WASHINGTON The U.S. Air Force will contract to have its Space Based Space Surveillance (SBSS) system satellite placed into storage due to continued technical difficulties with the Minotaur 4 rocket that have delayed the spacecraft’s launch indefinitely, according to government documents.

The Minotaur 4 rocket, built by Orbital Sciences Corp. of Dulles, Va., and based in part on excess missile motors, was originally planned to debut in October 2009 with the SBSS launch. But the Air Force issued a statement that month saying the rocket had problems and would remain grounded indefinitely, though no further explanation was given.

In a solicitation posted Dec. 22 on the Federal Business Opportunities Web site, the Air Force stated it plans to issue a new contract to store the SBSS satellite and prepare it for launch when the rocket problems are resolved. The posting also said the estimated launch date had slipped to December 2010.

Responding to a Dec. 28 request for a further explanation of the first Minotaur 4’s delay, Air Force spokeswoman LaGina Jackson said the service would be unable to provide more detailed information by press time. On Dec. 29, the service revised the Dec. 22 posting to say that the SBSS launch date is “unknown pending the availability of the launch vehicle.”

The Minotaur 4 relies on retired U.S. Peacekeeper missile motors for its first three stages with a commercial fourth stage. The rocket’s problem lies with the gas generator on the third-stage motor, according to an industry source. The generator continues to run after the motor shuts off, creating residual thrust that affects the rocket’s ability to place a satellite into a precise orbit.

The SBSS spacecraft is intended to keep tabs on objects in space, particularly in geosynchronous orbit 36,000 kilometers above the equator — the operating location of most communications satellites. SBSS has encountered numerous delays due to technical issues during its development, and the program was restructured in 2007.

The Air Force said responses to its SBSS storage solicitation are due Jan. 15 and that it has not yet decided whether to issue a sole-source award to the program’s prime contractor, Boeing Space and Intelligence Systems of Seal Beach, Calif. Ball Aerospace & Technologies Corp. of Boulder, Colo., is responsible for the SBSS space segment.