he U.S. Air Force, whose costs on a space-surveillance satellite have more than doubled, now is considering buying an additional spacecraft to provide expanded coverage of the geostationary-orbit arc, service officials said in a written response to questions.

It was not clear at press time exactly why the Air Force would contemplate a move that would further increase the cost of the Space-Based Space Surveillance (SBSS) system – especially with the service now asking Congress for additional funding just to keep the first satellite on its latest schedule. An industry source said the reason is that a single satellite will not have the coverage that was originally expected, but the Air Force said design issues are not a factor.

In its response to questions, provided May 3 by Jo Adail Stevenson, a spokeswoman for Air Force Space and Missile Systems Center, the service said a second SBSS satellite would be launched together with the first and provide extended coverage and more frequent updates. The Air Force said the idea is being discussed among the “senior leadership” but that no decisions have been made.

Meanwhile the cost of the first satellite has grown from $189 million to $425 million, Joe Davidson, a spokesman for Air Force Space and Missile Systems Center, said in a written response to questions. He attributed the cost growth to a restructuring undertaken in April 2006 after the program encountered difficulties.

The SBSS system is designed to keep tabs on objects in Earth orbit that might be of interest to U.S. military officials. The program originally was to consist of an initial, or pathfinder, satellite, to be followed by an operational constellation. The pathfinder, also known as SBSS Block 10, would replace the space-based visible sensor aboard the Missile Defense Agency’s Midcourse Space Experiment satellite, which provides what the military refers to as space-situational awareness but is nearing the end of its operational life.

Boeing Space and Intelligence Systems of Seal Beach, Calif., is building the SBSS pathfinder satellite under an unusual contracting arrangement that originally featured Northrop Grumman Mission Systems of Carson, Calif., in an oversight role as the Air Force’s Mission Area Prime Integration Contractor for counterspace programs. Ball Aerospace and Technologies Corp. of Boulder, Colo., is supplying the spacecraft frame, or bus.

The satellite originally was supposed to launch in 2007, but the deployment date has slipped to late 2008 or spring 2009. The Air Force recently told Congress that it would need $35 million on top of its $157.5 million SBSS budget request for 2008 to maintain a high likelihood of the pathfinder satellite launching that year. The Air Force also recently moved its anticipated date for starting deployment of an operational SBSS constellation from 2013 to 2014.

The Air Force awarded a contract to Northrop Grumman May 9 intended to cover a “subcontract cost overrun of $97 million,” according to a Pentagon contract announcement that did not provide further details other than to say that no additional work is involved. Northrop Grumman no longer serves in the Prime Integration Contractor role, but program funding still is channeled through the company.

Davidson said the SBSS cost growth is related to the program restructuring rather than contractor performance. However, Air Force Lt. Gen. Michael Hamel, commander of Space and Missile Systems Center, said last September that the restructuring was undertaken due to delays and concerns with the contracting team.

Stevenson declined to provide a cost estimate for the second satellite, but noted that since it would essentially be a clone of the first, its cost would be substantially lower.

The Air Force had planned to use a Minotaur 4 rocket built by Orbital Sciences Corp. of Dulles, Va., to launch the SBSS satellite, but

likely would turn to an Evolved Expendable Launch Vehicle built by United Launch Alliance if it

adds a second spacecraft to the manifest, Stevenson said.

Air Force Gen. Kevin Chilton, commander of Air Force Space Command, made improving the service’s space situational awareness capability a top priority when he arrived in the job last summer. He commissioned a study of alternatives that looked at whether SBSS duplicated other programs, but later said that was not the case.

A congressional source said given the importance of the space situational awareness, Congress might be receptive to the idea of buying a second SBSS satellite. But the aide said Congress would be more inclined to approve a reprogramming of funds rather than a request for new money for that purpose.

The staffer expressed concern, however, about the ability to have a second satellite ready to launch along with the first without causing more delays. With the Midcourse Space Experiment on its last legs, the United States could be faced with a gap in its space surveillance capability, the staffer said.