Attitude Determination and Control System (ADCS)
Attitude Determination and Control Systems (ADCS) is the subsystem of a satellite team dedicated to the determination of the satellite, as well as the position. In order to determine its orientation and position, a combination of sensors is used to calculate a reliable estimate of its coordinates.
In order to calculate the attitude and position, Sensors such as Sun Sensors, GPS, Magnetometers and Gyroscopes are used together to create an array of processable data. By using the controller algorithm, designed in advance, the position and orientation may be calculated.
Once the position and orientation have been calculated, the satellite may need to re-position in order to face a particular direction, such as pointing the solar panels towards the sun for recharging, or pointing the camera at a desired coordinate on earth. There are a few different types of methods that are used on CubeSats for controlling the attitude, but they all fall under two main brackets: Active control and Passive control.
An active control system simply means the satellite may be fed commands in order to activate some actuators which re-position and reorient the satellite. A passive system, on the other hand, will continuously orient the satellite but it cannot change its attitude or position based on external feedback. The easiest example of this type of system is a passive magnetic system, which will continuously align the satellite parallel to the earth's magnetic field. As the satellite orbits around the earth, the magnetic field changes direction and so too will the direction of the satellite. By using this method, the satellite will have a predictable and calculable orientation everywhere in its orbit.
The beauty of ADCS is that if you are interested in Mechanical, Electrical or Software engineering, there is some sub-project available for you to work on. Even if you are unsure what you want to work on, the three fields are intertwined with each other as we design and fabricate our own actuators as well as program the firmware which controls everything.
For additional information about ADCS, we have a few slides introducing some of the basics of our team here. Alternatively, keep reading our Wiki and don't be afraid to ask more questions from one of our team members!
What are we working on right now?
The Canadian Satellite Design Challenge (CSDC) is our ongoing project. The current iteration of the competition involves designing a satellite which can receive coordinates from amateur radio operators, take an image of the coordinates and down link the image within a reasonable time frame. To take the image, the satellite will need to actuate into a position such that the camera is directed at the earth by the time it passes over the coordinates; furthermore, it will require a high pointing accuracy in a short period of time.
Magnetic torque rods, or magnetorquers, are a type of electromagnets composed of a long range of wire looped around a magnetic core. When a current is run through the wire, a magnetic dipole moment is generated which interacts with the external magnetic field of the earth. A detailed analysis of the magnetorquer design can be found here.
Here is the first iteration of our magntorquer:
Reaction wheels are fly wheels that spin at high angular velocities and leverage the Angular Momentum generated to rotate the satellite in zero gravity. By the conservation of energy, the angular momentum generated from the reaction wheel will rotate the satellite in equal and opposite direction. A detailed analysis of our reaction wheel design is currently in progress.
Part of the attitude determination system is determining the current orientation of the satellite; the determination portion will involved a series of sensors which will take a "heart beat" of the position of the satellite, which the processor will then interpret into a set of coordinates relative to a reference frame. By feeding the set of information into a filtration algorithm, such as a Kalman Filter, the data can then be used to determine and project the position and orientation of the satellite. Sensors and processing is a future project that will need to be considered before the end of the competition.
Managing the actuators and sensor information is a very computing-heavy operation. The on-board computer (OBC) will have higher priorities, such as communicating with the ground-base, and will not be able to manage actuation and sensor filtration on top of its other responsibilities. To manage the extra computing power, an additional processor will need to be designed and built parallel to the main OBC. The processor is a future project that will likely copy the computing teams design and modify it for our purposes. Although it is not currently being worked on by the ADCS team, it will need to be considered before the end of the competition.