Inertial navigation systems, or INS devices, are used in a wide variety of applications. In this blog, we’re going to look at the role of inertial navigation systems in aircraft – from passenger planes to unmanned aerial vehicles (UAVs).
When most people think of aircraft, they think of passenger or cargo planes. In these types of aircraft, the inertial navigation system is one of multiple technologies used to help tell the pilots where the plane is, as well as its heading, pitch and roll.
Depending on who you talk to, an INS contains either one or two key components. An INS will always contain an inertial measurement unit, or IMU, which the INS uses to estimate its velocity, heading, orientation, and changes in pitch, roll, and yaw. In some circles that’s all an INS contains; some people (including us) define an INS as a combination of an IMU with a global navigation satellite system (GNSS) receiver. The receiver gives the INS position data from satellites orbiting the earth. The distinction is a bit moot, as all aircraft use data from GNSS satellites to work out their position and their course; it’s just a question of whether that data is integrated with the IMU, or not.
Inertial navigation systems in aircraft
Inertial navigation systems are useful in aircraft for the same reasons they’re useful everywhere else – they give you a reliable way to estimate your position. The position data is also immune to jamming or interference (for a short period) thanks to the IMU inside them. In an INS that combines IMU and GNSS data, the two work together to compensate for each others weaknesses. In areas where GNSS signal is blocked, the IMU helps keep the plane on course; the GNSS data in turn helps compensate for the position drift that all IMUs are vulnerable to.
So, that’s how inertial navigation systems are used in passenger and other commercial aircraft. But what about other types of aircraft?
Inertial navigation systems in UAV navigation
Unmanned aerial vehicles, whether miniature drones or larger intelligence, surveillance and reconnaissance (ISR) craft, require a localisation system that helps them get to where they are going and back. Inertial navigation systems are vital components of these systems. Just like in manned aircraft, an INS will provide data on the aircraft’s position, heading, pitch, roll, and yaw. In an autonomous UAV, that data is fed into the navigation computer to help it do a few things:
- Ascertain if it is still following its route correctly.
- Decide what actions need to be taken to keep following the route, or to get back to the correct route if the UAV has deviated.
- Provide other sensors and control modules with position and movement data, such as perception sensors and path planning or collision avoidance modules.
For a smaller drone that’s still piloted remotely by a human, the INS provides information about its position which can be used to guide the craft and/or (as we’ll talk about later) for georeferencing purposes.
INS technology is particularly useful in a UAV because it contains something called a Kalman Filter. A Kalman Filter is an algorithm that estimates the accuracy of the data the INS is gathering, which can help filter out any erroneous data that might send the UAV off-course.
One of the biggest differences between a commercial aircraft and something like a UAV is that if the craft is in an area with no GNSS signal for a long period of time – for instance, a contested space where someone is jamming the GNSS signal – it’s more likely to go off course. In a commercial vehicle the pilot has multiple techniques to help them fly without relying on their instruments; in a UAV, that is more difficult. Without GNSS signal, the position drift that all IMUs suffer from means that, over time, the UAV will start to deviate from its path. If the UAV is in sight of the person controlling it, then the impact will be minimal, however for UAVs that operate in a BVLOS (beyond visual line of sight) application, the effect can be more challenging to overcome.
To counter this, many UAVs will also utilise other sensors to reduce the position drift from the IMU and help keep the craft on course. Some INS devices, like ours, can integrate data from those other sensors to make the data the INS sends to the navigation computer even more reliable.
Inertial navigation systems and imaging/mapping payloads
Many UAVs are tasked with surveying the ground below them, or with flying around an object to survey it. In those applications the payload needs to include a variety of sensors depending on the task, including cameras, LiDAR scanners, hyperspectral imaging sensors and of course a GNSS/INS. Whatever they are, though, the data they gather needs to be georeferenced if it’s to be useful to the people analysing it.
Georeferencing is where the data gathered by the perception sensors is given a location on the earth. It allows you to build reliable maps of an area using survey data, and to accurately state the position of anything you uncover on your survey. Inertial navigation systems are a great way to georeference that data. A good GNSS/INS will give you highly accurate position and orientation data, among other things, which is vital for relating the position of your scanner to the position of the things on the ground that are being surveyed.
In fact, at OxTS we have a specialist application called OxTS Georeferencer that is designed to combine LiDAR and INS data with just a few clicks of a button to create a fully georeferenced point cloud.
The point clouds above were collected using an OxTS xNAV650 GNSS/INS combined with a Velodyne LiDAR sensor. The LiDAR data was georeferenced using OxTS’ georeferencing and boresight calibration software OxTS Georeferencer and the sensor payload carried by a Dronezone DZX8 heavy drone.
Protection from the elements
Of course, it’s important that any INS you use in an aviation setting is able to handle the conditions aircraft face. Freezing temperatures, pressure changes, and moisture are all a given. Electrical interference and impacts are also risks, depending on what your aircraft is doing and the role of the INS inside it. Not every INS will be able to keep functioning in those conditions!
It’s one of the reasons we developed the RT3000 T DO-160 v4. It’s a version of our flagship inertial navigation system that has passed almost all of the tests in the DO-160 standard, meaning it can handle aviation applications with ease, all while providing highly accurate position and orientation measurements.
In fact, you can get FOG-level performance from the much more cost effective, MEMS-based OxTS RT3000 T DO-160 v4:
The RT3000 T DO-160 v4
The RT3000 T DO-160 v4 GNSS/INS has been engineered to provide a cost-effective, reliable navigation solution for the most demanding environments.
Combining OxTS’ highest performing MEMS IMU technology with dual antenna RTK GNSS, in an IP67-rated enclosure, the RT3000 T DO-160 v4 delivers accurate position and inertial measurements even in the toughest environmental conditions.
Download the datasheet to learn more.
We hope you’ve enjoyed this article and found it informative. If you’re looking for an INS for an aircraft and would like to discuss your project with us, just complete the form below to get in touch.
