Density inhomogeneity in a laser cavity due to energy release

Density gradients, which refract laser light within the cavity, degrade beam quality. In addition to wall influences and viscous effects which cause density gradients, there is another mechanism. This mechanism, which is due to wakes and compression waves from heat (vibration energy to translation and rotation) addition in a supersonic stream, appears to have been overlooked. This appropriate equation is stated and discussed. A semigraphical solution procedure is outlined. Contours of constant density have been calculated for circular and rectangular cavities. Graphs of the isodensity contours are given. (Author)http://archive.org/details/densityinhomogen00fuhsN

Impulsive Loading from a Bare Explosive Charge in Space

The article of record as published may be found at https://doi.org/10.2514/3.2601

Aero-optics at shorter wavelengths

Using the optical system equation, the impact of a change in wavelength is determined. The rms phase variation at output aperture is critical and must be reduced by an amount equivalent to reduction in wavelength. If turret size is scaled with wavelength, the distortion due to the inviscid flow remains constant. Decreased wavelength offers the flexibility of greatly reduced turret weight, volume, and aerodynamic drag. Multiple turrets become feasible on an aircraft. The distortion due to the turbulent boundary layer becomes magnified by reduction of wavelength; however, if the turbulent boundary layer originates on the turret and if the turret is scaled, the boundary layer thickness decreases. Distortion becomes less significant in this casePrepared for: Air Force Weapons Laboratory/ARLB, Kirtland Air Force Base, NM, 87117.http://archive.org/details/aeroopticsatshor00fuhsMIPR # 80-MP-084Distinguished ProfessorApproved for public release; distribution is unlimited

Semi-Inverse Marching Characteristics Scheme for Supersonic Flows

The purpose of this Note is to present a modification of the inverse marching characteristics scheme for compressible flows that is designed to yield an exact computation of centered rarefaction waves, such as the Prandtl-Meyer corner expansion flow (PMF)

Phase distortion due to airflow over a hemispherical laser turret

Compressible flow over a laser turret creates a phase distortion. To gain insight to this problem a model of a hemispherical turret is developed. The flow field is obtained using a second order solution based on Janzen-Rayleigh expansion for the compressible potential flow equation. Contours of constant phase distortion were calculated; results at the critical Mach number are presented and discussed. It was found that the distortion at 0 degree elevation angle was equivalent to a positive lens whereas at 90 degrees the distortion is similar to a negative lens. At 45 degrees the main effect is beam tilting into the wind. For a ratio of beam radius to turret radius equal to 0.5, the focal length at beam elevation angle of 0 degrees is 16.5km. At beam elevation of 54 degrees the beam tilt was found to be 26.5 microradians. Cruise missiles with intercontinental ranges may use celestial navigation which requires precise measurement of angular location of stars. A distorted lens created by the ambient flow field causes an error in measurement. Knowledge of the external aerodynamics is importanthttp://archive.org/details/phasedistortiond00fuhsDistinguished Professor Allen E. Fuhs (Code 69Fu)Approved for public release; distribution is unlimited

An integral model for thermal backscattering from the exhaust plume of space-based HF laser

The operation of a space-based HF laser may be hampered due to self contamination by corrosive exhaust products. We estimate one effect contributing to contaminating blackflow: thermal backscattering from the rarefaction fans flanking the exhaust ring-jet. Our computational model is based on a first-iterate approximation to the Boltzmann equation in integral form. Results indicate that thermal backscattering of corrosive speies (HF, DF) is negligible

Laser heating and mirror distortion

This report presents the use of computer drawn graphs to facilitate solution of temperature profiles as a function of time. The solution of the one-dimensional unsteady heat-transfer equation for constant heat input due to laser radiation on one side of the sheet and insulation on the other was used to draw the graphs. Graphs have been drawn for three ranges of Fourier numbers: 0 to 1.0, 0 to 0.1, and 0 to 0.01. Sample problems are worked for three cases: temperature profiles within the metal plate as a function of time, time required to melt the front surface, and mirror distortion due to thermal expansionhttp://archive.org/details/laserheatingmirr00fuhsN

General Purpose Satellites: a concept for affordable low earth orbit vehicles

A general purpose satellite has been designed which will be launched from the Space Shuttle using a NASA Get-Away-Special (GAS) canister. The design is based upon the use of a new extended GAS canister and a low profile launch mechanism. The satellite is cylindrical. measuring 19 inches in diameter and 35 inches long. The maximum vehicle weight is 250 pounds, of which 50 pounds is dedicated to user payloads. The remaining 200 pounds encompasses the satellite structure and support components. which include a hydrazine propulsion system. a 75 watt solar power system an s-band telemetry transmitter and receiver, a 12 megabyte data storage unit and a 16 bit system microprocessor. Active nutation control techniques are employed for spin stabilization about the longitudinal axis. Using the hydrazine propulsion system. circular orbits as high as 835 nm or elliptic orbits with an apogee of 2200 nm are attainable. departing a nominal Shuttle orbit of 135 nm. Pointing accuracies of + /- two degrees are possible Total cost for the satellite and a GAS launch will be approximately $1 million dollars

Radar cross section lectures

These notes were developed while the author was on Sabbatical at NASA Ames Research Center during FY 1982. The lectures were presented to engineers and scientists at NASA Ames in March-April 1982. In August 1982, the RCS lectures were presented at General Dynamics Fort Worth Division

I. Experimental and theoretical studies on heterogenous diffusion flames. II. Spectroscopic studies of flames

Three topics concerned with heterogeneous diffusion flames are considered in Part I. Experiments have been conducted to determine the interference effects during burning for droplet arrays. The burning rate law applicable for single droplets has been found to be valid also for two-, five-, and nine-droplet arrays. A heterogeneous diffusion flame formed between liquid sodium and gaseous titanium tetrachloride was found to deposit small particles of titanium on the combustion chamber wall. The burning rate of liquid sodium, which is related to the rate of production of titanium, was determined experimentally. The scaling procedures developed by several authors for liquid-fuel rocket engines have been generalized. In these theoretical studies we have used the functional results derived in our investigations of droplet burning. The generalized analysis indicates that an attempt to maintain complete similarity on scaling results in contradictions. For this reason a program on selected scaling procedures is indicated. In Part II the apparent emission profiles of a turbulent flame are described in terms of a wrinkled laminar flame model. A distribution function, which assigns a probability for the occurrence of the laminar flame at a particular position within the turbulent flame brush, determines the apparent emission profiles. The inverse problem of determining the probability function from observed emission profiles has also been solved. It is possible to correlate the ratio of the apparent spectral intensities of two rotational lines with the equivalence ratio of a laminar flame. Assuming that this correlation applies also to other flames, we have determined the equivalence ratio in the critical zone of a reverse-jet stabilized flame in a duct. The equivalence ratio as a function of radial distance from the duct axis has also been measured. The results indicate that there appears to be a single equivalence ratio curve at blow-off, regardless of jet composition, provided the blow-off velocity is considered to be a function of critical zone equivalence ratio