Titan IV rockets were involved in three of the six American rocket failures in the last nine months.

The Titan IV rocket blasted off from the Vandenberg Air Force Base in California the early hours of Saturday morning, heading for a polar orbit.

Information on whether the satellite reached its proper orbit is classified. But an air force spokesman said the satellite separated from its booster several minutes into flight.

The satellite will be used by the National Reconnaissance Office, the US Government agency responsible for reconnaissance satellites.

Series of failures

Over the past nine months, six US launches involving expendable rockets have ended either in destruction or with satellites stranded in useless orbits.

The series of failures led President Clinton to order a Pentagon review into the problems.

The cost of the the failures have totalled about $3.5 billion. Nearly $3 billion represents lost government flight hardware and more than $500 million in lost commercial satellites and rockets.

The Titan IV is a two-stage rocket built by Lockheed Martin, with both liquid and solid fuel motors. It can place 38,800 pounds into a low Earth polar orbit.