The Menace of Hypersonic Glide Vehicles

Deployment of U.S. Falcon Hypersonic Technology Vehicle (HTV2)
AFP Photo/Defense Advance Research Projects Agency (DARPA)

While Obama’s administration is cutting back on defense spending and futuristic defense development programs, both China and Russia are pressing forward with developments that could place us at their mercy. The fast developing capabilities they are trying to make practical are of hypersonic glide vehicles (HGVs), particularly for the delivery of nuclear weapons. Hypersonic vehicles are somewhat arbitrarily defined as aircraft traveling through the atmosphere at faster than five times the speed of sound. Since the speed of sound depends on both air temperature and density (mostly temperature), this definition varies with altitude. At sea level the speed of sound is about 760 mph, at an altitude of 30,000 feet (where commercial passenger jets fly) it is about 680 mph, and at 60,000 feet it is approximately 660 mph. Since the hypersonic vehicles with which we are interested will travel at these rarified altitudes, hypersonic air vehicles of interest will travel at 3,300 mph or faster.      

The Emerging Threats From China and Russia

Both China and Russia have been developing HGVs for some time now and both have been conducting flight tests. What makes these reentry vehicles so dangerous is that they add two capabilities that ordinary ICBMs do not have: the ability to go hypersonic in mid-flight and an ability to maneuver. The concept of the flight of an HGV ICBM’s flight, oriented toward the U.S. HTV-2 program, is shown below. Normally, an ordinary ICBM’s reentry vehicle goes hypersonic only during the terminal phase of the flight just before the missile hits its target.

Under many anti-ballistic missile (ABM) scenarios, an ABM missile would already have destroyed an ICBM’s warhead before that point, sometimes during the mid-flight phase. However, both the Russian and Chinese HGVs have been designed to go hypersonic in the mid-flight phase. Coupled with this added speed is a capability to maneuver to evade ABM missiles, which is particularly effective against U.S. kinetic kill ABMs. A kinetic kill vehicle would need to hit an HGV head on to destroy it; a miss of even a few feet would allow the HGV to continue to its target. In addition, the ability to glide in between course corrections extends the range of the HGV.

The Chinese HGV, once known by the Pentagon’s code name of WU-14 and now called the DF-ZF, was first flight-tested on January 9, 2014. Since then it has been flight-tested an additional six times, the most recent of which was just a week ago on April 27.

Apparently all of these tests were successful with the exception of the August 7, 2014 test, which was described as a failure by U.S. officials. Reputedly, the DF-ZF can reach speeds between 3,863 mph and 7,680 mph, i.e. between Mach 5 and Mach 10. Also, after reentry into the atmosphere and pull-up into a glide, the DF-ZF stays within the stratosphere, making the missile invulnerable to exo-atmospheric kill vehicles. While gliding, more of the vehicle’s momentum is in horizontal motion and less in vertical motion, extending the range of the vehicle.

While it can be nuclear armed, many speculate that with a conventional warhead it could be used in a non-nuclear precision strike role, particularly against ships such as aircraft carriers.

Possible defense responses to the DF-ZF’s invulnerability to exo-atmospheric kill vehicles are laser weapons and rail guns.

Meanwhile, the Russians have just successfully tested an HGV system, the Yu-71. However, unlike the Chinese program, most Russian flight-tests are believed to have been failures. The Yu-71 is also said to have a top speed of Mach 10 or about 7000 mph and is reputed to be highly maneuverable. A June 2015 report from Jane’s Intelligence Review suggests Russia might have 24 nuclear-capable Yu-71 by 2020. The same report said there is a possibility that Russia’s next generation strategic bomber, the Tupolev PAK-Da, might be outfitted to fire the Yu-71. If the HGV is employed in this fashion, it might remain within the atmosphere for its entire flight, making it harder to detect, track, and intercept.

U. S. Efforts for an HGV

All U.S. efforts to build an HGV are currently being run by the DARPA Falcon project. The Defense Advanced Research Projects Agency is the Defense Department’s research agency for investigating possible breakthrough technologies for national security. The Falcon Project (Force Application and Launch from the CONtinental United States) is a joint project between DARPA and the U.S. Air Force, which has two major sub-projects. The first, which is of interest to us in this post, is to develop a reusable Hypersonic Weapon System (HWS), which has been renamed the Hypersonic Cruise Vehicle (HCV). The second sub-project is to develop a launch system able to accelerate an HCV to hypersonic speeds, or alternatively to be able to launch small satellites into earth orbit.

A Falcon HCV of great current interest as a possible ICBM nuclear warhead is the Hypersonic Technology Vehicle 2 (HTV-2). It was to be capable of flying up to

13,201 mph, considerably faster than either the Chinese or Russian HGVs. Its first flight test on April 22, 2010 was to be a 4,800 mile trip across the Pacific to Kwajalein at Mach 20. Nine minutes into the 30-minute flight the on-board computer commanded an auto-destruct after the missile began to roll violently. Apparently, the HGV’s skin could not handle the high heat of reentry. A second test flight on August 11, 2011 ended in a similar fashion. A planned third flight test was cancelled because it was thought that all that could be economically learned from the vehicle had been obtained.

Another DARPA project was the X-51 WaveRider. which is an unmanned scramjet designed to fly at an altitude of around 70,000 feet at a speed of Mach 5. Its fourth

and final test om May 1, 2013 was the only fully successful flight-test. It accelerated to Mach 5.1 and flew for 210 seconds before running out of fuel and plunging into the Pacific with over six minutes of flight time. This test completed the program, which gave the Air Force Research Laboratory data for practical applications of hypersonic flight. These possible applications involve a lot more than merely a vehicle for delivering a nuclear warhead. They include:

• Reconnaissance vehicles
• Transport of supplies
• The air-breathing first stage for a space launch system.

In the Next Post: Possible Defenses Against HGVs and Political Reactions

Besides trying to build an HGV system to deliver nuclear weapons to enemy targets, an urgent priority for the United States is to find ways to defend against Chinese and Russian HGVs. One way is to attack an HGV in its boost phase, when the missile is subsonic or at lower supersonic speeds. Another possibility is the use of rail guns, which conceivably could be used even in the terminal phase of HGV reentry. The advent of HGVs may even be stirring up new interest in high power laser weapons to shoot down HGVs. I will discuss attempts to find an HGV defense, together with political reactions to the HGV threat in my next post.

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