Antenna Contact During Calibration Maneuvers

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Antenna Contact During Calibration Maneuvers

• Joseph A. Hashmall
• Laurie Mann
• a.i. solutions, Inc.

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Agenda

• Handovers
• Calibration Maneuvers
• Constraints

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Handovers

• Antennas are always on
• Antenna beam can not hit the spacecraft
• Loss of Signal
• Possible Damage to Instruments
• Antenna Masks
• Masks implemented in onboard software to prevent
  violation
• Masks created and validated by Mechanical
  Engineering
• Handovers do not violate vibration constraints

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Antenna Masks
3-d plot of unit vectors
-Z antenna can not point here
Z antenna can not point here
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Antenna Masks in Antenna Coordinate System
Azimuth/Elevation Coordinates
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Handover and Eclipse Seasons
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Gimbal Angles During Handovers
HANDOVER
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Gimbal Path
Without Handover
With Handover
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Calibration Maneuvers

• HMI/AIA Roll (360 deg)
• 22.5 degree steps (10 minutes)
• 15 minute dwell times for calibration
• About 7 hours duration
• Twice a year (near eclipse season)
• EVE Cruciform (2.5 deg)
• No more than 2.5 degree offset
• Offset in pitch and yaw
• About 9 hours duration
• Four times a year
• Other calibration maneuvers are small

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Constraints

• Maintain Contact
• For HMI/AIA Roll during dwell times
• Observe gimbal rate constraints
• Calibration during daylight (non-eclipse)
• Star trackers not both occulted

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Scheduling Strategy

• EVE Cruciform
• Schedule during non-handover season
• or
• Schedule so that Z excursion occurs near
  northern extreme or Z excursion near southern
  extreme
• HMI/AIA Roll
• Schedule to replace a handover during handover
  season

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EVE Cruciform Schedule
Z
N
White Sands
-Z
Plus Pitch here or Minus Pitch here
Sun
Z
-Z
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HMI/AIA Roll Schedule
Z
N
White Sands
-Z
Roll Maneuver
Sun
-Z
Z
Roll Maneuver Replaces Handover
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HMI/AIA Roll Schedule Constraints

• No antenna interference
• Minimize required gimbal rates
• Minimize periods with both Star Trackers occulted
• All dwell periods in Sunlight (during eclipse
  season)

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HMI/AIA Roll Variables

• Maneuver time
• Roll direction
• IF NEEDED
• Dwell time (greater than 15 minutes)
• Step time (greater than 10 minutes)

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Maneuver Planning Parameters

• Maximum Gimbal Rates
• If below limit then continuous tracking possible
• Vibrations damp during settling period
• Maximum Mean Gimbal Rates
• Mean rate over each maneuver segment
• If mean rate less than limit then antenna can
  target final required gimbal position
• Tracking after settling period
• Minimize Rates

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Planning Parameter Results (1)
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Planning Parameter Results (2)
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Planning Parameter Results (3)
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Planning Parameter Results (4)
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Summary(1)

• No problems scheduling most calibration maneuvers
  are anticipated
• HMI/AIA roll calibration maneuvers will require
  significant planning
• There are periods in any day during which all
  gimbal angle and rate constraints are met

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Summary(2)

• Precise criteria for optimizing maneuver times
  must be specified
• Tracking or Direct Slew?
• Minimum vibrations after settling
• Beam path over land (if direct slew)
• Changes in calibration maneuver profiles
  (maneuver dwell times or slew rates) are not
  anticipated