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Global Positioning System Systems Engineering Case Study

Posted Tuesday, December 11, 2007

 

The Global Positioning System Systems Engineering Case Study describes the application of systems engineering during the concept validation, system design and development, and production phases of the GPS program.  The case examines the applied systems engineering processes, as well as the interactions of the GPS Joint Program Office, the prime contractors, and the plethora of government agencies that were associated with the programs development and fielding.  The systems engineering process is traced from the initiation of studies and the development of key technologies that established the vision of a satellite navigation system in the 1960s, through the multi-phase joint program that resulted in a full operational capability release in 1995.  Numerous interviews were conducted with individuals who personally directed, managed and engineered the program, from which the systems engineering story emerged.  While the GPS program continues to incorporate system enhancements through the Blocks IIM, IIF, and III, this report does not cover these later efforts.

GPS is a space-based radio-positioning system nominally consisting of a 24 satellite constellation that provides navigation and timing information to military and civilian users worldwide.  GPS satellites, in one of six Earth orbits, circle the earth every 12-hours emitting continuous navigation signals on two different L-band frequencies (Ref. 23).  The system consists of two other major segments: a world-wide satellite control network and the GPS user equipment that is either man portable or integrated into host platforms such as ships, vehicles or aircraft.

Block IIR Satellite

The genesis of GPS occurred soon after the Russians launched Sputnik on October 4, 1957.  While the satellite circled the Earth broadcasting its tone, an engineer at the Applied Physics Laboratory at Johns Hopkins University postulated that he could use the Doppler Effect from an orbiting satellite to actually compute where something was located on the Earth.  The Navy and the Air Force established separate programs to satisfy their unique service needs.  Under these programs, key technologies such as precise atomic clocks, quartz oscillators, spread spectrum signals, precise ephemeris[1] tracking and prediction, and reliable space systems were developed and demonstrated.

Seeing the lack of coordination and cooperation, and in some cases duplication of similar efforts, in 1972 the Department of Defense proclaimed that navigation development for space would be accomplished using a single Joint Program Office.  The purpose of the new space-based navigation system was to replace the plethora of land-based navigation aids such as LORAN, VOR, TACAN, VHF omni-directional ranging, and radio beacons.  Further, the Air Force was assigned to lead the JPO to be located at the Air Force facility in El Segundo, California.  The first program director was Air Force Col Brad Parkinson.  The program was directed to develop a joint concept solution, through coordination with all services and the Coast Guard.  Col Parkinson assembled his staff, which included Air Force, Navy, Army, and Coast Guard personnel, and a true joint program evolved under his leadership.

The fundamental systems engineering approach was to first construct the system specification, which is now known as the “functional baseline.”  The strategy of the program office was to manage the performance-level requirements, as well as manage all interfaces between the interrelated segments of the satellite constellation, ground stations, and user equipment.  The program office was staffed with technically oriented military officers and civilians, and augmented by the technical, scientific, and engineering staff from the Aerospace Corporation.  This Government oversaw and managed the Interface Control Working Groups and retained ownership of the functional baseline.  If the systems engineering process highlighted areas of the specification that were causing cost, schedule, or performance risks, the combined program office and industry teams quickly derived alternatives and presented them to the decision-making body.  Decisions were made quickly because of the close-knit, integrated, and focused efforts of the combined team.  Managing the interfaces, achieving insight over the technical development, leading the systems engineering trade studies, and retaining control of the system specification were essential and critically important strategies for the JPO.

The case study revealed that key DoD personnel maintained a clear and consistent vision for this unprecedented, space-based navigation capability.  The case study also revealed that good fortune was enjoyed by the JPO as somewhat-independent, critical space technologies matured in a timely manner.  Although the system required a large degree of integration, both within the system and external amongst a multitude of agencies and contractors, efforts were taken to directly address it.  Lastly, the reader of the GPS case study will gain an increased understanding of the effect that GPS has on the military and commercial industry.  A system originally designed to help “drop 5 bombs in one hole” has increasingly grown in use and now affects our everyday lives.

To read the entire executive summary or to download the case study, click here.

[1] A table listing the future positions of the Sun, Moon, and planets over a given period of time.

 

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