Intercontinental Ballistic Missiles (ICBMs): how they work

Kim Jong Un has yet again fired another Intercontinental Ballistic Missile (ICBM) in a test launch that ended in failure. However, the failure looks like it occurred upon re-entry, and if they solve this problem, the “Hwasong-15” will have the range to conceivably reach the east coast of the United States along with much of the rest of the world—that is, if it didn’t get shot out of the sky first.

An ICBM is a missile fired off with the intent to deliver and detonate a thermonuclear warhead on another continent. It is possible that other types of weapons could be delivered using this system, but it has never happened before. The land based system is different from the Submarine-launched ballistic missile (SLBM), which, as the name implies, delivers the nuclear payload from a submarine.

The ICBMs are often housed and launched from a nuclear silo. The United States still has silos ready for launch, though they generally rely more upon SLBMs. With that said, North Korea moves their ICBMs (often under the cover of darkness) to launch pads. Launch pads can be problematic, as you can’t fuel up the missiles before transporting them—which means you have to fuel them on the pad itself. They have to fuel their ICBM out in the open, vulnerable to air strikes, and wait until the missile is ready to go. DPRK controls these missiles with the Strategic Rocket Forces, otherwise known as the Missile Guidance Bureau, of the North Korean military.

There are four phases in launching and delivering a nuclear payload via ICBM: the boost phase, the post-boost phase, the midcourse phase and the terminal phase (reentry).

Boost

This is the launching part. The engines fire and the missile goes from ground level to approximately 90-125 miles up in the air. During this stage, the missile is still all in one piece, gaining altitude and readying itself to break apart and begin its targeting process.

Interception: Ideally, an enemy country would take out the missile in this phase. The missile is all in one piece, and they don’t have to worry about attacking decoys, multiple warheads in some cases, and they can even just bump it off course. Weapons designed to attack missiles in this stage are generally able to do so due to the tracking of the missile’s exhaust, as it must put out an immense amount of heat in order to reach high altitudes. The window of opportunity is small here, as the entire process generally takes from 3-4 minutes.

Post-boost

This is where the nuclear payload gets released. While the first stage just got it to altitude, now it turns and aims towards its target. If there are multiple warheads, they all turn to point at their respective targets. The multiple warheads are transported on what’s known as a “bus.”

Interception: Like the boost phase, knocking it out here will generally destroy all of the decoys and warheads at the same time—though as the warheads separate and continue onto their missions, this becomes more problematic. The fire and brimstone of the earlier launch has since died down, so that makes it more difficult to track via similar heat signatures.

Midcourse

In a regular plane, you taxi, take off, fly and land. “Midcourse” describes the actual flight itself. The warhead (or warheads) fly to their targets, which can take minutes or maybe hours, depending on how far the missile needs to travel.

Interception: This can prove difficult, as warheads generally now have active countermeasures during this phase. The “target cloud” is a mixture of decoys and radar reflectors that all serve to make trouble for incoming intercepts. This cloud can range from a mile to 10 miles. As of yet, there isn’t a tried and true method of deterring a warhead travelling under the concealment of a target cloud. Dozens of intercepts could be fired up into the cloud in an effort to knock out the warhead.

Terminal

When an ICBM has reached high enough altitude, it has left the earth’s atmosphere. The terminal phase describes reentry, as the missile once again enters the atmosphere as it plummets down toward its target. If you have seen any movies where spaceships enter the earth’s atmosphere to find flames licking across their ship’s bow, this is that stage. The friction of newly introduced oxygen turns to heat and can threaten to rip apart the entire mechanism altogether. North Korea’s most recent ICBM seems to have suffered a catastrophic loss during this phase, as oxygen blew the missile into harmless bits to fall on the land or water below. If this happens, the warhead will not detonate as it hits the ground.

Interception: If they are successful, the warheads are obviously designed to withstand reentry—but many decoys are not. This gives countermeasures a small window in which the decoys are burned in the atmosphere and the real warhead reveals itself in a phenomenon known as “atmospheric decluttering.” At the very least, the warhead will be the incoming object with the least amount of deceleration. The longer the nation with the countermeasures waits, the easier it becomes to tell which incoming object is the warhead and which are decoys—though you can see the obvious difficulty here: the longer they wait, the more difficult it will be to launch a missile to intercept and the more dangerous of a situation they are in should the countermeasures fail.

After all this, the missile detonates and the world enters a new era of difficulties.

Featured image courtesy of the U.S. Air Force