The U.S. Air Force tentatively plans to award study contracts in March 2007 for a space-surveillance system consisting of four to five satellites that would launch starting in late 2013, according to an industry source.

The service’s plans for the operational Space Based Space Surveillance (SBSS) system were outlined during meetings Jan. 25-26 for potential bidders on the project. The meeting was hosted by Air Force Space and Missile Systems Center in Los Angeles, and attendees were required to have security clearances, according to a Dec. 20 announcement on the Federal Business Opportunities Web site.

A notional program schedule outlined at the meetings has the Air Force issuing a draft solicitation for the study contracts this coming August, the source said. The schedule calls for award of the contract to build the satellites in July 2008, the source said.

The SBSS is intended to detect and track objects in Earth orbit that could pose a threat to U.S. military space assets. The military does this today using ground-based sensors and an aging satellite called the Midcourse Space Experiment (MSX), whose original purpose was to demonstrate space-based missile tracking.

Boeing Space and Intelligence Systems of Seal Beach, Calif., is building an initial SBSS satellite under an $189 million contract awarded in March 2004. That satellite is slated to launch in December 2008, but it is not clear that the MSX spacecraft will still be operating by then, according to Gary Payton, deputy undersecretary of defense for space programs.

With the MSX “limping along,” it is critical that Boeing stay on track with its space surveillance satellite, Payton said in a Feb. 7 interview.

Reached by telephone Feb. 23, Joe Tedino, a spokesman for Boeing Space and Intelligence Systems, referred questions regarding the SBSS program to the Air Force. Peggy Hodge, a spokeswoman for Air Force Space and Missile Systems Center, which buys military space hardware, did not return a phone call seeking comment by press time.

The MSX spacecraft was launched in 1996 and uses a sensor called the Space Based Visible telescope to conduct Earth-orbit surveillance. According to the Dec. 20 Federal Business Opportunities posting, that sensor — the only one still operating aboard MSX — is expected to “soon reach the end of its life.”

The Air Force maintains a network of ground-based space-surveillance telescopes, but those sensors can have their view blocked by clouds, Payton said.

Keeping tabs on objects in space has risen in priority as Pentagon officials have grown more sensitive to the possibility of attacks on U.S. satellites, according to Air Force Col. Anthony Russo, chief of the space division under U.S. Strategic Command’s Joint Functional Component Command for Space and Global Strike, which oversees the operation of military satellites .

If the Pentagon cannot closely monitor objects in Earth orbit , it cannot distinguish events such as a debris collision or malfunction involving one of its satellites from a deliberate attack , Russo said during a Feb. 8 luncheon here hosted by the Center for Media and Security, a nonprofit organization that promotes public understanding of national security issues.

U.S. Marine Corps Gen. James Cartwright, commander of Strategic Command, is telling personnel to consider the possibility that any anomaly with a satellite could be the result of an enemy attack, Russo said. This does not mean Strategic Command automatically assumes satellite problems are the result of hostile acts , but it does represent a shift in from the recent past, when the presumption was the opposite — even during exercises where participants were advised of the possibility of enemy tampering, he said.

Despite the elevated priority it has placed on space surveillance, the Pentagon recently canceled a development program in this area due to budget constraints.

That program, called the Orbital Deep Space Imager, was intended to complement the SBSS satellites by focusing on objects in geosynchronous orbit. The Pentagon had planned to award a contract to build multiple Orbital Deep Space Imager satellites in 2008, and begin launching them in 2013, according to a Defense Department budget document.

Theresa Hitchens, director of the Center for Defense Information, a think tank here, said canceling the Orbital Deep Space Imager program may have been a mistake.

Researchers in recent years have been finding fields of debris in geosynchronous orbit that could damage or destroy a satellite, Hitchens said. Unlike debris in low Earth orbit, which loses altitude over time and re-enters the atmosphere, debris in geosynchronous orbit remains there for extremely long periods of time, posing a threat to operational satellites in this crowded belt of space, she said.