Inertial navigation systems (INS) use accelerometers and gyroscopes to provide real-time positional information for aircraft, ships, missiles, and spacecraft. INS is immune to electronic warfare techniques, but its high cost and complexity limit its use to specialized applications.
An inertial navigation system (INS) is a computerized aid used in aviation, marine, missile guidance, and spaceflight applications. The system uses a positional orientation calculation style based on inputs from accelerometers and gyroscopes and calculated by an on-board computer. INS systems do not require any external reference or input to maintain their navigational integrity and are accurate to just over 600 m (650 yd). This independence from external reference makes the INS immune to most electronic warfare techniques, such as jamming or decoy signaling. Unfortunately, INS devices are expensive and complex, often preventing their use outside of specialized applications.
This form of navigation system provides the necessary inputs to the operators or automatic steering mechanisms of aircraft, ships, guided missiles, and spacecraft. This navigation information is calculated by an on-board computer based on two main internal inputs. The first is a manually inserted set of information about the starting point and all subsequent waypoints along the route. This information is usually available on global positioning satellite (GPS) charts or equipment and is usually entered into the INS computer by the crew. Once the flight or journey is underway, the motion sensors in the vehicle supply the inertial reference system with a constant stream of real-time positional information that the computer uses to compare actual and predicted positions.
If these two sets of information differ, the inertial navigation system computer will provide updates to the crew or an autopilot system for necessary course corrections. The sensors that supply the positional information used as reference by the inertial navigation system fall into two basic categories: accelerometers and gyroscopes. Accelerometers establish the proper acceleration and therefore the speed at which the vehicle is traveling. Gyroscopes are guidance instruments that accurately measure any deviation in the vehicle’s axial position as it rotates along any axis. Between them, these two instruments paint an accurate, real-time picture of course and speed for the inertial navigation system computer to use as a position reference.
One of the strengths of an inertial reference system is that once initialized, all the information is generated internally in real time. This prevents external influences, such as interfering electronic warfare systems, from interfering with the vehicle’s navigation. This is of particular value for INS systems on guided missiles and other military vehicles. Unfortunately, the many benefits of inertial navigation systems are largely offset by the complexity and high cost of the systems, which typically restrict their use to specialized applications.
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