What’s different about electronics for hypersonic flight?

Hypersonic flight electronics operate in highly challenging environments and must withstand extreme heat, high levels of shock and vibration, and large G forces. This article begins with a brief review of hypersonics’ place in the aircraft and missile technologies hierarchy.

It then examines specific challenges when designing electronics for hypersonic platforms, delves deeper into the challenges resulting from the high-temperature plasma surrounding hypersonic platforms, and concludes with a look at a recent design for a Mach 4+ platform that’s “almost hypersonic.”

To be classified as hypersonic, an object must travel at Mach 5 or faster (Table 1). Mach 5 is 3,836 mph (6,173 kph). Some classifications break hypersonic down into two subcategories: hypersonic from Mach 5 to Mach 10 and high hypersonic from Mach 10 to Mach 25.

Speeds of Mach 25 and greater are classified as reentry speeds. For example, the SpaceX Crew Dragon capsule and the Space Shuttle reenter the atmosphere at around Mach 25, the orbital speed of the International Space Station.

At Mach 5, electronics must be protected from the intense heat, over 1,000 °C. They can be subjected to over 50 G during the acceleration phases and turns. Steady-state G forces are much lower, just a few Gs during cruising. The pilot in a stealth fighter jet can experience up to 10 G in a dogfight.

The air compresses on the leading edges at hypersonic speeds, creating intense shock waves. Those shock waves produce pressure fluctuations, buffeting the vehicle and causing strong vibrations. The heat generated by friction with the air at hypersonic speeds can cause the thermal expansion of various materials, further elevating the vibrations and causing structural deformations or failure.

Communication and control challenges

Serious communication challenges arise when a plasma sheath surrounds a vehicle traveling at hypersonic speed. Plasma can reflect, absorb, and scatter electromagnetic waves, disrupting or corrupting communication signals. The plasma sheath can also attenuate signals, reducing the received signal-to-noise ratio. It can also prevent the reception of GPS signals needed for navigation.

A hypersonic craft’s control and guidance computer requires a different design approach than the same system in a commercial airliner or fighter jet. For example, the airliner travels about 50 m during the pilot’s 0.2-second reaction time.

A hypersonic craft could travel at least 1 km in 0.2 seconds. This requires that the craft’s flight path be well understood prior to takeoff or that advanced artificial intelligence (AI)- based guidance algorithms and sensor fusion be included to anticipate changes in direction and effectively remove the pilot’s reaction time limitation from the equation. In addition, the speed of travel demands high-precision controls.

Almost hypersonic

The U.S. Navy is developing the Hypersonic Air Launched Offensive (HALO) anti-surface missile (Figure 1) as a step toward deploying hypersonic weapons. It’s designed to launch from the Navy’s F/A-18E/F Super Hornet, and its initial operational capability is expected in 2028. While the goal is to reach Mach 5, current development efforts may result in a weapon capable of “only” Mach 4+, almost hypersonic. True hypersonic flight is exceedingly difficult to achieve.

Summary

Operating over Mach 5 creates numerous challenges for electronics designers of hypersonic airframes. Atmospheric friction creates intense heat that the electronics must be protected from, creating a plasma shield that can disrupt communications around the craft. The high speed also makes designing the control and guidance computer difficult since there’s very little reaction time. Finally, the speed means that the controls must be very precise.