The System: The Promise of OCX
September 1, 2008 By: Art Gower GPS World
The Next Generation GPS Control Segment (OCX) will provide significant benefits to military and civilian users around the world, as well as to GPS operators, maintainers, and analysts. With a planned initial operational date in 2012, OCX will begin a phased transition of the next generation of GPS services and capabilities. Like the GPS III satellites, OCX capabilities will be developed and deployed as a series of block upgrades. The block approach will incorporate new technologies and requirements in response to changing world events.
The OCX program is underway after many years of studies, requirements definition, and risk reduction efforts. On November 21, 2007, two $160 million OCX Phase A contracts were awarded by the U.S. Air Force (USAF) Space and Missile Systems Center to contractor teams led by Northrop Grumman and Raytheon. Each has 18 months to conduct System Design Reviews and develop a modernized capability engineering model that will support a final down-select to one contractor team in 2009. Both teams have completed successful System Requirements Reviews and are working towards System Design Review.
The Architectural Evolution Plan (AEP) currently provides the operational capability bridge to OCX. AEP supports global users with GPS services and maintains the Block II, IIR, IIR-M, and future IIF constellation until OCX comes on line. AEP successfully transitioned to 24/7 operations September 2007 (see “AEP Goes Operational,” June 2008 GPS World) thanks to the efforts of the United States Air Force, Boeing, Lockheed Martin, and the Aerospace Corporation. This team conducted “apples to apples” accuracy comparisons between the legacy Control Segment and AEP, ensuring a continuous, accurate worldwide service.
AEP also continued the 20-year tradition of beating the GPS accuracy requirements that began with the original operational system. AEP provides 73 percent better Zero Age of Data User Range Error (ZAOD URE) than required. This level of performance was achievable thanks to the improvements already made by the Legacy Accuracy Improvement Initiative (see “New, Improved GPS,” March 2006 GPS World) and by AEP.
Prior to transition of OCX, it is critical that the Air Force and the OCX contractor team perform “apples to apples” accuracy comparisons between AEP and OCX. This will help ensure an uneventful transition, keeping the world’s navigation users safe and the GPS system continually operable. The detailed comparison effort must be planned from the beginning, with transition tools an integral part of the development and the analysis an integral part of the schedule.
OCX will bring greater information flow, not only from the outside world into the GPS Control Segment, but also vice versa. Today’s system is virtually closed, with only the navigation message (via satellite), NANUs/NOTAMs, and daily dilution of precision (DOP) plots provided for the general user. The GPS Operations Center (GPSOC) provides a ZAOD navigation service for military applications, removing the majority of GPS clock errors.
Newer, More Improved. OCX will provide easier access to more information for users, including military, commercial, and all forms of civilian use. Greatly improved user situational awareness of GPS performance, both current performance and predicted, will be available, as well as greater coordination capability with other GNSS and space-based augmentation system (SBAS) providers. This will yield a more precise capability to plan missions (for example, urban operations, car, river, and air travel) from availability, accuracy, integrity, and continuity standpoints, affording lower separation limits and higher traffic volume.
OCX will be created using aviation safety-assured integrity standards and processes. GPS users should benefit directly from this increased focus on integrity. Actual safety-certification of the Control Segment and potentially the system are not expected for several years after the first operational date. These years of operational usage data should aid the safety certification process.
Automation of many current manual operational tasks will also aid safety certification. AEP provides the option to automate many tasks such as contact set-up, satellite commanding and configuration, telemetry checks, and Kalman filter processing. OCX will automate these and even more of the operational tasks, allowing operations to focus more on ensuring service quality and the performance of new missions.
A detailed analysis of OCX operator workloads showed that operations loading should remain less than 75 percent, even with the newly integrated missions of the GPSOC: Launch, Anomaly, and Disposal Operations (LADO); Navigation Warfare (NavWar); and increased net-centric services and information provision to users. In addition to personnel efficiencies, OCX saves money by integrating these additional systems into a single flexible, componentized services-oriented architecture that provides easy technology upgrade.
Updated Dataset. OCX will bring better situational awareness to all GPS users. A robust and rapidly updated information set is expected to become available publically, both directly from OCX and through the Coast Guard Navigation Center (NavCen). This information set will include more detailed constellation, coverage, DOP, accuracy, and planned schedule information than is currently available. The new information will allow users to more effectively plan their missions based on expected GPS performance and that of GPS combined with other navigation and augmentation systems.
As part of the block upgrade approach for GPS III, performance will improve even further as the first eight GPS IIIB satellites are launched and set healthy. The GPS IIIBs will have high-speed ground and crosslink communications. This capability will greatly reduce the age of GPS navigation data from today’s 13-hour average to between 15 and 75 minutes. Navigation errors due to clock age of data effects will be mostly eliminated, greatly improving performance for all users and applications.
Constant Contact. The Control Segment will have continuous access to every GPS IIIB satellite (compared to one or two contacts per day), providing operators continuous access to telemetry to help detect potential impending problems. Instead of learning about failures after the problem has occurred, operators will be able to better predict potentially hazardous situations and take corrective action before they impact navigation service. System accuracy, availability, integrity, and continuity will improve incrementally with every high-speed communications-capable satellite launched.
The OCX net-centric services will provide the public with more in-depth knowledge of Control Segment plans, performance, and operations, enabling better decision-making and the use of tighter performance tolerances.
OCX alone improves GPS accuracy, integrity, availability, and continuity. In combination with the high-speed communications of the GPS IIIB satellites, even greater improvements in accuracy, integrity, availability, and continuity of the system will be achieved.
ART GOWER has worked for 25 years on the GPS Control Segment, WAAS, and MSAS, the last eight years on requirements, architecture, risk reduction, and prototyping for OCX. He has an M.Sc. degree in nuclear engineering from Virginia Tech, has certification as a Lockheed Martin System Architect in Information Systems Architecture and in System of Systems architecture, and is a member of GPS World’s Editorial Advisory Board.
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