1. Attitude Determination and Control System (ADCS)

2. What is a satellite anyway?
Satellite is any object that orbits or revolves around another object.

4. Example of Communication Satellite
Antennas and transceivers send and receive radio signals to and from the Earth or another satellite;
Rocket motors move the satellite in space;
Fuel tanks store the fuel for the rocket;
Solar panels use solar cells to turn the sun's energy into electricity;
Batteries store the electricity generated by the solar panels; and.
On-board processors provide the “brain” of the satellite and tell the satellite to do what humans want it to do.

5. Iridium Network
There will be 66 Iridium satellites in all that will provide mobile telephone and paging services worldwide

8. Use of Satellite
Our society depends on satellites for weather information, communications, navigation, exploration, search and rescue, research, and national defense.

9. All satellites have two principal subsystems:
The platform
The payload

10. Platform
The platform is the basic frame of the satellite and the components which allow it to function in space, regardless of the satellite's mission.
Structure of the satellite
Power
Propulsion
Stabilization and Attitude Control
Thermal Control
Environmental Control
Telemetry, Tracking and Command

11. Payload Communications Position/Navigation
Reconnaissance, Surveillance and Target Acquisition (RSTA)
Weather and Environmental Monitoring
Scientific/Experimental
Manned

12. Low Earth Orbit
Satellites in LEO are just miles ( kilometers) high
Satellites in LEO speed along at 17,000 miles per hour (27,359 kilometers per hour)! They can circle Earth in about 90 minutes

13. Polar Orbit
For this reason, satellites that monitor the global environment, like remote sensing satellites and certain weather satellites, are almost always in polar orbit.

14. Geosynchronous Equatorial Orbit
A satellite in geosychonous equatorial orbit (GEO) is located directly above the equator, exactly 22,300 miles out in space. At that distance, it takes the satellite a full 24 hours to circle the planet.

15. Elliptical Orbit
One part of the orbit is closest to the center of Earth (perigee) and the other part is farthest away (apogee). A satellite in this orbit takes about 12 hours to circle the planet.
Communications satellites in elliptical orbits cover the areas in the high northern and southern hemispheres that are not covered by GEO satellites

16. Satellite Anatomy

17. Satellite Orbits

18. Satellite Anatomy

19. Attitude Determination and Control System (ADCS)
ADCS can be divided into 2 subsystems i.e. Attitude Determination (ADS) and Attitude Control (ACS) ADS will give information on the orientation of spacecraft through the sensor measurements ACS is to measure and control the orientation of the spacecraft and its instrument throughout the mission

20. Schematic Diagram of a Satellite ADCS
Control Algorithms
Actuators
Sensors
Reference Signal
Spacecraft dynamics

21. Attitude Determination System
Attitude Determination is one of the most important subsystems on-board a satellite. This component determinates the satellite’s orientation relatively to the Earth, Sun or other object.

22. Where ADS in the satellite systems?
Block diagram for satellite subsystem

23. Attitude Determination Components
The analysis of attitude determination
The attitude sensors
The attitude determination method
The mathematical model for attitude determination

24. ADS Sensors
To determine the attitude of the satellite with respect to a defined reference frame.
The attitude sensor includes :
(1) Earth sensor
(2) Sun sensor
(3)Star sensor
(4)Rate and integrating sensor, based on gyroscope, laser or other solid state principles
(5) Horizon scanners
(6) Magnetometer

25. Sun Sensor
Sun sensors are used for providing a vector measurement to the Sun

26. Earth Sensor
The earth sensor is composed of four thermopile-optical assemblies viewing four fields of view through a single 13.5mm cut-on optical filter/window
Each earth sensor measures the attitude of the spacecraft relative to its axis

27. Magnetometer
Used mainly for Low Earth Orbit, where the magnetic field of the Earth is well defined and strong a 3-axis magnetometer will provide valuable attitude information.

28. On Board Magnetometer Sensor

29. Selection of ADS Sensors
Magnetometers: low accuracy
Earth sensors: low cost, low risk, moderate accuracy
Sun sensors: low cost, low risk, moderate accuracy
Star sensors: high cost, high risk, high accuracy
Gyroscopes: high cost, high risk, high accuracy
Directional antennas

30. Satellite Orientation
In flight dynamics, the orientation is often described using three angles called roll, pitch and yaw.

31. Orbit coordinate and body coordinate

32. Attitude Control System (ACS)
Keeps the satellite pointed towards the desired location on the Earth. it is very susceptible to external forces of the Sun and Earth that will cause the satellite to move. There are two ways to control a satellite's attitude. First,

33. Satellite Actuator
To modify the attitude of a spacecraft orbiting the Earth, there is only three direct ways: * Firing opposed thrusters to gain angular momentum without perturbing the orbit; * Accelerating or decelerating a momentum wheel inside the spacecraft; * Applying current to magnetic torques.

34. Types of Satellite Actuator
Momentum wheels
Fire thrusters
Magnetotorquer

35. Attitude Control System
Formultion of Roll-Pitch-Yaw for Satellite Orientation

36. Attitude Control Laws Extended Kalman Filter Fuzzy Control
Neural Network Controller
Sliding Mode Control
Projection based Control Law.

37. Space Disturbance
Satellites are subjected to a number of forces in space such as particles streaming from the Sun, meteorites, atmospheric drag, gravity from the Moon, gravity gradients and other perturbations.

38. Stabilization and attitude control
The satellite can be spun up or down (usually between 30 and 300 rotations per minute, or “rpm”) around its axis which provides stability and keeps the satellite pointing in the right direction. These satellites are cylindrical in shape and often referred to as “spinners.”

39. Attitude history of July 2004

40. Three axis stabilization
Roll, pitch and yaw
Satellite controllers send signals to the satellite to fire thrusters in short spurts to control roll, pitch, yaw and to make corrects in orbital altitude
To reduce size, mass, complexity and cost some small satellites are designed to tumble freely through space without any stabilization or attitude control.

41. Two axis stabilization
Many communications satellites are designed to rotate about their longitudinal axis (roll)

42. 3.0 Introduction
Magnetometer
Magnetorquer
Driver
OBC
ACS
Torque command for the MT
Processed attitude data
Attitude Ref
Figure 1: Concept of operations with ADCS subsystems required to meet the attitude modes of operations