GOES-East Co-Location Operations with BRASILSAT-B1 Kevin T. Work ASRC Aerospace February 11, 2008

2/13/20142 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.

2/13/20143 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.

2/13/20144 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 to resolved the issues around long cycles without a negative impact to the ECC Control Strategy. –Also increase offset in Y direction to.00025

2/13/20145 Sample ECC Control Plan

2/13/20146 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.

2/13/20147 Longitude (3/25/07 – 4/15/08) EW#25 EW#26 EW#27 NS#7 EW#28 EW#29 EW#30 Minimum Range at Longitude Crossings: 4/23/ km 12/5/ km 5/24/ km 12/16/ km 7/10/ km 2/10/ km 8/7/ km 3/29/ km 9/28/ km BRASILSAT-B1GOES-12

2/13/20148 Eccentricity (3/25/07 – 4/15/08) BRASILSAT-B1 GOES-12 EW#29 EW#28

2/13/20149 GOES-12 Eccentricity Vector 2006 One point/day. Does not show daily variations. Vector points to orbit perigee. G12 Start 2006 Five EW maneuvers at perigee One NS maneuver

2/13/ 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 /-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.

2/13/ 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.

2/13/ Sample Prediction Error 0.4 deg Longitude Error by next EW Predictive Definitive

2/13/ 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.