Five times the speed of sound, or 6,200 kilometres per hour: that’s the minimum speed of a hypersonic weapon – a missile or other type of projectile, such as a gun-fired artillery round – designed to strike targets hundreds or even thousands of miles away before an enemy has time to respond.
At mach five, the projectile is racing towards the target at 1.7 kilometres per second.
The US has long feared it is falling behind in what analysts are calling a “hypersonic arms race” with China and both the Trump and Biden administrations have boosted funding to develop the terrifyingly fast weapons.
North Korea on Tuesday tested a hypersonic “glide vehicle” – a projectile boosted to high altitude or even into space before detaching from its rocket and manoeuvring to a target using its wings while hurtling to earth at colossal speed, according to state news reports.
Swarms and global strikes
In the past week, the US has showcased two weapons systems, one hypersonic, the other for delivering swarms of cruise missiles from cargo planes.
On Monday, it said it had tested an “air-breathing hypersonic weapon”, the first successful US trialling of a hypersonic device since 2013.
Air-breathing hypersonic weapons acquire their name because they travel through the Earth’s atmosphere using an advanced jet engine called a scramjet, which compresses air moving at hypersonic speed.
Because of the friction produced by air at hypersonic speeds they need to be able to withstand extremely high temperatures.
Air intake on the experimental X-51A US jet aircraft tested between 2010 and 2013 reached temperatures of 1,000°C.
Those tests preceded the secretive Hypersonic Air-breathing Weapon Concept (HAWC), developed with the Defence Advanced Research Projects Agency, better known as Darpa, one of the US government’s foremost research agencies.
"The missile, built by Raytheon Technologies, was released from an aircraft seconds before its Northrop Grumman scramjet (supersonic combustion ramjet) engine kicked on," Darpa said.
Darpa says its mission is to ensure the US remains “the initiator and not the victim of strategic technological surprises”.
Raytheon announced work on the project with defence aviation company Northrup Grumman in June 2019, although the HAWC project was first announced in 2014 – an indicator of how little information was made public.
The Pentagon "has identified hypersonic weapons and counter-hypersonic capabilities as the highest technical priorities for our nation's security," said Wes Kremer, president of Raytheon's Missiles & Defence business unit, after the test.
The successful test of the HAWC comes after a number of notable failures in the country, including the failed test of the US Air Forces’ AGM-183A Air-launched Rapid-Response Weapon (ARRW) in July, when the missile’s rocket motor failed to ignite.
The Air Force hopes the ARRW will be able to reach speeds up to Mach 20, or faster than 24,000kph.
Cruise missiles in a box
But the US is not merely placing all bets on hypersonic flight: there are also much slower, stealth weapon systems, such as the Joint Air-to-Surface Standoff Missile, or JASSM, a “low observable” or “stealth” cruise missile which is designed to be difficult to detect on radar creeping into enemy territory, unlike first-generation cruise missiles which became well-known during the first Gulf War.
On September 24, Lockheed Martin released a computer-animated video demonstrating a bizarre new concept: dropping JASSM missiles out of cargo planes by parachute.
Successful tests were conducted in August, the company said.
The devices are loaded on to pallets, which then jettison the missiles while parachuting to Earth. The missiles can be given targeting data by the aircraft, turning planes used for ferrying troops and cargo into lethal attack aircraft.