CAPE CANAVERAL, Fla. - Two Atlas rockets, sidelined by questions about their upper-stage motors, are being taken off their Cape Canaveral launch pads, while a third booster is being prepared for a satellite-delivery mission targeted for next month.

Lockheed Martin, which manufacturers the unmanned Atlas booster rockets, ordered the removal of an Atlas 3 rocket from Cape Canaveral Air Station's Launch Complex 36 when its customer, Loral Space Systems, decide it had waited long enough for delivery of a Telstar communications satellite into orbit and opted to fly with European competitor Arianespace.

The rocket, which was to be the debut flight of the company's newest, most powerful Atlas booster, will be put into storage in a hangar at the Air Force station's industrial area. The Atlas 3 joins an Atlas 2 rocket, already in storage, that could not make its launch window to place a weather satellite into orbit before a series of eclipses.

Both rockets have been grounded by an ongoing investigation into possible manufacturing problems with the boosters' upper-stage engines. The malfunction of a similar engine, used on a Boeing Delta 3 rocket, left a communications satellite thousands of miles short of its intended orbit.

While Lockheed Martin continues to work with engine manufacturer Pratt & Whitney to clear the rockets for flight, the booster earmarked to deliver an Echostar satellite has arrived at Cape Canaveral.

International Launch Services, which sells and flies the Atlas rockets, has requested a launch date of Sept. 10, said company spokeswoman Julie Andrews.

"That engine has checked out fine," she said.