16 research outputs found
Aerodynamic Stability of Satellites in Elliptic Low Earth Orbits
Topical observations of the thermosphere at altitudes below are
of great benefit in advancing the understanding of the global distribution of
mass, composition, and dynamical responses to geomagnetic forcing, and momentum
transfer via waves. The perceived risks associated with such low altitude and
short duration orbits has prohibited the launch of Discovery-class missions.
Miniaturization of instruments such as mass spectrometers and advances in the
nano-satellite technology, associated with relatively low cost of
nano-satellite manufacturing and operation, open an avenue for performing low
altitude missions. The time dependent coefficients of a second order
non-homogeneous ODE which describes the motion have a double periodic shape.
Hence, they will be approximated using Jacobi elliptic functions. Through a
change of variables the original ODE will be converted into Hill's ODE for
stability analysis using Floquet theory. We are interested in how changes in
the coefficients of the ODE affect the stability of the solution. The expected
result will be an allowable range of parameters for which the motion is
dynamically stable. A possible extension of the application is a computational
tool for the rapid evaluation of the stability of entry or re-entry vehicles in
rarefied flow regimes and of satellites flying in relatively low orbits.Comment: 18 pages, 16 figure
On the structural theory of II_1 factors of negatively curved groups, II: Actions by product groups
This paper includes a series of structural results for von Neumann algebras
arising from measure preserving actions by product groups on probability
spaces. Expanding upon the methods used earlier by the first two authors
\cite{CS}, we obtain new examples of strongly solid factors as well as von
Neumann algebras with unique or no Cartan subalgebra. For instance we show that
every II factor associated with a weakly amenable group in the class
of Ozawa is strongly solid, \cite{OzSolid}. There is also the
following product version of this result: any maximal abelian
-subalgebra of any II factor associated with a finite product of
weakly amenable groups in the class of Ozawa has an amenable
normalizing algebra. Finally, pairing some of these results with cocycle
superrigidity results from \cite{IoaCSR}, it follows that compact actions by
finite products of lattices in , , are virtually
-superrigid.Comment: final versio
Agent-based Control of Multiple Satellite Formation Flying
Formation flying is an enabling technique for numerous proposed satellite missions. The TeamAgent software system, based on ObjectAgent technology, is designed to enable multiple satellites to cooperate autonomously with particular focus on formation flying. A generalized agent-based software architecture for formation flying has been devised and is being applied to the Air Force Research Laboratory’s TechSat 21 technology demonstration mission
Aerodynamic Stability of Satellites in Elliptic Low Earth Orbits
Topical observations of the thermosphere at altitudes below 200 km are of great benefit in advancing the understanding of the global distribution of mass, composition, and dynamical responses to geomagnetic forcing, and momentum transfer via waves. The perceived risks associated with such low altitude and short duration orbits has prohibited the launch of Discovery-class missions. Miniaturization of instruments such as mass spectrometers and advances in the nano-satellite technology, associated with relatively low cost of nano-satellite manufacturing and operation, open an avenue for performing low altitude missions. The time dependent coefficients of a second order non-homogeneous ODE which describes the motion have a double periodic shape. Hence, they will be approximated using Jacobi elliptic functions. Through a change of variables the original ODE will be converted into Hill’s ODE for stability analysis using Floquet theory. We are interested in how changes in the coefficients of the ODE affect the stability of the solution. The expected result will be an allowable range of parameters for which the motion is dynamically stable. A possible extension of the application is a computational tool for the rapid evaluation of the stability of entry or re-entry vehicles in rarefied flow regimes and of satellites flying in relatively low orbits