Software Engineering Institute | Carnegie Mellon University
Software Engineering Institute | Carnegie Mellon University

Global Positioning System Program Coordinates COTS Product Upgrades

The U.S. Air Force's Global Positioning System (GPS) is a satellite-based radio navigation system that allows land, sea, and airborne users to determine the time, their position, and their speed at all times, in all weather, anywhere in the world. It uses a set of more than 28 orbiting satellites that continuously broadcast position and time data, together with a ground control system and many thousands of GPS receivers in aircraft, ships, land vehicles, and hand-held units.

The GPS Operational Control Segment (OCS) tracks all of the GPS satellites, collects information from their broadcasts, and computes satellite orbits. The first GPS Block I Satellite was launched in February 1978 and OCS development began in September 1980. Next, OCS capabilities were incrementally deployed, first at Vandenberg Air Force Base, as the Initial Control Segment and finally at Falcon Air Force Base (now Schriever AFB), as the OCS. The GPS reached Full Operational Capability in April 1995. The OCS now supports Block I, Block II, Block IIA, Block IIR, and IIRM satellites. The ground system has been in the process of being upgraded and modernized since 1996. This upgrade supports the planned launch of new Block IIF satellites beginning in 2006, which will feature greater accuracy and security.


The modernization of the GPS OCS is a large-scale replacement of the existing ground system. While not unprecedented, a ground system modernization of this magnitude is a major undertaking, involving over 20 different commercial off-the-shelf (COTS) products, affecting millions of military and commercial users.

The substantial use of COTS products on the program and the issues that arose when a major COTS product was upgraded led to questions about the effectiveness of the commercial systems used in the OCS. In 1998, organizational changes within the GPS team increased the complexity of coordinating the project with all contractors.

Approach and Results

In 2003, the U.S. Air Force Space and Missile Systems Center (SMC) Commander requested that an Integrated Program Baseline Review (IPBR) be performed by the Aerospace Corporation with support from the SEI to assess the overall program status and to identify key challenges. An IPBR is a short-duration management and technical assessment that is used to help ensure that the program and contractors are on track and operating correctly.

The questions regarding the use of COTS products and coordinating contractor work became the focus of the IPBR. The SEI staff on the review team helped to determine that the specific concerns about the problematic COTS product upgrade were resolved and that the upgrade was on track. The final briefing pointed out that the contractors worked well together and that the existing processes for communications between the organizations were both sufficient and continually improving.

In a third area investigated during the IPBR, the Joint Program Office (JPO) had been working to address the issue of transitioning the final system to the master control station team at Falcon Air Force Base, who would ultimately be using the system to control the GPS satellites. As a result of the review, the SEI emphasized the importance of addressing this key transition effort even more proactively.

The SEI brings years of practical software development experience and can help organizations conducting large software-intensive system acquisitions by addressing the questions and issues that arise during extended projects. SMC commander Lt. Gen. Brian Arnold (ret.), system program director Col. Allan Ballenger, Aerospace Corporation, and the contractors were all pleased with the participation and contributions made by the combined Aerospace and SEI review team. The program manager at Lockheed Martin pointed out the value of the "…real experience of the team—in software development, in large system management, and in effective listening." Dr. William Ballhaus, president and CEO of Aerospace, stated that "The briefing and review were well done, to-the-point, and fair. This was due, in no small part, to the expertise and common sense of the SEI members of the team."