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ACS Dave Auslander, Dave Pankow, Sandhu Jaikarn, Yao-Ting Mao, UC Berkeley Space Sciences Laboratory University of California, Berkeley February 8, 2010. ACS Agenda. AGENDA Hardware Requirements Software Requirements Control Design Model Issues. Requirements. ACS Hardware.

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ACS Dave Auslander, Dave Pankow, Sandhu Jaikarn, Yao-Ting Mao,

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  • ACS

  • Dave Auslander,

  • Dave Pankow,

  • Sandhu Jaikarn,

  • Yao-Ting Mao,

  • UC Berkeley Space Sciences Laboratory

  • University of California, Berkeley

  • February 8, 2010


ACS Agenda

  • AGENDA

    Hardware Requirements

    Software Requirements

    Control Design

    Model Issues


Requirements

ACS Hardware

  • Actuators

    • Torque Coils:

      • 1.23 Am2 (62 turns copper wire 26 inch gauge) at 5.2W

      • 10% Duty  5.3 x 10-5 N-m at 650km orbit altitude

      • Orientation perpendicular to spin axis : Pointing

      • Orientation parallel to spin axis: Spin

  • Sensors:

    • Sun Sensor

      • V-Slit sun sensor oriented looking up at the spin plane

      • Contains two collimated photodiode devices with a

      • 5° x 80° FOV

    • Magnetometer

      • 25 nT resolution in engineering mode

      • Cadence: 1 vector/s at 0.1W

      • Note: Torque coils and magnetometer can be active simultaneously.


Requirements

Software Modes

  • Detumble Mode

    • Detumble maneuver using B-Dot control

  • Initialization Mode

    • Acquire attitude using currents in solar panels

    • Spin-up and initialize sun sensors.

  • Spin-Up/Precession Modes

    • Establish desired spin rate of 4 RPM

    • Establish sun normal orientation (Spin axis normal to sun vector)

  • Nominal Mode

    • Idle mode. ACS OFF.


Design

ACS Control Laws

  • Detumble

    • B-Dot controller from magnetometer data to reduce angular velocities from launch vehicle separations .


Design

ACS Control Laws

  • Spin/Precession Controller

  • Same laws apply in ground based control

    • Spin Controller

    • Precession Controller

E = hf - h (hf is desired final angular momentum)

E = kB - k (kB is desired final orientation)


Issues

Sun Sensor Model

kss is a constant derived geometrically and through simulations.


Issues

Sun Sensor Model

Non-Linear!

Need to investigate sun sensor activation model


Issues

Sun Sensor Model

  • Must rely on uplinked data, system clock, and magnetometer data when the sun is outside the range of the sun sensors or the satellite is in shadow.

  • Multiple pulses (glint) and/or lack of pulses from failed sensor may affect satellite behavior. This behavior is difficult to predict and design for


End


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