Sagem is the only company outside the US that has completely mastered the successive inertial technologies and that develops both high performance inertial sensors and GPS receivers for air, land and navy applications. Today, Sagem is capable of proposing the “right technology at the right place”.
Policy
Sagem policy consists of the following:
- Control all technologies making up an inertial unit/a piece of inertial equipment:
- Gyroscopes / gyrometers,
- Accelerometers,
- Embedded GPS receivers,
- Electronics (ASIC),
- Navigation processing (multimode Kalman filter techniques, integrity processing, …)
- Master all emerging inertial technologies,
- Control the entire manufacturing process of its systems.
This policy prevents Sagem from relying on external suppliers for highly critical components.
The technologies used in Sagem navigation systems are entirely EU and Sagem owned.
This provides customers with a guarantee that it is built to last, with long-term support.
Gyroscopes
These are by far the most demanding in terms of advanced technology. They were initially a French specialty (the first gyroscope was invented by Léon Foucault in the 1850s). They have become so once more, as Sagem is now the only company in the world to master all the pertinent technologies across the board for precision classes.
The typical drift of Sagem gyroscopes ranges from the 100 °/hr "flight control" or "short-range tactical weapons" class to better than 0.0001°/hr : "star in a bottle" class. Different technologies are implemented for the various precision classes and operating constraints of the vehicle.
These include the following:
Floating gyroscopes: the beginnings of the "great inertia" of the 1950s
Dynamically tuned wheel gyroscopes– platform or strap-down
Ring-laser gyros, today’s most popular "strap-down” gyroscope; state-of-the-art technology for the most demanding military applications
Fiber optic gyros (FOG) in the "fly-by-wire" class for today’s civil applications, which are usually less demanding than military applications, in particular regarding the environments they’re used in.
Electrically suspended gyroscopes: “star in a bottle” class
Quapason™: rugged, single-axis, solid-state vibrating gyro designed for low-cost applications
As a result of its drive to reduce costs while maintaining high performance levels, Sagem made a gyro technology, which until now seemed marginal, more effective.
This is the Hemispheric Resonator Gyro (HRG), the future high-end solution for the next decade.
Accelerometers
Sagem has developed its own accelerometers, and is manufacturing these devices in its own facilities. Critical components are based on proprietary technologies. Together with gyroscopes, they provide the necessary input to allow inertial navigation.
Three types of accelerometers are currently in production:
Pendular accelerometers : state-of-the-art strap-down navigation and guidance systems are currently based on this technology. Their measurement range can reach up to one hundred g's. Their precision can reach up to one in one hundred thousand for the most demanding applications.
Theses devices have been in production in significant quantities for many years.
> The Sagem family includes among others the A600 and the A305.
Vibrating Beam Accelerometers : this technology has been developed for several years and is currently under production for tactical products. It offers cost-effective performances, a small size and is well suited for state-of-the-art digital systems due to their digital output.
> The AD301 accelerometer is used on the Sagem AASM navigation system.
MEMS-based accelerometers : Sagem is also manufacturing the cost effective MEMS-based ACSIL accelerometer, based on a micro silicon chip pendulum. It is used for intermediate precision needs and other stabilization purposes.
GPS receivers
Sagem began working in the field of GPS in the early 1980s, at a time when receivers were an imposing electronic component. This enabled it to get to know this type of sensor from the inside and to thoroughly assess its complementarity with inertial navigation. Since then, GPS receivers have greatly decreased in size and in price. They are now a small electronic module - a kind of plug-in - which can be directly inserted in inertial units.
Hybrid navigation
Sagem has more than 20 years of experience in the development and validation of hybrid navigation systems that combine inertial navigation with various sensors to increase the navigation accuracy or to provide operational flexibility:
- Kalman filtering is the optimal hybridisation technique used by Sagem in all its navigation systems. Land navigation systems are fitted with large multi-mode Kalman filters that provide unique operational features (odometer-only and GPS-only alignment on the move) as well as automatic mode management, optimal accuracy and fine error estimation,
- On-the-move alignment capability is considered a major improvement for operational readiness,
- Autocalibration of hybrid navigation systems is fully mastered by Sagem. This automatic feature greatly simplifies the maintenance constraints by suppressing the preventive maintenance tasks.
