts(Dro lshagen), 500 kmMeteoroids: smaller, less dense,
faster, less populous in LEO except in the 100 micron size range; in GEO persistent meteoroids have caused several failures
Potential Encounters Flight Safety InstabilityLEO: VR ~ 10 km/s
Source: McKnight and Di Pentino, “Controlling the Future Growth of Orbital Debris”, ISU Space Sustainability Conference, Strasbourg, France, February 2012
“Trackable” Fragments
LNT.
OperationalSatellites
Derelict Objects
OBSERVATIONCascading effect known asKessler Syndrome will takedecades to manifest itself, not hours… even though mathematically we havesurpassed the “critical density” in some parts of LEO.
Two Derelicts
Destroyed
. . . . . . . . . .
II III
. . . . . . . . . . . . . . . . . . . .
Destroy DerelictII
III
Degrade or Terminate Mission
I
. . . . . . . . . .10,000 2,000
I
One Derelict Object?
6
6E-8
5E-8
4E-8
3E-8
2E-8
1E-8
0
Mapping of Space DebrisIridium and C2251790km in Feb 2009Major collision event(80% still in orbit; 20%will remain in orbitpast 2040)
Chinese breakup eventFengyun-1C860km in Jan 2007Major intentional collision(91% still in orbit; 33% will remain in orbit past 2040)
7Data plot courtesy of NASA/JSC
Trackable(Catalog)SpatialDensity(#/km3)
200 400 600 800 1000 1200 1400 1600 1800 2000Altitude (km)
ISS
Hubble
Tiangong
Fengyun-1C vs “Gravity”
Fengyun-1C (Reality)• 860km/750kg• 3,000 cataloged pieces• Altitude range of initial debris
spread 0-4000km but ± 150km for about 75%
• Potential “targets” are many operational satellites whose aggregate collision cross-section 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
Debris is Distributed In AltitudeGabbard Diagram for Fengyun-1C
9
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…
LEO Breakup EvolutionFengyun-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
10Figure compliments of NASA/JSC
One Month Six Months One Year
Probability of Collision (PC)• PC = VR * SPD * AC * T
– PC = probability of collision– VR = relative velocity– SPD = spatial density
= number of objects per km3
– AC = collision cross-section
– T = time over which PC is determined
• Gravity Scenario– VR = 10 km/s– AC = 900 m2 (ISS only) or
7500m2 w/solar arrays 11
V
MI
V
SPD
AC
Collision Hazard Evaluation/EvolutionWorst 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
12
Time After Fragmentation Total PC
Probability ofEncountering
Cloud
PC Within Cloud
Number of Fragments Used
(Out of 3000)
Time in Cloud
10 sec 4x10-11
One pass ~5x10-11 ~0.75 ~3000 ~0.1 sec
75 min(3/4 orbit)
4x10-8
One pass ~9x10-5 ~4x10-4 ~2500 ~30 sec
6 months 4x10-6
Per orbit ~1 ~4x10-6 ~1500 ~90 min
Debris will rapidly decay at this altitude so hazard will diminish quickly over time
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 anti-satellite system and a lot of luck.
13
“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 hazard14
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
FOUR “MAINSTREAM” AREASLIKELY 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 anyADR system except for propulsive tug
16
• Propulsive Tug• Traditional propulsion system still the
most mature capability• High impulse and controllability for
reentry risk mitigation• Exemplar for several satellite
servicing initiatives
• Solar Sail• Uses solar photon
pressure to move derelicts
• Similar systems deployed previously but not for operational ADR applications
• Fragile system & slow deorbit process
THREE “NICHE” EFFORTSNOT LIKELY TO EVER BE FIELDED
• 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
• Laser Removal from ground or space
• No need to detumbleor even go to space for groundbased version
• Physics of dwell time and laser interaction are unproven
• Feasibility for ADR unclear
17
• 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
ADR-RELATED OBSERVATIONSKEY 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
18SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63rd International Astronautical Congress, Naples, IT; October 2012.
19
1. Identify2. React
3. Deflect
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.
JCA Operation
Ground Detection
Original Orbit
New Orbit
Launch Vehicle Trajectory
Aircraft Trajectory
4. Prevent
JCA Operations:Prevent imminent orbital collision w/o going into orbit
SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63rd International Astronautical Congress, Naples, IT; October 2012.
PREVENTING DERELICT COLLISIONS (PDC)ADR AND JCA
Removal Avoidance
Active Debris Removal (ADR)-Requires many launches-Requires grapple/detumble-Execute over decades-Manage reentry risk
STRATEGIC - Statistical
Just-In-Time CA (JCA)-Want low false alarms-Need enhanced el set accuracy-Hourly/daily response-No reentry risk
TACTICAL - Deterministic
20
SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63rd International Astronautical Congress, Naples, IT; October 2012.
ADR AND JCA (PDC)BOTH ARE DIFFICULT AND EXPENSIVE
ADR JCA
Number of objects moved/removed per collision prevented
Costs per collision prevented
Game Changer(s)Needed
21
~30-50 ~5-3,000
~$100M’s-$B’s ~$10M’s-$10B’s
Improve el set accuracy by 25x (250m 10m)
andballistic launch less
than $1M
10s-100s of derelicts removed per launch
SYSTEM ENGINEERING ANALYSIS OF DERELICT COLLISION PREVENTION OPTIONS, 63rd International Astronautical Congress, Naples, IT; October 2012.
PDC REALITIES“PAY ME NOW OR PAY ME MORE LATER”
• Timing for PDC…
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
Operational Satellites
LEO vs GEOGeosynchronous Orbit
(GEO)35,785 ± 200km
i = 0 -15°
400,000,000,000 km3
~ 450
~ 3,000
Synchronized in time and clustered by altitude and
longitude
20-800 m/s
Low Earth Orbit (LEO)400-2000km
i = 0-135°
20,000,000 km3
~ 450
~ 12,000
Randomly distributed by longitude and latitude but
clustered by altitude
6-14 km/s
<<< 20,000x
=
Volume
4x >Objects > 10cm
Orbital Distribution
23Collision Velocity
20x >
Contrasting LEO and GEOAverage Spatial Density (SPD): Number of objects per km3
LEO Peaks ~ 5E-8 > 55x > GEO Peaks ~ 9E-10
1.E-13
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
0 10000 20000 30000 40000
Spat
ial D
ensi
ty (n
umbe
r/km
3 )
Altitude (km)Data plot courtesy of NASA/JSC
The “mean is often meaningless”
Gravity Wells in GEO
25
• 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)
-150 -100 -50 0 50 100 150Longitude (deg)
circular circular
Period of Oscillation
10 days
90% @ 2-3yrs
6 yrs
2 yrs
4 yrs
90% @ 2-3yrs
Objects in the Wells
26
Characteristic 75° East Well
105° West Well
Trapped in Both Wells(Left at “hills”)
Payload: Radugas (29),Gorizonts (9), Ekrans (8), etc.
85 40 13
Rocket Body: Largely Proton-K Fourth Stages
18 0 3
Debris: 2006 Feng Yun and1978 Ekran 2
2 0 0
Total 105(75% Russian)
40(2/3 US)
16(75% Russian)
27
Probability of Collision at GEOLongitudinally-Dependent
Note: Peak hazard at center of wells is
only 10x below muchof LEO.
GEO Video: Inertial24hr Larger Simulation
28
GEO Video: Earth-CenteredDEC 2010
29
GEO Video: InertialExcel Simulation of Only Derelicts
30
Proton Rocket Body Explosion in GEOSimulation by University of Colorado
31
>Breakup at 83.7°E>Near center of eastern well>All six trackable fragments remained trapped in the Eastern well
Hazard Understanding in GEO
32
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
33Hazard is low but no drag so any mistake will linger…
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
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