The angular response of LWIR telescopes is measured to verify predicted off-axis rejection (OAR) performance. The data are also useful to guide any necessary modifications for performance improvement. The off-axis response must be 9 to 12 bels (orders of magnitude) below the on-axis maximum response to reject the influence of strong off-axis sources. Collimated lasers serve as the strong, highly directional test sources required in the characterization measurements. Carefully used optical attenuators permit the application of detectors which can normally cover only 4 or 5 bels. This paper describes the apparatus and methods employed in measuring the OAR of specific telescopes at wavelengths of 1. 06 and 10. 6 4m. Illustrative data are given for telescopes built by Honeywell under the sponsorship of Air Force Geophysical Laboratories.

Two integrating spheres have been developed to act as in interface between a monochromator and instru-ments under calibration. The spheres are designed to provide a diffuse, extended source and attenuate the signal sufficiently so as not to saturate sensitive instruments. One sphere is coated with a BaSO4 paint which provides a diffuse, highly reflecting surface in the 0.3 to 1.5μm spectral region. This sphere is operated at ambient temperatures. The second sphere is peened to create a diffuse surface and then is coated with copper to obtain a high reflectivity fran 1.5 to 8μm. The latter sphere is cooled to liquid nitrogen temperatures to eliminate self radiation in the spectral region of interest. Comparisons between observed spectral performance and theoretically predicted results are presented, and the gonianetric characteristics are described.

The near-axis scatter of infrared (10.6 µm) energy from high reflectivity metal mirrors is described. Effects of contamination on the scatter are described. Methods of evaluating various forms of contamination are presented and selected data are presented. Finally, the recording techniques for surface characteristics photographically are described along with a typical photograph of a large aspheric mirror.

The radiant efflux from a cylindrical cavity having nonisothermal bounding surfaces is determined by solving a problem of combined radiation and conduction. The cavity may be visualized as a circular hole machined into the exposed face of a solid, with the solid being heated uniformly from behind. A two-dimensional temperature distribution is set up in the solid owing to radiative heat losses from the cavity and from the exposed face of the solid. A solution method is employed whereby the radiation and conduction problems are dealt with successively. Results are obtained for parametric values of the cavity emittance and depth-radius ratio and of a group which fixes the axial temperature variation. The results indicate that the radiant efflux from the cavity increases with increasing values of the aforementioned parameters. The effect of the presence of the cavity is confined to a region of the solid whose depth and radius are, respectively, twice and four times the depth and radius of the cavity.

Technical Briefs Effect of Film Thickness on the Infrared Reflectance of Very Thin Metallic Films E. M. Sparrow, E. M. Sparrow Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minn. Search for other works by this author on: This Site PubMed Google Scholar R. P. Heinisch, R. P. Heinisch Honeywell, Inc., St. Paul, Minn. Search for other works by this author on: This Site PubMed Google Scholar K. K. Tien K. K. Tien Honeywell, Inc., St. Paul, Minn. Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information E. M. Sparrow Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minn. R. P. Heinisch Honeywell, Inc., St. Paul, Minn. K. K. Tien Honeywell, Inc., St. Paul, Minn. J. Heat Transfer. Nov 1973, 95(4): 534-535 (2 pages) https://doi.org/10.1115/1.3450102 Published Online: November 1, 1973 Article history Received: September 21, 1972 Online: August 11, 2010

Analytical results are presented for radiation interchange in cavities having nonisothermal walls in order to implement experimental methods for determining the emittance of solids. The cavity may be visualized as a hole that is machined into the exposed face of a solid whose emittance is to be determined, with the solid being heated uniformly from behind. The results were obtained by solving the coupled problems of radiant transport in the cavity and two-dimensional heat conduction in the solid that bounds the cavity. From the solutions, results for the radiant flux leaving the base surface of the cavity are presented as a function of the emittance, of the depth-radius ratio of the cavity, and of a temperature gradient parameter. This information can be used in conjunction with measurements of the radiances of the base surface and the exposed face of the solid to determine the emittance. A method is also described for simultaneously determining both the emittance of the material and the temperature of the exposed face.

Monte Carlo ray tracing (MCRT) methods are important for solving the radiative transfer equation. However, the particular ray-tracing procedure used has a significant impact on the calculational performance. In this paper, we analyze and compare the performances of MCRT pathlength (PL) and collision-based (CB) methods for different surface and medium parameters and different degrees of uniformity. The results show that in a gray medium and with a radiation heat balance system, the PL method is superior when the surface emissivity is less than 0.15 for surface elements, and when the mean optical thickness per element (MOTE) is small and the emissivity is large for space elements; otherwise, the CB method is superior. Also the overall performance of the PL method is better than that of the CB method. However, PL method is more sensitive to non-uniformity of medium parameters than the CB method, and that the PL method is more sensitive to uniformity of the scattering coefficient than to the absorption coefficient. In addition, for a gray body and uniform optical parameters, reducing the number of grids improves the performance of the MCRT. And the performance index of the PL method is the best when the cutoff level of energy beam tracking is 10–7 and 10–6 for surface and space elements respectively. These quantitative conclusions will help in selecting suitable MCRT methods for engineering calculations, based on the physical properties of materials and conditions.

An analysis is made to determine how the radiant energy streaming from an isothermal-wall conical cavity is affected by a baffle that partially obstructs the cavity opening. Consideration is given both to baffles that are maintained at the same temperature as the cavity wall (emitting baffles) and to baffles that are cooled to a temperature well below that of the wall (non-emitting baffles). The cone-apex angle and the emissivity of the cavity wall are varied parametrically. The results are obtained by employing a newly devised Monte Carlo method, the application of which is described in detail. The presentation of results is made in terms of the apparent emissivity, which is the ratio of the radiant energy actually streaming from the cavity to the radiant energy emitted by a black surface whose size is the same as the baffle aperture. It is found that the apparent emissivity increases as more and more of the cavity opening is blocked by the baffle. The increases of apparent emissivity are greater when the baffle is emitting than when the baffle is non-emitting.

Collection efficiencies are determined for integrating hemi-ellipsoids and integrating hemispheres used in connection with radiation surface property measurements. The Monte Carlo method is employed to simulate the trajectories of photon bundles which leave a source of radiation and are collected and focused onto (or adjacent to) a receiver. The radiation source may be a test surface whose reflectance or emittance is to be determined, while the receiver may be a radiation detector. Results are obtained for a wide range of source and receiver sizes and positions. The results show that in the case of the hemi-ellipsoid, the attainment of good collection efficiency requires that the radius of the receiver be at least twice that of the source. The hemisphere is, in general, a less efficient collector than the hemi-ellipsoid When the source and receiver are only slightly displaced from the center of the base plane circle of the hemisphere, then the two collectors are comparably efficient.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

A technique is described for measuring near-axis scatter of infrared (10.6 μm) energy from high-reflectivity metal mirrors. Typical scatter data are presented for several samples. The data are applicable to optical instruments such as the Lyot Coronagraph. The measurement apparatus is described in detail. Surface roughness and contamination are considered. The preparation of the surfaces is discussed in detail.

Diffraction has been numerically modeled using a Monte Carlo statistical analysis. The Heisenberg uncertainty principle has been applied to attain this goal. Example solutions have been studied and are presented to illustrate the utility and accuracy of the technique.

Spacecraft windows optical degradation from contamination with condensed particles, presenting light scatter measurement results

Experimental results, obtained using photometry, are obtained to assess the attenuating capability of three baffle geometries. The data obtained include the effect of sensor location in the baffle aperture as well as the type of coating on baffle surfaces. The baffles attenuate best at large viewing angles with surfaces coated with black paint.

A measurement technique for determining the directional spectral emittance of blackbody cavities was developed and subsequently applied to several specific cavity geometries. The emittance was deduced from cavity reflectance measurements performed with a laser energy source (10.6 micro) and an integrating hemi-ellipsoid. It was demonstrated that this technique is capable of providing highly precise emittance values with a resolution of five significant figures for high emittance cavities. The emittances of four specific cavity configurations were measured. One of these, an elongated off-axis cone with an entrance lip, gave emittances greater than 0.99999 when coated with nominally specularly reflecting or nominally diffusely reflecting black paints. The emittances of this cavity were on the order of 0.95 in the absence of a coating, the actual emittances of the cavity surfaces being approximately 0.05. Three other cavities with length-to-diameter ratios of three were also studied. These include a cylinder, cone, and off-axis cone having internal surfaces which were coated with black paints. Although the measured emittances were not so high as those for the 12.45-L/D off-axis cone, the level of blackness that was determined is sufficient for most engineering applications.

Predicting star magnitude visible through contaminated spacecraft window by naked eye or sextant