Browsing by Author "Merkowitz, S. M."
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Item Modernizing and expanding the NASA Space Geodesy Network to meet future geodetic requirements(Springer Nature, 2018-10-06) Merkowitz, S. M.; Bolotin, S.; Elosegui, P.; Esper, J.; Gipson, J.; Hilliard, L.; Himwich, E.; Hoffman, E.D.; Lakins, D. D.; Lamb, R. C.; Lemoine, F. G.; Long, J. L.; McGarry, J. F.; MacMillan, D. S.; Michael, B. P.; Noll, C.; Pavlis, Erricos C.; Pearlman, M. R.; Ruszczyk, C.; Shappirio, M. D.; Stowers, D. A.NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA’s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.Item NASA’s Next Generation Space Geodesy Network Typical Core Site Requirements and Layout(NASA, 2014-10-14) Esper, J.; Long, J. L.; Lemoine, F. G.; McCormick, D. R.; Merkowitz, S. M.; Ma, C.; McGarry, J. F.; Hilliard, L.; Pavlis, Erricos C.; Pearlman, M. R.; Stowers, D. A.; Wetzel, S. L.NASA’s renewed commitment to the deployment of a new network of “core” space geodetic sites requires careful planning and consideration for location selection, instrument and facility layout, and required infrastructure. Following on National Research Council (NRC) recommendations [1] to upgrade U.S. stations with modern SLR, VLBI, and GNSS systems, and make a long-term commitment to maintaining the ITRF (among others), the Space Geodesy Project (SGP) at NASA Goddard has been defining the exact requirements and layout for a “typical” geodetic site, which includes Satellite Laser Ranging--SLR, Very Long Baseline Interferometry--VLBI, Global Navigation Satellite System--GNSS, and Doppler Orbitography and Radiopositioning Integrated by Satellite--DORIS stations (French system provided by CNES, France) tied together with a Vector Tie System (VTS), utilizing a Robotic Total Station (RTS). Within programmatic constraints, Core Site (CS) identification follows a systems engineering process where site characteristics are evaluated against identified requirements. Taking into consideration site stability, radiofrequency interference, infrastructure, and a host of other requirements this paper describes the process leading to identification, and it will illustrate the generic layout of an idealized CS with unencumbered terrain.