Satellite Collocation and Collision Avoidance Docume… · · 2013-05-16Satellite Collocation and Collision Avoidance Joseph Chan ... • SOCRATES-GEO ... – Two Tier system with

Satellite Collocation and Collision Avoidance

Joseph Chan

Intelsat

The 19th Improving Space Operations Workshop, April 30 – May 01, 2013

2

Intelsat History on Conjunction Assessment


Intelsat became active in conjunction monitoring in the summer of 1999

– Contract with Aerospace Cooperation

– Contract with MIT Lincoln Lab

– In-house monitoring tool

– Prototype active data sharing center to improve safety of flight with SES, Inmarsat, Telesat and CSSI

• SOCRATES-GEO

• Intelsat, Inmarsat, SES founding members of Space Data Association (2010)

– Legal framework to protect the sharing of data (conjunction monitoring and RFI mitigation)

– Physical systems to make data sharing efficient, secure and reliable reducing operators workload and mitigating risks

– Technical support to ensure operations integrity

– Shared costs and ‘not-for-profit’ ethos to reduce individual expanses

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Current Conjunction Monitoring Tools (1/2)

• In House Monitoring

– Fully automated system based on probability and miss distance for collision assessment

– Monitoring to 14 day time span

– Two Tier system with TLE and validation via JSpOC Form-1 process

• Space Data Association

– Cooperated with other satellite owners/operators orbit ephemeris including maneuver effects

– TLE to supplement drifters and non-cooperated satellites

– Conjunction alerts currently based on miss-distances only

– Monitoring to 7 day time span

– Two Tier system with TLE and validation via JSpOC Form-1 process


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Current Conjunction Monitoring Tools (2/2)

• JSpOC Support

– Conjunction monitoring using SP data

– Conjunction alerts based on miss-distances only

– Monitoring to 3 – 4 day time span

– Automatic email to owner/operators and via. online CSM

– Two Tier System with SP data and validated via Operation Ephemeris data


All Current Monitoring tools

are Two Tier Systems

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Close Conjunction – A Real Case Study (1/2)• The satellites

– SatA

• Intelsat operated active satellite with high efficiency low thrust SPT engines

• Maneuvered one day earlier and loaded with SPT maneuvers onboard (2 daily maneuvers)

– SatB

• Decommissioned non-active satellites (drifter)

• SatA ephemeris vs. TLE for SatB (~ 48 hours before predicted conjunction)

– Collision risk between at 2012/01/27 23:50:20.000

• DT =14.33 km, DN = 1.65 km, DR = 0.44 km, TLE Age = 2.367

– Would normally not flagged as potential close approach using distance base only criteria

– Intelsat CA detection using equivalent distance (account for uncertainties of OD solutions and TLE age)

• SP for SatA vs. SP for SatB

– Using SP versus SP analysis, the United States Joint Space Operations Center (JSpOC) has identified no conjunctions within 3 days and less than 5Km

• SP data for SatA did not account for the maneuver the data before

• SP predictions for SatA did not consider the planned SPT maneuvers loaded onboard


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Close Conjunction – A Real Case Study (2/2)

• SatA ephemeris vs. SP for SatB

– Time of Closest Approach: 27 JAN 2012 23:40 UTC

• Overall miss distance: 601 meters (R = -382 m, T = 462 m, N = 54 m)

– Cancelled SatA remaining SPT maneuvers

• SatA ephemeris vs. SP for SatB (re-screening with cancelled SPT maneuvers)


• Overall miss distance: 3935 meters (R = -59 m, T = 3909 m, N = 449 m)

• SP for SatA vs. SP for SatB (updated with addition tasking for both satellites ~ 12+ hours)


• Overall miss distance: 3313 meters (R = -420 m, T = 3265 m, N 376 m)


Multi-tier Monitoring Systems

are inefficient nor sufficient

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Detected Conjunction Statistic

• 12 months period from June 2010 – June 2011

• Most conjunctions using SP and TLE only were downgraded with more accurate ephemeris data and maneuver information

• Majority of confirmed conjunctions are with high inclination non-active objects

• Most avoidance maneuvers were achieved with shifting the timing and adjusting the delta-v of already planned station-keeping maneuver

• Sometimes warnings came too late (< 12 hours) to respond


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The Issues• Risk of using inaccurate data for CA

– Sensor biases

– Data Fusion

– Independent and distributed observations

• CA detections methodology

– Minimum miss distance does not always represent highest risk of collision

– Improved algorithm and definitions

• Risk of using multi-tier monitoring process

– False warnings

– Missed conjunctions

– Data sharing (everybody works hard but are we safer !)

• Creative data sharing model

– Security vs. Safety

– May require policy changes to encourage and promote sharing


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Summaries

• Conjunction monitoring is a critical component in Intelsat’s satellite concept of operations

– Three different processes to overcome different constraints

• Multi-tier systems are inefficient nor sufficient

– Limitations apply to satellite operators, SDA, JSpOC and …

– Creative data sharing model to promote safe of operations

• Tasks ahead

– Improve conjunction detection algorithm

– Data fusion to improve orbit accuracies and error estimates

• Independent and distributed data sources

• Fusion techniques and methodologies


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Monitoring for Close Approach Objects

• A potential close approach between a primary and secondary object is identified

– Primary object – Intelsat satellite

– Secondary object – Non-active space object

• Current approach

– Orbit for the primary object – dual station ranging

– Orbit for the secondary object – TLE or other measurement or ephemeris source

– Compute miss distance and conjunction risk

• Proposed solution

– Orbit for the primary object – dual station ranging

– Orbit for the secondary object – relative measurement from the primary object

– Compute miss distance and conjunction risk


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Proposed Scenario for Monitoring Close

Approach


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Relative Angle Measurement

between Two Objects

•Relative position accuracy ~ 0.2 arc seconds

•Absolute position accuracy ~ 1 to 4 arc seconds

2.58 deg

1.7

2d

eg

enlarge

JCSAT3A & JCSAT12

Image Taken on March 16

using IHI Orbital Object Optical Observation Demonstrator: IO4D

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Thank You


Documents

Satellite Collocation and Collision Avoidance Docume… · · 2013-05-16Satellite Collocation and Collision Avoidance Joseph Chan ... • SOCRATES-GEO ... – Two Tier system with