Improved Conjunction Analysis via Collaborative SSA

T.S. Kelso, D. Vallado (CSSI)J. Chan, B. Buckwalter (Intelsat)

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Overview

• Motivation

• Background

• Proposed Solution

• Validation

• SOCRATES-GEO

• Future Enhancements

• Summary & Conclusions

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Motivation

• Recent events emphasize need for improved SSA for conjunction analysis– Chinese ASAT test (2007 Jan 11)

• 2,529 pieces cataloged to date (only 49 decayed)

– USA 193 intercept (2008 Feb 21)• 174 pieces cataloged (1 still on orbit)

– ISS maneuver to avoid Cosmos 2421 debris (2008 Aug)• 509 pieces cataloged (48 still on orbit)

– Iridium 33/Cosmos 2251 collision (2009 Feb 10)• 999 pieces cataloged to date (822 public); only 6 decayed

– ISS evacuation (2009 Mar 12), move (2009 Mar 22)

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SATCAT Growth: 1957 to Present

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Motivation at GEO

• Geostationary orbit (GEO) is a limited resource– More satellites = more conjunctions

• 30 payloads launched in 2008• >369 active payloads

– Implications of a collision are significant• Potential loss of colliding satellites and associated revenues• Increase in debris, putting other satellites at risk

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Background

• Conjunction analysis needs full-catalog orbital data– TLEs are currently the only such source

• Low accuracy results in high false-alarm rate

• Current system limited to non-cooperative tracking– US SSN uses combination of radar and optical resources

• Operational satellites most difficult to track due to maneuvers– Maneuvers typically not known ahead of time

– Delays in detecting maneuvers can result in poor accuracy or even ‘lost’ satellites

– Requires more SSA resources to maintain orbits

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Proposed Solution

• Satellite operators already maintain orbits– Active ranging, GPS can be very accurate

• Develop Data Center to collect operator data– Use operator data to improve conjunction analysis– Provide analysis/data to all contributors

• Current Data Center participation (133+35)– Intelsat (55+6), Inmarsat (11), EchoStar (6), SES (41+1:

Astra, New Skies, Americom), NOAA (4), Star One (6), Telesat (6+18), EUMETSAT (4)

• Pending: IAI (3), Paradigm (7)

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Analysis of Orbital Data Sources

• Many sources of operator orbital data– Direct from satellite operator (Data Center)– Public sources

• GPS (almanacs, precise ephemerides)• GLONASS (precise ephemerides)• Intelsat (11-parameter data, ephemerides)• NOAA, EUMETSAT (state vectors)

• Challenges– User-defined data formats– Variety of coordinate frames & time systems used

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Supplemental TLEs

• Uses public orbital data– GPS almanacs– GLONASS precise ephemerides– Intelsat 11-parameter data

• Import data into STK to generate ephemerides

• Generate TLE from ephemerides– Allows users to see benefit

• Test cases with supporting data

– Overcomes limitations in most orbital software that can only handle TLEs/SGP4

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GPS Almanacs vs. TLEs

Mean: 1.292 km

Max: 3.073 km

Mean: 7.544 km

Max: 32.449 km

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GPS Supplemental TLEs

Mean: 0.872 km

Max: 2.366 km

Mean: 7.544 km

Max: 32.449 km

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GLONASS Supplemental TLEs

Mean: 3.301 km

Max: 9.388 km

Mean: 0.201 km

Max: 0.539 km

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Case Study: Intelsat Data Comparisons

IS-6B IS-3R IS-11

IS-6B IS-3RIS-11

Owner ephemeridesAFSPC TLEs

43.25° W 43.00° W 42.75° W

Spacing = 184 km

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Case Study: ASTRA 1 Cluster

• Open source image of cluster– http://www.foton.co.za/assa_imaging.htm

• Taken 2009 Jan 21 at 20:21:11 UTC

• Site location: 33.94058 S, 18.51294 E, 10 m– Pinelands, a suburb of Cape Town, South Africa

• Telescope: 6-inch, f/2.7 reflector

• FOV: 54.7 x 40.2 arcminutes

• Compared SES ephemerides and latest TLEs

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SES EphemeridesHipparcos StarsAFSPC TLEs

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SES EphemeridesHipparcos StarsAFSPC TLEs

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SES EphemeridesHipparcos StarsAFSPC TLEs

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1H to _1H = 71 km

SES EphemeridesHipparcos StarsAFSPC TLEs

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SES EphemeridesHipparcos StarsAFSPC TLEs

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SOCRATES-GEO

• Extension of SOCRATES– Satellite Orbital Conjunction Reports Assessing

Threatening Encounters in Space– Running since 2004 May

• Looks for any time anything gets within 5 km of payload– 2,959 payloads vs. 12,817 total objects (as of 2009 Mar 31)– 13,979 conjunctions (2009 Mar 31 + 7 days)

• Runs automatically twice per day• Generates standard reports available via the Internet• Uses only TLEs

– Limited accuracy due to non-cooperative tracking– Does not account for maneuvers well– US SSN tracks over 19,000 objects

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SOCRATES-GEO Today

• Includes all objects which pass ±250 km of GEO– 752 payloads vs. 1,334 total objects (as of 2009 Mar 31)– 1,094 conjunctions within 50 km (2009 Mar 31 + 7 days)

• Uses best data sources available

• Generates standard reports– Runs in under 15 minutes on standard PC– Provides links to standard (OEM) orbital data

• Allows user-defined notification criteria

• Automatically sends notification

• Web access to latest data via secure system

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Data sources

Owner ephemeris

Public orbital data

TLE data

Convert to standard format

Generate ephemerides

Produce enhanced TLEs

Select GEO data

Data preparation

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Future Enhancements

• Process new data as received– User defines notification interval– Parallel analysis tool for maneuver planning

• Improved data status page– Data type, age, and quality– Direct contact information for operational satellites

• Enhanced graphs, reports, visualization– Customizable tool kits

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Summary & Conclusions

• Bottom line:– Technical solution is easy

• Biggest obstacle:– Data sharing policies

• Other issues:– Organization– Resources & Funding

• Together we can work today to mitigate risk

Questions?