1. ACS UC Berkeley Space Sciences Laboratory
Dave Auslander,
Dave Pankow,
Sandhu Jaikarn,
Yao-Ting Mao,
UC Berkeley Space Sciences Laboratory
University of California, Berkeley
February 8, 2010

2. ACS Agenda AGENDA Overview Requirements Environments Development Plan
Issues

3. 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
Operational: Spin Control ; Precession Control; OFF for Science

4. PC Overview dsPIC33FJ256GP710 Simulation Satellite Ground Station
Development Board PC

5. Requirements
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)

6. Environments Development Hardware: 1.dsPIC33FJ256GP710
2.CubeSat Kit. Development Board (DB)
3.Laptop
4.I/O (DAQ card plug in Laptop,TBD)
Development Software:
1.MATLAB
2.Simulink
3. Real-Time Windows Target software
4 MPLAB

7. Development Plans Development
Hand coding the controller from the Simulink model with C code.
Incorporating the code and Simulink model
Building the ground station block in Simulink
Using the same C code of controller implementing in the Pluggable Processor Module (PPM)
Comparing the results from the simulation
Investigating the internal signal flows from each satellite input

8. PC First Step Simulation –PC Simulated Ground Station
Simulink - Matlab
Simulated Satellite Dynamics
Simulated Sensors
Sun Sensor & Mag
Controller
Simulink - Matlab
Simulink - Matlab
Simulink S function in C Code
Simulated Actuators PC
Simulink - Matlab

9. Requirements
Ideal conditions, Spin Rate Controller Verification

10. Requirements
Precession Controller Verification

11. Simulated Satellite Dynamics
Second Step
Simulink (PC) + Board controller
(with the same controller code from 1st Step) PC
Simulated
Ground Station
Simulink - Matlab
Development Station
Simulated Satellite Dynamics
Simulated Sensors
Sun Sensor & Mag
Controller
C Code
Simulink - Matlab
Simulink - Matlab
Simulated Actuators
Simulink - Matlab
DAQ

12. Second Step
Investigate the way for the DB to communicate with Simulink:
One solution now identified:
National Instruments DAQCard-6024E supports real-time module in Simulink.
PC/104  connector block cable( 68-pin series D-type connector and VHDCI 68-pin connector )
DAQ card PCMCIA Laptop

13. Third Step
Investigating the real internal control signal between the control and sensors and actuators or other devices.
Others
Actuators
dsPIC33Family
Magnetic sensors
Sun sensors

14. CINEMA Integration & Test Phase
The so called “PHASING & POLARITY TESTS”
Inject signals on the CINEMA data bus and monitor coil currents
Compare to PC based simulations
Rotate CINEMA (in Earth’s B field) and also illuminate sun sensors
Monitor coils with a hiking compass or test magnetometer

15. Issues
The controller code (c code) from the s-function running in Simulink will need to be verified against the code in the MPLAB IDE (c 30 compiler). Both codes should be as identical as possible.
Verify that the Simulink model is not altered by including the DAQ and the necessary Real Time Kernel for data acquisition

16. Issues
The satellite uses onboard sun sensors to determine angular velocity and sun vector.
Sun sensors alone cannot determine desired attitude, magnetometer data and orbit position are also needed
The satellite communicates with the ground station once every n orbits. The ground station software must determine the satellite attitude and send commands to the satellite to resolve errors in attitude.