Two U.S. Missile Defense Agency (MDA) missile tracking demonstration satellites were successfully launched Sept. 25 from Cape Canaveral Air Force Station, Fla., aboard a United Launch Alliance Delta 2 rocket, according to a Sept. 25 Air Force press release.

The Space Tracking and Surveillance System (STSS) satellites, built by Northrop Grumman Aerospace Systems of Los Angeles, are designed to demonstrate the ability to track ballistic missiles in every stage of flight, something current U.S. space-based assets cannot do. Northrop Grumman had originally built the satellites under an experiment dubbed the Flight Demonstration System that was canceled in 1999. The program was given a new lease on life in 2002 when the MDA awarded Northrop Grumman an $868 million contract to prepare the satellites for launch. The agency has spent $1.35 billion on the program since 2002, and the MDA has requested another $180 million next year to conduct testing activities.

The launch, which experienced several short weather-related delays, clears the way for the planned Oct. 8 Delta 2 launch that will carry Longmont, Colo.-based DigitalGlobe’s WorldView-2 commercial imaging satellite to space. That satellite had been slated to launch Oct. 6.