The German V-2 Rocket: Adapting Navigation and Guidance Technology for Wartime

Imagine yourself awakening on the morning of September 8, 1944, in newly-liberated Paris. Suddenly, an explosion intrudes on your tranquility. Later that same day, two explosions rock the London environs. The German V-2 rocket campaign had begun.

The V-2 (Vengeance Weapon 2, also known as the A-4) was the world’s first ballistic missile. But wait a minute. First, you called it a rocket, now you call it a missile. What’s the difference?

According to Webster’s, “rocket” can mean anything like a firework or firework engine. It can be a vehicle or missile powered by the exhaust of a jet engine. A missile is an object (e.g., a weapon) thrown or projected to hit a target at a distance. Many people describe a missile as a rocket with a weapon aboard. The military community uses the term missile to mean something that “has a guidance system or brain to get to its destination.” They define a rocket as something that “just goes where it is initially pointed.” The V-2 may have been called a rocket in the 1940s, but today we see it has attributes of a modern missile.

The V-2 was a liquid-fueled rocket that stood 14 meters tall. It had a launchpad mass of nearly 12,700 kg and carried a 738 kg explosive warhead. It traveled at supersonic speeds, covering 320 kilometers from its launch site in the Hague (Netherlands) to London (England) in about 5 minutes.

How did the V-2 navigate its way to London? The Germans aimed the V-2 towards the target on the launch pad, but forces on the rocket during lift-off could skew this direction. They tried using a Lorenz beam (see last week’s blog) but were unsuccessful. To fix this, the Germans added a simple analog computer that “combined the beam rider circuitry with the attitude [orientation] control system.”

The attitude control system contained several components. One component was a primitive version of a pendulous integrating gyroscopic accelerometer (PIGA). It had a gyroscope with a mass suspended from it which acted like a pendulum. As it sensed acceleration (force) from the craft, it precessed (see this blog two weeks ago) at a rate proportional to the craft’s velocity. During the 60-70 seconds the engines burned during lift-off, the accelerometer monitored the V-2’s velocity. When the craft reached the desired velocity, it sent the computer a signal to turn the engines off.

The computer used feedback from two other gyroscopes to steer the rocket with four rudders (on the rocket’s fins) and four vanes (in the exhaust plume) during engine burn. This information keeps the rocket aimed in the correct direction. The rocket initially traveled straight up, but by the time the engines cut off, it had transitioned to an angle of 43 degrees with the horizon. It then followed a parabolic (ballistic) trajectory, achieving a maximum height of 80 kilometers. Setting up your coordinate system so that the point (-160, 0) is London, (160, 0) is the Hague, and (0,80) is the point of its maximum height, this parabolic trajectory could be modeled as

y = -x2 /320  + 80.

Unlike its predecessor, the noisy V-1 buzz bomb, the V-2 was stealthily quiet. One source described it’s sound as follows:

“First, a whip cracking sound of a blast wave created by the rocket (moving faster than the speed of sound) bounces off of the point of impact just split seconds before the flash of impact. This was followed by the chaos of the explosion with debris and earth churned skyward. Soon, the whine and rush of whistling air as the sound catches up with the rocket followed by a deafening roar of the incoming rocket, which tapers off to silence. There could be no warning. The … V-2 impacted at 3 times the speed of sound.”

Despite its sophisticated guidance system, the V-2 was largely unsuccessful. The Germans launched over 3000 V-2’s, but still lost the war against the Allied Powers.

Why should we care about World War II technologies like this? War drives technological innovation with urgency. By looking at the challenges the scientists and engineers grappled with, we appreciate why they incorporated different capabilities. By studying such evolution, we understand how we got to the modern versions of technologies. For example, the V-2’s guidance system was “the first fully electronic active control system and … [became] the basis for the use of analog computers in aircraft flight control systems as advanced as those in the F-16 and F-117A”. Indeed, the V-2 “contained the essential components of a fly-by-wire system: sensors, a central computer, and navigation information.”

Today, we learned about V-2 rockets. They relied on internal computers to navigate to their destinations. Now you probably wonder where such computers came from, right? Next week, we’ll start talking about the history of computing devices and how they evolved.