In autonomous flight: how the inertial navigation system works

rostec.ru

4 min

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Once upon a time, travelers were satisfied with the simplest devices for determining the location, but over time, the distances and speeds of movement increased, and increased requirements began to be placed on navigation equipment. Radar has been replaced by satellite navigation, but it still has its weaknesses - dependence on satellites, vulnerability to interference and suppression. Therefore, autonomous inertial navigation systems developed in the second half of the 20th century still remain relevant and continue to develop.

The largest manufacturer of inertial navigation equipment in our country is the Radioelectronic Technologies Concern of the Rostec State Corporation. His businesses have been developing and manufacturing inertial navigation systems for over 60 years. Recently, the Ramensky Instrument-Making Plant produced the thousandth unit of the unique INS-2000 inertial navigation system.

We tell how the inertial navigation system is arranged and works, what helps it not to depend on earthly landmarks and the vagaries of nature.

Without external references

Inertial navigation systems (INS) are currently the only means for autonomous, that is, not dependent on external sources of information, determining the position and orientation of an object in space. Similar systems are used in aviation, astronautics, on ships and submarines, in unmanned and robotic devices. With the help of INS, moving objects can determine their location, their orientation and speed with high accuracy without satellite communication. In addition, unlike conventional GPS navigation, inertial systems are more resistant to interference and interception.

The INS device can be divided into two key elements: the measuring equipment that collects data and the navigation computer that processes the information. Gyroscopes and accelerometers are responsible for measurements in the INS. Gyroscopes - they can be mechanical or laser - determine the angles of the object relative to three main axes: pitch, yaw and roll. Accelerometers read linear acceleration. The INS can be supplemented with other sensors, such as a magnetometer that measures the magnetic field, or a barometric altimeter.

ANNs are platform and strapdown. In the first case, the measuring equipment is installed on a gyro-stabilized platform, which rotates independently of the INS. In the second case, accelerometers and gyroscopes are rigidly connected to the body of the device, and the functions of the platform are modeled by a mathematical computing system. The advantage of platform systems is their higher accuracy, while strapless versions are more compact, consume less power and have unlimited measuring angles.

How an inertial system works

In a simplified form, the work of the ANN can be represented as follows. The source data for calibrating the navigation system and orientation of the inertial sensors are loaded into the initial information input block. Then this data gets into the block of measurements, the computing block and the block of time which is synchronized with world time. In the course of movement, the measurement unit registers changes in parameters, on the basis of which the computing unit determines the speed and coordinates of the object, after which they are transmitted to the control system.

The most important parameter in the work of ANN is the frame of reference. It provides the initial orientation to start navigation. Roughly speaking, the reference system every time tells the device where is the right, where is the left, where is the top, and where is the bottom, as well as the starting point of the movement. Astronomical objects, the Earth or the horizon can act as a reference system, it can also be arbitrary.

Despite the rather high accuracy, inertial navigation systems have their drawbacks. The weak point of the ANN is the measurement errors that accumulate over time in the information received from the instruments - the so-called drift. As the navigation computer adds up each measurement to find out how the position has changed from the previous estimate, the small error increases over time and the overall estimate becomes more and more inaccurate. To correct such errors, inertial systems are usually supplemented with GPS sensors.

Navigation from Ramenskoye

In our country, the first devices based on inertial navigation appeared in the 1960s. The pioneer in this direction was the Ramenskoe Instrument-Making Design Bureau (RPKB), in which the first ANN projects for aircraft have been developed since 1958. In subsequent years, inertial systems have been improved many times. The Ramenskoye enterprise created navigation systems and other equipment for aircraft of the Sukhoi Design Bureau, Mikoyan, Tupolev, Ilyushin, Kamov, Mil, and others.

The Ramensky Instrument-Making Plant (RPZ), which once created a design bureau, has also been producing inertial navigation systems for many years. Both enterprises are part of the Radioelectronic Technologies Concern of the Rostec State Corporation. One of the main serial inertial navigation systems produced by RPZ today is the INS-2000 system and its modifications.

INS-2000 refers to platform systems using mechanical gyroscopes. It is made in the form of a monoblock consisting of a gyro-stabilized platform based on dynamically tuned gyroscopes, service electronics, a calculator, and an interface unit. If necessary, the system can be equipped with a magnetometer and integrated with satellite navigation.

INS-2000 is distinguished by high accuracy of work. When used autonomously, the system error is no more than 3.7 km per hour of flight, and when working with the built-in satellite correction unit, it does not exceed 40 m per hour.

The Ramensky instrument-making plant has created five modifications of the system, which allow using the development for almost any aircraft. Products are distinguished by functional software - each of them is adapted to specific on-board equipment systems, takes into account the characteristics of a certain type of aircraft and helicopters.

Today, INS-2000 is used as an onboard navigation information sensor in most domestic helicopters and aircraft. In 2016, the Ramenskoye enterprise upgraded the product to replace the imported element base with the domestic one as part of import substitution. In February 2022, the Ramensky Instrument-Making Plant produced the thousandth unit of the INS-2000 inertial navigation system.

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