1. KUFASAT STUDENTS’ SATELLITE
GRAVITY GRADIENT STABILIZATION OF SMALL SATELLITE USING FUZZY LOGIC CONTROLLER
kufasat
KUFASAT
STUDENTS’ SATELLITE
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

2. INTRODUCTION (KUFASAT)
Kufasat is a student satellite program , the goal of this program is to design and launch a cube satellite.
The satellite is intended to fly in a low earth orbit at 600km altitude , its mission is to perform scientific measurements.
It have a total mass of approximately 1kg and be three -axis gravity gradient stabilized.
The satellite consists of (1.5) m long gravity gradient boom which has a tip mass of (40) g to improve the gravity gradient stabilization.

3. INTRODUCTION (THE COILS)
kufasat
Three magnetic coils are added to improve both the three axis stabilization and the pointing properties.
Magnetic coils around the satellite's XYZ axes can be fed with a constant current-switched in two directions-to generate a magnetic dipole moment which will interact with the geomagnetic field to generate a satellite torque, which is used to control the rotation of the satellite.
The magnetic coils are controlled by using fuzzy logic controller, based on a combination of membership functions and rules.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

4. INTRODUCTION (AIM OF WORK)
kufasat
The purpose of this study is to design and to develop an efficient ADCS - attitude determination and control system for the satellite.
The controller consists actually of 3 MIS0 fuzzy control laws, one for each magneto torquer (MX, MY and MZ coils).
Each control law embodies a fuzzy rule base to decide on the control desirability and output level when using the corresponding torquer.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

5. Attitude Determination
SATELLITE SUBSYSTEMS
kufasat
Space Segment
Payload
Bus
Structure
Attitude Determination
And Control
Thermal
Propulsion
Power
Command and
Telemetry
Data Handling
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

6. STABILIZATION OF SATELLITE
kufasat
Stabilization of spacecraft is the process of maintaining an existing orientation with respect to some external frame (coordinate system) .
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

7. GRAVITY GRADIENT STABILIZATION
kufasat
The only completely passive attitude control which has been used with any success is the gravity gradient method
Gravity-gradient stabilization uses the Earth's gravitational field to keep the spacecraft aligned in the desired orientation.
The spacecraft is designed with a mass distribution that keeps one end closer to the Earth.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

8. MODE OF STABILIZATION OF SATELLITE
kufasat
It can be divided into three modes:
1- Detumbling mode: A detumbling mode is activated in order to calm down the movement .
2- Boom deployment mode: The gravitation boom will be deployed first when the movement of the satellite is sufficient small.
3- Three-axis stabilization mode (pointing mode):This study deals with this mode after the detumbling mode has successfully been completed and the boom is fully deployed.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

9. SATELLITE’S ATTITUDE
kufasat
Orientation of satellite as perceived in a certain frame of Reference
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

10. CHANGE IN ATTITUDE
kufasat
Satellite tends to change its orientation because of environmental torques
Drag of residual atmosphere
Solar radiation pressure
Gravity gradient
Interaction of Satellite electronics with earth’s magnetic field
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

11. PARAMETERIZATION OF ATTITUDE
kufasat
There are 3 common ways of describing attitude:
1) Direction Cosine Matrix
2) Euler Angles
3) Quaternions
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

12. ATTITUDE CONTROL Needed because- Payload requirements
kufasat
Needed because-
Payload requirements
Focusing the satellite camera to a particular location on earth
Communication requirements
Pointing the antenna towards ground
Power system requirements
Tracking the sun to achieve maximum power generation
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

13. COMPONENTS OF ADCS Sensors- To determine the orientation and
kufasat
Sensors- To determine the orientation and
position of the satellite
Algorithms- To calculate the deviation from the desired orientation and to generate actuation command to counter the deviation
Actuators- To act upon the signals given by the
control algorithms and to produce the necessary
torques
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

14. ADCS HARDWARE Sensors: Actuators: Sun sensor Magnetometer (MAG)
kufasat
Sensors:
Sun sensor
Magnetometer (MAG)
Star tracker
Gyro
GPS receiver
Actuators:
Magnetorquer (torque rod) (MTQ)
Reaction wheel (RW)
Thruster
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

15. ATTITUDE CONTROL – CONTROL LOOP
kufasat
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

16. THREE PROPOSED CONTROLLERS
kufasat
In this work the controller achieved by using magnetic coils as actuators via some control techniques to do three-axis stabilization satellite .
Three control schemes are proposed which are:
1- Proportional-Integral-Derivative controller (PID ).
2- Linear Quadratic Regulator (LQR).
3- Fuzzy Logic Controller (FLC).
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

17. PID CONTROLLER
kufasat
A Proportional-Integral-Derivative controller (PID controller) is the most widely used controller with feedback mechanism. It is one of the simplest control algorithms, and in the absence of knowledge of the underlying process, PID controller is often the best choice.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

18. PID CONTROLLER BLOCK DIAGRAM
kufasat
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

19. INITIAL CONDITIONS Initial conditions values for attitude response
kufasat
Case No.
ωx (rad/s)
ωy (rad/s)
ωz (rad/s)
Roll (rad)
Pitch (rad)
Yaw
(rad)
Case 1
(attitude only)
0.1
-0.2
0.15
Case 2
(nutation only)
-0.3
0.2
Case 3
(attitude & nutation)
Initial conditions values for attitude response
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

20. PID CONTROLLER RESULTS 1
kufasat
Angular positions for case 1
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

21. PID CONTROLLER RESULTS 2
kufasat
Angular positions for case 2
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

22. PID CONTROLLER RESULTS 3
kufasat
Angular positions for case 3
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

23. LQR CONTROLLER
kufasat
A more advanced method than PID and common controller investigated for satellites with magnetorquers is the Linear Quadratic Regulator (LQR), Which is used state-space approach to analyze a system.
𝑥 𝑥 𝑥 3 𝑥 𝑥 𝑥 = − 4 𝜔 𝑜 2 𝐼 𝑦 − 𝐼 𝑧 𝐼 𝑥 𝜔 𝑜 𝐼 𝑥 − 𝐼 𝑦 + 𝐼 𝑧 𝐼 𝑥 0 − 3 𝜔 𝑜 2 𝐼 𝑥 − 𝐼 𝑧 𝐼 𝑦 − 𝜔 𝑜 2 𝐼 𝑦 − 𝐼 𝑥 𝐼 𝑧 − 𝜔 𝑜 𝐼 𝑥 − 𝐼 𝑦 + 𝐼 𝑧 𝐼 𝑧 0 0
𝑥 1 𝑥 2 𝑥 3 𝑥 4 𝑥 5 𝑥 𝐵 𝜓 / 𝐼 𝑥 −𝐵 𝜃 / 𝐼 𝑥 − 𝐵 𝜓 / 𝐼 𝑦 0 𝐵 𝜑 / 𝐼 𝑦 𝐵 𝜃 / 𝐼 𝑧 − 𝐵 𝜑 / 𝐼 𝑧 𝑚 𝑥 𝑚 𝑦 𝑚 𝑧
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

24. LQR CONTROLLER kufasat
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

25. LQR CONTROLLER RESULTS 1
kufasat
Angular positions for case 1
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

26. LQR CONTROLLER RESULTS 2
kufasat
Angular positions for case 2
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

27. LQR CONTROLLER RESULTS 3
kufasat
Angular positions for case 3
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

28. FLC CONTROLLER
kufasat
Fuzzy control provides a formal methodology for representing, manipulating, and implementing a human's heuristic knowledge about how to control a system . The main elements of the fuzzy logic controller (FLC) are a fuzzification, inference mechanism, rule-base and a defuzzification .
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

29. FLC CONTROLLER
kufasat
Here we used MISO fuzzy controller for each coil, proving that the fuzzy controller solves the control constrain problem by choosing the best magneto-torque, polarity and switching instances. The Takagi-Sugeno -type of fuzzy processing is used in controlling of kufasat system . This controller has nine rules, three linguistic variables for its membership functions.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

30. Three-axis Fuzzy Controller Design
kufasat
Rule base for the controller of roll, pitch and yaw angles
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

31. Three-axis Fuzzy Controller Design
kufasat
Two inputs one output Fuzzy Inference Structure (FIS) ,
MISO fuzzy controller
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

32. Three-axis Fuzzy Controller Design
kufasat
Membership functions for the input Ephi (Error)
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

33. Membership functions for the input CEphi (Change of Error)
kufasat
Membership functions for the input CEphi (Change of Error)
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

34. Three-axis Fuzzy Controller Design
kufasat
Membership functions for the output U
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

35. Three-axis Fuzzy Controller Design
kufasat
List of rules for fuzzy inference structure (FIS)
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

36. Three-axis Fuzzy Controller Design
kufasat
Implementation of FIS
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

37. Three-axis Fuzzy Controller Design
kufasat
The output surface of the fuzzy inference system
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

38. FLC CONTROLLER kufasat
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

39. FLC CONTROLLER RESULTS 1
kufasat
Angular positions for case 1
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

40. FLC CONTROLLER RESULTS 2
kufasat
Angular positions for case 1
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

41. FLC CONTROLLER RESULTS 3
kufasat
Angular positions for case 1
A Roll
B Pitch
C Yaw
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

42. System analysis of (PID , LQR & FLC) case 1
kufasat
Controller
Angles
Delay Time (Td) sec
Rise Time (Tr) sec
Peak Time (Tp) sec
Settling Time
(TS) sec
Peak Overshoot
PO%
Steady State Error %
PID
Roll 44 56 76
480 65 4
Pitch 18 21 23
105 80
0.5
Yaw 19 22 55 62
0.2
LQR
338
540
617
907 10 3
501
608
800 30
598
791 12 1
Proposed FLC
2.75
3.5 5
17.5
3.25
0.4
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

43. System analysis of (PID , LQR & FLC) case 2
kufasat
Controller
Angles
Delay Time (Td) sec
Rise Time (Tr) sec
Peak Time (Tp) sec
Settling Time
(TS) sec
Peak Overshoot
PO%
Steady State Error %
PID
Roll 33 44 68
510 88 6
Pitch 16 18 20
103 70
Yaw 17 54 62
LQR
613
627
679
849
110 1
598
607
656
4926
200 80
600
617
665
5216 85
Proposed FLC
1.75
2.25
0.5
4.5
14.75
2.75
0.4
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

44. System analysis of (PID , LQR & FLC) case 1
kufasat
Controller
Angles
Delay Time (Td) sec
Rise Time (Tr) sec
Peak Time (Tp) sec
Settling Time
(TS) sec
Peak Overshoot
PO%
Steady State Error %
PID
Roll 33 44 68
510 88 6
Pitch 16 18 20
103 70
Yaw 17 54 62
LQR
613
627
679
849
110 1
598
607
656
4926
200 80
600
617
665
5216 85
Proposed FLC
1.75
2.25
0.5
4.5
14.75
2.75
0.4
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

45. Attitude Control Maneuver (ACM) test
kufasat
ACM 1 for initial Euler attitude [0° 0° 0°] , and the reference [10° 20° 30°]
ACM 2 for initial Euler attitude [10° 20° 30°], and the reference [-10°- 20° -30°]
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

46. Attitude Control Maneuver (ACM) test
kufasat
ACM 4 for initial Euler attitude [20° 60° 80°], and the reference [50° 0° -20°]
ACM 3 for initial Euler attitude [-10°- 20° -30°], and the reference [40° 60° 80°]
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

47. Attitude Control Maneuver (ACM) test
kufasat
ACM 5 for initial Euler attitude [-60°- 60° -60°], and the reference [40° 60° 80°]
ACM 6 for initial Euler attitude [180° -170° 50°], and the reference [10° -10° 20°]
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

48. CONCLUSIONS
kufasat
1-Gravity gradient stabilized system has limited stability and
pointing capability.
2- Magnetic coils are added in order to improve the attitude
control.
3- By comparison between FLC, PID and LQR controllers it can
be observed that the fuzzy logic controller has satisfactory
robustness for any sudden change in the satellite
parameters and provides better stability, tighter control,
better performance in both steady state and transient state
responses over the conventional PID and LQR controller.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

49. FUTURE WORKS
kufasat
1- Due to an onboard power limitation only one magneto-torquer coil can be switched on at a time. A control algorithm must be modified to allow for the choice of the coil that will achieve the best results, given the local geomagnetic field vector.
2- The performance of the attitude control using fuzzy logic controller can be tested experimentally using Helmholtz cage and test bed which provides air bearing and air gap control.
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS

50. Thank you
kufasat
UNIVERSITY OF KUFA COLLEGE OF SCIENCES DEPARTMENT OF PHYSICS