Last week, the Russian defence ministry claimed that its military launched Kh-47M2 Kinzhal “hypersonic missiles” to destroy an ammunition warehouse in western Ukraine. On 21 March, US President Joe Biden confirmed the Russian claim. This is the first-ever instance of hypersonic weapons used in combat, marking the beginning of a new era of warfare.
What are hypersonic weapons?
The term ‘hypersonic weapons’ is usually used to refer to objects flying at speeds surpassing five Mach or five times the speed of sound. Most ballistic missiles travel at hypersonic speeds and execute terminal manoeuvres in their atmospheric re-entry phase. If we go by the standard of speed, most ballistic missiles would fit the classification of hypersonic weapons.
Hypersonic weapons are not just about speed but also manoeuvrability and low-altitude flying. Hypersonic flight, by definition, is an atmospheric flight. It is defined by the sustained flight of an aerodynamic vehicle at an altitude of around 20 km to 60 km within the earth’s atmosphere. In atmospheric conditions, an object flying at hypersonic speed experiences aerodynamic and thermal forces unencountered at lower speeds. For example, cruise missiles fly in atmospheric conditions at a much lower altitude than most hypersonic weapons. Still, they are not exposed to hypersonic flight conditions such as overheating, laminar flow disruption, ionisation of surrounding gases, and plasma formation. Moreover, since the speed of sound depends on the density and temperature of surrounding gases, hypersonic flight doesn’t make sense for the objects flying in space with minimal particle density.
Why all ballistic missiles can’t be hypersonic weapons?
Ballistic missiles reaching hypersonic speeds during mid-course and terminal phase cannot be characterised as hypersonic weapons for two reasons: First, ballistic missiles in their mid-course trajectory travel in space and thus don’t come across aero-thermal complications associated with hypersonic flight. Second, while ballistic missiles in their terminal phase might run into momentary hypersonic flight (lasting only for tens of seconds), hypersonic vehicles must survive that environment for many minutes. Thus, hypersonic flight is not just about encountering aero-thermal forces but sustaining across them for a period lasting in minutes.
In addition to sustained low-altitude flying, the ability to manoeuvre defines hypersonic weapons. Unlike ballistic missiles, hypersonic weapons have an unpredictable midcourse/glide phase flight and carry out manoeuvres in the terminal phase. Even though ballistic missiles with manoeuvring warheads can execute terminal manoeuvres, they have a reasonably predictable (parabolic) midcourse trajectory and thus are not characterised as hypersonic weapons.
Thus, hypersonic weapons can be defined as aerodynamic vehicles capable of sustained low-altitude flight at hypersonic speed and can execute manoeuvres throughout their trajectory.
What are the types of hypersonic weapons?
Hypersonic missiles are typically characterised as rocket-boosted hypersonic glide vehicles (HGV) and hypersonic cruise missiles (HCM). HGVs are aerodynamic vehicles propelled by rockets into space. Shortly after launch, they carry out a pull-up to attain equilibrium gliding and rely on the aerodynamic lift to travel unpowered over long distances in the atmosphere, reducing surface radar detection range. In proximity to its target, the weapon exits the gliding trajectory, carries out terminal manoeuvres using internal boosters, and impacts the target. HGVs have an unpredictable gliding trajectory than ballistic missiles, which follow a predictable parabolic trajectory. In a way, HGVs combine the speed of ballistic missiles and manoeuvrability and low altitude flying of cruise missiles.
HCMs are nothing but hypersonic versions of traditional cruise missiles. Both of them are powered throughout their trajectory and thus are capable of executing manoeuvres during the flight. While the cruise missiles are propelled through the turbofan or ramjet engine, hypersonic cruise missiles are powered by a supersonic combustion ramjet or scramjet engine. Scramjets are superior ramjet engines. While the airflow in a ramjet engine remains subsonic, airflow through a scramjet engine is supersonic. Thus, scramjet-powered cruise missiles are faster (hypersonic) than ramjet-powered missiles (supersonic).
While the bifurcation between HGV and HCM might be helpful, it oversimplifies the possibilities of hypersonic missile design. Future hypersonic weapons might combine the attributes of glide vehicles and cruise missiles. For example, scramjet engines can be integrated with glide vehicles, enhancing their range, manoeuvrability, and speed. Many such possibilities cannot be captured by HGV/HCM dichotomy.
What are the strategic implications of hypersonic weapons?
There is an ongoing debate over the implications of hypersonic missiles on strategic ability. One set of observers argues that the speed, low-altitude flight, and the ability of hypersonic weapons to evade missile defence systems has upset the great power strategic stability by violating the key nuclear deterrence principle of mutual assured vulnerability. Their argument can be summarised in four parts.
First, the ability of hypersonic weapons to evade missile defence systems might incentivise an aggressor to launch a pre-emptive offensive strike, forcing the defender to move towards a high-alert launch on warning (LOW) posture, increasing the risk of miscalculation and nuclear escalation.
Second, the extreme speeds of hypersonic weapons accelerate the timeline of response available to national leaders, increasing the risk of crisis escalation and worsening strategic stability.
Third, hypersonic weapons bring in warhead and destination ambiguity. Hypersonic missiles can be tipped with both conventional and nuclear warheads. In the heat of the moment, a conventionally tipped missile might be misperceived as nuclear-tipped and responded in kind, inadvertently leading to nuclear warfare. Also, given the unpredictable trajectory of hypersonic weapons, the defender can never be ascertained of the target under attack. Expecting the worst, the defender might assume that its strategic assets and command and control are under attack and launch before the adversary sabotages them.
Fourth, hypersonic weapons have unlocked an offence-defence spiral risking arms race and strategic instability. The three major players of the hypersonic race, the US, China and Russia, have developed or are on the verge of achieving hypersonic capabilities. At the same time, they are looking for countermeasures to address emerging hypersonic threats.
The second school of thought argues that hypersonic weapons are not a stand-alone but an evolutionary development against the Ballistic Missile Defenses (BMD). The US development of BMDs threatened the retaliatory capability of its adversaries, violating the critical nuclear deterrence principle of assured vulnerability. The ability of hypersonic missiles to overcome existing and prospective missile defence systems re-establish the mutually assured vulnerability, strengthening strategic stability.
Hypersonic programmes in Russia, China, the US, and India
In the March 2018 Presidential address to the Federal Assembly, Russian President Vladimir Putin unleashed a new generation of ‘invincible’ nuclear weapons, including the hypersonic glide vehicle ‘Avangard’ and hypersonic aircraft missile system ‘Kinzhal’. In February 2019, among other weapons, Putin revealed a hypersonic cruise missile, ‘Tsirkon’, capable of launching from both underwater and surface platforms. Russia is deploying the Avangard glide vehicle—installed on SS-19 Mod 4 boosters—at the rate of two per year. The first two missiles went on combat duty in December 2019, and another two in December 2020. The regiment received the last two missiles in December 2021, achieving the full strength of six missiles. By the end of 2027, Russia is expected to deploy another regiment of Avangard. MiG-31K fighter jets armed with Kinzhal hypersonic missiles were deployed on experimental combat duty in December 2017. Recently, Russian defence minister Sergei Shoigu announced that a “separate aviation regiment has been created and equipped with the MIG-31K interceptors armed with Kinzhal hypersonic missiles.” In 2021, Russia carried out an array of test launches of the Tsirkon missile from the surface and underwater positions. Tsirkon will likely enter service with the Russian navy in surface and underwater roles in 2022 and 2025, respectively.
China displayed the dual-capable DF-17 medium-range ballistic missile carrying DF-ZF HGVs at the 70th National Day parade in October 2019. According to unconfirmed reports, China might have started deploying the DF-17 missiles in the late 2020s. According to a Congressional Research Service report, DF-41 ICBM could also be modified to carry hypersonic gliders. In addition to DF-ZF HGV, China is progressing on a hypersonic cruise missile, ‘Starry Sky 2’. In October 2021, Financial Times revealed that China conducted two hypersonic tests in July and August. The missile test carried out in July reportedly circumnavigated the globe before hitting its target, demonstrating China’s ability to incorporate a glide vehicle into a Fractional Orbital Bombardment System (FOBS).
United States is developing hypersonic weapons under multiple programmes overseen by US Navy, Army, Air Force, and Defense Advanced Research Projects Agency (DARPA). DARPA is developing a wedge-shaped ground-launched tactical boost-glide (TBG) system. Under its Conventional Prompt Strike (CPS) programme, US Navy is leading the development of a common glide vehicle for use across services. Under the Long-Range Hypersonic Weapon programme, the US Army would pair the common glide vehicle with the Navy booster system. The US Air Force (USAF) is building upon DARPA’s TBG technology to develop AGM-183 Air-Launched Rapid Response Weapon (ARRW), an air-launched hypersonic glide vehicle. The Air Force recently launched a programme to develop Hypersonic Attack Cruise Missile. US hypersonic programmes are in various research, development, and flight-testing stages. Last year, USAF conducted three flight tests of the ARRW weapon and experienced failures in all three. Despite the setbacks, USAF hopes to achieve the early operational capability of ARRW in late 2022.
Hypersonic weapons are going to become a reality sooner than later in India. On 7 September 2020, DRDO successfully flight-tested Hypersonic Technology Demonstration Vehicle (HSTDV), showcasing the hypersonic air-breathing scramjet technology. In addition to the indigenous HSTDV, India is working in collaboration with Russia on BrahMos-II, a Mach 7 HCM based on the Russian Tsirkon missile.
In addition to the above countries, several other countries such as Australia, France, Germany, the United Kingdom, and Japan are also developing hypersonic weapons technology.
Abhishek Saxena is a Research Associate at the Centre for Air Power Studies, New Delhi. He Tweets @Abhisaxena3690. Views are personal.