The Threat Of Orbital Debris And Protecting NASA Space .

National Aeronautics and Space AdministrationThe Threat of Orbital Debris andProtecting NASA Space Assets fromSatellite Collisions28 April 2009

National Aeronautics and Space AdministrationExecutive Summary Collision avoidance processes are in place for all NASA human space flightmissions and for maneuverable robotic assets in low Earth orbit and within200 km of the geosynchronous orbit.– Required by NASA Procedural Requirements 8715.6A (Section 3.4). DoD screens for close approaches (conjunction assessments) and providesmiss distance and uncertainty information to NASA. NASA computes the probability of collision, analyzes the risk, and makesmaneuver decision. During 2008, this process led to five collision avoidance maneuvers:S p a c ec r a f tM a n e u v e r D a teO b je ct A v o id e dA ura2 6 - J u n -2 0 0 8T R IA D 1 d e b ri sC lo u d s at2 0 - J u l- 20 0 8D e l ta r o c k et b o d y d eb r isIS S2 7- A u g -2 0 0 8C o s m o s 2 4 2 1 d e b r isTD RS 51 -O c t-2 0 0 8C os m o s 1 8 8 8P A R A S O L (F ra n c e)1 9- O c t-2 0 0 8F e n g y u n -1 C de b r is2

National Aeronautics and Space AdministrationGrowth of the Satellite Population1960196519701975198019852005January 200919901995 95% of Tracked ObjectPopulation are Debris20003

National Aeronautics and Space AdministrationWhat is Orbital Debris? Space debris encompasses both natural (meteoroid) and artificial(man-made) particles. Meteoroids are in orbit about the Sun, while most artificial debris arein orbit about the Earth. Hence, the latter are more commonly referredto as orbital debris. Orbital debris is any man-made object in orbit about the Earth whichno longer serves a useful function. Non-functional spacecraft Abandoned launch vehicle stages Mission-related debris Fragmentation debris For most size regimes, the flux of orbital debris within 2000 km of theEarth’s surface already exceeds the flux of meteoroids.4

National Aeronautics and Space AdministrationRecent Growth of Satellite Populationin Low Earth OrbitThe growth of the cataloged satellite population during the past 15 yearshas been primarily influenced by China’s ASAT test in January 2007.5.E- 084.E- 08Spatial Density (objects per km3) Altitude ofChineseASAT testSite of 10FebruaryCollision19 9419 9920 043.E- 0820 092.E- 08ISSAltitudeRegime1.E- 080.E 002004006008001 0001 200A ltitu de (km )51 4001 60018 0020 00

National Aeronautics and Space AdministrationSatellite Environment Characterization NASA and DoD cooperate and share responsibilities for characterizing the satellite(including orbital debris) environment. DoD’s Space Surveillance Network discretely tracks objects as small as 5 cm in lowEarth orbit and about 1 m in geosynchronous orbit.–– Currently, 14,000 officially cataloged objects are still in orbit.Total tracked objects exceeds 19,000.Using special ground-based sensors and inspections of returned satellite surfaces,NASA statistically determines the extent of the population for objects less than 10cm.–Number of debris in Low-Earth Orbit (LEO)* 1 cm or greater exceeds 300,000. The combined results are used for spacecraft and launch vehicle design andoperations.*Low-Earth Orbit (LEO) refers orbits ranging in altitudes from up to 2000 km above the Earth’s surface;Geosynchronous Orbit (GEO) refers to orbits at 36,000 km above the Earth’s surface; at that distance,an orbits the Earth in a 24-hour period.6

National Aeronautics and Space AdministrationCollision Risks Collision risks are divided into three categories depending upon size ofthreat. 10 cm and larger: Conjunction assessments and collision avoidancemaneuvers are effective in countering objects which can be tracked by theU.S. Space Surveillance Network.– Collisions of this type are potentially catastrophic. 1 – 10 cm: Objects in this category are usually too small to track and toolarge to shield against.– Collisions of this type can disable or disrupt a mission. 1 cm: Debris shields can be effective in withstanding impacts of particlesin this category.– Unshielded portions of satellite subject can lead to mission degradation or loss. The greatest risk to space missions comes from non-trackable debris.7

National Aeronautics and Space AdministrationU.S. Space Surveillance NetworkOrganized as: Dedicated primaryTHULEGLOBUS IICLEARFYLINGDALES Collateral secondary Contributing contractedservicesCAVALIERBEALESOCORROLSSCCAPE CODAFSSSMOSSCOBRA DANEEGLINMAUI &MSSSKwajASCENSIONDIEGOGARCIATracking RadarDetection RadarLSSC Lincoln Space Surveillance CenterMillstone, Haystack, HAXMSSS Maui Space Surveillance System(former AMOS/MOTIF site)AFSSS Air Force Space Surveillance SystemImaging RadarOptical TelescopePassive Receiver8

National Aeronautics and Space AdministrationSpace Shuttle VulnerabilitiesPotential Shuttle Damage6.5Window ReplacementEVA Suit Penetration5.5Radiator PenetrationRCC Penetration4.5TPS Tile PenetrationCabin Penetration3.5Cargo Bay DamageGoldstone RadarsSpace Surveillance Network2.5Haystack Auxiliary RadarSpacecraftSurfaceInspections1.5Haystack Radar0.50.0010.010.11Debris Diameter in Centimeters9101001000

National Aeronautics and Space AdministrationDebris Environment for International Space Station1.E 031.E 02SSNCatalogne arlycomplete forobjectsgreater than10 cm1.E 01Flux (no/m2/year1.E 0020091.E-01No SSNtra cking datafor objectssmaller than 5cm1.E-021.E-03Some SSNdata onob jects 5 1 0 cm1.E-04Imp acts by debrissmaller than 0.3 cmnot critical to ISS1.E-051.E-061.E-070.00 10.010.11Particle Diameter (cm)1010100

National Aeronautics and Space AdministrationEvolution of NASA Collision Avoidance Process NASA implemented a conjunction assessment and collision avoidanceprocess for human spaceflight beginning with STS-26 in 1988.– Initially based upon simple miss distance and a 4-km by 10-km by 4-km ellipsoid(picture a protected football-shaped volume [keep out] around the Shuttle). Before launch of the first element of ISS in 1998, NASA and DoD jointlydeveloped and implemented a more sophisticated and higher fidelityconjunction assessment process for human spaceflight missions.– Also adopted by other USG national space assets. In 2005, NASA implemented a similar process for selected robotic assets,e.g., the Earth Observation System satellites in LEO and TDRSS in GEO. In 2007, NASA Procedural Requirements 8715.6 extended the conjunctionassessment process to all NASA maneuverable satellites within LEO andwithin 200 km of GEO.11

National Aeronautics and Space AdministrationBasic Conjunction Assessment andCollision Avoidance Process DoD maintains high accuracy satellite catalog on objects which pose athreat to designated NASA space assets.– Lower fidelity, publicly available data (“two-line element sets”) are NOT used. DoD’s Joint Space Operations Center (JSpOC) is responsible for performingconjunction assessments for all designated NASA space assets inaccordance with an established schedule, i.e., every 8 hours for humanspaceflight vehicles and daily Monday through Friday for robotic vehicles.– All objects tracked by SSN are considered: cataloged and uncataloged. JSpOC notifies NASA (JSC for human spaceflight and GSFC for roboticmissions) of conjunctions which meet established criteria.– Data are exchanged 24/7 via direct links and telecon between JSpOC and JSC/GSFC. JSpOC tasks SSN to collect additional tracking data on threat object toimprove conjunction assessment accuracy.12

National Aeronautics and Space AdministrationBasic Conjunction Assessment andCollision Avoidance Process (continued) NASA computes the probability of collision, based upon miss distance anduncertainty provided by JSpOC. Based upon specific flight rules and detailed risk analysis, NASA decides ifa collision avoidance maneuver is necessary. If a maneuver is required, NASA provides planned post-maneuver orbitaldata to JSpOC for screening of near-term conjunctions. This process canbe repeated if planned new orbit puts the NASA vehicle at risk of futurecollision with the same or another space object. In the case of a NASA robotic satellite, a second maneuver might berequired for the vehicle to resume its mission. This maneuver also wouldbe coordinated with JSpOC. NASA also informs JSpOC prior to normal operational maneuvers to aidfuture conjunction assessments.13

National Aeronautics and Space AdministrationDebris Avoidance Maneuver Planning forHuman Spaceflight Operations Debris avoidance maneuvers are planned when the probability of collisionfrom a conjunction reaches limits set in the Shuttle and ISS flight rules:– Probability 1 in 100,000: Maneuver if it will not result in significant impact to missionobjectives.– Probability 1 in 10,000: Maneuver unless it will result in additional risk to crew (reflight, additional spacewalk, etc.). Debris avoidance maneuvers are usually small and occur from one toseveral hours before the time of the conjunction.– Shuttle can plan and execute a debris avoidance maneuver in a matter of hours.– ISS requires around 30 hours to plan and execute a debris avoidance maneuver,mainly due to dependence on Russian propulsion assets. Both the Shuttle and ISS have conducted several collision avoidancemaneuvers during the past 10 years.14

– Shuttle can plan and execute a debris avoidance maneuver in a matter of hours. – ISS requires around 30 hours to plan and execute a debris avoidance maneuver, mainly due to dependence on Russian propulsion assets. Both the Shuttle and ISS have conducted several collision avoidance maneuvers during the past 10 years.