Everyone is talking about ‘hypersonics’ – but what are they and how will they change things? We asked Justin Bronk, Royal United Services Institute (RUSI)’s Research Fellow for Airpower and Technology, to find out more. 

What are ‘hypersonics’?

“Hypersonics are objects which fly at hypersonic speeds, which are generally considered to be Mach 5 and above. There are two main types of hypersonic vehicle types; aerodynamic ones which generate lift by (extremely fast) powered forward flight through the atmosphere, and ballistic/glide vehicle ones – both of which are given their speed by a missile booster which places them on a high-arcing trajectory and then either fall to their targets on a ballistic arc or use a specially shaped and controllable glider re-entry vehicle to manoeuvre to evade defences and strike targets in a non-ballistic trajectory.”

Which nations have operational hypersonic weapons or aircraft?

“Technically, any nation with an intermediate range or certainly intercontinental ballistic missile (ICBM) capability operates hypersonic missiles, although ones which follow a largely ballistic trajectory.
The United States and Russia have various surface-to-air missile and anti-ballistic missile interceptor types which regularly operate at hypersonic speeds during boost phase and immediately afterwards, including the 40N6 missile used by the S-400, as well as the Standard Missile 3 (SM-3) series and the THAAD missile.
In terms of what most people refer to as hypersonics today (hypersonic glide vehicles and cruise missiles), Russia and China have fielded systems and the United States has several in testing that we know of. The US also flew the X-15 series of manned hypersonic aircraft for many years after its first flight in 1959, reaching a maximum speed of Mach 6.7.”

How many types of propulsion are there for hypersonic flight? What are the pros and cons of each?

Rocket propulsion
Pros: Great acceleration, relatively simple, relatively cheap, compact
Cons: Limited fuel necessitating short boost phase followed by unpowered rest of the flight, hazardous and toxic chemicals, large plume making launches conspicuous.

Scramjet propulsion
Pros: Best option for sustained hypersonic speeds in atmosphere, comparatively good fuel efficiency, once working – few moving parts, range.
Cons: Only works in atmosphere, needs hypersonic airflow to work, so needs either a rocket booster or a jet/ramjet to get it to operating speeds, difficult technology to master.

What are the advantages of hypersonic weapons?
“Firstly, they offer very little warning time for potential targets. As NATO and the Soviet Union discovered during the Cold War as hypersonic ICBMs started to become the backbone of nuclear arsenals, such flight speeds make warning times for even intercontinental strikes a matter of minutes rather than hours. For a naval task force or land based airbase or command post facing hypersonic weapons launched from 1000km or less, warning times would be very short indeed. This would make moving assets in response to hostile launches to try and get out of seeker acquisition range before the missile(s) arrived very unlikely to work, reduce the decision time available for the defender and make any attempts at interception more difficult.

The second main advantage is that there are currently few interceptor missiles rated to intercept hypersonic threats. There are some, such as the aforementioned SM-3 and 40N6, but these are only capable at present of interception hypersonic targets following predictable ballistic trajectories at high apex altitudes and even then only if the interceptor launch tubes are positioned in the right place under the target’s flight path. The ability of hypersonic glide vehicles to manoeuvre significantly in flight, coupled with their extremely high speed makes plotting a viable intercept trajectory almost impossible with current generation interceptors. Hypersonic cruise missiles are more advanced weapons in many ways, but if they can be made to work, they should be even more difficult to successfully intercept than ballistic-missile lofted hypersonic glide vehicles. This is because cruise missiles fly at much lower altitudes, meaning radar horizon ranges are much shorter (reducing warning times further), ground clutter becomes an issue for radars looking down from above to try and pick them out, and interceptor missiles have to work down in the dense air of the lower atmosphere which increases drag and other forces at work in flight. Even if a hypersonic cruise missile is intercepted close to (let’s say) a naval task group by gunfire or directed energy weapons, the disabled missile may still have sufficient momentum and kinetic energy to cause serious damage to the ships.
The third major advantage of hypersonic glide vehicles over traditional ballistic missiles is that the ability of the warhead to manoeuvre makes it impossible to accurately predict where the missile is going to land from its boost trajectory – a technique which is vital to both ballistic missile defence and nuclear early warning systems.”

 

What’s China up to?

“China and Russia have both developed hypersonic glide vehicles mounted on ballistic missile bodies to produce precision strike weapons capable of penetrating current generation missile defence systems. Notable Chinese systems include the DF-21D ‘carrier killer’ and the DF-17 medium range ballistic missile with DF-ZF hypersonic glide vehicle. Russian systems include the Kh-47M2 Kinzhal* air-launched quasi-ballistic missile and Yu-74 Avangard hypersonic glide vehicle for use by nuclear ICBMs.

Russia is also developing an aerodynamic cruise missile with hypersonic performance, called the 3M22 Zircon for use against American carrier battle groups and protected static targets on land. Essentially, both China and Russia have identified that the United States and NATO more broadly are extremely dependent on certain key assets for their way of warfare – such as aircraft carriers, combined air operations centres, forward logistics hubs and airbases. The US has developed a range of systems since the end of the Cold War to protect such assets with layered air and ballistic missile defences such as Patriot PAC-3, THAAD, SM-6 and SM-3, so the Chinese and Russians have turned to hypersonic missiles to give them a way to hold such targets at threat once more.”
And the US?
“The US has come somewhat late to the party on hypersonics – at least in the public domain. This is not simply an issue of being blinded by the demands of counterinsurgency, but also about priorities. Put simply, the US already has the means to hold pretty much any Russian or Chinese high value target at risk if it wishes to – albeit at increasing levels of strike package risk these days as the IADS of both China and Russia continue to improve. Russia and China also depend more on massed forces and comparatively less on limited numbers of exquisite high value assets than the US and NATO, so are less comparatively open to being coerced by a US equivalent of the DF-21D or Kh-47M2*.

However, what the US does have a serious demand for is for smaller, more tactically focused hypersonic missiles to enable it to bypass Chinese and Russian point defence systems and hit mobile targets which are critical to the latter nations’ anti-access/area denial capabilities once they have been identified and before they can relocate. Obvious candidates for such a hypersonic weapons system include mobile DF-21D and DF-17 transporter erector launchers (TELs), long range SAM batteries, anti-ship missile batteries and naval assets.”

*Editor notes: some observers describe ‘Kh-47M2’ as a fictional designation. ‘Kinzhal’ is  the name of the airborne system or ‘aviation complex’, of which the missile is a part

“To that end, there are now multiple funded hypersonic cruise missile programmes running in the US to develop air-launched and naval prompt strike weapons. One of the longest running of these is the High Speed Strike Weapon (HSSW) programme which produced the X-51A Waverider experimental demonstrator. There is also the more recent AGM-183A Air-Launched Rapid Response Weapon (ARRW) project, as well as evidence of large numbers of classified efforts in congressional budget submissions.”

 

What’s the biggest myth about hypersonics?
“That they will replace other missiles. Hypersonic weapons are by nature more expensive and shorter ranged than a supersonic or subsonic missile of a comparable size. The higher the mach number and range desired, the greater the cost, complexity and size the weapon is likely to call for, and correspondingly the more limited your affordable and deployable arsenal will be as any given country. Given that one of the biggest hurdles for Western militaries facing a renewal of great power competition is the unaffordable demand signal for adequate stocks of existing precision guided munitions to hit the number of targets likely to be needed in even a limited state-on-state conflict, going all out towards even more expensive and less numerous weapons seems an odd bet to take.”

What is the likely future?
“Hypersonic weapons will (and already are) erode the advantage which the US has managed to gain over its main state rivals in terms of being able to rely heavily on largely invulnerable key assets within easy striking range by dint of advanced air and missile defence systems. Russia and China will be able to credibly threaten to destroy airbases, aircraft carriers, forward logistics hubs and command centres within at least 1000km of their borders – just as the Soviet Union could during the Cold War.
The US and its allies will eventually have access to a range of air launched and naval hypersonic missiles which will also make it harder for the Russian or Chinese assets which make up their anti-access/area denial networks to be survivable in the face of a determined suppression of enemy air defences/destruction of enemy air defences campaign.
In other words, having swung significantly in favour of the defender in recent decades, the age old competition between military offense and defence is swinging back somewhat towards parity and that means a comparatively increased emphasis on which side can take losses and have sufficient reserves or overmatch to still remain effective at the point of maximum effort.
Having said that, I think it is highly likely that the majority of Western and Eastern firepower will remain subsonic and supersonic.”

What should I have asked you?

“About the role likely to be played in this domain by directed energy weapons. To which I will say I think high-powered microwave weapons are much more interesting than lasers for hypersonic interception purposes, but that’s for another article!”

 

 

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