1. Attitude Determination
and Control
By Ahmad Farrag
ADCS Team Leader

2. Outline
•Terminology
•Why ADCS is needed ?
• Relation Between Satellite Mission And Other
Subsystems Upon ADCS
•ADCS Tasks
•Satellite Operational Modes
•ADCS Sensors
•ADCS Actuators
•Disturbance Torques
•Attitude Control Techniques
By Ahmad farrag

3. By Ahmad farrag

4. Euler angels
X
Velocity Vector
Y
Z
Nadir
By Ahmad farrag

5. Why ADCS is needed ?
By Ahmad farrag

6. Why ADCS is needed ?
disturbances
By Ahmad farrag

7. Influence of Satellite Mission And Other
Subsystems Upon ADCS
By Ahmad farrag

8. 8
ADCS Tasks
 damping of angular velocities, obtained by the satellite during its
separation from a LV and initial construction of the satellite attitude
in OCS during the established time
 the satellite teliting with respect to OCS to the required angles
and its stabilization in the turned position with the required
accuracy during the imaging mode
By Ahmad farrag

9. 9
ADCS Tasks
 the satellite three-axis attitude control in OCS during the
non imaging modes with low accuracy to save the consumed
power
 check the ADCS components function during any failure
 satellite attitude determination with the required accuracy.
By Ahmad farrag

10. 10
ADCS operational modes
Finishing imaging
session
DM SM IM
DM
finished
ADCS
failure
EM
Imaging
command
ADCS
failure
ADCS
failure
Fixing of ADCS
failure
By Ahmad farrag

11. ADCS devices
• A satellite in space must point to a given direction
as assigned by the mission requirements.
• Many satellites are earth orientated while others
are inertial space object oriented such as sun or a
star of interest.
• The orientation of the satellite in space is known
as its attitude.
• In order to achieve control and stabilization of the
satellite
• Attitude sensors are used to determine the current
attitude & actuators are used to generate required
torque to maintain the required attitude. By Ahmad farrag

12. ADCS Sensors
• Earth’s sensor
By Ahmad farrag

13. ADCS Sensors
• sun sensor
By Ahmad farrag

14. ADCS Sensors
• Star sensor
By Ahmad farrag

15. ADCS Sensors
• Magnetometer
By Ahmad farrag

16. ADCS Sensors
• Gyro
By Ahmad farrag

17. ADCS Sensor Performance Summary
By Ahmad farrag

18. 20
Reaction wheel
ADCS Actuators
SC
RW
By Ahmad farrag

19. 21
N S
N
S
Magnetic actuators
ADCS Actuators
By Ahmad farrag

20. Thrusters
ADCS Actuators
By Ahmad farrag

21. 23
Disturbances
Magnetic
Dis.
External Disturbance Torques
N
S
By Ahmad farrag

22. 24
External Disturbance Torques
Disturbances
Magnetic
Dis.
Gravity
Dis.
F1 F2
By Ahmad farrag

23. 25
Disturbances
Magnetic
Dis.
Gravity
Dis.
Aerodynamic
Dis.
Solar
Pressure Dis.
Cg
R
Cps
External Disturbance Torques
By Ahmad farrag

24. External Disturbance Torques
NOTE: The magnitudes of the torques is
dependent on the spacecraft design.
Orbital Altitude
Torque
Solar
Press.
Drag
Gravity
Magnetic
LEO GEO
By Ahmad farrag

25. ADCS Control Techniques.
Earth
Accuracy from 0.10 to 10
•Accuracy within 50
Need large spinning platform
•No maneuvering capabilities
Large control systems needed to adjust spacecraft
orientation
Gravity Gradient
Control Techniques
Passive Active
Spin Stabilized Dual Spin Stabilized Three-Axis Stabilization:
MT
Three-Axis Stabilization:
RW
Passive
Magnetic
control
By Ahmad farrag

26. 28
ADCS Control Techniques.
Type Pointing Options Typical Accuracy
Passive Magnetic North/south only ±5 deg (2 axes)
Gravity-gradient Earth nadir pointing only ±5 deg (roll and pitch axis)
Single-Spin Stabilization
Inertial fixed any
direction
±0.1 deg to ±1 deg in 2 axes
(proportional to spin rate)
Dual-Spin Stabilization
Inertial fixed any
direction
Same as above for single spin
Despun dictated by payload
reference and pointing
Three axis stabilization
using reaction wheels
No constraints ±0.001 deg to ±1 deg
Three axis stabilization
using magnetorqure
Best suited for nadir
pointing
±5 deg
Three axis stabilization
using thrusters
No constraints
±0.1 deg to ±5 deg High rates
possible
By Ahmad farrag

27. By Ahmad farrag