Iran Exaggerates Missile Accuracy

August 4, 2012
David Wright
Former contributor

Iran announced today that it had successfully test launched a new version of its short-range Fateh 110 missile, claiming it has an upgraded guidance system that gives it high enough accuracy to “hit and destroy both land and sea targets, enemy concentration points, command centers, missile sites, ammunition dumps, radars and other targets with 100 percent precision.”

This claim is not credible, for the following reason.The Fateh 110 is reported to be a domestically built ballistic missile with a range of 300 km and a 250 kg warhead. Note that a warhead of this mass is too light to be a nuclear weapon.

A ballistic missile is only guided during the first minute or so of flight when its engines are burning. During that time, the guidance system attempts to steer the missile to put in on the right trajectory to hit the intended target. Once the engine burns out, the missile flies without power and cannot be steered. This is like throwing a ball: you aim the ball by the speed and direction your arm gives it, but once the ball leaves your hand it flies on its own. (The fact that missiles fly unpowered for most of their flight is why ballistic missiles are called “ballistic.”)

Once they are launched, ballistic missiles have two main sources of inaccuracy.

  1. The guidance system steers the missile while the missile’s engines are burning. One source of inaccuracy is the inability of the guidance system to put the missile on exactly the right trajectory to hit the target. These errors in accuracy are called “guidance and control errors.”
  2. A missile of this range will reach a maximum altitude of about 75 km, which is above the bulk of the atmosphere. When the missile reenters through the atmosphere toward the ground at high speed, it is subjected to a number of forces that can knock it off its intended trajectory. It is buffeted by high altitude winds and density variations in the atmosphere. In addition, atmospheric forces due to asymmetries in the missile body or warhead or a spiraling of the missile as it reenters also affect its reentry. These are called “reentry errors.”

Even if Iran had developed a perfect guidance system so there were no errors of type (1), there would still be very significant reentry errors, which are not reduced by a better guidance system. The reentry errors could be many hundreds of meters.

As a result, the idea that this missile has an accuracy high enough to allow it strike relatively small targets like ships, command centers, or radar bases, is simply not credible.