GOES-EastCo-Location Operations

with BRASILSAT-B1

Kevin T. WorkASRC AerospaceFebruary 11, 2008

04/22/23 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.

04/22/23 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.

04/22/23 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

Eccentricity Control Maneuver Time Planner GOES-12Method A Method B

Input SRP area/mass ratio 0.030407 m^2/Kg Input Vernal Equinox date 3/21/2008Input/Calculate natural eccentricity radius (Rn) 0.000320 0.000339038Input/Calculate control eccentricity radius (Rc) 0.000250 0.000215841 Assumes 1.19 m/s annual EW Delta-V for 75degW (Soop has 1.22) and 3074.662 m/s Geosyn velocity

Input/Calculate Sun right ascension on burn day 24.641 24.641 deg Input maneuver date 4/15/2008 106 DOYInput/Calculate Sun right ascension on next burn day 86.735 86.735 deg Input second maneuver date 6/17/2008 169 DOY

Calculate Delta Sun right ascension this maneuver cycle 62.094 62.094 deg Check Delta 62.137 degCalculate Beta value to lead/lag Sun during cycle 10.264 23.060 deg Cycle Length 63 days

Calculate ECCx target 0.000242 0.000216 0.000000 Input ECC circle offset in x-directionCalculate ECCy target 0.000312 0.000256 0.000250 Input ECC circle offset in y-direction

Input averaged initial ECCx on maneuver date 0.000307 0.000307 Use ECCxy tab to average 24hr EVENTS file with Kepler elementsInput averaged initial ECCy on maneuver date 0.000421 0.000421 Use ECCxy tab to average 24hr EVENTS file with Kepler elements

Calculate Delta ECCx -0.000065 -0.000091Calculate Delta ECCy -0.000109 -0.000165

Calculate maneuver right ascension 239.324 241.121 deg Use 1rst time for Boost maneuversLookup 1rst manever time in UTC 7 22 0.0 7 30 0.0 UTC Must sort data due to LOOKUP problemLookup 1rst manever time in SLT 2 21 0.5 2 28 60.0 SLT Verify near 06?? SLT

Calculate maneuver right ascension + half orbit 59.324 61.121 deg Use 2nd time for Retrograde maneuvers (Nominal for GOES East)Lookup 2nd manever time in UTC 19 21 0.0 19 28 0.0 UTC Must sort data due to LOOKUP problemLookup 2nd manever time in SLT 14 20 5.7 14 27 6.2 SLT Verify near 18?? SLT

52535455565758596061626364656667

0.000000

0.000050

0.000100

0.000150

0.000200

0.000250

0.000300

0.000350

0.000400

0.000450

0.000500

0.000000 0.000050 0.000100 0.000150 0.000200 0.000250 0.000300 0.000350 0.000400

ECC

y

ECCx

GOES-12 Predicted ECC Vector on 4/15/2008 EW#31

ECC vector ECC Average ECC Target

04/22/23 5

Sample ECC Control Plan

04/22/23 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.

04/22/23 7

GOES-12 and BRASILSAT-B1 Longitude

72.2

72.4

72.6

72.8

73.0

73.2

73.4

73.6

73.8

74.0

74.2

74.4

74.6

74.8

75.0

75.2

75.4

75.6

75.8

76.0

3/20/07 4/17/07 5/15/07 6/12/07 7/10/07 8/7/07 9/4/07 10/2/07 10/30/07 11/27/07 12/25/07 1/22/08 2/19/08 3/18/08 4/15/08 5/13/08

Date

Long

itude

(Deg

W)

Longitude (3/25/07 – 4/15/08)

EW#25 EW#26EW#27

NS#7

EW#28

EW#29EW#30

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

BRASILSAT-B1 GOES-12

04/22/23 8

Eccentricity (3/25/07 – 4/15/08)GOES-12 and BRASILSAT-B1 Eccentricity Vector

-0.0007

-0.0006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

0

0.0001

0.0002

0.0003

0.0004

0.0005

-0.0010 -0.0008 -0.0006 -0.0004 -0.0002 0.0000 0.0002 0.0004 0.0006 0.0008 0.0010

ECC-x

ECC

-y

BRASILSAT-B1

GOES-12

EW#29

EW#28

04/22/23 9

GOES-12 Eccentricity Vector 2006GOES-12 Eccentricy Vector 2006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

-0.0005 -0.0004 -0.0003 -0.0002 -0.0001 0.0000 0.0001 0.0002 0.0003 0.0004 0.0005

ECC-X

ECC

-Y

One point/day. Does not show daily variations.

Vector points to orbit perigee.

G12 Start 2006

Five EW maneuvers at perigee

One NS maneuver

04/22/23 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.

04/22/23 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.

04/22/23 12

Sample Prediction ErrorGOES-12 EW#30 Prediction Accuracy

74.5

74.6

74.7

74.8

74.9

75.0

75.1

75.2

75.3

75.4

75.5

75.6

75.7

75.8

1/01/0

8

1/08/0

8

1/15/0

8

1/22/0

8

1/29/0

8

2/05/0

8

2/12/0

8

2/19/0

8

2/26/0

8

3/04/0

8

3/11/0

8

3/18/0

8

3/25/0

8

4/01/0

8

4/08/0

8

4/15/0

8

4/22/0

8

Date

Long

itude

(Deg

W)

Definitive OADR Initial Plan Final Plan Post Burn 034 Current Pred 099 STK Prop Ck 034

0.4 deg Longitude Error by next EW

Predictive

Definitive

04/22/23 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.