Maneuverability and guidance systems, not just raw speed, are key differentiators for hypersonic missiles. That requires aerodynamic pressure sensors, optical sensors, inertial sensors, space-based tracking, infrared sensors, and more. All are combined into a single guidance system using sensor fusion.
This article reviews the sensor types for hypersonic guidance, navigation, and target acquisition systems.
Hypersonic guidance systems and associated sensors are an evolving technology. One tool used to refine the technology is the Kratos hypersonic testbed, also called the multi-service advanced capability hypersonic test bed (MACH-TB). It’s designed to speed the development of sensors and related subsystems in real-world hypersonic flight conditions at speeds exceeding Mach 5 (Figure 1).
Guidance
Accurate guidance of a missile moving at Mach 5 differs from the guidance system used for slower aircraft like manned fighters. Hypersonic missiles rely on aerodynamic pressure sensors to provide information about the surrounding air pressure. That information is critical for maintaining stability while making hypersonic maneuvers.
The guidance system detects changes in the aerodynamic forces and makes continuous real-time adjustments to the control surfaces to maintain the correct trajectory and stability.
During the mid-course segment of the flight, radar combines with digital maps to support navigation and enable the missile to avoid obstacles.
Navigation
Sensor fusion is important during all hypersonic missile flight segments. For example, IR, optical, and radar sensors are used for guidance, navigation, and targeting. Navigation relies on combining data from IR and radar with GPS data to create a comprehensive understanding of the surroundings and how they are changing, especially in complex battlefield environments. That can enable rapid responses to unexpected threats.
While inertial measurement units (IMUs) don’t help with threat detection, they are indispensable in hypersonic missile navigation. They provide precise real-time measurements of angular velocity and acceleration on multiple axes, which is critical data for maintaining stability during course changes at extreme speeds.
IMUs in hypersonic missiles must be rugged to survive the extreme temperatures, vibrations, and aerodynamic forces. They must be compact. The requirements for miniaturization and ruggedness can place contradictory demands on IMU designs. But surviving and being small are not enough.
Hypersonic missiles’ extreme speeds and complex trajectories demand IMUs with high measurement accuracy for acceleration and angular dynamics. Rugged, miniaturized IMUs that support high accuracy at Mach 5 in real-time are challenging to design.
MEMS-based and vibration-isolated IMUs have been developed for extreme applications like hypersonic missiles. They are designed to provide the reliability needed in GPS-challenged environments.
These IMUs combine high vibration immunity, excellent common-mode rejection, and insensitivity to external accelerations found in tuning fork designs with the high accuracy and durability of ring gyroscopes.
For example, one available MEMS quad mass gyroscope (QMG) includes a fully mode-symmetric silicon MEMS gyro with closed-loop mechanization that eliminates vibration rectification errors. This high-performance IMU has a latency < 1 ms, a power consumption of 2.5 W and is delivered in a 6.4 in3 package (Figure 2). It provides inertial, sensor-based incremental velocity and incremental angle output data over a digital serial data bus.
Target acquisition
Initial target acquisition can be made using radar. But at hypersonic velocities, the extreme heat creates a plasma sheath around the missile that interferes with radar. Using sensor data, sophisticated algorithms are required to compensate and get a useful radar signature.
Instead, hypersonic missiles can use radar information from the hypersonic and ballistic tracking space sensor (HBTSS) satellite system.
The final target acquires using a combination of IR and optical sensors through a sapphire or silicon “seeker” window. That window is designed to survive hypersonic flight’s extreme heat and pressures while maintaining its optical clarity.
The IR sensors are used for target identification, and that information is combined with optical sensors for detailed shape recognition and specific targeting locations.
Summary
The MACH-TB is an example of a platform used to develop advanced sensor technologies under hypersonic conditions. A variety of sensors are needed to fly hypersonic missiles. Their outputs are combined using sensor fusion to support the diverse needs of guidance, navigation, and target acquisition.
References
Artificial intelligence and hypersonic weapons drive sensing, fusion research, Aerospace America
High-temperature, high-pressure, in-flight status sensor for hypersonic missiles, TechLink
Hypersonic Weapon Sensors Inform Missile Maneuverability, TE Connectivity
Hypersonics & Aerothermal Technology Development, ReLogic Research
Quad Mass Gyro (QMG) Inertial Measurement Unit, Northrop Grumman
SINS/BDS tightly coupled integrated navigation algorithm for hypersonic vehicle, Scientific Reports
Space and Hypersonics Technologies, NASA
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