ACS Dave Auslander, Dave Pankow, Han Chen, Yao-Ting Mao, UC Berkeley Space Sciences Laboratory

1. ACS Dave Auslander, Dave Pankow, Han Chen, Yao-Ting Mao, UC Berkeley Space Sciences Laboratory University of California, Berkeley August 10, 2010

2. Overview • ACS creates Magnetic Torques to control CINEMA attitude & spin • Torque = M (coil moment = mnIA) X B (Earth’s magnetic field) • Precession (or pointing) coil is parallel to spin axis (quasi-DC currents) • Spin coil is orthogonal to spin axis (AC current to spin) • SENSORS: Sun Sensor & Magnetometer •ACTUATORS: two onboard coils • Direction of B changes over each orbit (this data is not available on Cinema) • Ground Station will daily uplink direction of B vs. time (ground ephemeris) • ACS MODES • After Launch: B dot de-tumble mode (has limit function) • Operational: Spin Control ; Precession Control; OFF for Science

3. The Goal of ACS • Mission Requirements: maintain the appropriate attitude for science operations • Spin rate 4RPM • 20 degree cone of pointing accuracy • Each torque coil is required to be operated at a 10% duty cycle for the duration of ACS operations • ACS software is required to use no more than 50% of the available resources. • ACS Requirement on Spacecraft Bus: • Magnetometer data, sun pulses (in real time) • Spacecraft clock,: synchronization with the ground station. • Ground commands: provide B field and adjust controller tasks or parameters • Others( actuator outputs) Desired direction (elliptical normal) parallel

4. SimMechanics Yard Boom ECI ecuator Body Simulink: SimMechanics toolbox: 1 design a simple geometry 2 design for each component’s mass center, inertia of moment

5. Before summer Elliptical normal Spin rate Attitude of the cinema With prefect sensors , no estimators, sample time 0.1 second

6. Before summer Simulink/satellite(complicated) ?? dsPIC33FJ256GP710 ?? (real-time) Simlink/simple model ok ok ok ok Development Board Laptop Serial signal RS232

7. This summer Simulations of simulink ACS in PIC, Environment of space and sensors in PC Test communication of ACS and sensor and ground station Evaluation the results

8. This summer Desired attitude estimator omega x,y,z estimator s t Bang-bang control S>0 , current >0 S<0, current <0

9. Sun ECI estimator sun sun ? R Desired attitude B field Body frame ECI B The cinema knows the B field (ECI) and B field (body), sun attitude (body) Now, using three vector, computing desired attitude (body)

10. Desired attitude estimator Desired attitude cone ECI Desired attitude vector Body frame Over a little bit θ θ θ Sun Desired attitude vector plane Desired attitude vector Correct direction Body frame cone

11. omega Sun ECI estimator attitude

12. Z Y elevation X Sun sensor estimator Z Y Y elevation elevation X X

13. Precession mode Error Real sun position Spin up mode Estimate sun position From sun sensor

14. Solar Panel model Solar panel 10 degree 30 Unable degree Sun sensor 30 Solar panel Elevation determination for sun sensor and solar panel

15. Omega estimator Result from previous computation for desired attitude Want to know Bonus Note: We can also get spin rate from this computation

16. Gravity of disturbance m1 x1 x2 m2 Gravity Disturbance

17. Effect of inertia of moment Real inertia of moment Due to derivation in inertia of moment Inertia of moment in controller Final attitude:1.4 degree

18. Effect of the sample time of the controller Attitude of the cinema Sample time 0.5 second Sample time 1.5 second limitation for sample time precession(1.4 sec)< speed up (2.5 sec)< detumble(5 sec)

19. Instrument control toolbox (simulink) Interfaces from COM and simulink 1 Timeout: waiting time for serial port signals 2 Block sample time: time for sample (a big effect to the simulation model )

20. Protocol design and tasks Data set Begin byte Begin byte Serial data 0 1 2 3 0 1 2 3 ….. ….. data0 data1 Each variable (total 17) is float, each float includes 4 bytes (17x4=68) 1 separate each variable (float->byte) 2 transmit them in the serial port of Simulink 3 receive them in the serial buffer of PIC 4 combine them in the PIC (byte-float)

21. Data flow Simulink PIC B field Body Spin rate from sun sensor Solar Panel current Sun elevation from sun sensor Flag from sun sensor Timer B field ECI (just 2) Ground station command Serial Receiver (decode) ACS code Serial send block Sensor, command Serial send (encode) CINEMA, Ground torque Serial Receiver Interface betweeen COM and simulink

22. Comparing results of Simulink and PIC PIC Simulink Simulink PIC Gravity disturbance

23. Current of coil off Gravity disturbance off off on on On/off 1: coil off 0: coil on

24. Review Control logic I/O Shadow (on or off) Sun sensor and solar panel switcher Sun ECI estimator Rotation matrix Desired attitude of body frame Sun position estimator (for sun sensor) Omega X,Y,Z estimator Control logic B field Body Spin rate from sun sensor Solar Panel current Sun elevation from sun sensor Flag from sun sensor Timer B field ECI Ground station command Desired attitude ECI Sun ECI initial value Lyapunov function Spin rate Mode: detumble, spin up, precession, auto,off, sun normal(yet) Coil on, off, negative on

25. Serial send block Serial Receiver Review the full structure Shadow analysis Ground Station Dynamics of the satellite (c code, *exe) *Solar panel model (Area, unable 10 degree) Data sets of magnetic field and sun (c code,*exe) Sun sensor model (update each revolution) Control logic Gravity Disturbance *magnetometer Physical body of the satellite Actuator * Magnetometer assume prefect model *Color text box means finish

26. Sun sensor simulation form Prof. Auslander and Han Chen (Least square ) Time degree * period rotation Nonlinear region Maybe due to the number of the data Elevation degree

27. Q & A