Exploring the Trade-offs of Aggregated versus Disaggregated Architectures for Environmental Monitoring in Low-Earth Orbit

Traditionally, government space agencies have developed aggregated systems that co-host multiple capabilities on shared spacecraft buses. However, in response to cost growth and schedule delays on past programs, leaders in the government space community have expressed an interest in disaggregation, or distributing their capabilities across multiple spacecraft. Since their aggregated National Polar-orbiting Operational Satellite System (NPOESS) program was cancelled in 2010, both the National Oceanic and Atmospheric Administration (NOAA) and the Department of Defense (DoD) have investigated opportunities to reduce program costs through disaggregation. This paper expands their initial investigation and explores the cost impacts of aggregation and disaggregation across a large trade space of candidate architectures for environmental monitoring in low-Earth orbit. We find that on average, aggregated architectures are less costly than fully disaggregated ones but also find opportunities for cost savings by developing semi-aggregated systems, or systems with one or two satellites per orbital plane. Finally, we investigate several trades that are currently under consideration by NOAA and the DoD and make recommendations for future environmental monitoring systems in low-Earth orbit.Massachusetts Institute of Technology (Sandia Corporation Excellence in Engineering Graduate Fellowship)Skolkovo Institute of Science and Technolog

Beyond horizons : a half century of Air Force space leadership /

U.S. G.P.O. sales statement incorrect in publication.Shipping list no.: 2011-0339-P.Includes bibliographical references (p. 346-368) and index.Mode of access: Internet

Prediction of total electron content using the international reference ionosphere /

The International Reference Ionosphere (IRI) is a model of the ionosphere, based on experimental data, that has been proposed as a standard ionospheric model. As such, it should be tested extensively to determine its range of validity. One of the ways in which the electron density profile given by the IRI, especially above the peak of the F layer, can be tested is to compare calculated and observed values of total electron content (TEC). We have therefore studied the discrepancies between calculated and observed values of TEC recorded at 15 stations covering a wide range of longitudes and latitudes mainly in the northern hemisphere, and mainly for high levels of solar activity. We have found that the IRI produces reasonably accurate values of TEC at mid- and high-latitudes, but that if greatly underestimates the daytime values of TEC at low latitudes. We conclude therefore that the daytime electron density profile given by the IRI is reasonably accurate at mid- and high-latitudes; at least above the peak of the F2 layer. The situation at low latitudes clearly requires more work, and we have suggested two possible lines of study. The generally low discrepancies at night indicate that the nighttime electron density profiles given by the IRI correspond fairly closely to the actual profiles."20 September 1983."Distributed to depository libraries in microfiche."Project 4643."Cover title.Includes bibliographical references.Final.The International Reference Ionosphere (IRI) is a model of the ionosphere, based on experimental data, that has been proposed as a standard ionospheric model. As such, it should be tested extensively to determine its range of validity. One of the ways in which the electron density profile given by the IRI, especially above the peak of the F layer, can be tested is to compare calculated and observed values of total electron content (TEC). We have therefore studied the discrepancies between calculated and observed values of TEC recorded at 15 stations covering a wide range of longitudes and latitudes mainly in the northern hemisphere, and mainly for high levels of solar activity. We have found that the IRI produces reasonably accurate values of TEC at mid- and high-latitudes, but that if greatly underestimates the daytime values of TEC at low latitudes. We conclude therefore that the daytime electron density profile given by the IRI is reasonably accurate at mid- and high-latitudes; at least above the peak of the F2 layer. The situation at low latitudes clearly requires more work, and we have suggested two possible lines of study. The generally low discrepancies at night indicate that the nighttime electron density profiles given by the IRI correspond fairly closely to the actual profiles.Mode of access: Internet

Effect of contact surface bluntness on massive blowing from a wedge in hypersonic flow /

An inviscid, compressible analysis is given for massive blowing from the porous surface of a wedge or flat plate in a hypersonic free stream. An inverse procedure is used whereby the specified geometry of the contact surface is that of a blunted wedge. The resulting mathematical formulation which uses natural coordinates and the Fourier cosine transform, is notable for its simplicity. Attention is focused on the induced pressure field in the injected gas due to the contact surface's bluntness. Detailed results, however, are given only for the flat plate. For this case, appreciable induced tangential and normal pressure gradients occur in the injected gas flow near the leading edge. An interesting result is that the pressure and velocity distribution on the plate is given by a single universal curve, when distance along the plate is properly scaled. (Author)."October 1966."Includes bibliographic references (pages 23-24).An inviscid, compressible analysis is given for massive blowing from the porous surface of a wedge or flat plate in a hypersonic free stream. An inverse procedure is used whereby the specified geometry of the contact surface is that of a blunted wedge. The resulting mathematical formulation which uses natural coordinates and the Fourier cosine transform, is notable for its simplicity. Attention is focused on the induced pressure field in the injected gas due to the contact surface's bluntness. Detailed results, however, are given only for the flat plate. For this case, appreciable induced tangential and normal pressure gradients occur in the injected gas flow near the leading edge. An interesting result is that the pressure and velocity distribution on the plate is given by a single universal curve, when distance along the plate is properly scaled. (Author).Report prepared by Aerospace Corporation, Laboratories Division, El Segundo, California, for Space Systems and Ballistic Systems Divisions, United States Air Force, under contract No.Mode of access: Internet

Unsteady aerodynamics for advanced configurations.

Includes bibliograpical references (page 42).Air Force Contract No.Mode of access: Internet

Stagnation point heat transfer in a relaxing gas /

Stagnation point heat transfer in a gas undergoing relaxation of its internal energy is examined by solution of the equations of motion using the two temperature approach of Wang Chang and Uhlenbeck. The results are presented in parametric form and show that relaxation effects produce an adiabatic wall temperature above the free stream stagnation temperature, which is related to the thermal conductivity of the ''inert" mode, the dimensionless relaxation length, the ratio of the translational mode temperature to the temperature of the relaxing mode at the edge of the boundary layer, and the magnitude of the internal energy undergoing relaxation. An experiment is described whereby the thermal conductivity of the "inert" mode, which is unknown, may be determined from adiabatic wall temperature measurements."November 1963."Includes bibliographic references (pages 47-48).Stagnation point heat transfer in a gas undergoing relaxation of its internal energy is examined by solution of the equations of motion using the two temperature approach of Wang Chang and Uhlenbeck. The results are presented in parametric form and show that relaxation effects produce an adiabatic wall temperature above the free stream stagnation temperature, which is related to the thermal conductivity of the ''inert" mode, the dimensionless relaxation length, the ratio of the translational mode temperature to the temperature of the relaxing mode at the edge of the boundary layer, and the magnitude of the internal energy undergoing relaxation. An experiment is described whereby the thermal conductivity of the "inert" mode, which is unknown, may be determined from adiabatic wall temperature measurements.Report prepared by Aerospace Corporation, Fluid Mechanics Department, El Segundo, California, for Commander Space Systems Division, United States Air Force, under contract No.Mode of access: Internet

Unsteady aerodynamics for advanced configurations.

"May 1965."Includes bibliograpical references (page 37).Air Force Contract No.Mode of access: Internet

Unsteady aerodynamics for advanced configurations.

"May 1965."Includes bibliograpical references (page 55).Air Force Contract No.Mode of access: Internet

Axisymmetric hypersonic flow with strong viscous interaction /

Stewartson's theory for axisymmetric hypersonic flow of a model gas with strong viscous interaction and strong shock wave is extended to power-law viscosity variation, nonunit Prandtl number, and body shapes other than power laws. For power-law bodies, the generalized theory is obtained in closed form without recourse to numerical integration. In addition, numerical computations are presented for axisymmetric flow over a three-quarter power-law body with strong shock wave and viscous interactions that range from weak to strong. (Author)."July 1967."Includes bibliographic references (page 39).Stewartson's theory for axisymmetric hypersonic flow of a model gas with strong viscous interaction and strong shock wave is extended to power-law viscosity variation, nonunit Prandtl number, and body shapes other than power laws. For power-law bodies, the generalized theory is obtained in closed form without recourse to numerical integration. In addition, numerical computations are presented for axisymmetric flow over a three-quarter power-law body with strong shock wave and viscous interactions that range from weak to strong. (Author).Report prepared by Aerospace Corporation, Laboratories Division, El Segundo, California, for Space Systems and Ballistic Systems Divisions, United States Air Force, under contract No.Mode of access: Internet

Unsteady aerodynamics for advanced configurations.

"May 1965."Includes bibliograpical references (pages 41-42).Print reproduction.Air Force Contract No.Mode of access: Internet