Attitude control are the actions carried out to control the orientation of an object in relation with a specified reference system. The term is often used in the aerospace sector because it is used with regard to the orientation of Spacecraft and satellites in relation with the firmament, certain regions or nearby objects. In a nutshell, it is the compass that is used in outer space.
The sensors are the main resource when it comes to determining the attitude of a vehicle or object with precision. The so-called actuators are also necessary to provide the torque that is needed to position the satellite in the desired attitude, with the algorithms that can interpret the data and drive actions in the Spacecraft.
The discipline that studies these three essential elements for the control of attitude (sensors, actuators and algorithms) is referred to as GNC, which stands for Guidance, Navigation and Control.
Sensors with one or more axes are used to measure the movement references, and some of them are made using Microelectromechanical Systems (MEMS). These are sensors that combine micro-electronic elements with micro technology prepared to produce complete high-precision systems of a size so small that they fit onto a chip, and they are a revolution in the field of inertial sensor technology.
There are different types of sensors to control attitude in space, such as solar sensors, horizon sensors or star trackers, and we produce them all here at Solar MEMS.
Horizon Sensors are optical instruments that detect the light at the edge of the Earth’s atmosphere, which means the horizon. This type of technology offers satellites and Spacecraft orientation in relation with the geometric planes of our planet. The horizon sensor we make in our company is the Horizon Sensor for Nano and Micro Satellites (HSNS). It is a Quad Thermopile sensor for Earth detection and Nadir vector determination. This device measures the infrared radiation from Space and from Earth with 4 IR-eyes, providing accurate and reliable detection and attitude determination.
In contrast, Solar Sensors are devices that detect the direction of the Sun. This is one of the special strengths of Solar MEMS and we have various types of sensor to match the requirements of the mission. There are the SSOC and nanoSSOC sensors, that latter being a sensor with two axes that offers high precision at low cost and already there are 500 of them working in nanosatellite.
Finally, Star Trackers are optical devices that can measure the positions of the stars by using photosensors or cameras. The newest developments of Solar MEMS include the STNS, a low-cost star tracker based on a CMOS image sensor for highly accurate satellite attitude determination. The device captures images of a Star Field with an internal camera device and identifies star constellations to determine the orientation of the satellite in an absolute reference frame and attitude with high accuracy. In fact, the first Solar MEMS Star Tracker will soon be in orbit on a European Space Agency (ESA) satellite.