A leak of nitrogen gas used to cool two infrared sensors on the US Ballistic Missile Defense Organization's experimental National Missile Defence (NMD) interceptor's exoatmospheric kill vehicle (EKV) was the cause of the failure of a $100 million test firing on 18 January.

A problem with the infrared sensors was pinpointed as the cause immediately after the test, but the reason for the sensor malfunction has only now come to light.

The "hit-to-kill" test, the second for the NMD programme, was to be followed by a third in late April, but the need to investigate the leak has pushed it back to at least May. Despite the malfunction, US defence secretary William Cohen says the NMD project "is on track" for President Bill Clinton to make a deployment decision this year.

The Raytheon-built EKV uses two infrared sensors and a visible-light sensor to acquire and destroy re-entry vehicles.

The next NMD test will include first use of the In-Flight Interceptor Communications System. This links the NMD's battle management, command, control and communications systems with the EKV.

• The Lockheed Martin Patriot Advanced Capability (PAC-3) missile made its third successful intercept of a tactical ballistic missile target on 5 February at White Sands, New Mexico.

Source: Flight International