What Is an Intercontinental Ballistic Missile and How Does It Work?

Intercontinental ballistic missiles (usually shortened to ICBMs) have been the iconic image of the cold war since their creation in the late-1950s. They are the natural extension of technology developed by Nazi Germany during World War 2 and further developed by the Allies and Soviets post-war.

Various nations field a variety of designs, with, for example, the United States developing the silo-launched Minuteman series of missiles in the 1960s. There are also submarine equivalents called submarine-launched ballistic missiles, or SLBMs, which have similar ranges to ICBMs but can be fired from, well, submarines. Notable examples of this kind of ICBM include the Trident missile system in use by the United Kingdom.

But how do they work? Obviously, a detailed analysis of the workings of such weapons is not possible, but we'll take a quick glimpse at these incredible feats of engineering. 

What is an ICBM?

ICBMs, like the one reportedly tested by North Korea several years ago, have the capability to be used for carrying payloads, like nuclear warheads, over very long distances. This could, in theory, offer an equipped nation with an unparalleled projection of force capabilities far in excess of any of their other weapons. 

They differ from other forms of ballistic missiles by their much greater range and payload capacity. 

On a very basic level, these missiles work by launching from a ground-based (or submarine-based) launcher, reaching suborbital space-flight at about 620 miles (1,000 kilometers), and eventually releasing their payloads to re-enter Earth's atmosphere and plummet towards their target back on Earth.

This is usually achieved by providing the missile with enough energy to fly very high up - usually into space. After this point, what will return to Earth is left to fall under the influence of gravity, although some also have rocket thrusters to help them orient themselves. In fact, this is, to a certain extent, how most ballistic weapons work. 

Think of a cannonball. Initially, it is provided with a massive amount of energy and then let to travel the rest of the distance without additional propulsion. Compare this to something like a cruise missile that is provided with constant propulsion from its thrusters or most of its flight path. 

This means that ICBMs need very powerful boosters for relatively small payloads. The launch must also be done with great precision because errors accumulate throughout the flight. 

Most ICBMs will travel over a very long parabola-like trajectory (typically more than 3,400 miles/5,500km), in a similar way to how a ball travels when thrown at an angle - but over very long distances. And, just like a ball, an ICBM can be launched at any angle of attack you'd like.

However, for most "real" launches the objective will be to send the missile, and its payload, into near space. 

Despite their tactical utility, to date, no ICBMs have ever been used in combat. Though according to Philip Coyle, a senior science advisor to the Center for Arms Control and Non-Proliferation, a nonprofit organization based in Washington D.C., some countries have tested missiles for trial runs.

Early models of ICBMs were not very accurate and would have been used against large targets, like cities. Modern-day, so-called second-and third-generation ICBMs are highly accurate and can be used to target pretty much anywhere in the world. 

What is important to note is that although countries like North Korea, test their missiles by firing them straight up, resulting in a somewhat random landing, they wouldn't aim ICBMs straight up during an actual attack. Missiles would be aimed towards their intended target. 

That means that even though North Korean test missiles travel about 620 miles (1,000 kilometers) from their launch site, they can travel much farther — probably more than 8,100 miles (13,000 km) from the launch site if it uses a standard trajectory

To give you an idea o how dangerous these weapons potentially are, one ICBM can deliver a warhead between North America and central Eurasia in around 30 minutes.

However, this also adds in some potential errors when launching your ICBM. In that time, the Earth will have rotated a little, so you actually need to aim it where you predict the target will be at the time you expect it to land. 

On top of that, you have to consider the forces that are going to be disturbing the missile’s flight path. To fly the missiles, engineers use elements like flight surfaces (the fins you see on some missiles) or small thrusters to help steer the ICBM by determining where they are compared to where they ought to be.

Another important tool is the ICBM's Inertial Navigation System (INS). This uses gyroscopes and accelerometers to measure the missile’s orientation in space and the forces acting on it. More modern ones also come with more sophisticated guidance systems like GPS, etc. 

And that is all just to get the thing into space. 

A long-range ballistic missile goes well outside the atmosphere, in some cases to altitudes in the 1,100 miles (1,800 kilometers) range. This means that the payload — the warhead, for a military missile — has to re-enter the atmosphere.

When it does this, it will be moving at the speed of a meteor, something in the order of 10 km per second. The warhead needs to be built into a re-entry vehicle, complete with a heat shield, in order to survive this ordeal.

What are the main launch phases of an ICBM?

ICBMs are multi-phase rockets and will go through a preset sequence of events prior to the rocket reaching its target. At takeoff, the ICBM goes through what is called the boost phase. The American Minuteman III ICBM, for example, has a three-stage booster. 

During the boost phase, the rockets get the missile airborne. This phase lasts around 2-5 minutes until the ICBM has reached its intended height. ICBMs can have up to three rocket phases with each one ejected, or discarded after it burns out.

Rockets tend to be fuelled by either liquid or solid propellants. Liquid fuel rockets tend to burn longer in the boost phase than solid ones according to Coyle. Solid ones, however, "provide their energy in a shorter amount of time and burn faster."

Both liquid and solid fuels can send their rockets equally as far. "But most countries start out with liquid propellant technology because it's well understood," Coyle explains. "[As] they graduate, they move to solid propellant to get the faster burn times. It also avoids the hazards of dealing with dangerous liquids that are both flammable and toxic."

The second phase of the ICBMs journey is the point where the rocket has reached space. Here it continues along its ballistic trajectory. At this point, the rocket will be traveling very fast indeed. This could be around 15,000 mph or 17,000 mph (24,140 to 27,360 kph). This is the stage where the ICBM achieves its greatest speeds.

Such speeds are achieved due to the lack of air resistance in space. Some ICBMs are also equipped to allow them to take a "star shot". This lets them use the location of stars to help them orient themselves towards their target.

The third and final phase sees the ICBM's final separation and re-entry into Earth's atmosphere. The nose cone section carrying the warhead separates from the final rocket booster, orientates itself, if needed, and 'drops' back to Earth.

At this point, the ICBM is just minutes from its target. If the ICBM has rocket thrusters these would be used at this point to orientate itself towards its target. Some ICBMs have more than one warhead too.

This means that a single ICBM could be used to pepper multiple locations on Earth at the same time. Quite incredible and, frankly, scary. 

Should we be worried about ICBMs?

In short, yes and no. 

It's important to note that although countries like the United States, Russia, China, and India have ICBMs, none have ever been fired in anger against another country. 

"We all have tested them to show we can do it, [which is] exactly what North Korea is doing now. [But] we've never actually used them in war, and the reason is it would be an all-out nuclear war and we'd all be dead," said Coyle.

It's also important to note that American and Soviet crewed space missions used modified ICBMs as launch vehicles. So, they are not just about delivering death over the horizon. 

And that, ICBM fans is your lot for today. This is a very brief overview of how these amazing pieces of kit work. With well over 80 years, or so, of development, ICBMs are simultaneously some of the most dangerous, and most useful pieces of technology ever built by humans. 

They have the power to either wipe out our species (if nuclear-armed) or be our ticket off this planet and into our future as a multi-planet species.