Orbital Debris Prevention and Protection for GSFC projects February 2, 2010 GSFC Code 592 Contacts:...

Orbital Debris Prevention and Protection

for GSFC projects

February 2, 2010

GSFC Code 592

Contacts: Scott.Hull@NASA.gov

Ivonne.M.Rodriguez@nasa.gov

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

Problem Description

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

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

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

Long-term Growth of LEO Debris Population

Collision Predictions with and without disposal efforts

Debris Flux in the A-Train Orbit

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

Methods of Protection

• Mission Design

• Hardware Design

• Shielding

• Prevention

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

Debris density vs. Altitude

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

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

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

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

Light Gas Gun

Typical Whipple Shield Ballistic Limit Curve

Geometrical Shielding of Instrument Sensors

Sensor

Debris Baffle

Debris Particle

Orbital Debris Prevention

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

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

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

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

Passivation Scenarios to retain high reliability

VentTank

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

* Cataloged objects (> 10 cm)

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

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

Orbital Debris Removal

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

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

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

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$$$$$

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

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

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

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

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

NASA Orbital DebrisRequirements

NASA Orbital Debris Structure

Headquarters/OSMAODPO(at JSC)

JPL KSCGSFC

Policy

Technical Support

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

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

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

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

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

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

Large Objects vs. Small Objects

Large ObjectsCatastrophic impact

> 10 cm

Spacecraft average area

< 0.001 (1 in 1000)

Shielding ineffective

Small Objects

Prevents disposal

Based on design (typically <1 cm)

Critical component area

< 0.01 (1 in 100)

Shielding can be effective

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

Available Storage Orbits

35,986 km

35,286 km

2000 km

Low AltitudeStorage Orbit

Super GEOStorage Orbit

12 Hour Orbits

High AltitudeStorage Orbit

20,200 km

19,100 km

Earth Surface

Not to Scale

• 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

Debris Casualty Area (DCA)

When an object survives, a 0.3 m “man-border” is essentially added to the circumference of the object

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

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.

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.

GSFC Orbital Debris Contacts

• Scott Hull– 301-286-7597 (captioned)– Scott.Hull@NASA.gov

• Ivonne Rodriguez– 301-286-5837– Ivonne.M.Rodriguez@NASA.gov

Orbital Debris Prevention and Protection for GSFC projects February 2, 2010 GSFC Code 592 Contacts:...

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