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Attitude Determination
and Control
By Ahmad Farrag
ADCS Team Leader
•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
Outline
By Ahmad farrag
By Ahmad farrag
Euler angels
Velocity Vector
X
Y
Z
Nadir
By Ahmad farrag
Why ADCS is needed ?
By Ahmad farrag
Why ADCS is needed ?
disturbances
By Ahmad farrag
Influence of Satellite Mission And Other
Subsystems Upon ADCS
By Ahmad farrag
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
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.
ADCS Tasks
By Ahmad farrag
10
ADCS operational modes
DM
finished
ADCS
failure
DM SM IM
EM
Imaging
command
Finishing imaging
session
ADCS
failure
ADCS
failure
Fixing of ADCS
failure
By Ahmad farrag
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
ADCS Sensors
• Earth’s sensor
By Ahmad farrag
ADCS Sensors
• sun sensor
By Ahmad farrag
• Star sensor
ADCS Sensors
By Ahmad farrag
ADCS Sensors
• Magnetometer
By Ahmad farrag
ADCS Sensors
• Gyro
By Ahmad farrag
ADCS Sensor Performance Summary
By Ahmad farrag
20
Reaction wheel
ADCS Actuators
SC
RW
By Ahmad farrag
21
N S
N
S
Magnetic actuators
ADCS Actuators
By Ahmad farrag
Thrusters
ADCS Actuators
By Ahmad farrag
23
Disturbances
Magnetic
Dis.
External Disturbance Torques
N
S
By Ahmad farrag
24
Disturbances
Magnetic
Dis.
Gravity
Dis.
F1 F2
External Disturbance Torques
By Ahmad farrag
25
Disturbances
Magnetic
Dis.
Gravity
Dis.
Aerodynamic
Dis.
Solar
Pressure Dis.
Cg
R
Cps
External Disturbance Torques
By Ahmad farrag
Orbital Altitude
Torq
ue
Solar
Press.
Drag
Gravity
Magnetic
LEO GEO
NOTE: The magnitudes of the torques is
dependent on the spacecraft design.
External Disturbance Torques
By Ahmad farrag
•Accuracy within 50
•No maneuvering capabilities
Accuracy from 0.10 to 10
Need large spinning platform
Large control systems needed to adjust spacecraft
orientation
Gravity Gradient
ADCS Control Techniques.
Control Techniques
ActivePassive
Spin Stabilized Dual Spin Stabilized Three-Axis Stabilization:
MT
Three-Axis Stabilization:
RW
Earth
Passive
Magnetic
control
By Ahmad farrag
28
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 StabilizationInertial fixed any
direction
±0.1 deg to ±1 deg in 2 axes
(proportional to spin rate)
Dual-Spin StabilizationInertial fixed any
direction
Same as above for single spin
Despun dictated by payload
reference and pointing
Three axis stabilization
using reaction wheelsNo constraints ±0.001 deg to ±1 deg
Three axis stabilization
using magnetorqure
Best suited for nadir
pointing±5 deg
Three axis stabilization
using thrustersNo constraints
±0.1 deg to ±5 deg High rates
possible
ADCS Control Techniques.
By Ahmad farrag
By Ahmad farrag
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