10-08-2012, 10:11 AM
Attitude and Orbit Control Systems
DetumblingSatellites.ppt (Size: 309.5 KB / Downloads: 69)
After deployment from the launcher the satellite will tumble until the attitude control System (ACS) stabilizes the satellite.
The purpose for the detumbling of the satellite is to prevent the satellite from becoming inoperable due to a loss of control.
It is probable that the satellite will experience the detumbling mode only once right at the beginning its life..
Sensor Used in Detumbling Mode
The three-axes-magnetometer is suitable to be used for small satellite requests low cost, low weight,close to earth and reliable attitude sensor.
The three-axis-magnetometer is used to calculate the magnitude of the dipole moment with the magnetic torques that is amplified and reversed-directed to the derivative of the earth's magnetic field vector in the rotating body frame.
The attitude determination system needs to use a sequence of magnetometer measurements. These measurements process recursively in a Kalman filter
Actuators-Detumbling Mode
Magnetic torquers can beused as the actuators.
Magnetic torquers enforces a torque on the satellite by creating a magnetic field which interacts with the earths magnetic field.
One of the other advantages with the torquers is that it is equipped with digital nine pin connection, which eliminates the need for the power supply and current control hardware needed for the magnetic coils.
Control Algorithm-Detumbling Mode
The B-Dot control law is a simple and reliable method that is suitable for this purpose.
The detumbling system activates when a critical point of 0.9 kg-m2/s of momentum in any direction is reached and begins to regain control of the satellite via the b dot control law.
This law operates by reducing the satellite’s kinetic energy to zero, which in turn slows down the satellite until control is regained.