Hypersonic Weapons: Fast, Furious…and Futile?

Cruise missiles and boost gliders that can travel at a maintained speed greater than Mach 5 along an unpredictable trajectory and without revealing their target until the very last moment have become a reality. Russia’s periodic testing frenzy continues to intimidate foreign audiences with the latest showcasing of its hypersonic cruise missile, while the Pentagon keeps asking for more money for its hypersonic research, jumping from $800 million in 2017 to a request for a whopping $3.8 billion for 2022.

Hypersonic weaponry represents the most significant advancement in missile technology since ICBMs. Thanks to their extreme speed and ability to manoeuvre, hypersonic weapons are on their way to undermining nuclear deterrence postures and creating cracks in strategic stability by the mid-2020s. Compared to ballistic missiles, which are fast but travel along a predictable trajectory like a bullet, and cruise missiles, which are more accurate but slower, hypersonic weapons combine the advantages of both: speed and accuracy. By introducing an element of surprise and compressing the response time within the Observe–Orient–Decide–Act loop, hypersonic weapons represent a transformative warfighting capability.

At least this is how hypersonic weapons are usually advertised to the public. The military effectiveness and reliability of hypersonic weapons remain a known unknown. The craze around hypersonic weapon systems does not seem to be technically justified and policymakers tend to overestimate the capabilities of hypersonic weapon systems, especially in the strategic stability context. Yet the leading weaponisers of hypersonic technology – the US, Russia and China – are confidently engaging in the ‘glide or die’ competition for this technological edge, which seems to be mostly a matter of national pride and prestige.

However, it is important to recognise the possibility that while the impact of hypersonic weapons on nuclear strategic stability may indeed be minimal, their theatre-level effects could have real military value. Despite important shortcomings of weaponry based on hypersonic technology, both China and Russia believe that these new weapons could answer their security concerns, as theatre range weapons against command posts and naval strike groups, and as a hedge against the US homeland ballistic missile defence system.

Not So Impressive

Hypersonic weapons are not a game-changer, at least with regard to strategic stability at intercontinental ranges. Even though cruise missiles, propelled by a scramjet, and boost gliders, unpropelled and lifted into the atmosphere by a rocket, certainly do bring a set of challenges, their novelty pales in comparison with ‘good old’ long-range ballistic missiles. This is for two reasons: first, hypersonic weapons are portrayed as revolutionary in terms of overcoming anti-missile defences, as if an effective ballistic missile defence against ICBMs already existed; and second, the necessary trade-offs between speed, range, manoeuvrability and accuracy imply performance limitations that need more understanding.

Speed, Range and Manoeuvrability

The extreme speed of these weapons drastically limits the defender’s time for decision-making, but so do ICBMs as they are already hypersonic. Combined with their flight trajectory at unusual altitudes, hypersonic weapons are thought to be unstoppable by existing terrestrial and space-based sensors. However, gliders lose energy and speed as they travel down to their target. Any manoeuvre results in increased drag, which requires additional thrust to maintain speed, yet scramjet engines are not able to compensate for this induced drag (not to mention that gliders have no engine). The more and further they manoeuvre, the lower the actual speed of impact is, which can certainly go below Mach 5. This imposes important limits on the vehicle’s manoeuvrability and calls into question the possibility of relying on the missile’s kinetic energy impact alone at intercontinental ranges.

Accuracy

Hypersonic weapons seem to be betrayed by their extreme speed. The high speed and friction heat the surfaces of hypersonic vehicles to levels exceeding 2,000°C and produce a line of ionised gas that can disrupt navigation signals. In fact, anything that travels intercontinental distances has issues with accuracy; ICBMs have a circular error probable of 120 m. Moreover, the resulting plasma can be visible on radars, space-based sensors and even to large surveillance drones, more than the vehicle itself. Thus, while it is thought that greater manoeuvrability can deceive the defender as to which target the missile will strike, physical limitations imposed by low-altitude atmospheric flights expose hypersonic weapons hiding from surface-based radars behind the Earth’s curvature.

At the theatre level, however, the situation can look different. Fast-moving manoeuvring hypersonic weapons can be good at frustrating existing layered defences against both shorter and intermediate range ballistic and cruise missiles, such as Terminal High-Altitude Area Defense (THAAD) and Aegis. Many countries rely on ground-based radars for early warning, which are not equipped to defend against hypersonic missiles flying at lower altitudes, that is, below the altitude of ballistic missile interceptors but above the altitude of the Patriot system. As these weapons travel at unusual altitudes and can pass around the radars, at shorter distances these weapons can fly fast, undetected by radars towards the target before the defender can even process what is happening, let alone launch a missile.

Here the experts are split. On the one hand, the introduction of hypersonic weapons could actually change strategising for regional conflict theatres. On the other hand, as mentioned above, the actual speed of manoeuvring gliders can be much lower, which means that the THAAD may be able to detect hypersonic weapons during the glide or terminal phases. However, while these systems could be adapted to intercept hypersonic weapons, they can cover only small areas and it would be prohibitively expensive to use them for continental defence.

Trajectories of National Hypersonic Weapons Programmes

Although the advantageous capabilities of hypersonic weapons still await sober technical assessment, both Russia and China continue to invest in hypersonic capability development programmes due to their genuine geostrategic security concerns, in addition to status-seeking motivations, a vanity competition against the US for the technological edge and national prestige.

Reportedly, Russia deployed its first hypersonic weapon system, Avangard, in December 2019 and China its hypersonic glider DF-ZF in 2020, while the US is likely to field its hypersonic weapons by 2023. In addition, Russia has been working on an air-launched ballistic missile Kh‑47M2 Kinzhal that is, allegedly, able to reach Mach 10 within a range of 2,000 km, while China has been testing a 2,500-km-range ballistic missile DF-17 and intercontinental ballistic missile DF-41, which is supposedly able to carry conventional or nuclear hypersonic gliders to improve Chinese second-strike capabilities. The dual capability and target ambiguity of Kinzhal and DF-41 are particularly disturbing, since they can carry both conventional and nuclear low-/high-yield warheads, meaning deployment of these missiles can lead to unintended escalation.

Both Russia and China intend to acquire a tactical hypersonic weapon capability as well, in the form of anti-ship missiles able to sink aircraft carriers, such as Russia’s 3M22 Tsirkon and China’s Starry Sky-2 (or Xing Kong-2). The actual performance of these new weapon systems has been difficult to corroborate, while some evidence indicates that the hypersonic industrial base in Russia is under-resourced.

Russia has been eyeing nuclear-capable hypersonic weapons to strengthen its nuclear deterrence posture, which Moscow believes was undermined when the US withdrew from the Anti-Ballistic Missile Treaty in 2002. For Russia, hypersonic weapons represent a qualitatively new capability for overcoming US missile defences. Even though the advantage of hypersonic weapons is weakest at intercontinental ranges, for Russia they represent a hedging strategy.

In contrast, China has been developing hypersonic weapons to further project its power in the South China Sea and over Taiwan, while circumventing US missile defences in the Asia-Pacific region. The Chinese fear of a US pre-emptive strike that would disable China’s nuclear arsenal and deprive China of its ability to retaliate seems to be the motive behind fitting its DF-41 with multiple gliders.

Although the US has been investing in hypersonic research as part of the Prompt Global Strike programme, the recent budget boost in hypersonics is a reaction to the recent Russian and Chinese technological advances in fielding operational hypersonic weapon systems. Interestingly, the Pentagon has officially only been developing prototypes and has no weapon acquisitions programme, yet this might change soon. And unlike China and Russia, the US has publicly ruled out acquiring nuclear-capable hypersonic weapons (despite some rumours).

Each of the US armed services has its own research programme. The US Navy’s flagship hypersonic programme is developing a submarine-launched glider with the intention to deploy it on Zumwalt-class destroyers by 2025 and Virginia-class submarines by 2028. The US Army is expecting to field an experimental prototype of its mobile ground-launched, rocket-powered glider Long-Range Hypersonic Weapon in 2023. The US Air Force is working on the AGM-183 Air-Launched Rapid Response Weapon programme, which develops a glider compatible with B-52s and F-15s. In 2022, the US Air Force intends to launch a new Hypersonic Attack Cruise Missile programme, while consulting the industry on Project Mayhem, the Expendable Hypersonic Air-Breathing Multi-Mission Demonstrator Program, that seeks to design a hypersonic cruise missile with longer ranges and greater payloads.

As there are no countermeasures against the hypersonic threat, the US Missile Defense Agency (MDA) has been developing missile defence systems against hypersonic threats together with the Space Development Agency as part of the National Defense Space Architecture. This layered space architecture of 550 satellites will primarily aim to provide resilient communication systems, yet it will also include a sensor layer to enable the US to track and target advanced hypersonic threats at both high and low altitudes. However, the ambition of fielding a counter-hypersonic space-based sensor layer with full global coverage might turn out to be unaffordable for the time being. The MDA is also looking into the possibilities of using directed energy, such as laser guns, hypervelocity projectiles and new interceptors to counter manoeuvring hypersonic missiles.

Time to End the Hypersonic Hyperbole

While this is far from being an arms race situation, the ongoing research and development in hypersonic weaponry has already distorted threat perceptions.;The hypersonic technology per se is not the problem. This new generation of hypersonic systems that is flying faster, striking the target harder and from further away may be simply evolutionary, rather than revolutionary, and some doubt that it can offer any strategic advantage or real added value to the existing systems with intercontinental ranges. However, their tactical use may indeed have some real military potential against time-sensitive targets or in naval warfare as anti-ship missiles.

Yet overly enthusiastic leaders about weapon systems that continue to suffer from serious engineering problems, combined with unstable relations among the great powers, create a rather fertile ground for misperceptions and unintended escalation. Although hypersonic weapons might be an overkill, this technological competition may potentially lead to further nuclear build-up. Hypersonic weapons are becoming a new strategic stability nightmare.

Hypersonic weapons should be included in future arms control agreements to limit their proliferation. Regardless of their actual military performance and expected advantages, weaponised hypersonic technology has the potential to further destabilise the security environment by changing the perceived vulnerability.

Capping the number of strategic nuclear-capable hypersonic weapons under New START is one option. For instance, Russia’s Avangard is counted within the limits of this treaty. However, this option is frail as New START does not cover weapons that fly on a ballistic trajectory for less than 50% of their flight, as do most hypersonic gliders and missiles, and is only temporary since New START is due to expire in 2026.

While an outright test ban on hypersonic weapons would be ideal, it is an unrealistic scenario. Leaders are less likely to pay policy attention to limiting a class of weapons at a time when they are intensively engaged in perfecting them. Informal measures could do the job of conflict prevention. This can include reciprocating unilateral gestures, such as reducing national investments into hypersonic weapon programmes and even cancelling those without rationale or credibility.

Confidence-building measures to install greater transparency are the first step towards any future binding agreement. These measures could take the form of exchanges of observers during the hypersonic tests and demonstrations of the systems, regular professional dialogue between political, military and technical experts from all three countries, avoiding storing conventional and nuclear hypersonic capabilities at the same site, conducting joint technical studies, and providing advanced notices. Representatives from the US and Russia have already discussed that their bilateral strategic stability dialogue could include hypersonic weapons.

Hypersonic technology will not provide the weapons of the future nor revolutionise military affairs. It is the kind of emerging technology that will keep promising to deliver revolutionary results ‘in the near future’, yet it will likely remain in the niche box of experimental capabilities. Scramjets and glide vehicles operating under extreme conditions pose significant engineering and technical challenges in terms of aerothermodynamics and resistant materials. The wider use of hypersonic weapons is unlikely as their technical requirements remain complex and costly. However, when considered within the big picture of technological advancement, hypersonic weapons can multiply the disruptive impact of other emerging technologies, increase the chances of conflict escalation due to the lack of transparency that surrounds these programmes, and aggravate security dilemmas.

The views expressed in this article are the author’s, and do not represent those of RUSI or any other institution.