A Titan 4A rocket at SLC-4E. Photo: Lockheed Martin

A hush-hush problem with a top-secret satellite cargo has forced another postponement for the upcoming U.S. Air Force Titan 4B rocket launch from California, officials said Tuesday.

Liftoff of the Lockheed Martin-built rocket from Space Launch Complex-4 East at Vandenberg Air Force Base along Central California's Pacific coastline is expected no sooner than August 16, and could very well slip further into the month.

It was just last week Air Force officials confirmed the launch would be delayed from July 31 to August 10 so a leaky hydraulic steering device on one of the solid rocket booster nozzles could be replaced. And before that, Lockheed Martin ordered precautionary checks of wiring harnesses installed aboard the rocket, which scuttled a July 17 targeted launch date.

The latest glitch involves the classified National Reconnaissance Office payload the Titan will carry into Earth orbit.

"We are having some issues with the payload," NRO spokesman Art Haubold said Tuesday.

Haubold declined to comment on the nature of the problem or when the situation might be resolved. The NRO is also keeping the identity of the payload shrouded in secrecy for national security reasons.

"We are working as quickly as possible," he said, noting the launch is being delayed on a day-to-day basis.

Pre-launch preparations have been stalled with about two weeks of work left to do, starting with propellant loading, Air Force spokespeople say.