4 Interesting Facts About Inertial Navigation Systems

Precision, velocity and balance are key to any moving object. When it comes to complex vehicles, like airplanes, autonomous vehicles, ships, spacecraft, submarines and even unmanned aerial vehicles (UAVs), the need for an accurate system that helps maintain and control perfect movement is essential. With the help of inertial navigation systems, moving vehicles can accomplish their tasks safely and precisely without using GPS. 

How does an inertial navigation system work? 

An inertial navigation system (INS) calculates the location, orientation and velocity of a moving object without the need of GPS technology.

An INS device typically uses accelerometers and gyroscopes, meaning motion and rotation sensors, that communicate with a computer unit which then translates the data into actionable controls. This is your basic inertial navigation system, to which other features can be added. For example, inertial navigation systems can be upgraded with magnetic sensors and barometric altimeters.

INS devices operate on a dead reckoning system, which means that the initial position, velocity and orientation of the vehicle are provided by an external source, which can be a GPS satellite receiver or an operator. Equipped with this data, the INS can begin calculating position, velocity and other movement elements. As the vehicle continues to move, the INS device will keep calculating and updating, on its own, all motion elements via the information received from motion sensors. 

Inertial navigation system components

As previously mentioned, inertial navigation systems are mainly comprised of accelerometers and gyroscopes, along with a computer that processes the information delivered by the motion sensors.

Gyroscopes are used for measuring the sensor frame’s angular velocity relative to the inertial reference frame. The inertial reference frame provides the original orientation of the system, to which angular velocity is added so that the inertial navigation system’s direction is always available.

While gyroscopes provide orientation, accelerometers deliver information on speed and direction of acceleration, based on a measurement of linear acceleration of the vehicle relative to itself. Angular velocity together with linear acceleration can provide accurate information for all position changes of the moving vehicle.

These motion sensors are part of the core of every inertial navigation system, which is an inertial measurement unit (IMU). This is a device that reports on movements and characteristics of a moving vehicle and usually comprises three gyroscopes and three accelerometers. Certain IMUs are also equipped with magnetometers. An inertial navigation system needs to contain at least three accelerometers and three gyroscopes to deliver accordingly.

The INS uses the measurements delivered by the IMU in order to calculate data necessary for navigation and control of the vehicle, like altitude, velocity, orientation and more.

A computer synthetizes all information, by integrating data collected from the motion sensors in order to calculate the vehicle’s current location. 

Inertial navigation systems vs GPS technology

GPS technology refers to a navigation system enabled by satellite transmission, a ground control segment and dedicated equipment. The system provides data on geographical location, time, velocity and other information for land, air and sea travel. In order to convey exact measurements, the GPS device needs to stay connected to at least four satellites from the satellite system that is orbiting the Earth.

GPS technology is mainly used for data on location, mapping, moving object tracking, navigation and timing estimations and measurements. However, this information is dependent to satellite connection, and if the GPS device cannot connect to a minimum of four satellites, the provided data will not be enough for the device to be fully operational. 

A GPS device is a useful addition to your smartphone, enabling you to easily arrive to any destination, estimate traffic and inform others about your location. However, when it comes to complex or critical activities, like air transportation or on-ground military operations, a self-contained solution is required in addition to GPS technology.

Inertial navigation systems are autonomous after initialization, do not rely on satellite connectivity and can convey more granular data than a GPS device used alone. Moreover, they are resistant to radar jamming and deception, as they are self-contained. 

Inertial navigation systems: advantages and challenges

Inertial navigation systems are the perfect solution for complex operations on land, sea, air and space and can be used in a wide range of applications, including for smartphone location and tracking, which are called mobile inertial navigation systems. However, they are mostly used for aircraft and ships navigation, along with tactical and space missions.

With the advancements made in the field of microelectromechanical systems (MEMS), it is now possible to develop smaller sized and lightweight inertial navigation systems, like the HGuide n380.

The HGuide n380 inertial navigation system comes in a lightweight package, is equipped with a powerful inertial measurement unit, the i300, and provides data with impressive granularity, like time stamped position, velocity, angular rate, linear acceleration, roll, pitch and heading information.

However, inertial measurement units are still facing certain challenges, which are mostly related to integration drifts – minor errors that come up in the measurement of angular velocity and linear acceleration. These errors can grow and become more prominent as each new position of the vehicle is calculated upon the previous one. The accumulation of errors can lead to persistent problems, which is why the vehicle position needs to be corrected, from time to time, with help from a different navigation system.

This is the main reason why inertial navigation systems are usually used in tandem with other navigation technologies. This helps to secure data accuracy more than by means of a single navigation system.

However, a number of measurement systems have been specifically developed to identify inertial navigation system inadvertences, like the LASEREF Inertial Reference Systems. LASEREF systems are the most advanced in the field and come with updated microprocessor on-aircraft data load capability. Such systems use both GPS and air data computer outputs to secure navigation performance and eliminate errors.

Inertial navigation systems have been a daring challenge for longer than one might imagine. This technology dates back to the 1940s, when first attempts were made at adjusting the azimuth for rockets in flight. The prototype consisted of an analog computer, two gyroscopes and one accelerometer. Progress, curiosity and need for safety and precision have brought us to a generation of inertial navigation systems that deliver crucial information in real time.