WASHINGTON
— U.S. Air Force officials are working to resolve two remaining hardware issues on a pair of long-delayed missile tracking demonstration satellites, according to an official with the Missile Defense Agency (MDA), which is funding the experiment.

The two Space Tracking and Surveillance System (STSS) demonstration satellites likely will be launched together in spring or summer 2009, depending on the availability of the Delta 2 rocket, which is having its own technical and scheduling issues, Air Force Col. Jay P. Morgan, commander of MDA’s Missile Defense Systems Group, said via e-mail.

The demonstration satellites most recently were scheduled to be launched in January, but will not make that launch date, Morgan said.

The demonstration satellites are a precursor to a proposed constellation that would track missiles during the midcourse portion of flight, after their motors burn out, providing important targeting information for interceptors. The spacecraft, left over from an effort that was scrapped in the late 1990s, were supposed to launch in 2006 or 2007, but have encountered numerous technical difficulties.

The most recent delay prompted Congress this year to deny 2009 funding for the follow-on project. For 2008, Congress provided $222 million for the STSS program but cut $100 million the MDA had requested for the STSS follow-on satellites.

“MDA’s work on the STSS operational program has been delayed at least another year due to the lack of funding,” Morgan said. “The STSS program is focused on getting the Demo and ATRR satellites in orbit and demonstrating the benefit of a space-based tracking system.”

In addition to the demonstration satellites, the MDA plans to launch a classified STSS satellite, called the Advanced Technology Risk Reduction, or ATRR.

Morgan did not elaborate on the outstanding issues with the demonstration satellites and did not respond to follow-up requests for more information.

The STSS demonstration satellites, built by Northrop Grumman Space Technology of Redondo Beach, Calif., have completed thermal vacuum and acoustic tests, according to press releases issued by Northrop Grumman. Bob Bishop, spokesman for Northrop Grumman, said Oct. 2 that the demonstration satellites would be delivered by the end of the year. He referred further questions on the hardware problems to the Air Force.

One of the two demonstration satellites successfully completed thermal vacuum tests in May 2007. The second satellite experienced hardware problems primarily with a space-to-ground system transceiver, according to the Aerospace Corp.’s 2007 annual report released in August. The Aerospace Corp. of
El Segundo
,
Calif.
, which provides engineering support to
U.S.
military space programs, helped identify and troubleshoot “a large number of anomalies” during testing, the report said.

The second satellite completed thermal vacuum tests in November 2007, according to a Northrop press release issued at the time. Northrop Grumman issued a press release Aug. 28 announcing that the demonstrator satellites had completed acoustic testing at the company’s
Redondo Beach
facility.

The ATRR satellite also encountered delays in environmental testing, forcing a delay in its scheduled April 2008 launch on a Delta 2, Morgan said. Due to the Delta 2’s crowded manifest, compounded by a third-stage timing problem that has pushed launches of two GPS satellites aboard the rocket into 2009, the STSS-ATRR tentatively is scheduled for launch in April 2009.