Shaun Standley

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Cassini Engineering Operations at Saturn

• Shaun Standley

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S. Standley
19 June 2006
2
Cassini Engineering Operations at Saturn

• Types of engineering operations needed for
  Cassini
• Process for integrating engineering with science
  operations
• Orbit Trim Maneuver (OTM) operations process
• Reaction Wheel Biasing RWA Operations process

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19 June 2006
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The Cassini Spacecraft

• 1N thrusters provide three axis attitude control
• Reaction wheels provide good pointing stability
  but have less control authority
• Attitude is derived from Sun sensors, gyros, and
  a star sensor
• Two Main Engines each provide 100lbs thrust, for
  orbit trim maneuvers not attitude control
• Main engine cover to protect against dust impacts

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S. Standley
19 June 2006
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Cassini Engineering Operations

• Orbit trim maneuvers (OTMs)
• Inertial Reference Unit (IRU) calibrations
• Main engine cover is deployed and stowed in
  response to dust hazards
• Stellar Reference Units (SRU) calibration and
  response to dust hazards
• Suspend Star Identification in response to
  bright bodies
• Reaction Wheel Assembly (RWA) biasing
• RWA friction tests
• Backup RWA exercises
• Pyrotechnic firing operations
• Engine Gimbal Actuators (EGAs) exercise
• On-board parameter update
• Command Loss Timer (CLT) adjustment
• Optical navigation images
• Operational Mode (OpMode) transitions between
  power states

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Integration of Engineering and Science operations
Next Sequence
Previous Sequence
Current Background Sequence
Science Observations
Engineering Operations
OpModes
DSN Passes
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Maneuver Strategy

• Three maneuvers per targeted encounter, periods
  as low as 7 days, often 16 days, maneuver
  magnitudes from 393m/s to 0.02m/s
• Nine hour long primary and backup DSN passes
  reserved for each maneuver
• op mode transitions which support OTMs are placed
  in background sequence during sequence
  development, all other commands have to be
  developed within hours of the maneuver
• Maneuvers executed during a single station pass
  state of health determined, uplink, maneuver
  performed, engineering data recorded and played
  back, science playback before and after maneuver

Approach Targeting Maneuver
?V
Titan (inbound encounter)
?V
Near Apoapsis Maneuver
?V
Cleanup Maneuver
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Main Engine Maneuver Block
Nine hour ground station pass
Main Engine block 244 hr worst case
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Cassini Spacecraft
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Cassini RWA Biasing Process
Vectors
Predicted Events File
Science Activities
Is a new biasing event needed?
Lay out fixed events that effect
wheels OTMs, RCS Flybys, Sequence end
Add biases where required
Kinematic Predictor Tool
RWA Bias Optimization Tool
Selection of wheel bias for each segment
Yes
Body Rates
Optimal and Suboptimal initial wheel speeds
No
Agree time of event with Navigation team
Next Port
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S. Standley
19 June 2006
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Conclusions

• Cassini is a complex mission, kept on track by
  meticulous attention to engineering detail.
• Our approach to operational complexity is
  progressive automation of ground processes to the
  extent possible.
• Automation of ground processes has improved the
  efficiency and accuracy of operations.
• Developing tools and processes for the optimal
  selection of momentum bias has ensured efficient
  use of reaction wheel consumables.
• The spacecraft is in excellent health and we look
  forward to implementing the remainder of the
  Saturn Tour and an extended mission.

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19 June 2006