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Attitude Determination & Control System Conceptual Design Review

Attitude Determination & Control System Conceptual Design Review. Jason Tunis. Presentation Outline. Derived Requirements Sensing Actuation Control Disturbances Spin Stabilization Conclusions Schedule. Derived Requirements. Pointing accuracy of: ± 1 ° [TBC] during de-orbit burns

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Attitude Determination & Control System Conceptual Design Review

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  1. Attitude Determination & Control System Conceptual Design Review Jason Tunis

  2. Presentation Outline • Derived Requirements • Sensing • Actuation • Control • Disturbances • Spin Stabilization • Conclusions • Schedule Jason Tunis

  3. Derived Requirements • Pointing accuracy of: • ± 1° [TBC] during de-orbit burns • ± 4° [TBC] at impact • Mass < 4 kg [TBC] • Power < 3 W [TBC] Jason Tunis

  4. Sensing • Inertial Measurement Unit (IMU) • 3 gyroscopes • 3 accelerometers • Position and attitude awareness • Minimal drift over mission length Jason Tunis

  5. Actuation • 8 thrusters for pointing control • 2 or 4 thrusters for spin control • Ideal for short missions • High Torque capabilities Jason Tunis

  6. Control • Negative feedback loop • Variable gain controller Disturbances θdesired θactual Control Actuation Dynamics + - Sensing Jason Tunis

  7. Disturbances • Detachment from carrier • Separation of propulsion units • Thrust misalignment • Gravity gradient Jason Tunis

  8. Thrust Misalignment TP = De-orbit thrust [N] Le = Thrust Error [m] TC = Control thrust [N] LC = Control moment arm [m] LC TC TP TC Jason Tunis

  9. Thrust Misalignment Torque (con’t) Jason Tunis

  10. Gravity Gradient µ = Gravity constant of the moon IT = Transverse moment of inertia IL = Longitudinal moment of inertia R θ Jason Tunis

  11. Gravity Gradient Torque (con’t) Jason Tunis

  12. Spin Stabilization • Spin about the longitudinal axis • Produces gyroscopic stiffness • Disturbance effects are averaged out • Energy dissipation must be minimized • Active control typically required Jason Tunis

  13. Conclusion • Disturbances during de-orbit are large for 4500 N thrust case • Large attitude control thrusters required • Mass budget of 4 kg unfeasible for this case • Disturbances during descent are small • Passive spin stabilization shall be analyzed for descent phase Jason Tunis

  14. Schedule Jason Tunis

  15. Questions?

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