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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Long term cryogenic storage system integration

Investigations have revealed significant increases in performance when a reliquefier and solar shield in conjunction with a zero-gravity vapor vent system are utilized. Application of a reliquefier and solar shield in long term deep space missions may effect a 60% reduction in propellant loss, compared to that associated with the vapor vent system only. Significant improvements in storage system performance are possible for low earth orbit applicatons; for the typical system that was evaluated, system performance gains were realized for mission durations exceeding 7 days. Spherical solar shields are generally not competitive for low earth orbit applications.

Stonemetz, R. E.↗
NASA NTRS2001

Radiation transport modeling and assessment to better predict radiation exposure, dose, and toxicological effects to human organs on long duration space flights

NASA is very interested in improving its ability to monitor and forecast the radiation levels that pose a health risk to space-walking astronauts as they construct the International Space Station and astronauts that will participate in long-term and deep-space missions. Human exploratory missions to the moon and Mars within the next quarter century, will expose crews to transient radiation from solar particle events which include high-energy galactic cosmic rays and high-energy protons. Because the radiation levels in space are high and solar activity is presently unpredictable, adequate shielding is needed to minimize the deleterious health effects of exposure to radiation. Today, numerous models have been developed and used to predict radiation exposure. Such a model is the Space Environment Information Systems (SPENVIS) modeling program, developed by the Belgian Institute for Space Aeronautics. SPENVIS, which has been assessed to be an excellent tool in characterizing the radiation environment for microelectronics and investigating orbital debris, is being evaluated for its usefulness with determining the dose and dose-equivalent for human exposure. Thus far. the calculations for dose-depth relations under varying shielding conditions have been in agreement with calculations done using HZETRN and PDOSE, which are well-known and widely used models for characterizing the environments for human exploratory missions. There is disagreement when assessing the impact of secondary radiation particles since SPENVIS does a crude estimation of the secondary radiation particles when calculating LET versus Flux. SPENVIS was used to model dose-depth relations for the blood-forming organs. Radiation sickness and cancer are life-threatening consequences resulting from radiation exposure. In space. exposure to radiation generally includes all of the critical organs. Biological and toxicological impacts have been included for discussion along with alternative risk mitigation methods--shielding and anti-carcinogens. c 2001. Elsevier Science Ltd. All rights reserved.

STS-91 Shuttle Project↗
NASA NTRS1992

Composite materials microstructure for radiation shielding

Shielding against radiation is a concern for applications on earth, in space, and on extraterrestrial surfaces. On earth EMI is an important factor, while in space and on extraterrestrial surfaces particle (high charge-Z and high energy-E) radiation is a critical issue. Conventional metallic materials currently used for EMI shielding incur large weight penalties. To overcome this weight penalty, ultra-lightweight composite materials utilizing fillers ranging from carbon microballoons to silver coated ceramic microballoons are proposed. The crucial shielding requirement is conductivity of the constituent materials, while the hollow microballoon geometry is utilized to yield low weight. Methods of processing and composition effects are examined and these results are compared to the effectiveness of varying the conductive microballoon material. The resulting ultralightweight materials, developed for EMI shielding, can be tailored through the application of the understanding of the relative effects of variables such as those tested. Initial experimental results reveal that these tailored ultralightweight composite materials are superior to traditional aluminum shielding at only a small fraction of the weight.

Radford, Donald W.↗
NASA NTRS1972

Impact of radiation dose on nuclear shuttle configuration

The impact of nuclear radiation (from the NERVA propulsion system) on the selection of a reference configuration for each of two classes of the reusable nuclear shuttle is considered. One class was characterized by a single propellant tank, the shape of whose bottom was found to have a pronounced effect on crew radiation levels and associated shield weight requirements. A trade study of shield weight versus structural weight indicated that the minimum-weight configuration for this class had a tank bottom in the shape of a frustum of a 10 deg-half-angle cone. A hybrid version of this configuration was found to affect crew radiation levels in substantially the same manner. The other class of RNS consisted of a propulsion module and eight propellant modules. Radiation analyses of various module arrangements led to a design configuration with no external shield requirements.

Goetz, C. A.↗
NASA NTRS1972

Preliminary noise tests of the engine-over-the-wing concept. i: 30 deg - 60 deg flap position

The results of preliminary acoustic tests of the engine over the wing concept are summarized. The tests were conducted with a small wing section model (32 cm chord) having two flaps set at the landing position, which is 30 and 60 deg respectively. The engine exhaust was simulated by an air jet from a convergent nozzle having a nominal diameter of 5.1 centimeters. Factors investigated for their effect on noise include nozzle location, wing shielding, flap leakage, nozzle shape, exhaust deflectors, and internally generated exhaust noise.

Reshotko, M.↗
NASA NTRS1972

Silica reinforcement and char reactions in the Apollo heat shield.

Reactions of the silica reinforcement fiber and ablation char of the Apollo heat shield have been investigated by laboratory tests in an arc image furnace (at temperature levels up to 5000 R, pressures up to 0.7 atm, and heat flux similar to reentry) and by an actual reentry test. Microchemical analyses and X-ray diffraction studies have been made to determine the presence of SiC formation in the char. Experimental data and analytical predictions of thermal and density profiles have been compared for the ablation of virgin heat shield and precharred materials to determine the effects of SiC formation on ablation performance. In all analyses, general agreement was found between chemical composition and the thermal predictions for laboratory tests and reentry materials. In all ablated materials, SiC was formed in the front surface of the char. The highest SiC content found was 58% by weight and found in a high-pressure environment. The SiC formed was found to act as a heat sink in the ablation process and can lower the front surface temperature by 300 R.

Cagliostro, D. E.↗
NASA NTRS1974

Development of a high Reynolds number quiet tunnel for transition research

High noise levels in conventional supersonic and hypersonic wind tunnels prevent further advances in transition research. Recent data confirm previous results that transition is dominated by tunnel noise when the rms pressure intensities exceed about 1%. High facility noise levels also dominate fluctuating pressure loads under fully turbulent boundary layers. Recent data on the power spectra of surface pressures indicate that the basic structure of turbulent boundary layers may be modified by high facility noise levels. Experimental data for current techniques to control and reduce noise levels in supersonic and hypersonic wind tunnels by laminarization of nozzle wall boundary layers and by noise radiation shields are presented. These results and possible effects of Taylor-Gortler vortices observed in a nozzle wall boundary layer are used to predict the limits of quiet performance for a proposed 20-in. quiet tunnel.

Beckwith, I. E.↗
NASA NTRS1975

Evaluation of dispersion strengthened nickel-base alloy heat shields for space shuttle application

The design, fabrication, and testing of a full-size, full-scale TD Ni-20Cr heat shield test array in simulated mission environments is described along with the design and fabrication of two additional full-size, full-scale test arrays to be tested in flowing gas test facilities at the NASA Langley Research Center. Cost and reusability evaluations of TD Ni-20Cr heat shield systems are presented, and weight estimates of a TD Ni-20Cr heat shield system for use on a shuttle orbiter vehicle are made. Safe-line expectancy of a TD Ni-20Cr heat shield system is assessed. Non-destructive test techniques are evaluated to determine their effectiveness in quality assurance checks of TD Ni-20Cr components such as heat shields, heat shield supports, close-out panels, formed cover strips, and edge seals. Results of tests on a braze reinforced full-scale, subsize panel are included. Results show only minor structural degradation in the main TD Ni-20Cr heat shields of the test array during simulated mission test cycles.

Johnson, R., Jr.↗
NASA NTRS1976

Effect of probe configuration on radiative heating during Jovian entry

The radiative heating to the probe's surface and the effects of the recession of the heat shield caused by this heating are analyzed for five initial probe configurations for a Jovian entry. The initial configurations are spherically capped, conical bodies and hyperboloids. The results show that severe blunting of the nose region occurs for all configurations due to ablation of the heat shield caused by the large radiative heating rates. Recession at the nose region can possibly cause a concavity at the stagnation point. Furthermore, the recession of the heat shield, especially for the spherically capped, conical bodies, will be underpredicted if the change in the probe's shape during the entry is neglected in an analysis.

Sutton, K.↗
NASA NTRS1986

Use of chemical explosives for emergency solar flare shelter construction and other excavations on the Martian surface

The necessity to shelter people on the Martian surface from solar flare particles at short notice and the need for long-term habitats with thick cosmic ray shielding suggests that explosives could be used effectively for excavation of such structures. Modern insensitive high explosives are safe, efficient, and reliable for rock breakage and excavation. Extensive Earth-bound experience leads us to propose several strategies for explosively-constructed shelters based on tunneling, cratering, and rock casting techniques.

Richard D Dick↗
NASA NTRS1991

Pellet bed reactor for nuclear propelled vehicles: Part 2: Missions and vehicle integration trades

Mission and vehicle integration tradeoffs involving the use of the pellet bed reactor (PBR) for nuclear powered vehicles is discussed, with much of the information being given in viewgraph form. Information is given on propellant tank geometries, shield weight requirements for conventional tank configurations, effective specific impulse, radiation mapping, radiation dose rate after shutdown, space transfer vehicle design data, a Mars mission summary, sample pellet bed nuclear orbit transfer vehicle mass breakdown, and payload fraction vs. velocity increment.

Haloulakos, V. E.↗
NASA NTRS1995

Global electric field determination in the Earth's outer magnetosphere using energetic charged particles

Although many properties of the Earth's magnetosphere have been measured and quantified in the past 30 years since it was discovered, one fundamental measurement (for zeroth order MHD equilibrium) has been made infrequently and with poor spatial coverage - the global electric field. This oversight is due in part to the neglect of theorists. However, there is renewed interest in the convection electric field because it is now realized to be central to many magnetospheric processes, including the global MHD equilibrium, reconnection rates, Region 2 Birkeland currents, magnetosphere ionosphere coupling, ring current and radiation belt transport, substorm injections, and several acceleration mechanisms. Unfortunately the standard experimental methods have not been able to synthesize a global field (excepting the pioneering work of McIlwain's geostationary models) and we are left with an overly simplistic theoretical field, the Volland-Stern electric field model. Single point measurements of the plasmapause were used to infer the appropriate amplitudes of this model, parameterized by K(sub p). Although this result was never intended to be the definitive electric field model, it has gone nearly unchanged for 20 years. The analysis of current data sets requires a great deal more accuracy than can be provided by the Volland-Stern model. The variability of electric field shielding has not been properly addressed although effects of penetrating magnetospheric electric fields has been seen in mid-and low-latitude ionospheric data sets. The growing interest in substorm dynamics also requires a much better assessment of the electric fields responsible for particle injections. Thus we proposed and developed algorithms for extracting electric fields from particle data taken in the Earth's magnetosphere. As a test of the effectiveness of these new techniques, we analyzed data taken by the AMPTE/CCE spacecraft in equatorial orbit from 1984 to 1989.

Eastman, Timothy E.↗
NASA NTRS2005

Passive Stability on an Entry Vehicle to Enhance Crew Survival

The most desirable crew survival feature for an entry vehicle is probably a full coverage escape system. With full coverage escape, crew survival is maintained for a wide range of failures by the allowing the crew to escape from the failed vehicle and performing the entry to touchdown flight phase in an alternative system. However, there are considerable challenges in providing a separate entry capability, and for some programs, requiring full coverage escape could result in program cancellation. An alternative means of providing for crew survival if the flight control system fails is to design a return vehicle that can enter without active attitude control. A study was performed to assess the feasibility of performing a totally passive entry. Lift over drag has a major impact on performing a passive entry, so a parametric of three typical lift over drag concepts was performed. First an assessment of historical entry vehicles was completed. Second an assessment of end of mission entry trajectories and entry trajectories initiated from ascent abort profiles were made. Trajectories for a wide array of pitch, yaw, and roll rates were made. Third, six-degree-of freedom analyses of the entry were performed. FOP a truly passive return, the entry vehicle must trim in only the heat shield forward orientation. An assessment of the effect of center of gravity placement to achieve this orientation was made.

Deger, Daniel J.↗
NASA NTRS2003

Functionally Graded Nanophase Beryllium/Carbon Composites

Beryllium, beryllium alloys, beryllium carbide, and carbon are the ingredients of a class of nanophase Be/Be2C/C composite materials that can be formulated and functionally graded to suit a variety of applications. In a typical case, such a composite consists of a first layer of either pure beryllium or a beryllium alloy, a second layer of B2C, and a third layer of nanophase sintered carbon derived from fullerenes and nanotubes. The three layers are interconnected through interpenetrating spongelike structures. These Be/Be2C/C composite materials are similar to Co/WC/diamond functionally graded composite materials, except that (1) W and Co are replaced by Be and alloys thereof and (2) diamond is replaced by sintered carbon derived from fullerenes and nanotubes. (Optionally, one could form a Be/Be2C/diamond composite.) Because Be is lighter than W and Co, the present Be/Be2C/C composites weigh less than do the corresponding Co/WC/diamond composites. The nanophase carbon is almost as hard as diamond. WC/Co is the toughest material. It is widely used for drilling, digging, and machining. However, the fact that W is a heavy element (that is, has high atomic mass and mass density) makes W unattractive for applications in which weight is a severe disadvantage. Be is the lightest tough element, but its toughness is less than that of WC/Co alloy. Be strengthened by nanophase carbon is much tougher than pure or alloy Be. The nanophase carbon has an unsurpassed strength-to-weight ratio. The Be/Be2C/C composite materials are especially attractive for terrestrial and aerospace applications in which there are requirements for light weight along with the high strength and toughness of the denser Co/WC/diamond materials. These materials could be incorporated into diverse components, including cutting tools, bearings, rocket nozzles, and shields. Moreover, because Be and C are effective as neutron moderators, Be/Be2C/C composites could be attractive for some nuclear applications.

Voronov, Oleg A.↗
NASA NTRS2003

Functionally Graded Nanophase Beryllium/Carbon Composites

Beryllium, beryllium alloys, beryllium carbide, and carbon are the ingredients of a class of nanophase Be/Be2C/C composite materials that can be formulated and functionally graded to suit a variety of applications. In a typical case, such a composite consists of a first layer of either pure beryllium or a beryllium alloy, a second layer of B2C, and a third layer of nanophase sintered carbon derived from fullerenes and nanotubes. The three layers are interconnected through interpenetrating spongelike structures. These Be/Be2C/C composite materials are similar to Co/WC/diamond functionally graded composite materials, except that (1) W and Co are replaced by Be and alloys thereof and (2) diamond is replaced by sintered carbon derived from fullerenes and nanotubes. (Optionally, one could form a Be/Be2C/diamond composite.) Because Be is lighter than W and Co, the present Be/Be2C/C composites weigh less than do the corresponding Co/WC/diamond composites. The nanophase carbon is almost as hard as diamond. WC/Co is the toughest material. It is widely used for drilling, digging, and machining. However, the fact that W is a heavy element (that is, has high atomic mass and mass density) makes W unattractive for applications in which weight is a severe disadvantage. Be is the lightest tough element, but its toughness is less than that of WC/Co alloy. Be strengthened by nanophase carbon is much tougher than pure or alloy Be. The nanophase carbon has an unsurpassed strength-to-weight ratio. The Be/Be2C/C composite materials are especially attractive for terrestrial and aerospace applications in which there are requirements for light weight along with the high strength and toughness of the denser Co/WC/diamond materials. These materials could be incorporated into diverse components, including cutting tools, bearings, rocket nozzles, and shields. Moreover, because Be and C are effective as neutron moderators, Be/Be2C/C composites could be attractive for some nuclear applications.

Choi, Michael K.↗
NASA NTRS1992

CRRES microelectronic test chip orbital data. II

Data from a MOSFET matrix on two JPL (CIT Jet Propulsion Laboratory) CRRES (Combined Release and Radiation Effects Satellite) chips, each behind different amounts of shielding, are presented. Space damage factors are nearly identical to ground test values for pMOSFETs. The results from neighboring rows of MOSFETs show similar radiation degradation. The SRD (Space Radiation Dosimeter) is used to measure the total dose accumulated by the JPL chips. A parameter extraction algorithm that does not underestimate threshold voltage shifts is used. Temperature effects are removed from the MOSFET data.

Soli, G. A.↗