504 research outputs found
URAT: astrometric requirements and design history
The U.S. Naval Observatory Robotic Astrometric Telescope (URAT) project aims
at a highly accurate (5 mas), ground-based, all-sky survey. Requirements are
presented for the optics and telescope for this 0.85 m aperture, 4.5 degree
diameter field-of-view, specialized instrument, which are close to the
capability of the industry. The history of the design process is presented as
well as astrometric performance evaluations of the toleranced, optical design,
with expected wavefront errors included.Comment: 12 pages, 7 figures, SPIE 2006 Orlando conf. proc. Vol. 626
Numerical computation of viscous flows on the lee side of blunt shapes flying at supersonic speeds
A numerical method for solving the parabolic approximation to the steady-state compressible Navier-Stokes equations is examined. The approximation neglects only the streamwise gradients of shear stress. An implicit finite difference method is used which advances the solution downstream from an initial data surface and determines the complete viscous-inviscid flow between the body and bow shock wave. It is necessary that the inviscid portion of the flow field be supersonic. Crossflow separation is determined as part of the solution. The method is applied to a 15 deg sphere-cone at 15 deg angle of attack, and the results are compared with an inviscid method-of-characteristics calculation
Catalytic surface effects on space thermal protection system during Earth entry of flights STS-2 through STS-5
An on going orbiter experiment catalytic surface effects experiment being conducted on the Space Shuttle is discussed. The catalytic surface effects experiment was peformed on four of the five flights of Columbia. Temperature time histories and distributions along the midfuselage and wing of the orbiter were used to determine the surface catalytic efficiency of the baseline high temperature reusable surface insulation. Correlation parameters are shown that allow the comparison of all flight data with predictions from the design and surface emittance decreased as a result of contaminants during the five flights of the Space Shuttle
Simulation of large turbulent structures with the parabolic Navier-Stokes equations
The theoretical basis for well posed marching of a Parabolic Navier-Stokes (PNS) computational technique for supersonic flow is discussed and examples given to verify the analysis. It is demonstrated that stable computations can be made even with very small steps in the marching direction. The method is applied to cones at large angle of attack in high Reynolds number, supersonic flow. Streamline trajectories generated from the numerical solutions demonstrate the development of vortex structures on the lee side of the cone
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