Adcs

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


By Ahmad farrag

25

Disturbances

Magnetic

Dis.

Gravity

Dis.

Aerodynamic

Dis.

Solar

Pressure Dis.

Cg

R

Cps


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.


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


using magnetorqure

Best suited for nadir

pointing±5 deg


using thrustersNo constraints

±0.1 deg to ±5 deg High rates

possible

ADCS Control Techniques.

By Ahmad farrag

By Ahmad farrag

Engineering

Adcs