GOES12 Eccentricity Control CoLocation with Brasilsat B1

1
GOES-12 Eccentricity Control(Co-Location with
Brasilsat B1)

• Richard McIntosh
• a.i. solutions, Inc.
• AIAA SOSTC Workshop
• April 15, 2008

2
Co-Location Requirements

• GOES-12 located at 75 deg W /- 0.5 deg
  longitude.
• Brasilsat B1 given OK to move from 70 deg W to 75
  deg W and maintain /- 0.1 deg longitude.
• B1 now occupies the middle 0.2 deg of GOES-12
  box.
• StarOne (B1 owners) suggested eccentricity vector
  control to avoid close approaches.
• GOES maneuver control software not capable of
  planning East-West stationkeeping (EWSK)
  maneuvers that include eccentricity vector
  control.
• NOAA desires to not perform any extra maneuvers
  for eccentricity control.
• Analysis performed to determine how eccentricity
  control could be incorporated into the normal
  1-burn EWSK operations.

3
(No Transcript)
4
Eccentricity Control Strategy Recommended By
StarOne
Eccentricity Vector ex e cos(O?) ey e
sin(O?)
5
Effect of Solar Radiation Pressure on
Eccentricity
6
Natural Eccentricity Circle (size depends on
Area/Mass)
EX e cos(O?)
EY e sin(O?)
7
(No Transcript)
8
Eccentricity Control

• Eccentricity vector will tend to follow the
  natural circle throughout the year.
• Desired control circle size is usually smaller.
• Objective is to try to make a short arc of the
  natural circle closely follow the control circle
  over the next EWSK cycle.
• EWSK frequency
• GOES-12 every 11 or 12 weeks
• B1 every 3 weeks

9
Sun at End
ß
?a Change in Sun RA over 1 East-West
Maneuver Cycle
EY
Sun at Start
ß
EX
?a
Control Circle
Natural Circle
10
EY
Next E-W Cycle
ß
?e
ß
EX
?a
Control Circle
Natural Circle
11
Equations (1 of 3)
12
Equations (2 of 3)
?e
RA1
13
Equations (3 of 3)
Note Delta-Vs are normally in negative velocity
direction for 75 West
14
1-Burn vs 2-Burn Control
1-Burn -0.268 m/s
2-Burns -0.478 and 0.211 m/s
15
Single Burn at Perigee
16
2-Burn Control 0.0003 Circle
17
2-Burn Control 0.0002 Circle
18
GOES-12 4-Year Simulation1-Burn East-West
Maneuvers
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
Conclusions

• Analysis has shown that sufficient eccentricity
  control can be accomplished by GOES-12 with
  little or no impact to the normal EWSK operations
  (single-burn).
• Only requirement is a change in the time of the
  burn (move from the normal perigee burn
  location).
• NOAA has incorporated the equations presented
  here into a spreadsheet that computes the nominal
  time of the burn.
• GOES-12 successfully performed the first EWSK
  maneuver with eccentricity control on July 24,
  2007.
• Subsequent EWSK maneuvers have shown that the
  single-burn strategy provides adequate
  eccentricity control.
• Further analysis needs to be done to verify that
  the desired spacecraft separation can be
  maintained in the long term.