As was reported in the TMT article “A modern view of the Army’s main equipment shortages” https://www.themilitarytimes.co.uk/defence-security/a-modern-view-of-the-armys-main-equipment-shortages/, one of the most recent developments in weapons technology is that of very high-velocity missiles. Some refer to their speeds as “hyper-velocity” – but in effect they are travelling at speeds in the region of 7,000mph.
The average bullet has a Muzzle Velocity (MV) of about 2,500ft/sec, or about 1,700mph. So a hyper-velocity missile travels over three times faster than a typical bullet. A tank’s anti-armour round goes somewhat faster than a bullet. The old Chieftain DS(T) had an MV of 1420m/sec, or about 3200mph. A modern anti-tank round leaves the barrel at up to 2000m/sec, or about 4,500mph.
Current missile speeds are somewhat lower than bullets or tank rounds – they are also more difficult to categorise as there are so many different types, and in addition, a single missile might have several different phases if flight. Typically, a missile first goes into a boost phase, followed by a coasting phase. Some, such as ICBMs, also have a terminal boost phase which might be provide by gravity alone.
The familiar Milan anti-tank missile fairly dawdles along at about 200m/sec, or just under 1500mph; which is fine as it has to be controlled to hit a small, often moving, target. A cruise missile is even slower, at about 550mph as it needs to conserve fuel for long range flights, and is guided by GPS for accuracy against static targets. An ICBM will build up speed as it ascends to reach a highpoint in its trajectory – but then really start to gain speed as it descends to what will usually be a static, and often an area target. At which point it might be doing 15,000mph or more.
High speed provides many advantages to the attacker. It gives the defence less time to detect and then respond to an incoming threat. It makes it much harder for an anti-missile missile to launch and engage the attacker at altitude or at a safe range. It also means that, even if a hyper-velocity missile is hit a few kilometres out from, say a ship, there is a good chance that some bits of scrap will still keep travelling on the same trajectory and cause a lot of damage through sheer kinetic energy.
The downsides of these “Flash-Gordon” weapons are that their propulsion system is more complex, and they are much harder to control or manoeuvre once on their way downrange. Both problems add up to a more expensive weapon – not an insignificant consideration these days. For ICBMs the accuracies achieved are in the order of a CEP of 600m; that is to say, half of the missiles launched will fall within a 600m circle around their average impact point. Not much good for an anti-tank missile – or even a conventional HE-warhead if it is aimed at a bunker, building – or even a ship.
Control in flight is, therefore, a critical issue – especially as the missile gets smaller. Traditional control-surfaces such as fins or small wings are not very effective at these speeds. Instead, small semi-explosive puffs of gas are sometimes used, jetting out of ports on one side or the other to apply course-corrections. Given the high speeds, any corrections have to happen pretty snappily and mean that they are no longer controllable by humans once at speed.
Another problem is that of heat caused by the friction of the air as the missile tries to push itself though the atmosphere. So far, no practical solution has been developed to produce a material that can withstand the heat and contribute to the missile’s construction. However, this is not such a problem for short-duration flights.
At the shorter end of the range-scale, a good example of a hyper-velocity anti-armour missile is HATM, Hypervelocity Anti-Tank Missile. Developed by Raytheon, it has is a kinetic-energy warhead (ie, it relies upon raw speed to penetrate the target), which can stop tanks but also wreck bunkers.
Somewhat larger are systems such as Kinzhal, a Russian missile, shown above. This is in effect a replacement for a cruise missile with a range of up to 3000km if air-launched. Referred to as “hypersonic” by the Russians, it has been known to fly at Mach 4 (about 3,200mph, but is reputed to be able to handle Mach 10 (over 6,000mph). However, the Russians are clearly experiencing problems with controlling this beast and, as far as is known in the West, all flights to date have ended in failure of some sort.
The US is not getting too worried (publically at least), about Kinzhal for the time being – but have still taken the trouble of announcing their own programme to reassure the US electorate they are on top of the technology. A US programme to develop a truly hypervelocity ballistic system is underway – but some say that the aim of fielding a workable system within four years is not realistic – one of the problems being that heat problem mentioned earlier.
Are the British on the game? Well, after a fashion (as is so often he case!). That said, if Reaction Engines Limited of Oxfordshire, the company involved in developing the Synergistic Air Breathing Rocket Engine or SABRE, are able to provide their concept, then it promises to be more capable than anything else in the Hyper-Velocity pipeline today.
If anyone does manage to perfect this technology then they would be well placed to claim that their missiles are invulnerable to any current defences. Perhaps the only system capable of reacting to this level of threat would be lasers – something that the US have been experimenting with for a while now.
However, although the speeds reduce the time to mount an effective defence, they do not preclude the possibility of an immediate counter strike – even if this consists of “conventional” nuclear missiles. Indeed, the shortened “decision window” suggests that the ability to make an informed and rational decision about whether or not to go for a response based upon “Mutually Assured Destruction” will become significantly more difficult and leave this sort of decision in the hands of incredibly complex Artificial Intelligence. It will, potentially, be a battle of Software Engineers and rather focuses the mind on recent Russian acts of cyber-warfare.
It also explains why there has been more attention to the need for some sort of worldwide limitations on the deployment of such weapons – though it seems unlikely that any country that gains any sort of significant lead will want to give up the huge advantages that their possession might confer. As a result, it has all the makings of another expensive and uncertain arms race – which cannot be good for anyone.
Aerodynamic heating – a quick look
If an aircraft or missile were to fly at about 5,500mph at a height of 10km, it would experience a heating effect of ten times the ambient temperature as measured in degrees kelvin. At a height of 10km the ambient temperature is about 223 Kelvin, so the total heating effect would be about 2,200 kelvin which equates to 2,000 degrees centigrade. Steel melts at about 1400 degrees C, and titanium at just over 3000 degrees. So for a missile doing 15,000mph, there has to be a way of dealing with a lot more heat than either steel or titanium can handle. Otherwise, the Russians, or whoever, would be launching what would in effect be nothing more than “shooting stars” which would burn up long before they reached their targets.