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Co-Location Operations with BRASILSAT-B1 and GOES-East

The background, implementation, and troubleshooting of the co-location strategy between BRASILSAT-B1 and GOES-East satellites. Discusses eccentricity control implementation, sample timeline, north/south maneuver plans, anomalies, orbit errors, and monitoring procedures.

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Co-Location Operations with BRASILSAT-B1 and GOES-East

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  1. GOES-EastCo-Location Operationswith BRASILSAT-B1 Kevin T. Work ASRC Aerospace February 11, 2008

  2. Background • After notification in February 2007 that BRASILSAT-B1 was moving to the same orbital longitude as GOES-East (75 deg W), NOAA and STARONE began coordination. • No frequency interference issues. (ITU) • Started routine orbit product exchange: • GOES Weekly Elements, Maneuver Notification, Predicted Post Maneuver Elements. (All pre-existing) • BRASILSAT-B1 Predicted/Post Maneuver Elements. • Both sides verified propagation accuracy. • Started to develop safe co-location strategy with support from NASA GSFC FDF.

  3. Eccentricity Control Implementation • GOES-East moved retro East/West control maneuvers from Perigee to time determined by external Eccentricity Control maneuver planner. • Spreadsheet tool developed to implement the equations of the Eccentricity Control strategy. • Input predicted Kepler elements for burn day to determine average Starting ECC-xy. • Fixed inputs for Natural ECC radius (Rn=.00032), Control ECC radius (Rc=.00025), and ECC control circle offset (Offset-X=0, Y=.00025). • Input maneuver cycle start and stop dates are used along with the ECC radius to determine the Beta angle. • Beta angle used to calculate the Target ECC-xy. • The delta between the Target and Starting ECC-xy is used to determine the maneuver Right Ascension angle and corresponding burn time.

  4. ECC Control Implementation (cont.) • Initial tool development calculated the Natural and Control ECC radius using SRP Area/Mass ratio as input. • Equation for Beta experienced problems when maneuver cycles were greater than 11 weeks. • Math error with arcsine of number greater than 1. • Longer maneuver cycles needed around eclipse season. (Constraint - No maneuvers during season) • Increasing Control radius from .00020 to .00025 resolved the issues around long cycles without a negative impact to the ECC Control Strategy. • Also increase offset in Y direction to .00025

  5. Sample ECC Control Plan

  6. Timeline Reference • February 2007 – Start NOAA/STARONE coordination • 3/7/07 – 3/23/07 – BRASILSAT-B1 move to 75 deg W with GOES-East • Evaluate BRASILSAT-B1 entry into GOES-East longitude for any close approaches. None. • 5/8/07 – GOES-East EW#25. Normal maneuver at Perigee. Ck COLA. • 7/25/07 – GOES-East EW#26. First ECC control maneuver. • 10/16/07 - GOES-East EW#27. ECC control. North/South pre-position. • 12/4/07 - GOES-East NS#7. Nominal North/South inclination maneuver. • Post maneuver thruster leak anomaly. • 12/7/07 - GOES-East thruster leak isolated. • 12/11/07 - GOES-East EW#28. Drift control. ECC control. • 12/17/07 - GOES-East EW#29. Drift stop. ECC control. • 1/29/08 - GOES-East EW#30. ECC control. • 4/15/08 - GOES-East EW#31. ECC control.

  7. Longitude (3/25/07 – 4/15/08) EW#27 EW#29 EW#25 NS#7 EW#26 EW#30 BRASILSAT-B1 GOES-12 Minimum Range at Longitude Crossings: 4/23/07 15.436 km 12/5/07 66.597 km 5/24/07 8.243 km 12/16/07 93.791 km 7/10/07 9.138 km 2/10/08 19.243 km 8/7/07 13.290 km 3/29/08 22.893 km 9/28/07 12.369 km EW#28

  8. Eccentricity (3/25/07 – 4/15/08) GOES-12 EW#28 EW#29 BRASILSAT-B1

  9. GOES-12 Eccentricity Vector 2006 Five EW maneuvers at perigee G12 Start 2006 One NS maneuver One point/day. Does not show daily variations. Vector points to orbit perigee.

  10. North/South Maneuver Plans • GOES (I-M series) North/South inclination maneuvers can include East/West control. • Two part maneuvers surrounding the node. • Due to East/West maneuver uncertainty during inclination maneuvers, NOAA agreed to perform North/South burns outside the BRASILSAT-B1 control box of 75.0 +/-0.1 deg W. • Option to use prior East/West maneuver to pre-position for North/South burn. • Evaluate multiple options to determine which is best for Eccentricity Control with minimal mission impact.

  11. GOES-East NS#7 Anomaly • After a successful North/South maneuver, failed to transition back to normal wheel control. • Maintain thruster attitude control for multiple days until fault isolated as leaking thruster valve (2B oxidizer). • GOES-East exited the longitude control box. • Anomaly lowered SMA -37 km. • Two East/West maneuvers used to correct Longitude. • No close approaches with BRASILSAT-B1. • GOES-East continues to experience venting of the remaining oxidizer in lines. Orbit errors.

  12. Sample Prediction Error 0.4 deg Longitude Error by next EW Predictive Definitive

  13. Co-Location Monitoring • Maneuver plans and post maneuver orbits checked for potential close approaches. • Tolerance 5 km. • Both parties maintain Eccentricity Control strategy. • Periodic check of CelesTrak SOCRATES tool.

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