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221.
Operational life improvement of SSME high-pressure turbopumps 总被引:1,自引:0,他引:1
The current Space Shuttle Main Engine Phase I engine has demonstrated excellent flight performance at power levels up to 104% of rated power level. Early certification testing at 109% power level showed the operational life of the high pressure turbopumps to be limited. A development program, Phase II, has been under way since 1983 to increase the operational life and provide additional margin. The history of the SSME Phase I engine and the design and results of the SSME Phase II Program are presented. Operational life limits and high-maintenance areas of the high-pressure turbopumps are identified. The Phase II design improvements, supporting analyses, and test results are described. The formal certification test program is discussed. Modifications have been made to the high-pressure fuel turbopump to reduce turbine operating temperature, to extend the life of the first- and second-stage turbine blades, and to reduce sheet metal maintenance. Modifications have been made to the high-pressure oxidizer turbopump to improve bearing life and to eliminate subsynchronous whirl. These are discussed in detail, as is the design and use of special instrumentation to provide for rapid evaluation of merit. 相似文献
222.
Space exploration into the twenty-first century is contingent upon the ability of states to forge an appropriate vehicle for international cooperation. A theoretical framework that explains international cooperation in space exploration is proposed. This framework encompasses scientific, technological, political, and economic initial conditions, state and nonstate political actors, and models of cooperation that explain how initial conditions and actors interact to realize cooperative outcomes. It is hypothesized that the prevailing initial conditions favor certain political actors over others which, in turn, promote a specific model of cooperation. Cooperative policy outcomes are examined and assessed vis-à-vis case studies of cooperation in space exploration. On this basis, policy recommendations that engender effective cooperative outcomes in space exploration are suggested. 相似文献
223.
NASA's proposed roadmap for robotic Mars exploration over the next decade is influenced by science goals, technology needs and budgetary considerations. These requirements could introduce potential changes to the succession of missions, resulting in both technology feed forward and heritage. For long duration robotic surface missions at locations, where solar power generation is not feasible or limited, Radioisotope Power Systems (RPS) could be considered. Thus, RPSs could provide enabling power technologies for some of these missions, covering a power range from 10s of milliwatts to potentially a kilowatt or even higher. Currently, NASA and DoE with their industry partners are developing two RPSs, both generating about 110 W(e) at BOL. These systems will be made available as early as 2009. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG)—with static power conversion—was down-selected as a potential power source for the MSL mission. Development of small-RPSs is in a planning stage by NASA and DoE; potentially targeting both the 10s of milliwatts and 10s of watts power ranges. If developed, Radioisotope Heat Unit (RHU) based systems—generating 10s to 100s of milliwatts—could power small adjunct elements on larger missions, while the GPHS module-based systems—each generating 10s of watts—could be stacked to provide the required power levels on MER class surface assets. MMRTGs and Stirling Radioisotope Generators (SRGs) could power MSL class or larger missions. Advanced Radioisotope Power Systems (ARPS) with higher specific powers and increased power conversion efficiencies could enhance or even enable missions towards the second half of the next decade. This study examines the available power system options and power selection strategies in line with the proposed mission lineup, and identifies the benefits and utility of the various options for each of the next decade launch opportunities. 相似文献
224.
The technology of gallium arsenide field-effect transistors has advanced to the point where these devices can serve to replace traveling wave tubes in spaceborne communication transponders.This paper describes interim results of a C-band FET amplifier which is currently being developed by RCA for INTELSAT. The FETA is designed to provide a 6-W output with an efficiency greater than 25%, and a backed-off 1.5-W output level with low distortion and efficiency of 13%.The third order intermodulation () of a FETA at saturation is typically 15 dB as compared to 10 dB for a TWTA. At 10 dB input power back-off the improves to 24 dB while that of a TWTA is only 16 dB.We fabricated a breadboard 5-W FETA which demonstrates that a linear operation can be achieved at an output level of 1.5 W with 10% efficiency. By contrast the efficiency of a typical 5 W TWTA in the same linear region is no greater than 3–5%. 相似文献
225.
Segura A Krelove K Kasting JF Sommerlatt D Meadows V Crisp D Cohen M Mlawer E 《Astrobiology》2003,3(4):689-708
Coupled radiative-convective/photochemical modeling was performed for Earth-like planets orbiting different types of stars (the Sun as a G2V, an F2V, and a K2V star). O(2) concentrations between 1 and 10(-5) times the present atmospheric level (PAL) were simulated. The results were used to calculate visible/near-IR and thermal-IR spectra, along with surface UV fluxes and relative dose rates for erythema and DNA damage. For the spectral resolution and sensitivity currently planned for the first generation of terrestrial planet detection and characterization missions, we find that O(2) should be observable remotely in the visible for atmospheres containing at least 10(-2) PAL of O(2). O(3) should be visible in the thermal-IR for atmospheres containing at least 10(-3) PAL of O(2). CH(4) is not expected to be observable in 1 PAL O(2) atmospheres like that of modern Earth, but it might be observable at thermal-IR wavelengths in "mid-Proterozoic-type" atmospheres containing approximately 10(-1) PAL of O(2). Thus, the simultaneous detection of both O(3) and CH(4) - considered to be a reliable indication of life - is within the realm of possibility. High-O(2) planets orbiting K2V and F2V stars are both better protected from surface UV radiation than is modern Earth. For the F2V case the high intrinsic UV luminosity of the star is more than offset by the much thicker ozone layer. At O(2) levels below approximately 10(-2) PAL, planets around all three types of stars are subject to high surface UV fluxes, with the F2V planet exhibiting the most biologically dangerous radiation environment. Thus, while advanced life is theoretically possible on high-O(2) planets around F stars, it is not obvious that it would evolve as it did on Earth. 相似文献
226.
Space education is a discipline that has evolved at an unprecedented rate over the past 25 years. Although program proceedings, research literature, and historical documentation have captured fragmented pieces of information about student space experiments, the field lacks a valid comprehensive study that measures the educational impact of sounding rockets, Skylab, Ariane, AMSAT, and Space Shuttle. The lack of this information is a problem for space educators worldwide which led to a national study with classroom teachers. Student flown experiments continue to offer a unique experiential approach to teach students thinking and reasoning skills that are imperative in the current international competitive environment in which they live and will work. Understanding the history as well as the current status and educational spin-offs of these experimental programs strengthens the teaching capacity of educators throughout the world to develop problem solving skills and various higher mental processes in the schools. These skills and processes enable students to use their knowledge more effectively and efficiently long after they leave the classroom. This paper focuses on student space experiments as a means of motivating students to meet this educational goal successfully. 相似文献
227.
Blinn John C. Campbell James P. 《IEEE transactions on aerospace and electronic systems》1966,(5):585-590
This paper discusses the results of an analytic study of the feasibility of using microwave radiometry as a technique for navigation data sensing in Army aircraft. The study included a review of Army aircraft characteristics and navigation requirements. Various means of sensing passively aircraft velocity, altitude, and velocity-altitude ratio were considered. While there appears to be no practical method for direct measurement of either velocity or altitude separately, it does appear possible to measure velocity-altitude ratio by comparing radiometric signals received from the terrain along the aircraft ground track. When combined with a radar altimeter, such a sensor could yield navigation data compatible with Army aircraft requirements. Microwave radiometry may also be the basis for direction sensing (to known landmarks) in high-flying aircraft or satellites. 相似文献
228.
229.
The successful development of expendable instruments in oceanography is certainly one of the most exciting advances in the rapidly evolving technology of oceanography. It appears that microelectronics may be especially well qualified in this field. The economics of ship operations and expediency tend to dictate this new development. 相似文献
230.
Anderson Gorden F. Kelly James G. 《IEEE transactions on aerospace and electronic systems》1967,(4):613-622
An experimental method applying microwave techniques to obtain continuous measurement of both the shock and contact discontinuities bounding an air plasma generated in a cylindrical hypersonic shock tube is developed. X-band microwave signals excited in the TE11 mode reflect from the moving shock and contact surfaces. The resulting FM interference pattern is demodulated, yielding continuous velocity versus time data. Results depicting subtle detail of velocity behavior, particularly of the shock front, were obtained over a shock Mach number range of 9 to 13. 相似文献