Global Positioning System
The Global Positioning System (GPS) case study was developed by the United States Air Force Center for Systems Engineering (AF CSE) located at the Air Force Institute of Technology (AFIT), and is accessible through the following url: http://www.afit.edu/cse/cases.cfm?case=17&a=detail. The Global Positioning System (GPS) is a space-based radio-positioning system. A constellation of twenty-four satellites, including three spares, comprise the overall system which provides navigation and timing information to military and civilian users worldwide. GPS satellites, in one of six Earth orbits, circle the globe every twelve hours, emitting continuous navigation signals on two different L-band frequencies. The system consists of two other major segments: a world-wide satellite control network, and the GPS user equipment that can either be carried by a human user or integrated into host platforms such as ships, vehicles, or aircraft.
Application domains: aerospace, space, communications, transportation
- 1 Domain Background
- 2 Case Study Background
- 3 Case Study Description
- 4 Summary
- 5 References
- 6 Signatures
When looking at the Global Positioning System (GPS), it would be difficult to imagine another system that relies so heavily upon such a wide range of domains, with the possible exception of the world-wide-web. Additionally, the various systems operating within these domains must all function together flawlessly to achieve mission success. It is evident from reading this case study that it directly relates to the following domains:
This is also an example of Systems of Systems and is considered an innovative technology.
The GPS case study includes a detailed discussion of the development of the GPS and its components, their development, and other applicable areas. The reader of the GPS case study will gain an increased understanding of the effect that GPS has on the military and commercial industries in the context of the Systems Engineering support required to achieve success.
Case Study Background
The United States Air Force Center for Systems Engineering (AF CSE), established in 2002 at the Air Force Institute of Technology (AFIT), was tasked to develop case studies focusing on the application of systems engineering principles within various aerospace programs. (O'Brien and Griffin 2007) The Global Positioning System (GPS) was developed by AFIT in support of systems engineering graduate school instruction. Each of the case studies employs the Friedman-Sage framework that is comprised of the following nine concept domains:
- Requirements Definition and Management
- Systems Architecting and Conceptual Design
- System and Subsystem Detailed Design and Implementation
- Systems and Interface Integration
- Validation and Verification
- Deployment and Post Deployment
- Life Cycle Support
- Risk Assessment and Management
- System and Program Management
The Friedman-Sage framework is used in the GPS case study in several areas including in the discussion of Risk and Configuration Management in relation to Learning Principle 5 (see Learning Principles, below), and in the Summary of the case study.
Case Study Description
The GPS 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. This case study does not cover system enhancements incorporated through Blocks IIM, IIF, and III. The GPS case study derived four Learning Principles (LPs) that address the more broadly applicable areas of systems engineering knowledge that are addressed by the case study.
These four LPs inform the areas of the SEBoK that are most strongly related to the case study. These four areas are:
- Enabling Individuals (LP1),
- Configuration Management (LP2),
- Enabling the Organization (LP3), and
- Risk Management (LP4).
Learning Principle 1: Programs must strive to staff key positions with domain experts.
From program management to systems engineering, to design, to the manufacturing and operations teams, the people on the program were well-versed in their disciplines, and all possessed a systems view of the program. While communications, working relationships, and organization were important, it was the ability of the whole team at all levels to understand the implications of their work on the system that was vital. Their knowledge-based approach for decision making had the effect of shortening the decision cycle, because both the information was understood and the base and alternative solutions were accurately presented.
Learning Principle 2: The systems integrator must rigorously maintain program baselines.
The Joint Program Office (JPO) retained the role of managing and controlling the system specification and, therefore, the functional baseline. The JPO had derived and constructed a mutually agreed-to set of system requirements that became the program baseline in 1973. While conducting the development program, the GPS team was able to make performance/risk/cost trade analysis against the functional baseline to control both risk and cost. The JPO was fully cognizant of the implications of the functional requirements on the allocated baseline because they managed the Interface Control Working Group process. Managing that process gave them first-hand knowledge and insight into the risks at the lowest level.
Whoever has the system integrator role must rigorously maintain the system specification and functional baseline. There must be appropriate sharing of management and technical responsibilities between the prime contractor and their government counterparts to ensure success.
Enabling the Organization
Learning Principle 3: Achieving consistent and continuous high-level support and advocacy helps funding stability, which impacts SE stability.
Consistent, continuous high-level support provided requirements and funding stability. In this role, the OSD provided advocacy and sourced the funding at critical times in the program, promoted coordination among the various services, and reviewed and approved the GPS JPO system requirements. OSD played the central role in the establishment and survivability of the program. The GPS JPO had clear support from the Director of Defense Development, Research and Engineering (DDR&E), Dr. Malcolm Currie, and program support from the Deputy Secretary of Defense, Dr. David Packard. Clearly, the services – particularly the Navy and the Air Force early on, and later the Army – were the primary users and the eventual customers. However, each service had initial needs for their individual programs, or for the then-current operational navigation systems. Additionally, the Secretary of the Air Force provided programmatic support to supply manpower and facilities.
Learning Principle 4: Disciplined and appropriate risk management must be applied throughout the lifecycle.
The GPS program was structured to address risk in several different ways throughout the multiphase program. Where key risks were known up front, the contractor and/or government utilized a classic risk management approach to identify and analyze risk, and developed and tracked mitigation actions. These design (or manufacturing/launch) risks were managed by the office who owned the risks. Identified technical risks were often tracked by Technical Performance Measures (TPMs), (e.g. satellite weight and Software Lines Of Codes (SLOC)), and addressed at weekly chief engineer’s meetings.
The JPO, serving in the clear role of program integrator allowed the JPO to sponsor risk trade studies at the top level. The Program Office, serving as the integrator, would issue study requests for proposals to several bidders for developing concepts and/or preliminary designs. Then, one contractor would be down-selected to continue. This approach not only provided innovative solutions through competition, but also helped in defining a lower risk and more clearly defined development program for the fixed-price contracts approach that was being used for development and production.
The Program Office was closely involved with the technical development as the system integrator. To identify unforeseeable unique technical challenges, the Pro-gram Office would fund studies to determine the optimal approaches to new issues. For example, there were schedule risks associated with the scheduled first launch due to unforeseen Block II issues with respect to the space vehicle and control segments (software development). Although a catastrophic event, the Challenger accident actually provided much needed schedule relief. Using decision analysis methodology led the JPO to an alternative approach to develop the expendable launch vehicle for the Block II satellites.
Good communications, facilitated by cooperative working relationships, was a significant positive intangible factor, whether it was between the contractors and government (JPO or other agencies) or contractors to sub-contractors. A true team environment also played a significant role in reducing risk, especially considering the plethora of government agencies and contractors that were involved in the effort.
Life Cycle Management
The GPS case study takes the reader through the transition from concept (Mar 1942) through development, production, and operational capability release. The current GPS program traces its heritage from the early 1960s when Air Force Systems Command initiated satellite-based navigation systems analysis, conducted by Aerospace Corporation. The case study follows the execution of the GPS program from the inception of the idea to the Full Operational Capability (FOC) release, 27 Apr 1995. The concentration of the case study is not limited to any particular period, and the learning principles come from various times throughout the program’s life.
The GPS case study highlights the need for systems thinking throughout. GPS satellites, in one of six Earth orbits, circle the globe every twelve hours, emitting con¬tinuous navigation signals on two different L-band frequencies. The system consists of two other major segments: a world-wide satellite control network, and the GPS user equipment that can either be carried by a human user or integrated into host platforms such as ships, vehicles, or aircraft. The ability to conceive, develop, produce, field and sustain the GPS demands the highest levels of systems thinking.
The GPS case study is useful for global SE learning providing a comprehensive perspective on the systems engineering life cycle, and can be used equally effectively for detailed instruction in the areas of:
- Enabling Individuals
- Configuration Management
- Enabling the Organization
- Risk Management
- Life Cycle Management
- Systems Thinking
The GPS 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 Joint Program Office (JPO) as somewhat-independent, critical space technologies matured in a timely manner.
Although the GPS 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 industries in the context of the Systems Engineering support required to achieve success. The system was originally designed to help “drop 5 bombs in one hole” which defines the accuracy requirement in context-specific terms. The GPS signals needed to be consistent, repeatable, and accurate to the level that, when used by munitions guidance systems, the end result would be the successful delivery of multiple, separately guided, munitions to virtually the identical location anywhere at any time across the planet. 40-50 years ago very few outside of the military recognized the value of the proposed accuracy, and most non-military uses of GPS were not recognized before 1990. GPS has increasingly grown in use and now affects our everyday lives.
Friedman, G. and A. Sage. 2004. "Case Studies of Systems Engineering and Management in Systems Acquisition." Systems Engineering 7(1) p. 84-96.
O’Brien, P.J. and J.M. Griffin. 2007. Global Positioning System Systems Engineering Case Study. Wright-Patterson AFB, OH, USA: Air Force Center for Systems Engineering (AF CSE), Air Force Institute of Technology (AFIT). Available at: http://www.afit.edu/cse/cases.cfm?case=17&a=detail.
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--Hdavidz 15:29, 15 August 2011 (UTC)
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