Sudden impact in space

Heading for the edge of space, the interceptor takes off

By Dr David Whitehouse BBC News Online science editor

The United States has released details of the latest test of the technology designed to intercept a missile target in space - part of what used to be called the Star Wars project.

It took place over the central Pacific Ocean on 15 March, when a modified Minuteman Intercontinental Ballistic Missile (ICBM) was launched from Vandenberg Air Force Base in California.

Just before impact: The target is on the left, the impactor on the right

The prototype interceptor was launched 20 minutes later, 7,725 kilometres (4,800 miles) away from Kwajalein Atoll, in the Marshall Islands.

Ten minutes after the interceptor was launched, when it was at an altitude of 225 km (140 miles) above the Earth, it smashed into the target missile, destroying it completely.

According to analysts, the test, the fourth success out of six attempts, demonstrates that a so-called exoatmospheric kill vehicle (EKV) is able to intercept and destroy a long-range ballistic missile.

This would form an essential part of any "Star Wars" defence system, should it be deployed.

Coordinated system

To enable the EKV to reach its target requires a wide range of different systems and technologies to work together in just a few minutes with little margin for error.

It involves detecting the launch of the target missile, alerting the early warning radar to provide more detailed information about its trajectory.

The interceptor undergoes final checks

This is a prototype radar system based at Kwajalein and provides precise target data to the EKV via a high-speed communications link.

The EKV separates from its rocket booster more than 2,250 km (1,400 miles) from the target warhead. After separation, it uses on-board infrared and visual sensors, augmented with Kwajalein radar data, to locate, track and collide with the target.

Sensors aboard the EKV must also successfully select the target instead of three balloon decoys.

Although the Cold War has ended, many analysts believe the threat of an attack on the United States by long-range ballistic missiles remains real because many countries have ballistic missiles.

Some of them, the US says, are working on weapons of mass destruction: nuclear, chemical or biological.