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Orbital Debris Prevention and Protection
for GSFC projects
February 2, 2010
GSFC Code 592
Contacts: [email protected]
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
Outline
• Problem Description
• Protection from Existing Debris
• Prevention of Future Debris
• Removal of Existing Debris
• NASA Requirements
• Conclusions
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Problem Description
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Why is Orbital Debris a Concern?
• On-orbit Environment– Currently
~ 19,000 objects >10 cm in size~ 300,000 objects >1 cm in sizeMillions of objects <1 mm in size
– Growing rapidly• Already self-propagating
• Tracking limitations• Spacecraft damage potential
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Debris Sources
• Launch• Operations
– Lack of proper disposal• Collisions
– Small collisions as well as large• Explosions
– Batteries– Pressure tanks (usually propulsion system)
• Meteoroids– Natural random environment– Meteor showers
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Explosions
• Batteries– Overcharge generates gas pressure– NiH most susceptible, Li-ion less so
• Most Li-ion cells have cutoff switches• Li-ion must never be recharged after full drain
• Pressure tanks– Fuel and oxidizer mix from leaky valve– Overpressure from regulator failure– Small debris object impact
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Long-term Growth of LEO Debris Population
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Collision Predictions with and without disposal efforts
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Debris Flux in the A-Train Orbit
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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GSFC Missions(a wealth of diversity)
• Quantity– Typically about 20 Space Science and 10 Earth Science
missions actively operational– Usually ~70 total missions, including development
• Orbits– Typically LEO (300 to 700km)– A few GEO– A few high eccentricity orbits and Lagrange points
• Propulsion – About 60% have propulsion systems
• Construction– Many high Z materials in detectors– Substantial use of Titanium– Glass mirrors and lenses
10Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
Orbital Debris Protection
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Methods of Protection
• Mission Design
• Hardware Design
• Shielding
• Prevention
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Mission Design Considerations
• Orbit selection– Debris peaks at ~750, 900, and 1400 km– Usually driven by science needs, though
• Operations– Orbit change maneuvers to avoid predicted
close approaches– Reorient the spacecraft during meteor
showers or close approaches– Have plans in place to help diagnose and/or
respond to debris hits
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Debris density vs. Altitude
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Hardware Design Considerations
• Component location– Nadir and zenith are lowest exposure– Ram and sides are highest exposure– Take advantage of shadowing
• Wall thickness
• Add shielding
• Redundancy
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Shielding Considerations
• Mass
• Complexity
• Multi-wall much better than thicker wall– Depends on spacing– Material selection is important
• Direction of threat
• Use geometry to shield instruments
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Multi-wall Shield Mechanisms
• ‘Bumper’ layer– Breaks up and melts projectile– High temperature material (Nextel does well)
• Inner layer– Traps the slower moving secondary debris– High toughness material (Kevlar does well)
• Back wall– Usually the box wall– Provides the last line of defense– Can generate spalling from inside surface, even if not penetrated
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Shield Testing
• High velocity impact guns on actual samples– >$10,000 per shot– 3 to ~11 km/sec range (slow for
meteoroids)
• Tested across a range of velocities, sizes, impact angles, and densities
• Produces ballistic limit curves
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Light Gas Gun
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Typical Whipple Shield Ballistic Limit Curve
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Geometrical Shielding of Instrument Sensors
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
Sensor
Debris Baffle
Debris Particle
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Orbital Debris Prevention
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Prevention Methods
• Design for Safety• End of Mission Disposal
– Reentry (active or passive)– Storage orbits
• End of Mission Passivation– Disconnect battery– Vent pressure sources– Essentially minimize residual stored energy
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Design for Safetyduring and after the mission
• Pressure tank design– Burst strength >2X MEOP recommended– Composite tanks may be more robust
• Battery selection– Usually driven by power demands– NiH is an explosion risk if overcharged– Li-ion less susceptible, but has strict charging
considerations• Component location
– Locate tanks and batteries near center of spacecraft – Make use of multi-wall shielding in reverse
• Responsible DisposalOrbital Debris Prevention and Protection
Scott Hull, February 2, 201024
Battery Passivation
• Disconnect the battery from the charging circuit– Relays, instead of logic (redundant in parallel)
– Reducing charging rate is not enough
• Leave small loads attached to the bus
• Disable failure detection and correction modes at EOM
• Never recharge Li-ion after a deep dischargeOrbital Debris Prevention and Protection
Scott Hull, February 2, 201025
Pressure Tank Passivation
• Design for venting– Redundant valves in series on vent lines– Consider effects of cold gas thrust– Add vent lines for pressurant tanks or
diaphragms
• Vent pressure as much as practical– Latching valves left open if possible– Very small amount often remains
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Passivation Scenarios to retain high reliability
VentTank
+
-
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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LoadCharge
Recent Major Debris Events
Vehicle Type Date Objects* Cause
Fengyun 1C(PRC)
Spacecraft 1/11/2007 1999-025
~2850 Deliberate destruction
CBERS 1(PRC/BRZ)
Spacecraft 2/18/2007 1999-057
~425 Unpassivated propellant
Briz – M(CIS)
Launch Vehicle 2/19/2007 2006-006
~150 Unpassivated propellant
Iridium - Cosmos
Spacecraft x 2 2/10/2009 1997-051 1993-036
~1650 Collision
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
* Cataloged objects (> 10 cm)
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Chemical Energy Passivation
• Hypergolic Fluids– Can react outside spacecraft– Vent separately, use opposing thrusters, or
use propellant for disposal
• Monopropellant– Be sure catalyst bed heaters are off
• Corrosive Fluids
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Postmission Disposal Methods
• Reentry– Controlled or uncontrolled– With or without orbit lowering– Depends on demisability, orbit, propulsion
capacity, guidance reliability
• Storage– 2000 km to GEO-200 km– Above GEO+200 km
• RetrievalOrbital Debris Prevention and Protection
Scott Hull, February 2, 201030
Orbital Debris Removal
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Challenges to Debris Removal
• Cost– Value of removing a rocket body ~$3.7M– Cost of removing a rocket body ~10X value– Ignores the less tangible value of access to the orbit
• Legal Aspects– Salvage rights– Removal responsibility– No international jurisdiction or agreements
• Target Selection• Technology Selection
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Target Selectionfor debris removal
• Orbit selection– LEO: worst density, mostly science missions
(government funding)– GEO: low density, mostly commercial missions
(industry funding)• Debris size selection
– 1 mm to 1 cm: high quantity, low damage– 1 cm to 10 cm: moderate quantity, moderate
damage, not trackable– >10 cm: low quantity, catastrophic damage,
trackableOrbital Debris Prevention and Protection
Scott Hull, February 2, 201033
Technology Selectionfor debris removal
• Each is suited to a set of orbit and size conditions
• Cost varies widely• Most have yet to be demonstrated
– Tethers have been used for electric generation, but not necessarily drag or propulsion
– Some spacecraft retrieval and on-orbit servicing experience
• No single solution will work for all applications and orbits
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Examples of Removal Techniques
Technique Target Size Orbit Range Relative Cost
Ground Based Lasers
1 cm to 10 cm All of LEO $$
Drag Enhancement
10 cm to 5 m LEO <700 km $$$
Sweepers< 10 cm LEO $
Space Tugs (ADR)
1 m to 5 mLEO through
GEO$$$$$
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Lasers
Mechanism: Laser beam strikes one side of a piece of debris, causing a thin layer of material to evaporate – effectively like a rocket exhaust
Debris Size Range: 1 – 10 cm (bullets)Orbits: All of LEOBenefits: Ground based, cheaper, existing
hardwareChallenges: Undetectable debris size range;
unknown object material; tumbling objectsOrbital Debris Prevention and Protection
Scott Hull, February 2, 201036
Collection Devices (AKA Sweepers)
Mechanism: Place a relatively large (1 m to 1000 m diameter) rigidized balloon or foam ball in orbit to drift around, collecting small debris impacts until its eventual reentry (some are ballistic launch, not orbital)
Debris Size Range: < 10 cm (bullets)Orbits: LEOBenefits: Totally passive (launch and forget),
inexpensive, lightweightChallenges: Collision risk with large debris; many
needed to make a difference in small debris population
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Drag Augmentation
Mechanism: Attach a relatively large (10 to 1000 x object area) thin balloon or sail to object, and reduce its orbit by drag
Debris Size Range: 10 cm – 5 m (hubcaps to cars)
Orbits: LEO up to about 700 kmBenefits: Light weight, passive, fast decay,
sweeps small debrisChallenges: Collision risk; rendezvous and
capture difficultiesOrbital Debris Prevention and Protection
Scott Hull, February 2, 2010 38
Active Direct Removal(Space Tug)
Mechanism: Grapple object, and either attach a propulsion device or directly perform a controlled reentry
Debris Size Range: 1 – 5 m (cars)Orbits: LEO through GEOBenefits: Positive control of debris destination;
main vehicle may be reusableChallenges: Highest launch cost; rendezvous
and capture of tumbling objects
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Autonomous Rendezvous and Capture
• Required for most large debris removal• ‘Uncooperative’ targets
– Rocket bodies– Derelict spacecraft – Malfunctioning spacecraft
• Assumed to be tumbling• Approach and grapple, without collision• Combination of sensors
– Visible– Infrared– Radar/ LIDAR
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Sample of Capture Ideas
• Soft Capture Mechanism (equip all future missions with one)
• Robot Arms• Tethered Net• Free-flying Net• Tethered Free-flyer with Grapple Fixture• Lasso• Harpoon• Many others
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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NASA Orbital DebrisRequirements
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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NASA Orbital Debris Structure
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Headquarters/OSMAODPO(at JSC)
ARC
JPL KSCGSFC
Policy
Technical Support
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
WSFC
ODARs andEOMPs
Resources Policy
Orbital Debris Structure at GSFC
• Combination of efforts from Codes 300, 400, and 500• Code 32X Chief Safety Officer
– Responsible to enforce the requirements• Code 4XX Project Manager
– Responsible for generating and submitting the documentation
• Code 592 Orbital Debris Engineer– Assist with technical aspects
• Code 5XX AETD Discipline Engineers– Provide the technical inputs and designs to help meet the
requirements
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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NPR 8715.6 ResponsibilitiesProgram/Project Manager
Pre-launch• Establish a project orbital debris mitigation activity• Provide copies of ODARs and EOMPs to OSMA
for review• Ensure implementation of NASA-STD 8719.14 Post-launch• Monitor spacecraft for debris or disposal threats• Follow NPD 8010.3A at EOM• Notify JSpOC of significant maneuvers • Conjunction assessments• Review and update EOMP annually
45Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
NASA-STD 8719.14 Technical Requirements
• 15 Main requirements, in 6 sections• There are requirements in the text, though• Self-assessment helps to prevent holes, but
doesn’t catch everything• Most heavily scrutinized are 4-1, 4-2, 5-2,
6-1, and 7-1• Disposal and passivation are considered to
be separate activities• Report basically follows the same structure
46Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
NASA-STD-8719.14 Requirements
Section 4.3 (2) Operational Debris
Section 4.4 (4) Explosions, Passivation, Intentional Break-up
Section 4.5 (2) Collisions
Section 4.6 (5) Postmission Disposal
Section 4.7 (1) Reentry Risk
Section 4.8 (1) Tethers
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Requirement Group 4.4Accidental Explosions
Req. 4.4-1: Risk of Accidental Explosions During the Mission– Need to assess and report a quantitative estimate
for explosion risk– < 0.001 probability for all credible failure modes
Req. 4.4-2: Risk of Accidental Postmission Explosions – Also referred to as passivation– Disconnect battery from charging circuit– Vent pressure• The concern is the risk to other spacecraft, and to
the long-term orbital environment
48Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
NASA-STD 8719.14 Requirement 4.5-2
Collision with Small Debris (S/C only)– Size based on ability to prevent postmission
disposal– Function of vulnerable component area,
inherent shielding, nominal mission lifetime, and object flux
– Each disposal-critical component must be examined from ALL directions
– < 0.01 probability requirement– DAS 2.0.1 must be used for this calculation
49Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
Large Objects vs. Small Objects
Large ObjectsCatastrophic impact
> 10 cm
Spacecraft average area
< 0.001 (1 in 1000)
Shielding ineffective
50
Small Objects
Prevents disposal
Based on design (typically <1 cm)
Critical component area
< 0.01 (1 in 100)
Shielding can be effective
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
NASA-STD 8719.14 Requirement 4.6-1
Disposal from LEO orbits (choose one)6-1 a. Atmospheric reentry
• Orbit decay within 25 years after end of mission• No more than 30 years total orbital lifetime• Can be Uncontrolled Reentry or Controlled
Reentry
6-1 b. Maneuver to a storage orbitPerigee > 2000 km, Apogee < GEO – 500km
6-1 c. Direct retrieval
51Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
Available Storage Orbits
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35,986 km
35,286 km
2000 km
Low AltitudeStorage Orbit
LEO
GEO
Super GEOStorage Orbit
12 Hour Orbits
High AltitudeStorage Orbit
20,200 km
19,100 km
Earth Surface
Not to Scale
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
NASA-STD 8719.14 Requirement 4.7-1
• Risk of Human Casualty– For objects with impact energy >15J– Risk < 0.0001 (1 in 10,000)– For controlled reentry:
• Uncontrolled Risk X Pf < 0.0001• No object closer than 370km to foreign
landmass, or 50km to US landmass of Antarctica
53Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
Debris Casualty Area (DCA)
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When an object survives, a 0.3 m “man-border” is essentially added to the circumference of the object
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
Effect of DCA on Mission Lifefor Controlled Reentry
• DCA x Pop Den x Pf for reentry < 0.0001
• As the operational mission progresses:– DCA is fixed by design– Population density increases very slowly– Pf increases more rapidly
• By reducing DCA as low as possible pre-launch, it extends the time until 1 in 10,000 is reached
• Assumes that sufficient fuel remains for extended operations and controlled reentry
55Orbital Debris Prevention and Protection
Scott Hull, February 2, 2010
Conclusions (1 of 2)
• The accumulation of debris in operational orbits is a real and growing concern.
• Collisions will dominate the generation of additional debris in the future.
• There are design techniques for protecting most spacecraft and instruments from the effects of orbital debris.
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Conclusions (2 of 2)
• While it is presently impractical to remove derelict objects from orbit, there are agreements and requirements in place to limit the addition of more debris.
• Disposal and passivation planning are critical to limiting the long-term rate of debris growth.
• Code 592 and JSC/ODPO can assist with design optimization as well as documentation.
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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GSFC Orbital Debris Contacts
• Scott Hull– 301-286-7597 (captioned)– [email protected]
• Ivonne Rodriguez– 301-286-5837– [email protected]
Orbital Debris Prevention and Protection Scott Hull, February 2, 2010
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Orbital Debris Prevention and Protection Scott Hull, February 2, 2010