The Cold War gave the world intercontinental ballistic missiles (ICBMs) that could carry nuclear weapons, and cruise missiles that could be launched from ships and aircraft.
Now, like a lot of Cold War-era military equipment, these weapons are getting a 21st-century tune-up. But it is not the payloads that are becoming more advanced — it's the delivery systems.
Missiles that can fly at hypersonic speeds could render global missile defenses useless and, if left unchecked, could become the next global arms race amongst the nations of the world.
There are mainly two types of missiles being pursued in this race: hypersonic cruise missiles (HCMs) and hypersonic glide vehicles (HGVs). Both are being pursued by a number of nations, but China, Russia, and the US are leading the way.
Two types of weapons
HCMs are essentially faster cruise missiles and HGVs are basically replacements for conventional re-entry vehicles that are put on ICBMs.
Of the two, HGVs are the easiest to make, since they only have to overcome one of the three obstacles — material science.
HGVs are put on top of ICBMs. When they reach a maximum altitude, they separate from the missile and glide on top of the atmosphere to their target — in this case, at hypersonic speeds.
Because of their hypersonic speeds, there may not even need to be any explosives on the weapons themselves, since the kinetic energy could be strong enough to cause damage in a limited area — although nowhere near the size of a nuclear blast.
What makes both weapons so threatening is the fact that they are maneuverable, meaning they can change direction at any moment and keep their intended target secret until the last few moments before impact.
Current missiles can be intercepted because their flight paths are determined by momentum and gravity. Most, if not all, anti-ballistic missile defenses, like THAAD and Aegis Ashore, require a projectile to make physical contact for a successful intercept or be close enough so that shrapnel from a proximity explosion could damage an incoming missile.
Because HCMs and HGVs are maneuverable and fly at such high speeds, interception of such missiles is almost impossible.
Dangerous potential results of hypersonic weapons
Widespread proliferation of this technology could have results that increase the risk of conflict and destabilization, especially when these weapons are armed with nuclear payloads.
According to a report on hypersonic weapons that was published by the RAND Corporation, governments may be so concerned with maintaining first-strike capability, since the response time for these weapons is so short, that they may take be forced to take risky actions.
These include devolving the command and control of the weapons to the military instead of the national leaders, wider disbursement of the weapons across the globe, a launch-on-warning posture, and a decision to strike first.
The RAND report shows that at least 23 countries are active in pursuing hypersonic technology for commercial or military use. Currently, the US, Russia, and China are leading the race.
The report suggests that widespread proliferation of hypersonic technology could lead to militaries around the world, particularly those that have tense relations with their neighbors, having capabilities that could be destabilizing.
The RAND Corporation suggests that this could also spur changes or amendments to the Missile Technology Control Regime (MTCR), a voluntary agreement with 35 nations that aims to prevent the proliferation of missiles that can carry nuclear warheads.
RAND believes that the MTCR should include completed hypersonic delivery vehicles, scramjets, and other hypersonic components to the list of items that cannot be exported. At the very least, a trilateral agreement between the US, Russia, and China could be made to prevent hypersonic weapons from falling into dangerous hands.
RAND believes that hypersonic missiles will become operable on the battlefield in the next 10 years.
Obstacles preventing sustained hypersonic flight
Hypersonic technology allows cruise missiles and nuclear weapons to go as fast as Mach 5 or above — roughly 3,800 miles per hour, or 340 miles every six minutes.
Missiles and rockets have long been able to go hypersonic; space shuttles and ICBMs, for instance, both fly at hypersonic speeds, sometimes as high as Mach 20 or 24 (Mach 25 is the upper limit). However, they only do so for a short period of time.
Technology is now being developed that will allow sustained hypersonic flight, overcoming three different challenges: material science; aerodynamics and flight control; and propulsion.
The problem of material science is relatively straightforward. Because the missile will be flying at such high speed, materials with high melting points are needed so they can absorb heat that would be gathered over a long period of time, so as to prevent the disintegration of the missile.
"You can think of it as flying into this blow torch," Rich Moore, a senior engineer at the RAND Corporation, said. "The faster a vehicle flies, the pressure and temperature rises exponentially."
The problem of aerodynamics and flight control is somewhat related. In order to achieve hypersonic speeds, the body of the missile needs to be constructed so that air resistance is minimal. Furthermore, the shape of the missile must be structurally strong enough to prevent bending and flexing which would affect the flight performance.
"You're under such high pressures, you are going so fast, that the body itself may not keep its shape all the time," George Nacouzi, a senior engineer at the RAND Corporation, told Business Insider in an interview.
Propulsion is probably the most complex challenge after material science. Once an object reaches Mach 5, traditional jet engines cannot generate enough power to maintain the speed or go faster. "It has been compared to lighting a match in a 2,000 mile an hour wind," said Richard Speier, a political scientist at RAND.
Trying to keep the engine going is extremely complex.
"You have potential shockwaves, the combustion has to be just at the right rate, you have to have the right mixture of fuel and oxidizer," Nacouzi said of the difficulties.
The result of trying to overcome this problem is a scramjet, an uncluttered, air-breathing engine that uses oxygen from the atmosphere as the oxidizer for combustion. Though scramjets are currently in a testing phase, they have already reached hypersonic speeds.
Dr. Nacouzi believes that out of those three problems, flight control may be the easiest to overcome.