During the test, the WaveRider’s scramjet engine ignited high above the Pacific Ocean, thrusting the demonstrator to a speed of nearly 6,245 kilometers per hour (KPH), just over five times the speed of sound. Scramjet stands for supersonic combustion ram jet, which has no moving parts. Fuel is mixed with air rushing into the combustion chamber and then ignited to provide power.
The WaveRider flew for 3½ minutes on scramjet power, the longest such flight in history. At that speed, a flight from New York to Los Angeles could take less than 39 minutes.
While scramjet propulsion may one day be used in civil aviation and for outer space flight, the more immediate application is military. The U.S. Air Force, Army and the Pentagon’s research arm, the Defense Advanced Research Projects Agency (DARPA), have been testing various super-fast unmanned aircraft over the past few years as part of a futuristic program called Prompt Global Strike (PGS).
DARPA has been testing an experimental arrowhead-shaped plane, the Falcon Hypersonic Technology Vehicle 2 (HTV-2). It is an unmanned, rocket-launched, maneuverable craft that glides through Earth’s atmosphere at incredibly fast speeds.
The HTV-2 is designed to travel at 20 times the speed of sound, or Mach 20. This would cut the flying time between New York and Los Angeles to under 12 minutes, 22 times faster than today’s commercial airliners. DARPA says that the ultimate goal is “a capability that can reach anywhere in the world in less than an hour.”
The last flight test of the HTV-2 in April 2012 was only a partial success. After being released from its protective cover atop the rocket, it nose-dived back toward Earth, leveled out and glided above the Pacific at just over 20,900 kph for about nine minutes before the searing speed and heat caused parts of its carbon composite skin to peel away.
Initiated nearly a decade ago, after al-Qaida’s terrorist kingpin Osama bin Laden eluded capture in Afghanistan, these PGS tests are intended to develop a weapon armed with a nonnuclear high explosive warhead that could strike targets anywhere in the world in an hour or less.
The U.S. Quadrennial Defense Review Report in 2006 said that the PGS weapons would hit “fixed, hard and deeply buried, mobile and re-locatable targets.” At present, the only way the U.S. could with any certainty destroy such targets in an hour or less would be to use submarine-launched long-range ballistic missiles or U.S.-based intercontinental ballistic missiles (ICBMs).
Like the PGS weapons now being tested, these rocket-assisted weapons travel at hypersonic speeds. However, they are all armed with nuclear warheads. So the result of a strike could be devastating, globally destabilizing, and out of all proportion to the terrorist or other threat.
Among early PGS plans were proposals to retrofit a small number of existing U.S. submarine-launched missiles or land-based ICBMs with conventional warheads. But Congress in Washington refused to fund these plans because of concerns that Russia and other nuclear powers would be unable to distinguish between a PGS launch and nuclear weapons launch, raising the risk of an unintended nuclear missile exchange.
Since then, the list of potential PGS targets has grown as terrorist groups and missile-armed states hostile or potentially hostile to the U.S. have increased in number.
A conference hosted by the U.S. Strategic Command last August discussed instances in which the White House might some day order a nonnuclear rapid strike. They included a sudden move by China toward destroying a critical U.S. or allied communication satellite by rocket or laser, a danger accentuated by what U.S. defense officials say was a high-altitude Chinese anti-satellite test on May 13, the third reported since 2007.
They also included a North Korean ballistic missile being readied for launch against U.S. allies Japan or South Korea, or against U.S. bases in either of those countries or on the U.S. island territory of Guam in the western Pacific. Iranian long-range missile launches, and terrorist assembly points for nuclear explosive devices or so-called dirty bombs that use conventional explosives to spread radioactive material, might be other reasons for a PGS weapon to be used.
The latest PGS tests by the U.S. worry Russia, but they worry China more because it has far fewer nuclear-tipped missiles that can reach the U.S. than Russia, and less effective systems for destroying incoming missiles than Russia. U.S. analysts estimate that China currently has a total of only a few dozen nuclear-armed ICBMs that can strike the U.S.
Writing on the China-U.S. Focus website on April 22, Major Gen. Yao Yunzhu, director of China-America Defense Relations at the Chinese Armed Forces Academy of Military Science, said that Chinese concerns stemmed from two facts:
• The ballistic missile defense systems that the U.S. and its allies had deployed, or were planning to deploy, in the Asia-Pacific region could intercept residue Chinese nuclear weapons launched for retaliation after China had been attacked, thus potentially negating the deterrence effect of the Chinese nuclear arsenal.
• The U.S. was developing a series of conventional strategic strike capabilities. When deployed, they could be used to hit China’s nuclear arsenal.
Hu Yumin, a senior research fellow at the China Arms Control and Disarmament Association, wrote in January that the U.S. aimed to combine PGS with its space and anti-missile technologies to “form an integrated defense system, which could render other countries’ strategic weapons, including nuclear arms, almost useless.”
Hu was clearly referring to China. He added that this could put such countries in a dilemma: Either they would lose the ability to launch a strategic nuclear counter-attack or they would have to use nuclear weapons first to avoid devastation.
Chinese concerns are recognized by some U.S. officials and analysts. With swinging cuts in military spending biting in the U.S., the most likely outcome is a modification of the PGS program.
Existing shorter-range and slower-moving U.S. cruise missiles, launched from aircraft or submarines, could be used to strike PGS targets, while expensive research and development of hypersonic weapons is put on the back burner, at least for the time being.
Michael Richardson is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore.
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