BBC News Online Science Editor David Whitehouse: "So many failures are unprecedented"

The latest launch to misfire was a Delta III carrying a communications satellite. It was an unprecedented sixth failure in nine months.

Now the US space industry is carrying out a detailed inquiry to find reasons for the failures, each of which costs millions of dollars.

BBC correspondents say some insiders are blaming the cumulative effect of years of cost-cutting that they say has degraded the quality and reliability of US rockets.

Stranded cargo

The Delta III rocket launched on Tuesday from Cape Canaveral was 22 minutes into its flight when the second-stage engine failed to relight, leaving its cargo stranded thousands of miles too low.

Mission Director Rich Murphy said: "Everything had looked so good. I've really no idea what happened."

It meant that four out of six US satellite launches in one month have failed.

The military Titan IV failed twice and a satellite was also lost on a commercial Athena rocket.

Boeing, which developed the Delta III, said an investigation team would review data from the rocket.

The company had been hoping that its new rocket, a successor to the reliable Delta II, would help it win a larger piece of the lucrative space launch market, currently dominated by the French-led Ariane project.

Boeing and Hughes, which made the satellite that was on the Delta III launch, are also investigating whether the satellite's mission could be salvaged by using onboard rocket fuel to push it into its intended 22,300 (35,700km) orbit.

Boeing had postponed the launch by two days because the rocket's second stage used a similar engine to that on a Titan rocket that failed on 30 April.

Two days earlier, an Athena II rocket failed to place a commercial satellite into its intended polar orbit.