NavTK/TGRS Modeling: - AGI

NavTK/TGRS Modeling:Automating NavTK Output for Launch Range SafetyDr. Tom Lovern, Frank Grose, Linda LyonsAGIPg 1 of 10www.agi.com

TaskAnalyze the quality of theGPS navigation solution andpredict the performance ofthe Translated GPS RangeSystem (TGRS) to supportlaunch Go/No-Go decisionsby Vandenberg Flight Safety• Interceptors equipped with TGRS hardware• GPS-based Flight Safety System replacing radar-based systemAGIPg 2 of 10www.agi.com

Challenge• Model GPS satellite constellation and missile antennacharacteristics• Simulate launches at one minute intervals throughout 6-hourlaunch window– Simulate boosted flight from Launch through T+50 seconds at onesecondintervals– Predict TGRS performance in determining PDOP values– Conduct Critical Satellite analyses – simulating satellite outage x 30– Analyze primary day and four backup days• Analyze over 2.8 million unique time-position-configuration cases• Tag, manage, interpret, and condense large volumes of data• Provide useable products to launch team for Go/No-Go decisionsAGIPg 3 of 10www.agi.com

STEPAL PDOP ProcessClassified SystemSTKOrbit Data UpdateScenario Set UpOutput File ProductionGraphics and Sky PlotsNavTKRead In SatelliteOutage FilesScenario Set UpPDOP and NAssetOutput File ProductionInitial Post ProcessingRead Output FilesFilter OutputSatellite Outage FileProductionFinal Post ProcessingRead NavTK Output FilesProcess and OrganizeOutputOutput Product ProductionData Organization and DeliveryAGIPg 5 of 10www.agi.com

ProductsEach set of data includes –Colored tables depicting No-GotimesTabular listing of times whenPDOP =>3 for =>3 seconds(VAFB Safety No-Go Criteria)Sky Plots (nominal only) showingsatellite positions and last 30minutes of movement historyGo/No-Go TableNotional00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 1916:xx 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 3940 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 5900 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 1917:xx 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 3940 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 5900 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 1918:xx 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 3940 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59Sky Plots & Critical Satellite AnalysesAGIChart “PDOP Summary” for eachsecond of flight for each launchtimeSpreadsheet listing of PDOPvalues for each time analyzedChart “Number of Satellites”available over the entire periodanalyzedPg 6 of 10Notionalwww.agi.com

NavTK Mods• Development of PDOP and IIP support for VAFB Range Safetyhas required numerous modifications and additions to NavTK• Receiver modifications to include use of acquisition andthreshold specifications for determining receiverperformance.• Changes to algorithms to support time step increments aslow as 0.05 seconds• Script additions to support automatic execution of very largenumbers of time-phased scenarios• Many other specialized changes required to support the uniquerequirements of this taskAGIPg 7 of 10www.agi.com

Custom Applications1. NavTK Outage file is used to model the TGRS configurationSTK Numberof AccessesSTK AccessGapsSTK AccessElevationIf Accesses > 12Use 12 satelliteswith highestelevationCritical Satellites x 30For each satellitewithout Access,record each gap Startand Stop in NTKOutage file2. Processing NTK data to produce Go/NoGo chartsNTK PDOPdata filesIf PDOP > desiredfor >=3 secTime step isNoGoAGIPg 8 of 10www.agi.com

Current WorkNon-TerminatedTrajectoryError “Adjusted”Terminated TrajectoriesNotional• Adjust 1 sigma error computations in NavTK to 3sigma values (using empirically derived multipliersappropriate for GPS*)• Compute max/min ENU error positions combinedwith max/min velocity errors to get “adjustedlaunch points”NotionalError “Adjusted” IIPs• Fly “adjusted launch point” trajectories to impactusing two-body propagator• Measure against EWR-127 standards to get Go/No-Go times• Repeat for each second of flight and for eachminute of the launch window* This work, by Ted Driver, AGI, is in progress.AGIPg 9 of 10NotionalNominal IIP at aSpecified TerminationTimewww.agi.com

AGI AssistanceSTEPAL gratefully acknowledges continued assistanceby AGI personnel, without which this task would havebeen impossible– Brian Edwards created Sky Plot display technique– Bill Williams and Haroon Rashid provided many hours ofsupport– A special thanks to Ted Driver for answering countlessquestions on the use of NTK and for providing much neededguidance on a wide range of GPS technical issuesAGIPg 10 of 10www.agi.com