Understanding Hypersonic Missiles: Design and Technology

Connectors in hypersonic missiles need to be small and lightweight and provide robust signal integrity for high-speed connectivity. The challenge is to provide the required performance and durability while enduring extremely high temperatures and high levels of shock and vibration.

This article briefly examines the inside of a hypersonic missile and its operating environment. It then considers how silicon dioxide, ceramics, and superalloys are used in connectors for hypersonic missiles.

A hypersonic missile travels at Mach 5 or faster (about 3,800 mph), but many ballistic missiles travel at even higher speeds. What sets hypersonic missiles apart is their ability to navigate and maneuver. This requires avionics, including sensors, actuators, a flight computer, etc. Connectors must also stitch the various subsystems together into a coherent package (Figure 1).

Figure 1. Cutaway view of a prototype hypersonic missile. (Image: Stockholm International Peace Research Institute)

The skin temperature of a hypersonic missile can exceed 1000 °C, and even with good thermal management, the interior thermal environment is challenging. Electronics, including connectors, are also subjected to extreme thermal shock. The temperature can change rapidly at the launch and during maneuvers, adding to the thermal challenges.

Forces experienced during maneuvers can exceed 50 Gs. That can disrupt or destroy standard connector designs. So, the connectors need to be exceptionally rugged — the space constraints inside a hypersonic missile demand lightweight and miniaturized connector solutions.

Those miniaturized connectors must maintain signal integrity and quality to support high-speed interconnects. Designing compact connectors that can survive the harsh environment and minimize signal loss and interference can be daunting. It can require that connector designers turn to new materials.

Silicon dioxide coaxial cables

High-frequency coaxial cables are important components in hypersonic missiles. Designed with conventional materials, they can exhibit a deviation in phase characteristics at elevated temperatures. That can produce inaccuracies in systems where phase characteristics are important.

Hypersonic missile systems include multiple antennas and sensors that rely on phase-matched or time-matched cables. Maintaining the required performance demands new materials, such as silicon dioxide (SiO2). SiO2 dielectrics can support phase stability up to 1000 °C and provide low hysteresis: The phase and loss return to their original values even after extreme thermal shocks.

Figure 2. Examples of silicon dioxide coaxial cables for hypersonic missile systems. (Image: Times Microwave Systems)

These coaxial cables have a solid oxygen-free copper center conductor surrounded by an insulating SiO2 dielectric. The outer conductor is a copper-clad stainless steel jacket. A crack-free, fired glass hermetic seal completes the assembly.

Combining the SiO2 dielectric and tight assembly tolerances produces a coaxial cable with electromagnetic interference (EMI) shielding of over 110 dB. 50-ohm cables are available with outer diameters of 0.270, 0.141, and 0.090 in. with cutoff frequencies of 18.5, 36, and 64 GHz, respectively (Figure 2).

Ceramics and superalloys

Ceramics like alumina and superalloys like Inconel are used inside gas turbines and jet engines, where the temperatures, shock, and vibration demands are extremely challenging. This makes them suitable for use in connectors in hypersonic missiles.

Coaxial connectors are available based on a hermetically brazed ceramic-to-metal assembly that incorporates alumina and Inconel. These 50-Ohm matched impedance connectors also use non-magnetic metals, including gold-plated Inconel contacts and 304 stainless steel adapters.

Figure 3. Multi-contact coaxial connector with alumina insulators and Inconel contacts. (Image: *CeramTec*)

The receptacles can include multiple connections. The high-strength, low-loss insulators are fabricated from alumina metalized using the refractory-metal sintering process, which results in high heat resistance, wear resistance, and excellent electrical conductivity. Based on the application requirements, the assemblies are brazed together using copper, gold copper, and silver-copper alloys (Figure 3).

Summary

Hypersonic missiles’ extreme velocities require high-speed control electronics to support accurate navigation and maneuvering. The connectors in those systems must withstand extreme thermal and mechanical stresses and still deliver high-speed and glitch-free performance. This can require non-traditional materials like SiO2, alumina, and Inconel.