Unpacking the hypersonic hype

A truck carries an Iranian Fattah ‘hypersonic ballistic missile’ during the annual military parade in Tehran on September 22, 2023. It is worth noting that in the context of missiles, ‘hypersonic’ and ‘ballistic’ are mutually exclusive terms. Credit: AFP via Getty Images.

Hypersonic weapons have become a focal point for defence investments globally, with billions being poured into their development. But as funding skyrockets, so do questions about their practicality and effectiveness.

Programmes focussed on hypersonic weapon technologies have seen heavy investment in recent years, with a report from the US Congressional Research Service estimating that the US Department of Defense (DoD) investments in hypersonic technologies totalled $5.8bn across 2021 and 2022 alone, while the UK earmarked $2.5bn for hypersonic weapons from a larger investment of $8.1bn announced for defence research and design in 2022, according GlobalData’s 'Thematic Intelligence: Advanced Materials (2023)' report.

Bestowed upon a concept that has been actively researched since the 1950’s without producing results, this sudden surge in investment might come as surprise but for recent announcements from some governments that suggest some success in making hypersonic weapon technology work effectively, notably China and Russia.

There are reasons to doubt these claims, and whether the claims are true or not, there are tenable reasons to think that further investment is not an appropriate response.

Regarding the truth of the announcements, certain cues in hypersonic weapon delivery invite scepticism, while the inherent technical and engineering challenges make the stated design goals highly unlikely to be achieved.

That Russian President Vladimir Putin declared the development of its premier hypersonic glide weapon, Avangard, in his annual address to the Russian Federal Assembly marks status of the programme as inherently political, a point underlined by its announcement two weeks before a presidential election, in 2018. Later, Putin claimed to have fired a number of the missiles personally, in 2019.

There are benefits to maintaining a bluff on hypersonic weapon technologies. Stoking an arms race centred on expensive and redundant technology primarily benefits the nation that has a more marginal military industrial base and a lower research and design budget to spend - attriting alternative weapons and platforms before they are commissioned.

At the announcement, Avangard was heralded as a super-weapon, capable of acting as an effector with a vastly reduced time-to-target provided by its immense speed, while simultaneously evading missile defence systems through its ability to manoeuvre against huge velocities and avoiding radar detection with a lower flightpath than the intercontinental ballistic missiles that missile defence systems are designed to interdict. However, the effectiveness of the system is shrouded in secrecy, with all public knowledge limited to material from Russian state broadcasters, and it has not been proven whether test flights of the system included attempts to manoeuvre the missile or if it instead stayed with a simple direct flightpath.

Physically, the capabilities alleged of Avangard and other hypersonic glide weapons are very difficult to achieve. Writing for the London Review of Books, Andrew Cockburn interviewed Pierre Sprey, a US Pentagon analyst who was at the heart of the design of the F-16 and A-10 aircrafts, and expressed doubt in the credulity of claims of success in trialling hypersonic weapons.

Sprey cited the substantial resistance and drag encountered when traveling at hypersonic speeds (five times the speed of sound) through the atmosphere as a factor that would result in the missile becoming intensely heated. The same phenomena forces space capsules and ballistic missile warheads to employ blunt-shaped noses and heat shields in their design. 

These blunt-nosed configurations allow for the dissipation of the heat generated during the high-velocity re-entry into the atmosphere through the process of melting and burning off the heat shield, but for a hypersonic glider solution this is out of the question. If the hypersonic glider is to achieve significant range, explained Sprey, it cannot afford the excessive drag associated with the blunt, heat-dispersing design.

The increase in heat is not linear with the increase in velocity, and at Mach 5 this equates to temperatures in excess of 1000 degrees Celsius, at which point metals can weaken and fail. Even if the missile’s structure is protected against through some advancement in material sciences, the combination of excessive heat and speed can result in plasma sheathing. This is the envelopment of the hypersonic glider in a layer of ionised gas with the potential to blind the missile’s sensors, deafen it to communication or control from an outside operator, and render the missile unable to orientate itself by satellite GPS coordinates.  

In effect, plasma sheathing would leave the hypersonic glider rudderless, and as confined to a single unchanging trajectory as any standard intercontinental ballistic missile. This comparison is fair except, lacking a need to travel at hypersonic speeds, an intercontinental ballistic missile is less constrained in its design, and can carry a large warhead that is not in need of precision targeting. This contrasts starkly with a hypersonic glider that, optimised for speed, must carry a smaller payload, and so relies on precision guidance to catch its target within the area of effect.

Both China and the US have expressed some confidence in overcoming the issues with plasma sheathing, but it does currently represent a design limitation.  

As these limitations are encountered and overcome the cost of production begins to stagger, and at certain inflection points in programme development the capability will be evaluated against the goals of the mission and any alternative approaches. This raises the question of what problem the hypersonic glider a solution for?

The US has said it has no plans to use hypersonic weapons as a conveyor for nuclear warheads, in contrast to explicit comments from Russia stating that hypersonic glide weapons will allow its nuclear weapons to evade missile defence systems. The efficacy of hypersonic weapons to succeed in this goal are yet to be proven.  

However, even hypersonic gliders are successful in evading missile defence systems, what cause could Russia have for thinking that its current nuclear strike capability would not also be successful, given that its capacity for striking with intercontinental ballistic missiles armed with multiple nuclear warheads vastly outweighs any missile defence system in operation?

In theory, possessing nuclear armed hypersonic weapons is a greater liability than intercontinental ballistic missiles, as the adjustable trajectory of a hypersonic glider leaves no observer certain that they are not the intended target. Between a hypersonic weapon’s launch and its detonation, the potential for an unwarranted second-strike contingency imperils the user’s nation from every direction, not just from the intended target, as other nations respond as though they were under threat.  

The challenge for a military commander employing hypersonic glide weapons in conventional warfare is to find a target that is more expensive than the hypersonic glider, and then to decide that it can’t be destroyed by more conventional, cheaper means. Failing that, hypersonic weapons can be employed in scenarios where their target has a strategic value equivalent to the unit price of the hypersonic glider - some fraction of the many billions of dollars invested in research and development - where the mission also plays to its core strengths, in avoiding air defences and operating with an incredibly short time-to-target.

It is worth stressing that the advantage of hypersonic weapons in avoiding detection is generated by the relatively closer proximity their flightpath takes to the earth when compared with intercontinental ballistic missiles. Theoretically this means that early detection opportunities are limited by a far narrower arc near the weapon’s target. The higher up the missile, the further away it can be seen, because that leg of the journey is not obscured by the horizon.

Where this plan, espoused first in the 1950s, falls apart is in the assumption that the country being targeted only has missile detection systems within its own country and does not (as with the a number of nations) house them within the territory of other nations, or (as with a number of maritime nations) employ sea-going vessels with missile detection capabilities, or (as with a growing number of spacefaring nations) employ satellites that can provide missile detection capabilities from space. Adding sensors closer to the launch site of the hypersonic weapon massively advances the detection time.

Although alternative technologies put forward are as far ranging as the use of high-energy laser weapons to advanced magnetic railguns, there are two major concepts for the interception of hypersonic weapons once they are detected.

The first option is to use a hypersonic interceptor to interdict the hypersonic glider during the high-speed glide phase. This may be more challenging than the development of a hypersonic weapon.

The second option is to target the hypersonic glider during the terminal phase, when the glider descends to strike its target. Interception during the terminal phase requires adaptation of existing missile defence systems, as the US is engaged with in the Aegis missile defence system. Interception during the glide phase is considered preferable to avoid proximity to the target. 

While these two methods of defence against hypersonic weapons may have limitations, their presence does have advantages. Hypersonic weapon operators may be forced to consider their location when directing the weapon, making additional manoeuvres to avoid them, and reducing the weapon’s speed.

In the Ukraine war a certain level of success has been made in defending against the Kh-47M2 Kinzhal missile, which is claimed as a hypersonic weapon, and was responsible for an effective attack as early as 18 March 2022. When describing the nature of the Kinzhal missile, it is often understated that the missile would not normally qualify as a hypersonic weapon, were it not for the fact that it is launched from a MiG-31 travelling at high speeds.

The approach adopted by Ukraine is to detect when the one of the few MiG-31s especially adapted to carrying the Kinzhal missile take off from the ground, and then to issue an air-raid warning. The reduced warning time that hypersonic weapons are expected to produce is lost when used against an enemy prepared in this manner.

As nations pour resources into the hypersonic arms race, it is imperative to step back and assess not just the technological feasibility but also the strategic value of these investments. The myriad challenges, both technical and tactical, cast a shadow of doubt over the touted capabilities of hypersonic weapons. The true test for hypersonic weapons won't merely be in their development, but in their ability to provide tangible advantages over existing systems without disproportionate costs. Current spending patterns suggest pragmatism will not prevail over prestige.