1 AIAA Space Operations & Support Technical Committee 14th Annual Improving Space Operations Workshop Spacecraft Collision Avoidance & Co-location TrackNASA Robotic Conjunction Assessment Process: Overview and Operational ExperiencesLauri Kraft NewmanConjunction Assessment ManagerNASA Goddard Space Flight CenterSpace Systems Protection Mission Support Office/Code 590.1April 15, 2008GSFC Conjunction Assessment Team:D. McKinley, R. Frigma.i. solutions, Inc.
2 Agenda NASA Policy for Conjunction Assessment NASA Robotic Conjunction Assessment ProcessOperations ProcessTool Suite DescriptionStatisticsTerra vs Case StudyLessons Learned
3 NASA CA PolicyPolicy for Limiting Orbital Debris (NPR ) requires routine CA for all NASA assets with maneuvering capability (signed 8/17/07).FDAB has the capability to offer this service to any mission3.4 Conjunction Assessments during Mission Operations (for Earth-Orbiting Spacecraft)The NASA Program/Project Manager shall have conjunction assessment analyses performed routinely for all maneuverable Earth-orbiting spacecraft with a perigee height of less than 2000 km in altitude or within 200 km of GEO (Requirement 56891).Conjunction assessment analyses shall be performed using the USSTRATCOM high-accuracy catalog as a minimum (Requirement 56892).The NASA Program/Project Manager shall have a collision risk assessment and risk mitigation process in place for all maneuverable Earth-orbiting spacecraft that are performing routine conjunction assessment analyses (Requirement 56893).
4 Existing NASA CA Process NASA Performs CA for its Human space assets (Shuttle and Station) as well as for various unmanned assets.Requirements dictated by NPRNASA/JSC performs CA for Human Space Flight assets 3 times a dayNASA/GSFC manages the CA for all unmanned NASA assetsGSFC has performed CA routinely since January 2005 for:11 Earth Science Constellation members, including USGS-owned Landsat missions9 TDRS satellitesGSFC program is expanding to encompass all NASA unmanned missions per the new requirement.Plan to add 12 more missions over the next year.
5 Missions Supported [1 of 2] Earth Science Constellation Combination of NASA and Foreign assetsEach mission makes its own risk mitigation decisionsEach mission subject to own maneuverability, comm, and ops concept constraints
6 Missions Supported [2 of 2] Tracking Data & Relay Satellite System Relay system composed of ground systems and nine spacecraft in geosynchronous orbit positioned at various longitudinal slots about the Earth.WSCTDRS-8174.3°WStoredTDRS-7150°StoredTDRS-9062°WStoredGRGTTDRS-6173.7°WTDRS-5171°WTDRS-1049°WTDRS-4046°WTDRS-3275°WTDRS-10041°W
8 Current GSFC CA Effort Pertinent National Space Policy excerpt National Security Space Guidelines: To achieve the goals of this policy, the Secretary of Defense (SECDEF) shall: Have responsibility for space situational awareness; in this capacity, the SECDEF shall support the space situational awareness requirements of the Director of National Intelligence and conduct space situational awareness for: …. civil space capabilities and operations, particularly human space flight activities.GSFC has an agreement with the Joint Space Operations Center (JSpOC)/Space Superiority Cell to obtain conjunction assessment screening predictions for NASA robotic assets
9 CA Functional Overview JSpOCMission Owner/OperatorGSFC CA TeamCA ScreeningRiskAssessmentRiskMitigationCurvilinear Collision ProbabilityGenerate Close Approach PredictionsConsists of:Performing Orbit Determination for catalog objectsComputing separation distance between objects in high accuracy space object catalogSummarizing and reporting resultsAnalyze data to determine threatConsists of:Trending miss distance and specific orbit determination related parametersComputing collision probabilityPerforming collision probability sensitivity analysisCA analysts assist the Flight Operations TeamConsists of:Maneuver planningManeuver executionOur expertise is risk assessmentMention USSTRAT/1st SPCS are entity doing screening workNASA-dedicated OSAsEmphasize 3 parts of process.
10 GSFC CA Operational Summary Goddard-dedicated Orbital Safety Analysts at the JSpOC generate CA data M-F (weekends as needed) using the high-accuracy (SP) catalogClose approach predictions are made 7 days into the future for LEO missionsClose approach predictions are made 10 days into the future for GEO missionsAny planned maneuvers are modeled in the ephemerides provided by the mission.The CA data is provided to Goddard via secure FTP and .The GSFC CA team processes the data and provides risk assessment analysis results to the mission stakeholders
11 LEO Safety VolumesThree different mission safety volumes define data product delivery from JSpOC/SCC and data processing by GSFC CA teamThe safety volumes are expressed in the primary UVW coordinate frame: U (radial), V (in-track) and W (cross-track)Monitor Volume (ellipsoid) +/- 2 x 25 x 25 kmLargest filter used to initially identify and report potential close approachesTasking Volume (box) +/- 0.5 x 5 x 5 kmServes as a second warning and an elevated level of concernTasking level on the secondary object is increased (if necessary)Watch Volume (standoff distance) 1 km
12 GEO Safety Volumes Monitor Volume (standoff distance) 40 km Largest filter used to initially identify and report potential close approachesAlert/Tasking Volume (standoff distance) 15 kmServes as a second warning and an elevated level of concernTasking level on the secondary object is increased (if necessary)Watch Volume (standoff distance) 2 kmRisk mitigation maneuver planning options examined
13 Data Products from JSpOC All Monitor Volume violations are summarized in a Conjunction Screening Summary and delivered to the CA SFTP server. The Screening Summary contains:Time of Closest Approach (TCA)Total Miss DistanceMiss Distance Position and Velocity Components in RIC frameAn additional is sent documenting tracking data and tasking levelAn Orbital Conjunction Message (OCM) is provided for Tasking/Alert Volume violations. The OCM contains:TCAAsset State/Covariance at TCAObject State/Covariance at TCAOther orbit determination information helpful in performing collision risk assessment.Vector Covariance Messages (VCMs) for both objects are provided for Watch Volume violations.VCMs contain epoch state and covariance informationUsed for maneuver planning
15 Risk Assessment by CA Team Screening data is analyzed in two distinct waysRoutine OperationsDaily activity to assess most recent delivery of close approach predictionsDisposition conjunctions as a “threat”, “not a threat”, or “monitor” event based on analysisHigh Interest EventsEvents that have significant potential to be a threat or provide a unique analysis opportunityTrending of orbit determination parameters and conjunction geometryProbability of Collision Sensitivity analysisRisk Mitigation Maneuver planning
16 Routine OperationsAt the end of the day, the OSA provides data products to the GSFC CA teamJSpOC OSA posts data products to the SFTP site.CAS automatically parses the data and puts it into the database for trending and use with other toolsThe CAM Tool Suite is run each time new data is receivedData is processed by the automated CAS utility and generates various reportsA summary report is generated containing all pertinent information and delivered to the stake-holdersAn ‘OCM Analysis Report’ is generated for each event and posted to a secure websiteThe following morning the CA AnalystVerifies all data delivered to CA team and mission stakeholdersReviews Screening SummaryReviews all OCM Analysis ReportsCreates Watch List detailing all conjunctions in the Screening Summary and the action to be takenPerforms additional analysis on conjunctions using the Collision Risk Assessment Tool Suite
17 High Interest Event Risk Assessment Pc and miss distance data alone cannot be used to fully assess the threatAdditional analyses to help establish and quantify risk include:Orbit determination (OD) consistency from solution to solutionNumber of tracks and observationsBallistic CoefficientSolar Radiation Pressure CoefficientEnergy Dissipation RateRadar Cross Sectional AreaProbabilistic Risk Assessment AnalysisRealistic probability calculations based on ‘realistic’ state and covariance predictionsPc evolution as the time to the close approach event gets shorterPc sensitivity analysis based on changes to inputsConjunction Geometry (clock angle, approach angle)Position of hard body radius with respect to the 3-sigma covariance ellipse
18 Risk MitigationIf the threat evaluation indicates the need to plan and (possibly) execute a maneuverCA Team notifies Mission Owner/OperatorCA Team analyzes maneuver options that will mitigate the threat - first guessCA Team works with Mission Owner/Operator to plan risk mitigation options.Maneuver must sufficiently increase the separation distance and decrease the collision probabilityManeuver must meet orbit requirements if at all possibleCA Team analyzes sensitivity of Pc to expected variations in burn performance
19 Typical LEO Risk Mitigation Maneuver Planning Process Maneuver planning begins ~ TCA-3 daysAs TCA approaches, uncertainty decreases, but avoidance options decreaseAllows time to:Improve the OD solution on the secondary objectEvaluate several maneuver optionsHave 1st SPCS screen the options for post-maneuver close approachesplan the final maneuverUpload commands to the spacecraft
20 The Collision Assessment System Collision Assessment System (CAS) was developed to store and analyze the large volumes of data received.CAS is automated and comprised of several elements:Secure File Transfer Protocol ServerParser / Monitor ScriptsDatabaseCollision Assessment and Mitigation (CAM) Tool SuiteSecure WebsiteConfiguration Management System
21 Collision Assessment and Mitigation Tool Suite The CAM Tool Suite is the part of CAS that provides analysis utilitiesThe CAM Tool Suite consists of 6 modules:Conjunction Visualization Script2-D Collision Probability UtilityMonte Carlo Simulation3-D / Curvilinear Collision Probability ToolTime History Trending UtilityCollision Avoidance Planning ToolThe modules are built using FreeFlyerTM and MatlabTMOutput from tools is formatted into a single PDF report for each OCM
22 Screening Data Processing: Conjunction Summary Report Overlap compare computes differences between subsequent solutions for the same close approachJSpOC and Owner/Operator solutions are comparedResults are posted to the Portal website
23 Screening Data Processing: CA Calendar A CA Calendar is produced and posted to the PortalContains close approach predictions of less than 1 km, events having Pc > 1e-7, and planned maneuver dates/times.
24 Screening Data Processing: Watch List CA Analyst examines all data on Portal daily to produce a “watch list” of events warranting further analysis.
25 OCM Analysis: Conjunction Orientation Conjunction Orientation: Shows the position and position covariance of thePrimary (blue) and Secondary (green) Objects in Earth Centered Inertial (ECI) coordinates.
29 CA Statistics - ESC For the Earth Science Constellation: Each asset averages 15 unique conjunctions per week within the Monitor Volume (780/yr)Each asset averages 1 unique conjunction per week within the Tasking Volume (52/yr)Each asset averages 3 ‘high interest’ events per year - ops team engages in maneuver planning processInternational Space Station (ISS) statistics for comparison (~340 km altitude, 51.6 deg inc):For 2005, saw 24 Monitor Volume conjunctions, none with Pc > 1 x 10-5Have seen 251 conjunctions from 7/99 – 12/05Have executed 4 debris avoidance maneuversAverage of 1.2 maneuvers per year predicted
34 ASAT Event - Background On January 11th, 2007 China performed a successful test of an anti-satellite (ASAT) weaponThe ASAT test consisted of a medium-range ballistic missile destroying a Chinese weather satelliteEvent occurred at an altitude of ~535 miles (861 km)First close approach with an ESC mission was predicted weeks after the event (04 Feb)Current number of cataloged objects ~2000The NASA Orbital Debris Program Office estimates >35,000 pieces larger than 1 cm
35 Debris Environment Growth March 2007Tracked objects >10 cm diameter (FENGYUN 1-C Debris in red)Images courtesy NASA Orbital Debris Program Office
36 FENGYUN 1C DEB Mean Equatorial Height vs. Inclination - Height Statistics (Oct 2007)(Min, Max, Mean, Std)●ESC orbitInclination Statistics (Oct 2007)(Min, Max, Mean, Std)
40 Case Study Terra vs. 14222 TCA October 23, 2005
41 Pc TrendDay -6Day -5Day 0Day -3Day -1On Monday Oct 17th, 1st SPCS predicted a close approach between Terra and object (SCOUT G-1 debris)TCA: Oct 23rdMiss distance < 500 mPc ~1e-214222 characteristics at TCA:Period: minApogee Height: ~ kmPerigee Height: ~ kmInclination: ~ 82.39˚GSFC-Computed Pc ValuesFor Each OCM SolutionCollision ProbabilityDays to TCAThroughout the week, the Pc remained high primarily due to the decreasing miss distance and the close approach geometry.
42 Avoidance Maneuver Planning Day -6Day -5Day 0Day -3Day -1Throughout the week, the miss distance trended downward from solution to solutionOn Thursday, October 20th the miss distance had dropped to <200 m, risk mitigation maneuver planning took placeFour different maneuver options were generated and sent to JSpOC-Mountain for screening:Performing any of these maneuver options would increase the miss distance to a safe level and decrease the Pc by several orders of magnitudeOption #DV (m/s)Burn TimeDurationDSMA (m)TCA10.011410/21 22:30 Z2.0 sec+21.65.5 km20.01572.7 sec+29.67.5 km30.01723.0 sec+32.48.5 km40.017310/22 14:07 Z+32.6
43 Miss Distance TrendDay -6Day -5Day -3Day -2Day -1Day 0On Friday, October 21st the reported miss distance reached a local minimum and the collision probability reached a local maximumMiss distance 50 – 60 mCollision probability still on the order of 1e-2Decision was made to perform maneuver option #2Based on trends throughout the week and the post-maneuver close approach screening resultsExecuted at 22:30 ZActual miss distance = 4.6 kmActual Pc ≈ 0
44 Lessons LearnedAutomation is essential for managing the workload of routine data processingPersonnel experienced in orbit determination are required to assess the threat using multiple criteriaEach event appears to be sufficiently unique such that a standardized mitigation approach cannot be adaptedEach spacecraft sees a handful of conjunctions per year for which avoidance maneuver planning is considered
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