ATTITUDE DETERMINATION AND CONTROL SYSTEMS

Attitude Determination & Control System has the function of the estimation of the satellite’s attitude (pointing direction) , generation of the torque necessary to maintain the required attitude and  damping of angular velocity (attitude control). 

Attitude determination and control system is the largest system (in terms of mass, volume occupied and power consumed) of a satellite.

Why do we need ADCS in a satellite?

A lot of external disturbances act on a satellite in the so-called void of space. In a Low Earth Orbit (LEO- 160 - 2,000 km from surface of earth) or Polar Orbit a satellite experiences:

1)      Aerodynamic drag: from the residual atmosphere of the earth

2)      Magnetic disturbances: from earth’s magnetic field

3)      Gravity Gradient Torque: tends to align a non symmetrical satellite along its axis of least moment of inertia.

4)      Solar radiation pressure: Due to photons colliding with the relatively large surface of a solar panel.

All these tend to change the orientation of the satellite. As the satellite moves away from its pointing direction it causes disruption in smooth functioning of the other subsystems of the satellite like the payloads, communication and the power subsystems. ADCS steps in here to determine the orientation and keep it within the required values.

The major tasks include:

1)      Detumbling of the satellite upon insertion into orbit.

2)      Determining the orientation of the satellite.

3)      Generating the required torque for regular station keeping operations.

 Attitude determination can be done by using various sensors like MEMS gyro sensor, magnetometer, sun sensor, star sensors, etc. The OBC then calculates the attitude using sensor data from the satellite and the results are compared. As attitude control, reaction wheels, momentum wheels, magnetorquers, etc can be used as the control devices to generate the required torque and also damp the angular velocity.

What we will do as a part of ADCS?

During this project the ADCS include the following phases:

1)      The Pre-designing Phase: Includes the finalising the sensors and actuators, developing the attitude dynamics of the satellite for these sensors and determining the control laws.

2)      The Designing Phase: Includes the circuit design, Simulations of sensor data and actuator response as well as testing the working of the circuit under various flight circumstances.

3)      The Interfacing Phase: Includes the interfacing of the system with all the other sub systems and correction of errors.

4)      The Integration Phase: Includes the integration of satellite into a fully autonomous system and related testing.

This system plays a key role in the proper functioning of the satellite and failure is not what we are looking for. Perseverance pays. Enthusiasm to learn and patience to continue working when nothing seems to work is a must.