Anti-Ship Ballistic Missiles: A Reality Check Of Deadly ASBM

Editor’s Note

Anti-ship ballistic Missiles (ASBM) have piqued the interest of both Navy professionals and naval warfare enthusiasts. It has been suggested that ASBMs are reshaping naval doctrines, potentially signalling the end of the era of massive aircraft carriers. However, a more nuanced examination reveals a less definitive picture. This article is divided into three parts. In this section, the author delves into the intricacies of ASBMs, including their trajectory, guidance system, and the distinction between powered and glide flight paths, among other key aspects, inviting the reader to a deeper understanding of these complex weapons.

A recent Eurasian Times article titled China Rapidly Expands “Carrier Killer” Missiles To Keep US Navy At Bay; A Look At Beijing’s Deadly ASMs talks about a number of anti-ship missiles ranging from cruise missiles to the so-called Anti-Ship Ballistic Missiles (ASBMs) that ostensibly checkmate the superiority of American aircraft carrier groups in the South China Sea and the Pacific.

There has been breathless reporting on ASBMs for quite a while. The earliest enthusiastic, comprehensive reporting of this ‘wonder weapon’ has been by Professor Andrew Erickson, whose eminently readable book, Chinese Anti-Ship Ballistic Missile, was picked up by the military academia and reproduced as articles over the years. Pro Eriksson also appeared on the subject for a Congressional hearing. To add flavour, eminent underwater weapons expert HI Sutton, through his imaginative MS paint drawings, captivated the naval community with renderings of ship-launched ASBMs and air-launched ASBMs.

The Chinese, of course, lapped it up and went to town with excellent graphics appearing on their military websites, state-run media and an active ASBM programme complete with ‘successful’ field trials. Not to be outdone, the Iranians, too, claim to have ASBMs, which they have reportedly transferred to the Houthis. Not to be left behind, Pakistan, too, claims that they have an ASBM programme up and running. With so much hype surrounding this ‘wonder weapon’, let us examine some basic FACTS to determine whether this weapon class is a myth or a reality. At the outset, a disclaimer: the contents of this article are purely based on open-source information, and no reference to any ‘privileged’ information has been made.

So, let’s start with the reality. Yes! The Chinese have developed and manufactured DF 21D, which they claim to be an ASBM with a range of 1500 to 2000 km and the ability to travel ten times the speed of sound that can target American aircraft carriers to that range. We see photographs and videos of DF21Ds being exhibited at their various military parades.

They have also ‘operationalised’ DF21D batteries for deployment from Chinese territories, specifically targeting American aircraft carriers. All this is true. The US Navy, on its part, has also acknowledged the threat of ASBMs at various congressional hearings, and statements from its senior naval hierarchy hint that they do take the threat seriously.

How do the Chinese envisage using this ‘wonder weapon’? Well, for starters, the Chinese have informed the world that they have built a robust Anti Access Denial system, also known as A2/AD, with three layers protecting the Chinese mainland from seaward threat. The innermost layer consists of coastal defence forces comprising air, surface and subsurface assets up to 270nm. The second layer consists of air and subsurface assets deployed up to 540nm, and the outermost layer consists of ASBMs and subsurface assets up to 1000nm from the Chinese coast.

The entire area is serviced by a robust network of satellites, UAVs, long-range aircraft, and OTHT radars, all seamlessly passing information through a network. The satellites would pick up the position of American aircraft carriers beyond the outer layer and pass the information to the shore-based ASBM batteries. On receiving the data, based on target parameters, the ASBM battery would launch the missiles, which would get a mid-course update. Then, the missile would finally use terminal guidance to go home to the aircraft carrier. Sounds plausible? Believable? Sure, BUT let’s look at some FACTS.

This article will try to keep the ‘technical’ jargon to a minimum, but some recounting of high school physics and basic ballistic missile theory will be necessary.

When we term anything as ‘ballistic’, it means that after an initial push in the boost phase by using a propellant, the projectile, in this case, a missile, reaches a particular height and then starts falling in a trajectory under the influence of gravity towards it target without any more external propellant. If an external propellant is used in any phase except the initial boost phase, it can no longer be called a ballistic missile. It becomes a powered missile, a cruise missile. Also, in terms of ballistic missiles, they all necessarily leave the Earth’s atmosphere, which is approximately 100km and then re-enter following a ballistic trajectory, usually a parabola.

Now, we need to delve a little into the works of Johannes Kepler (1571-1630) and Isaac Newton (1642-1726) to clarify our understanding of how ballistic missiles work. Yes! All fancy ballistic missiles are based on the findings written 300 years ago. We will introduce a bit of Einstein later on to complete our understanding.

Kepler’s Law of Planetary Motion states that when a small heavenly body revolves around a larger heavenly body, such as Earth and the moon, the orbit of the smaller body around the larger body is an ellipse whose one of the foci goes through the centre of the larger heavenly body. It is essentially a Two-body problem, very predictable, unlike a three-body problem, which can generate infinite solutions.

A ballistic missile trajectory is a two-body problem where the trajectory is an ellipse, one foci being the apogee and the other passing through the Earth’s centre. To simplify our mathematical equations, we depict Earth as a perfect sphere and reference sphere. Pictorially a ballistic missile trajectory is depicted below:

(Source: George M Siouris, Missile Guidance and Control Systems, Springer, NY, 2004, Fig 6.1, P 369)

A little more high school physics is necessary, even though the reader may find it boring.

Newton’s Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. In high school, we were taught that force mass X acceleration. Acceleration is also termed the rate of change of velocity. Now, without delving into the actual derivation, we will skip to the last part to express acceleration in terms of integration as

It is essential for the reader to hoist. If we know the acceleration and velocity exactly, we can accurately arrive at our target position in terms of Lat and Long.

But to know our acceleration accurately, we need to know our initial position. To understand our initial position accurately in a three-dimensional space, we need to accurately know our X, Y and Z coordinates. In terms of ballistics, we refer to them as North, East and Down.

The accuracy of our position depends on how accurately we know the value of acceleration due to gravity at the initial position, and that depends on how accurately we know the Z component as also the centre of the Earth.

Without confusing the lay reader any further, it suffices to say that the missile must know its initial position accurately. Ideally, the Z component should be exactly vertical with no tilt. Unfortunately, that is not possible for a variety of reasons, and a certain amount of tilt in the Z component always takes place, which needs to be compensated. Since the position is a double integration, any error that creeps in the initial position grows quadratically with respect to time.

In a ballistic missile, the guidance is provided by an inertial navigation system that comprises accelerometers and gyros. The accelerometer needs to be very accurate to reduce the error, and the gyros, too, need to be accurate to reduce the drift, which we know by now increases quadratically with respect to time. No matter how accurate the accelerometer and gyros are, the drift is significant in any ballistic missile that will always require a position update in its boost phase to reduce the error. This could be by means of a star sensor or by GPS.

In a standard ballistic missile trajectory, the powered flight is about three to five minutes, and the missile reaches a velocity between 4 to 7 km per second till the burnout point. After that, the missile travels for about 25 minutes in a freefall till it reaches an apogee of 1200 km from thereon; the ballistic missile then starts falling towards the earth. It enters the atmosphere at high speed, where the velocity is almost 8km per second, and at this point, the re-entry to the target is about 2 minutes. The accuracy of the missile hitting the target depends, to a very large extent, on the accuracy of its initial position relative to its position on Earth.