SBIRS is an integrated "system of systems" that will include satellites in geosynchronous orbit (GEO), sensors hosted on satellites in highly elliptical orbit (HEO), and ground-based data processing and control. A complement of satellites in low earth orbit was planned as part of the program (SBIRS Low), but this has been moved into the STSS program. SBIRS ground software integrates infrared sensor programs of the U.S. Air Force (USAF) with new IR sensors. SBIRS continues to struggle with cost overruns, with Nunn-McCurdy breaches occurring in 2001 and 2005. By September 2007, the expected project cost had increased to $10.4 billion.