— Technical problems have compounded an already crowded manifest for the Delta 2 rocket, delaying until sometime next year the launch of two U.S. Air Force GPS navigation satellites that were supposed to fly by Sept. 30, and creating a ripple effect that has spread to other military and civil payloads.

A timing problem with the third stage of Denver-based United Launch Alliance‘s Delta 2 has left the GPS satellites stranded at Cape Canaveral Air Force Station in . Engineers will run tests at the end of October to confirm they have identified the problem, with construction and testing of new hardware to follow, said Bill Wrobel, NASA assistant associate administrator for launch services.

While the three-stage version of the Delta 2 is needed only for the GPS satellites, which operate in high orbits, other missions have been delayed as United Launch Alliance tries to juggle a tight manifest. These include the two launches of experimental missile-tracking satellites as part of the U.S. Missile Defense Agency’s Space Tracking and Surveillance System (STSS) program, and NASA’s Kepler spacecraft designed to detect hundreds of Earth-size or smaller planets, Wrobel said.

“We’re hoping that we can get the problem corrected as early as March,” he said. “The result of the problem with the launch vehicle is it causes all missions to slide.”

The third-stage timing problem is not the only one affecting United Launch Alliance’s fleet. Concerns about inadequate testing of about 20 pieces of gear on the Delta and Atlas launch vehicles also have slowed the launch schedule. Earlier this year, program managers discovered equipment that conducts vibration tests had not been properly calibrated for the past several years, said Gary Payton, deputy undersecretary of the Air Force for space programs.

“We’ve got a batch of piece parts in our supply stream that we thought had been tested to adequate levels but may not be,” Payton said. “We’re chasing down those parts, pulling them out and sending them through proper testing before we launch a rocket with one of those questionable piece parts.”

The new tests will take months, not years, to complete, Payton said.

The parts issue did not affect the Delta 2 that launched the commercial GeoEye-1 Earth observation satellite Sept. 6 from Vandenberg Air Force Base in . Meanwhile, a Delta 2 has been cleared for an Oct. 24 launch of ‘s third Cosmo- Skymed radar imaging satellite from Vandenberg in what will be the rocket’s fifth and final mission of the year, said Julie Andrews, spokeswoman for United Launch Alliance.

A scheduled Dec. 4 Atlas launch of the Air Force’s second Wideband Global Satcom satellite from Cape Canaveral

Delta 2 entered 2008 with an aggressive nine-launch schedule, compared to an annual average of six to eight launches. The second half of the year, however, brought surprises that delayed the two GPS satellite launches.

The Missile Defense Agency, meanwhile, has two launches of STSS demonstration satellites that have been delayed as a result of the Delta 2 concerns. One is a pair of satellites known as the STSS Block 2006 Demonstrators; the other is a classified payload known as STSS Block 2010 Advanced Technology Risk Reduction.

Northrop Grumman Space Technology of Redondo Beach, Calif., is prime contractor on the STSS program. NASA is overseeing both launches on behalf of the Missile Defense Agency.

Wrobel said the STSS Advanced Technology Risk Reduction launch has been delayed multiple times due to the crowded Delta 2 manifest and that the latest tentative launch date is April 2009. “They would love to go as early as they can,” Wrobel said. “We’ve been trying to find a slot for them as early as this summer. They originally tried to go in April [2008] but had to be pulled off and we’ve been trying to find a slot for them since.”

The launch of the two Northrop Grumman-built STSS Demonstrators has seen several delays related both to issues with the satellites and the Delta 2. Most recently that launch was scheduled for January but now is likely to get bumped to this summer, Missile Defense Agency spokesman Rick Lehner said.

Northrop Grumman spokesman Bob Bishop said the STSS Demonstrator satellites are slated for delivery before the end of the year.

Congress cited the fact that the experimental STSS satellites have yet to launch as the reason for refusing the Missile Defense Agency’s 2009 budget request of $30 million for work on follow-on satellites.

Launch priorities are set in regular meetings of , Defense Department and industry officials. As launches are delayed, those officials re-evaluate those priorities, Wrobel said.

NASA is managing eight more flights scheduled on Delta 2 before ending its use of the vehicle, with the final flight being the 2011 launch of the Gravity Recovery and Interior Laboratory to map gravity fields on the Moon.

The future of the Delta 2, a longtime reliable workhorse for government and commercial customers, is uncertain. NASA and the Defense Department are phasing out their use of the rocket in favor of the larger Delta 4 and Atlas 5, developed under the Air Force’s Evolved Expendable Launch Vehicle program.

“We’ve been saying throughout the year that the Delta 2 launch rate is going to come down,” Andrews said. “We are going to drop from six to eight down to about one or two starting in

Staff writer Turner Brinton contributed to this article