GOESEast CoLocation Operations with BRASILSATB1

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GOES-EastCo-Location Operationswith BRASILSAT-B1

• Kevin T. Work
• ASRC Aerospace
• February 11, 2008

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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.

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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-X0, 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.

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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

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Sample ECC Control Plan
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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 EW25. Normal maneuver at
  Perigee. Ck COLA.
• 7/25/07 GOES-East EW26. First ECC control
  maneuver.
• 10/16/07 - GOES-East EW27. ECC control.
  North/South pre-position.
• 12/4/07 - GOES-East NS7. Nominal North/South
  inclination maneuver.
• Post maneuver thruster leak anomaly.
• 12/7/07 - GOES-East thruster leak isolated.
• 12/11/07 - GOES-East EW28. Drift control. ECC
  control.
• 12/17/07 - GOES-East EW29. Drift stop. ECC
  control.
• 1/29/08 - GOES-East EW30. ECC control.
• 4/15/08 - GOES-East EW31. ECC control.

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Longitude (3/25/07 4/15/08)
EW27
EW29
EW25
NS7
EW26
EW30
BRASILSAT-B1
GOES-12
Minimum Range at Longitude Crossings 4/23/07 15.4
36 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
EW28
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Eccentricity (3/25/07 4/15/08)
GOES-12
EW28
EW29
BRASILSAT-B1
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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.
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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.

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GOES-East NS7 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.

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