Abstract
United Launch Alliance (ULA) and their United States Air Force (USAF) Evolved Expendable Launch Vehicle (EELV) customer initiated operational flights of both the Atlas V and Delta IV launch vehicle families in 2002. Both Launch Vehicle families have provided 100% mission success since their respective inaugural launch and have demonstrated launch capability from both Vandenberg Air Force Base (VAFB) on the Western Range and Cape Canaveral Air Force station (CCAFS) on the Eastern Test Range. However, the current EELV fleet communications, tracking, and control architecture & technology, which date back to the origins of the space launch business, require support by a large and high cost ground footprint. The United States Air Force has embarked on an initiative known as Launch Enterprise Transformation (LET) that will significantly reduce Test Range Operations and Maintenance (O&M) cost by closing facilities and decommissioning ground assets. An important phase of the LET initiative is implementation of Global Positioning System (GPS) Tracking Unit developed by ULA and Space Vector Corporation on launch vehicles that use these ranges. GPS Metric Tracking (MT) is a way to leverage the existing GPS satellite base navigation system's capability in order to significantly reduce the costs of Test Range O&M. United Launch Alliance (ULA), in partnership with the U.S. Government, is engaged in a project plan to evolve the EELV fleet from dependence on ground based range assets to a Space Based Range operational concept. The initial phase was the development of the GPS Tracking Unit (GTU). ULA worked closely with the USAF to define and document the requirements for a GPS MT System for an EELV-class launch vehicle in accordance with the Range Commanders Council documentation (RCC 324-01T-EELV, Global Positioning and Inertial Measurements Range Safety Tracking Systems' Commonality Standard Tailored for EELV). <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> The GTU provides precise launch vehicle position, velocity and timing information that can replace ground radar tracking resource functionality while utilizing Commercial Off The Shelf (COTS) components to reduce costs and increase capabilities. The availability of military grade components often limits system design and functionality. The GTU is designed to incorporate some of the most current commercial parts available that offer features not found in military components. These COTS components brought with them additional issues due to a lack of performance data in the launch vehicle environment for these new components. Space Vector utilized a stackable, modular design in developing the GTU for EELV. This approach allows for changes and upgrades to components within a specific module without adversely affecting the entire unit. The modular approach to the GTU design also allowed Space Vector to provide additional interfaces to accommodate both Atlas V and Delta IV unique power and ground interfaces into a single unit eliminating the need to develop separate configurations for each vehicle within the EELV family. The GTU also took advantage of an existing COTS receiver and processor that were ruggedized for the launch vehicle environments. The GTU completed all qualification testing in May 2011 and is currently in production. This paper summarizes the design approach, COTS issues, physical parameters and functional performance capabilities of the EELV GPS Tracking Unit. The implementation of COTS components in a launch vehicle environment required creating new methodologies and test processes to ensure reliability.
Published Version
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