ADCS

(Attitude Determination and Control System)

The purpose and the role of ADCS

ADCS is an abbreviation of "Attitude Determination and Control System".

XI, which is our first CubeSat and was launched in 2003, adopted passive attitude control system using permanent magnet and magnetic damper. This means XI cannot steer in the desired direction. In case of PRISM, we must control its attitude acticvely on the basis of the requirements of Optics subsystem.

PRISM ADCS aims at following achievement.

• Steer lens at Earth
  In space, the gravity gradient torque affects spacecrafts. For this reason, whether the lens or the satellite body steers at Earth and stabilizes. The lens may steer at Earth first, and vice versa. If PRISM has stabilized upside down, ADCS takes charge of its remediation.
  
  
• Prevent oscillation at capturing image
  When we try to take a picture with our digital camera, we somtimes get a blurred picture due to the shaky hands. The same holds true for PRISM. In order to get a picture with higher resolution, PRISM has to stop with respect to surrounding space at the moment of capturing.
  
  
• Steer in the desired direction
  This is an advanced mission. Optics does not require this function, but ADCS by ourselves tries to achieve the technology. Above functions realize only the state that PRISM always steers at Earth and gets pictures directly underneath. If PRISM can steer in the desired direction, it will take pictures with the edge of Earth like XI, or with Moon or Sun in it.

Success level of ADCS subsystem

We set the success level of ADCS subsystem as below.

Level	Setting
Minimum success	We can confirm normal operation of sensors.
Middle success	PRISM can estimate the attitude by the output of the sensors. We can confirm the attitude stabilization by the garvity gradient.
Full success	PRISM can control the attitude by the actuators.
Advanced success	PRIMS can control the atttiude so as to orient other direction than the earth center.

Functions of ADCS

The following figure is the function diagram of ADCS.

PRISM will be equipped with following sensors and actuators.

• Sensors: Magnetometers, Gyros (Angular velocity sensors), and Sun sensor
• Actuators: Magnet torquers

A magnet torquer is a coil rolled up with conductive wire. If we apply the current to this, the magnetic field will be generated and it will give torque by being interferred with geomagnetic field. This actuator is often adopted for the attitude control with satellites in LEO.

Components

Now, ADCS members develop FM boared.
We show 2nd EM components here.

Photo magnetic-torquer XYaxis

Photo magnetic-torquer Zaxis

Photo sunsensor

Photo　magneticsensor & Gyro board