What is a Hypersonic Missile?

Hypersonic missiles are very fast and are very difficult to intercept.

Episode Summary:

Hypersonic missiles were used for the first time in combat last month in Ukraine, as Russian jets launched Kinzhal missiles from jet fighters. Hypersonic missiles are fast, flying at speeds of Mach 5 or faster, and when combined with a flat trajectory compared to ballistic missiles and maneuverability, they present a difficult problem for defense.  

Hypersonic missiles are under development as long-range strategic weapons, but the most intense research is in air-launched standoff systems launched from conventional military aircraft. The Kinzhal system uses conventional rocket engines, but more advanced propulsion under development in China and the U.S. uses air breathing supersonic combustion ramjets to use air as the oxidizer, adding longer range compared to rocket systems. Heat is the primary technical challenge to “scramjet” development, but test systems with run times that could allow a 300-mile range have been demonstrated. 

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Transcript of this week’s show:

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Rocket propelled, guided missiles have been around for 80 years, and although the technology has advanced greatly, they all share two things in common: a sophisticated guidance system and very high speed.  

Guidance was the critical enabling technology, starting with the original military guided missiles, the German V1 and V2. Both were deployed against England in the latter half of World War II, inflicting over 30,000 civilian casualties. The V1 was a drone aircraft, but the V2 was a true ballistic missile, rocket powered and flying to the edge of space.  

With a peak velocity of approximately five times the speed of sound, the V2—unlike the jet-powered V1—could not be intercepted, and the missile attacks only stopped when the launching sites were overrun.  

The need for speed was well understood after World War II as multiple nations developed rocket-powered missiles—everything from portable, subsonic shoulder-mounted weapons to ground and submarine-launched intercontinental ballistic missiles.  

In between these systems are air launched standoff missiles used tactically to deliver payloads with minimal risk to the delivery aircraft. Here again, speed is essential to prevent interception, and Mach five speed, the definition of hypersonic, makes a missile very difficult to track and target. The U.S., China and Russia have active hypersonic missile programs, but only one system has been used in combat: the Russian Kinzhal weapon, which has been fired on Ukrainian targets since mid-March.  

Both the U.S. and China have active development programs for hypersonic air-launched missiles like the Kinzhal, with one critical difference: the Kinzhal is rocket powered. U.S. and Chinese hypersonic development programs focus on a type of propulsion called “scramjet,” a portmanteau meaning “supersonic combustion ramjet.” Ramjets, as the name implies, use fast flowing air entering a jet engine without mechanical compression to support a simple straight-through combustion cycle. They are extremely simple, and cheap to build, but suffer from some severe design constraints.  

The primary constraint is that they only operate efficiently at supersonic speeds, where shockwaves can be managed to produce the necessary compression for efficient operation. At hypersonic operating speeds, however, airframe heating is a major problem due to the friction of even rarefied high-altitude air. Performance limitations based on airframe heat are nothing new in high-performance aircraft, but at hypersonic velocities, heat resistant materials not unlike those used for space re-entry vehicles are needed. Even then, scramjet test missiles have engine lifetimes measured in seconds or minutes.  

Purely rocket-powered hypersonics are much simpler to engineer. With no intake, ceramic composites or ablative coatings on the nosecone can cope with the heat for the few minutes of flight time. So why use scramjets? The primary reason is range. Rockets must carry their own oxidizer, and for aircraft-delivered missiles, the fuel is usually solid. Scramjets gather their oxidizer from the air, meaning a greater proportion of airframe weight can be devoted to fuel, greatly increasing the potential range of the weapon.  

This standoff range is critical for the survivability of the carrier aircraft, and a recent test of a Lockheed Martin Hypersonic Air Breathing Weapon Concept missile was successfully flown over ranges widely reported as 300 miles. Any range over the radar horizon makes ground-based surface-to-air missile attack on the launching aircraft very difficult, and the speed of the missile itself makes it almost impossible to intercept with current technology.  

Of course, for every measure there is a countermeasure, and just as American efforts led by DARPA are producing workable scramjet-powered missiles, that agency is also developing a hypersonic missile interceptor program called Glide Breaker to counter the threat. On October 16, the Financial Times quoted unnamed sources as stating that the Chinese had test fired a nuclear-capable hypersonic missile using an orbital rocket booster. This application of hypersonic technology could replace conventional ICBMs with weapons that are both fast and highly manoeuvrable, making them very difficult to intercept, even from suborbital altitudes.  

At this point of development, hypersonics appear to be bifurcating into two primary classes of missile: aircraft-launched tactical weapons which will use scramjet engines to give the carrier aircraft safe standoff capability, and long-range surface-to-surface missiles that are nuclear capable and are just as difficult to intercept.  

Although “hypersonic” by the strict definition of the word, the Russian Kinzhal is not the technological leap forward that scramjets represent—but it does mean that defensive systems may need Star Wars type technology to cope with the threat; specifically, directed energy weapons. Mach 5 is fast, but photons move at 186,000 miles per second.  

Written by

James Anderton

Jim Anderton is the Director of Content for ENGINEERING.com. Mr. Anderton was formerly editor of Canadian Metalworking Magazine and has contributed to a wide range of print and on-line publications, including Design Engineering, Canadian Plastics, Service Station and Garage Management, Autovision, and the National Post. He also brings prior industry experience in quality and part design for a Tier One automotive supplier.