The U.S. Air Force is asking industry to explore options for quick delivery of a space-based missile warning system, a move which is likely connected to reports that the service's newest ballistic missile warning satellite is failing in orbit.

A broad sources sought notice was issued Nov. 24, and a more specific and classified request for information is expected Dec. 1.

This flurry of activity is likely a response to concerns of a space-based missile warning gap, according to industry officials. The 23rd Defense Support Program (DSP) satellite, launched into orbit last November, has drifted from its original position in geosynchronous orbit and is likely failing, says Theresa Hitchens, director for the Washington-based Center for Defense Information.

Amateur satellite monitors have observed the satellite drifting from its orbit, a sign that the Air Force may lack control of the system, and they note that it is broadcasting data only infrequently, she says. This is a sign of in-orbit failure. These problems have been noted since September, she adds.

Air Force officials refused to discuss the status of the satellite's health, citing security concerns.

The DSP constellation is used to detect the heat plumes of boosting ballistic missiles. As such, it is the first line of defense against such threats. Infrared signatures picked up by this system are used to tip off missile defenses about the location and trajectory of missile threats. DSP was designed and built by TRW, how owned by Northrop Grumman. The satellites have been providing missile warning data since the 1970s.

Air Force officials have not said how may DSP satellites are in orbit and if there is a gap in missile warning capabilities. Hitchens, however, notes that satellite trackers say at least six are in orbit. At a minimum three are needed to ensure global coverage. However, more are kept in orbit to ensure backups are ready in the event of a failure and to provide varied looks at targets.

The loss of the most recent DSP puts more pressure on Lockheed Martin to finally deliver the first Space-Based Infrared System (SBIRS) satellite bound for geosynchronous orbit. Two SBIRS sensors already have been placed on classified host satellites in highly elliptical orbit, but the first GEO spacecraft has suffered many setbacks. The first SBIRS launch is now expected in 2010, with others set for 2011, 2014 and 2016.

The worry of a missile warning gap is not new to the Pentagon. After encountering major problems with SBIRS in 2005, the Pentagon embarked on a backup program to develop an alternate system in the hopes of avoiding a gap.

SAIC and Raytheon each delivered new staring focal plane arrays capable of detecting infrared plumes, but these sensors are developmental and were not designed to conduct missile warning operations nonstop. Nor are they hardened from nuclear attack, as the SBIRS system is. SAIC's sensor is scheduled to fly on an SES Americom communications satellite over the Eastern United States in 2010. However, an industry source notes this sensor is only expected to operate for a few minutes a day.

Artist's concept of Defense Support Program satellite: Northrop Grumman