Safran’s HRG Crystal: Empowering Next-Gen Inertial Navigation Systems

Safran Electronics & Defense stands out as one of the few companies equipped with a comprehensive range of PNT technologies, further strengthened by the incorporation of proven inertial navigation solutions.

Utilizing cutting-edge manufacturing techniques, Hemispherical Resonator Gyro (HRG) Crystal technology delivers unprecedented performance and reliability compared to current technologies, catering to tactical and strategic applications across various domains. Having produced over 30,000 HRGs and accumulated more than 15 million operational hours, this technology has demonstrated its efficacy and resilience in military applications globally.


The HRG Crystal is a Hemispherical Resonator Gyroscope, characterized by its simplicity with only a few components housed in a silica half-shell, termed the “resonator”. Crafted from highly pure glass, it boasts an almost limitless lifespan, a resilient design capable of enduring harsh environments, and exceptional reliability (Mean Time Between Failures (MTBF) surpassing 1 million hours), all contributing to cost-effective ownership. What distinguishes the HRG Crystal is its unique capability to deliver consistent performance levels from standard to very high, all within a compact size.

The HRG is used to measure the rotation of a platform, whether aircraft, ship, tank, or other vehicle, to calculate its exact position and altitude. Safran is proving that the HRG Crystal innovative approach is a real game changer in high-end navigation. Over the past few years, Safran has introduced its new generation of HRG-based Inertial Navigation System (INS) designed to equip all types of platforms. Due to its straightforward design and mature technologies, the HRG Crystal enables Safran to create advanced inertial navigation systems with exceptionally high reliability for both civil and military applications. These systems provide a broad range of performance specifications, offering versatility in choice.


The Coriolis Vibratory Gyroscopes (CVG) operate on the principle that a resonating structure tends to persist in resonance within the same plane, even when its support undergoes rotation.

The HRG is a CVG that follows these principles:

  • The resonator is designed with perfect axisymmetric to showcase outstanding attributes in terms of balancing, natural frequency, and isotropic damping. In practical terms, precise tuning of the resonator is necessary to achieve optimal balance.
  • The resonator is connected to its support through a vibration node to guarantee optimal decoupling between the resonator and the external environment.
  • Electrodes situated near the resonator exert electrostatic forces to regulate the flexural waves.
  • The management of flexural waves occurs in Whole Angle mode to reduce the required energy. This mode minimizes errors arising from electronics, detector, and actuator imperfections. Additionally, it ensures an excellent scale factor based on the Bryan coefficient and enables a broad measurement range.

The HRG’s structure features a hemispherical shell to maximize the efficient utilization of each gram of resonator material for flexural energy storage. A stem, secured at the top of the hemisphere, supports and holds this shell in place.

It is constructed from amorphous fused quartz to achieve optimal isotropy (without crystallographic direction) and minimal energy dissipation (absence of internal friction).

The metallic coating, necessary for electrode creation and ensuring electrical continuity, is kept as thin as possible to reduce energy dissipation within the metal. These optimizations lead to exceptional performance of the HRG.

The main challenge with HRG lies in its manufacturing cost, particularly in the precise assembly of electrodes that must match the resonator’s shape, creating an isotropic hemispherical gap. Safran addressed this by adopting an innovative design, where electrodes are deposited on a plane, generating electrostatic forces on the resonator’s equatorial plane. This simplifies the assembly of the hemispherical shell and electrode plate into a basic 2D problem. Through the innovative design, Safran’s HRG can be produced cost-effectively, making its intrinsic performance accessible to the mass market.


Since the late 1990s, Safran Electronics & Defense has designed and produced a large number of HRG inertial systems and sensors for many different applications. The HRG Crystal is mature and proven in terms of accuracy and reliability. It plays a crucial role in a modern Inertial Navigation System (INS), engineered to be lightweight, compact, and rugged enough for deployment on both manned and unmanned aircraft, surface ships, submarines, and guided missiles.

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