If there’s one word that keeps military planners from sleeping at night, it’s “hypersonic.”
The ability to fly at more than five times the speed of sound holds the promise of getting to the antipodes in less time than it takes to drive across town. However, it also makes possible deadly weapons that can penetrate any defenses currently available while delivering the destructive force of a tactical nuclear weapon.
So, what is hypersonic flight and is its development an opportunity or a threat?
If you’ve been following defense or aerospace news in recent years, you may have noticed that there’s been significant buzz about hypersonics. The USA, China, Russia, Germany, Britain, India, Australia, and even Indonesia have been conducting research into various aspects and problems of flying at Mach 5 (3,800 mph, 6,125 km/h) and above. Much of this is basic research, but mixed into news feeds are reports of growing concern about hypersonic developments by America, Russia, and China for military purposes.
Why these reports should worry military analysts is fairly obvious. At the moment, defense systems operate at supersonic speeds and below. Fighter planes, bombers, missiles, anti-missiles, and artillery shells all fly at less than Mach 5. Even the fastest manned jet plane ever built, the now-retired SR-71, could only manage Mach 3.5. The only weapons that do count as hypersonic are ballistic missiles that fly out into space before returning to Earth, which makes them a very special case.
The fear is that if someone develops an aircraft or missile that can travel over Mach 5, it will have an effect similar that which jet engines had on military aircraft.
When the first fighter jets appeared in the skies over Europe in the last year of the Second World War, the effect was dramatic. When Nazi Germany’s Me 262 blasted by the Allies’ Spitfires and Mustangs like they were standing still, it was like being passed by the future. Today, the worry is that hypersonic weapons will be able to penetrate current defenses with the ease of a red-hot battering ram encountering a butter fortress.
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The development of a practical hypersonic weapon would clearly destabilize global security, a fact compounded by the mystery shrouding many countries’ hypersonic programs.
For example, Russia’s Zircon hypersonic cruise missile program keeps popping up in the news. Designed by NPO Mashinostroyeniya and allegedly in production since 2012, it’s been pushed aggressively by state-run Russian media and has been the subject of much speculation in the West.
Some reports claim that Zircon has already been fully developed and tested, and is now being widely deployed with the Russian armed forces. According to these reports, it has rendered the Royal Navy’s Sea Ceptor surface to air missile system obsolete before it’s even been cleared for service. This is because this version of Zircon can supposedly travel at Mach 8 (6,090 mph/9,800 km/h) and has a range of 620 mi (1,000 km) with 72 of the hypersonic missiles already being installed in a pair of Kirov-class battlecruisers, as well as on destroyers, submarines, and bombers, with the Russian Army set to get theirs by 2020.
However, other accounts claim Zircon has a speed of only Mach 5, a range of 250 mi (400 km), and hasn’t even been properly tested yet – much less deployed. That may seem like a large discrepancy, but the Russian government has long had a propensity for combining bluff with boasting.
As to where Russia really is with regard to hypersonics might be provided by India, which is currently developing BrahMos-II – a hypersonic version of its BrahMos missile that can reach Mach 7 or 8. What’s interesting is that a joint project with Russia’s NPO Mashinostroeyenia is aimed at developing a suitable hypersonic fuel. To some analysts, this joint work indicates that Russia’s hypersonic technology may not be as advanced as previously thought if they’re going back to basic research.
It’s a similar story with China’s WU-14 missile, also known as the DF-ZF, which is a weapon designed to be deployed on the edge of space by a ballistic missile before gliding back to Earth at Mach 10 (7,613 mph, 12,250 km/h). It’s been flight-tested seven times from 2014 to 2017 at the Taiyuan Satellite Launch Center in Shanxi Province and is claimed to be nuclear-capable and able to be fitted to ICBMs to give it a range of up to 7,500 mi (12,000 km).
This is all possible, but China has been boasting of having a ship-killing hypersonic ballistic missile for over 10 years, with little evidence to back up the claims. While the flight tests of the WU-14 have been tracked by the West, it’s more likely designed as a short-range ship killer armed with a conventional warhead rather than a strategic weapon.
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Whatever the state of Russian or Chinese hypersonics, the United States is taking them seriously enough to spend US$75 million on hypersonic defense.
“We must push the boundaries of technology in every area,” says Air Force Chief of Staff General David L Goldfein. “Our adversaries aren’t standing still. They are looking for every advantage they can get.”
The US has a robust hypersonic research program, mainly operating under the government’s Prompt Global Strike (PGS) umbrella with the intention of developing an Advanced Hypersonic Weapon as well as anti-hypersonic defenses. The main goal of PGS is to produce a hypersonic precision-guided conventional weapon capable of carrying out airstrike anywhere in the world within one hour of launching from American territory.
The idea is that such a hypersonic weapon could potentially replace 30 percent of the US nuclear arsenal. This would not only have a considerable impact on nuclear deterrent strategy, but would also allow the US to attack strategic targets in rogue states with less risk of sparking a larger war. This is because the trajectory of a hypersonic conventional missile would be very different from that of a nuclear-armed ballistic missile. To date, no system has been officially approved, though the previous US administration did issue contradictory statements with United States Secretary of Defense Robert Gates claiming in 2010 that the US did have a Prompt Global Strike capability.
Meanwhile, the US is working with Australia on the Hypersonic International Flight Research Experimentation (HIFiRE) program, which has had several successful hypersonic flights, including one that reached Mach 7.5. In addition, Lockheed Martin is working on a hypersonic Tactical Boost Glide (TBG) vehicle under a US$147 million DARPA contract.
What is hypersonic flight?
So what exactly is hypersonic flight, why is it so important, and why all the interest in it now?
The first thing to understand is that hypersonics isn’t just a souped up version of supersonics. It’s as different as supersonics is from regular flight, only the challenges are far greater and the solutions more elusive. In fact, it’s a classic example of the law of diminishing returns.
The term “hypersonic” was coined in 1946 by Caltech aerodynamic engineer Hsue-shen Tsien and refers to speeds above Mach 5, where a new series of aerodynamic properties come together and dominate the problems of flight. Mach 1 is the speed of sound at sea level and a temperature of 15° C (59° F). However, this is not the case all the time in the real world. The speed of sound changes with differences in air pressure and temperature, though the air behaves the same regardless of what that speed is. Engineers need to take into account the variable nature of Mach, but, for our purposes, we’ll be working with the standard definition of Mach.
Speeds under Mach 0.8 (609 mph, 980 km/h) are called “subsonic.” That may seem odd, but speeds between Mach 0.8 and Mach 1.2 (913 mph, 1,470 km/h) are “transonic,” that is, they straddle “sonic,” which is Mach 1 (761 mph, 1,225 km/h). Mach 1.2 to Mach 5 (3,806 mph, 6,125 km/h) are supersonic, while speeds over Mach 5 are hypersonic. Speeds above Mach 10 (7,613 mph, 12,250 km/h) are high hypersonic and those above Mach 25 (19,000 mph, 30,600 km/h) are the ultrasonic velocities only reached by space vehicles.
For a real world idea of what these speeds mean, a subsonic airliner can travel from New York to London in about 5 hr 30 min and a supersonic plane can do it in 3 hr 10 min. A hypersonic airliner could cover the same distance in 1 hr 35 min. But there’s much more to these categories than numbers. They affect the most basic of aerospace engineering problems.
They used to say you can make a tea tray fly if you put enough power behind it, and, at subsonic speeds, “they” were right. It’s the reason drones can look nothing like a conventional airplane and why hobby shops sell flying models of the very non-aerodynamic Millennium Falcon.
But as one approaches the speed of sound, things change. That’s why there’s a transonic category. During the Second World War, for example, some prop-driven and jet fighter planes came close to Mach 1 without reaching it. However, the tips of their propellers or turbines would exceed the speed of sound, causing all sorts of trouble as turbulence threatened to tear them apart.
Sonic is where we encounter the famous sound barrier. At Mach 1, the air doesn’t have time to get out of the way of the speeding aircraft and a shock wave starts to build up in front of it, causing drag to increase dramatically. This drag is so severe that, at one time, the sound barrier was regarded as a literal barrier that aircraft might never be able to penetrate.
That changed on October 14, 1947 when the rocket-powered Bell Aircraft X-1 piloted by Captain Charles “Chuck” Yeager pegged the speedometer at Mach 1.06, becoming the first manned aircraft to exceed the speed of sound in level flight and, as the X-1 outran its own shockwave, creating the first aerial sonic boom .