Analysis of Thermal-Protection Systems for Space-Vehicle Cryogenic-Propellant Tanks

Analytical techniques are presented that permit the calculation of heat-transfer rates with various thermal-protection systems for liquid-cryogenic-propellant tanks subjected to on-board, solar, and planetary heat fluxes. The thermal-protection systems considered include using closely spaced reflective surfaces (foils) and widely spaced reflective surfaces (shadow shields), insulation, arrangement of vehicle components, orientation with respect to radiant heating sources, and coatings for the control of solar absorptivity. The effectiveness of these thermal-protection systems in reducing propellant heating is shown both for ideal heat-transfer models and for a simplified hydrogen-oxygen terminal stage on a Mars mission. The proper orientation of a space-vehicle cryogenic tank with respect to the Sun is one of the more beneficial methods of reducing the heating effect of solar flux. Shadow shields can be extremely effective in reducing the propellant heating due to both solar and on-board fluxes. However, low-altitude planet orbits can result in high propellant heating rates due to planetary radiation reflected from the shields. For low-altitude orbits of more than a few days, foils appear to be desirable for all cryogenic-tank surfaces. Foils are also effective in reducing the on-board heating. A choice of shadow shields or foils cannot be made until a particular vehicle and a particular mission are chosen. The thermal conductivity of insulation materials would have to be lower by about two orders of magnitude with no increase in density before insulation could compete with reflective surfaces for use in long-duration thermal protection of cryogenic tanks in space. To demonstrate the application of the methods devised, thermal-protection systems are developed for a hydrogen-oxygen terminal stage for typical Mars missions

Two-Dimensional Laser-Doppler Velocimetry in Turbulent Flows

Localized measurement of the velocity of flow In fluids may be accomplished by detecting the Doppler shift In frequency from coherent, monochromatic light scattered from micrometer sized contaminant particles within the flow. The versatility of applications of this technique, first used several years ago, has been expanded by recent research. The basic geometry of measurement, in which the scattered energy is recombined with light energy at the original frequency on the face of the photocathode of a photomultiplier tube, can be rearranged in many alternative configurations to meet the needs of the experimenter. By using a single laser, additional arrangements are possible for obtaining two- or three-dimensional measurements of velocity components. Several different velocimeters are described for making two-dimensional flow measurements, including both backscatter and forward scatter systems. Effects of flow system geometries on capabilities for measuring specific components are investigated. Effects of laser beam polarization are discussed and conclusions reached on methods of optimizing signal strength in each of two orthogonal measurement systems. Results of the application of a two-dimensional measurement system used for obtaining velocity profiles in turbulent flow in a smooth walled four-inch diameter pipe are presented. Operating at a Reynolds number of about 1.1 x 106, relative turbulent intensities were measured in the axial direction and normal to that direction. Standard techniques were utilized. A second readout system was employed to make a measurement of this parameter without the requirement of adding scattering centers to the flow

Experimental Music in Black and White: The AACM in New York, 1970-1985

Since its founding on the virtually all-black South Side of Chicago in 1965, the African American musicians' collective known as the Association for the Advancement of Creative Musicians (AACM) has played an unusually prominent role in the development of American experimental music. The composite output of AACM members explores a wide range of methodologies, processes, and media. AACM musicians have developed new ideas about timbre, sound, collectivity, extended technique and instrumentation, performance practice, intermedia, the relationship of improvisation to composition, form, scores, computer music technologies, invented acoustic instruments, installations, and kinetic sculptures. In a 1973 article, two early AACM members, trumpeter John Shenoy Jackson and co-founder and pianist/composer Muhal Richard Abrams, asserted that, "The AACM intends to show how the disadvantaged and the disenfranchised can come together and determine their own strategies for political and economic freedom, thereby determining their own destinies" (Abrams and Jackson 1973:72). This optimistic declaration, based on notions of self-help as fundamental to racial uplift, cultural preservation, and spiritual rebirth, was in accord with many other challenges to traditional notions of order and authority that emerged in the wake of the Black Power Movement

Is the bang worth the buck? A RAID performance study

Expecting a high data delivery rate as well as data protection, the Lister Hill National Center for Biomedical Communications procured a RAID system to house image files for image delivery applications. A study was undertaken to determine the configuration of the RAID system that would provide for the fastest retrieval of image files. Average retrieval times with single and with concurrent users were measured for several stripe widths and several numbers of disks for RAID levels 0, 0+1 and 5. These are compared to each other and to average retrieval times for non-RAID configurations of the same hardware. Although the study in ongoing, a few conclusions have emerged regarding the tradeoffs among the different configurations with respect to file retrieval speed and cost

THE MEANING OF HEIRS IN WILLSA SUGGESTION IN LEGAL METHOD

A major task of the lawyer is the prediction of judicial action. No less than a quarter of a century ago Justice Holmes referred to the law as a body of systematized prediction. Today legal scholars are not content to base their predictions solely upon the body of rules announced in judicial opinions. By means of elaborate fact studies they have sought to ascertain how rules of law actually function in society. Not only have these studies dealt with problems of procedure and the administration of courts, they have also invaded the fields of commercial and property law. Among such studies may be named those of Moore and Sussman in banking practices, those of Powell and Looker in decedents\u27 estates, and those of Douglas in bankruptcy