The B-28 mission patch. Photo: NRO/Vandenberg AFB

Round-the-clock preparations are underway at Vandenberg Air Force Base for next month's launch of a Titan 4B rocket after officials Friday cleared a problem with the spy satellite cargo to be carried aloft.

The Lockheed Martin-built rocket, the most powerful in the U.S. fleet, is slated for liftoff on the evening of August 16 from Space Launch Complex-4 East along Central California's Pacific coastline.

Crews halted pre-flight work a week ago after an undisclosed issue arose involving the National Reconnaissance Office payload mounted atop the Titan. Details of the problem and how it was fixed were withheld from the public due to national security reasons.

NRO spokesman Art Haubold on Friday would only say: "We have resolved the issue we had with our payload."

The glitch was the third to delay the launch in recent weeks, pushing back the clandestine mission from an original July 17 target date.

Earlier, wiring harnesses aboard the rocket had to be rechecked to ensure they weren't damaged by technicians believed to have used the wrong tool during manufacturing; then to replace a leaky hydraulic actuator in a solid rocket booster nozzle needed to steer the vehicle in-flight.

The exact liftoff time on August 16 remains classified and it was unclear late last week if the Air Force would need to update the four-hour period in which the launch will occur. For earlier launch dates the period extended from 7 to 11 p.m. PDT (10 p.m. to 2 a.m. EDT; 0200-0600 GMT on 17th).

The two pads of Space Launch Complex-4. Photo: Spaceflight Now

Meanwhile, with the Titan 4 launch seemingly set to go, efforts continue at nearby Space Launch Complex-4 West where a refurbished Titan 2 intercontinental ballistic missile is being readied for liftoff carrying the U.S. weather satellite known as NOAA-L.

The Titan 2 has been stalled with every Titan 4 launch delay. The reason is managers do not want to risk the $156 million weather satellite at the pad until after the massive Titan 4 launches. Should the Titan 4 malfunction in the first moments of flight, the resulting explosion could severely damage the Titan 2 pad.

NASA officials, which are managing the deployment of NOAA-L, say the craft could be launched as soon as September 14 during a window of 3:22 to 3:32 a.m. local time (6:22-6:32 a.m. EDT; 1022-1032 GMT).