SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Computer code was developed to determine radioactive emission rates of nuclear fuels. Code is basically written for two different source geometries; however, unfolding routine can be executed for other source geometries.
A new reference design was prepared for the 5 kW(e) thermionic power supply. The safety equipment in this design is a passive containment system which does not rely on the operation of any mechanisms such as a launch escape rocket or deployment of parachutes. It includes: (1) a blast shield to protect against the explosion of the launch vehicle; (2) a combination of refractory thermal insulation and heat storage material to protect against a sustained launch pad fire; (3) a reentry body with a spherical nose and a large conical flare at the aft end to stabilize the reentry attitude and lower the terminal velocity in air; (4) composite graphite thermal protection to sustain the reentry heat pulse; (5) crushable honeycomb behind the nose to limit the deceleration of the radioisotope source due to impact on land at terminal velocity; (6) a double-walled secondary containment vessel surrounding the isotopic capsules; (7) neutron shielding to reduce external dose rates; (8) an auxiliary cooling system employing redundant heat pipes to remove the radioactive decay heat from the heat source and reject it to the surroundings or to a forced convection loop.
Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side. Further the same devices were used to obtain useful astronomical data during the return to earth.
The detection and measurement of the cosmic ray charge spectrum for nuclei heavier than iron (Fe, Z = 26) are discussed. These trans-iron nuclei are of great interest for several reasons. They promise to be one of the more sensitive clocks for use in determining the age of cosmic rays. The discovery of radioactive nuclides and their decay products in the primary flux, will allow an estimation of the elapsed time since these cosmic rays were synthesized. In addition, the relatively short interaction length of the very heavy trans-iron particles makes their relative abundance a source of information regarding the amount of interstellar matter that they had to traverse to reach the earth. A study of the trans-iron cosmic rays may provide clues as to the very processes of nucleosyntheses by which the bulk of the trans-iron nuclei in the universe are produced. This in turn may shed light on the mechanics of the supernova, which is postulated to be the major source of all cosmic rays. Finally, trans-iron cosmic ray experiments may demonstrate the existence of the recently postulated super-heavy nuclei.
Solar wind gases, cosmogenic gases from high energy spallation reactions from soxmic rays, and radiogenic gases from decay of radioactive potassium and from uranium and thorium isotopes were analyzed in lunar materials. Details are presented on two aspects of the studies: (1) The spatial distribution of Ar-40/Ar-38 ages in lunar breccia 14301 was determined. The ages of clasts within this breccia are 3.68 + or - 0.09 and 2.9 + or - 0.3 x 10 to the 9th power years. Parentless radiogenic Ar-40 exists within the fine-grained matrix. (2) The distribution of helium, neon, and argon isotopes within Apollo 15 samples results primarily from fractionated solar wind gases, accompanied by small quantities of cosmogenic gases. Comparison of this Apollo 15 data with Kapoeta and Fayetteville meteorite and Apollo 12 and 14 data indicates that solar wind implantation followed by fractionation of the gases was primarily responsible for incorporation of original gas phase within solid bodies of the solar system.
A sweep gas facility has been used to measure the release rates of radioactive fission gases from small UN specimens irradiated to 8-percent burnup at high fission-rate densities. The measured release rates have been correlated with an equation whose terms correspond to direct recoil release, fission-enhanced diffusion, and atomic diffusion (a function of temperature). Release rates were found to increase linearly with burnups between 1.5 and 8 percent. Pore migration was observed after operation at 1550 K to over 6 percent burnup.
Consideration is given for 26 streams of meteors classified according to Ceplecha's discrete levels of beginning height, 13 of which are associated with known comets. Comet Biela produced in the Andromedids a double-peaked distribution (Classes A and C). Apparently no known comets produce a stream of Class B. Consideration of Whipple and Stefanik's model of an icy conglomerate nucleus with radioactive heating and redistribution of ice leads to association of Ceplecha's Class C with the residue of the ice-impregnated surface of a cometary nucleus after sublimation of the ices, and of Ceplecha's Class A with the core of a cometary nucleus. Class B meteoroids are then associated with less dense cores of smaller cometary nuclei that have lost their surfaces and are too small to have been observed. It is concluded that the density of Class A meteoroids (1.2 g/cu cm) is so close to that of Type 1 carbonaceous chondrites (2 g/cu cm) as to suggest that the latter come from old cores of very large nuclei of comets, an idea originally proposed by McCrosky and Ceplecha.
The measurement of energy spectrum of the diffuse component of cosmic X-ray flux made on the OSO-5 spacecraft is described. The contributions to the total counting rate of the actively shielded X-ray detector are considered in some detail and the techniques used to eliminate the non-cosmic components are described. Positive values for the cosmic flux are obtained in seven energy channels between 14 and 200 keV and two upper limits are obtained between 200 and 254 keV. The results can be fitted by a power law spectrum. A critical comparison is made with the OSO-3 results. Conclusions show that the reported break in the energy spectrum at 40 keV is probably produced by an erroneous correction for the radioactivity induced in the detector on each passage through the intense charged particle fluxes in the South Atlantic anomaly.
Soils of continental Antarctica are forming in one of the most severe terrestrial environments. Continuously low temperatures and the scarcity of water in the liquid state result in the development of desert-type soils. In an earlier experiment to determine the degree to which radioactive Na(Cl-36) would migrate from a shallow point source in permafrost, movement was observed. To confirm this result, a similar experiment involving (Na-22)Cl was conducted. Significantly less movement of the Na-22 ion was observed. Ionic movement in the unfrozen interfacial films at mineral surfaces in frozen ground is held to be important in chemical weathering in Antarctic soils.
A preliminary examination is reported of several special ways for space disposal of nuclear waste material which utilize the radioactive heat in the waste to assist in the propulsion for deep space trajectories. These include use of the wastes in a thermoelectric generator (RTG) which operates an electric propulsion device and a radioisotope - thermal thruster which uses hydrogen or ammonia as the propellant. These propulsive devices are compared to the space tug and the space tug/solar electric propulsion combination for disposal of waste on a solar system escape trajectory. Such comparisons indicate that the waste-RTG approach has considerable potential provided the combined specific mass of the waste container - RTG system does not exceed approximately 150 kg/kw sub e. Several exploratory numerical calculations have been made for high earth orbit and Earth escape destinations.
An analysis was made of prospects for gamma rays coming from two sources outside the solar system: (1) radioactive decay of fresh nuclear products to explosive nucleosynthesis, and (2) scattering of low energy cosmic rays. The former should be detectable and will provide a factual base for many suppositions about the site and history of nucleosynthesis. The latter may be detectable and, if so, will probably provide factual information about high-flux regions of cosmic radiation.
When high energy protons from solar proton events or trapped radiation belts impinge on spacecraft structures, secondary particles are emitted. The most pernicious secondaries, from either a biological or physical standpoint, are the cascade and evaporation neutrons because of their reaction with matter leading to radioactive materials in the spacecraft structures. Empirically determined cascade and evaporation neutron emission spectra for protons of energy between 20 and 500 MeV incident on all materials at or above carbon in mass number are presented.
The possible thermal history of the moon is investigated by means of theoretical models. The calculations include the effects of melting and time-dependent redistribution of radioactive heat sources. The known constraints can best be satisfied by a model which is characterized by relatively high initial temperatures close to the melting range; melting and, consequently, fractionation and redistribution of radionuclides would occur during the first 1.5 b.y. and would then be followed by an effective cooling process. Heat flow measurements on the lunar surface should permit a distinction between such a completely fractionated model and a nonfractionated model or a model with restricted fractionation in the outer few hundred kilometers.
The Rb-87/Sr-87 ages of many of the lunar rocks suggest that the fundamental differentiation took place 4.5 b.y. ago and that remelting occurred without exchange of the rubidium and strontium with the surroundings. The Apollo A rocks are an exception to this. They appear to have acquired rubidium without all of the Sr-87 produced during the first aeon. Also in the remelting about half of the radiogenic leads were lost to the surroundings by a vaporization process. We interpret these results to mean that remelting occured in a system that was nearly closed to the surroundings and that the high early concentrations of radioactive elements in highly insulating surroundings made this possible.
Huntress' formalism (1968) is used to calculate the angular correlation behavior for an ensemble of radioactive nuclei, each of which is bound to an asymmetric-top molecule. The calculation is carried out both in an extreme narrowing limit (rapid motion) and in an adiabatic limit (slow motion). The two limiting cases span nearly the whole range of rates of rotational reorientation. It is shown that the problem of internal rotation is formally identical to that of rotation of a symmetric-top molecule. The experimentally observable time-integrated anisotropy is plotted for several rates of internal rotational diffusion.
Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma-rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side.
Located in the Science Instrument Module of Apollo 15 and 16, the Alpha Particle Spectrometer was designed to detect and measure the energy of alpha particles emitted by the radon isotopes and their daughter products. The spectrometer sensor consisted of an array of totally depleted silicon surface barrier detectors. Biased amplifier and linear gate techniques were utilized to reduce resolution degradation, thereby permitting the use of a single 512 channel PHA. Sensor identification and in-flight radioactive calibration were incorporated to enhance data reduction.
The Apollo Lunar Surface Experiments Package (ALSEP) measures lunar physical and environmental characteristics and transmits the data to receiving stations on earth. The data are used to derive information on the composition and structure of the moon. The electrical power subsystem generates and conditions all the electrical power for operations of the ALSEP system. The power source for the ALSEP is the Systems for Nuclear Auxiliary Power (SNAP) Radioisotope Thermoelectric Generator (RTG). The generator produces electricity by thermoelectric conversion. The radioactive isotope plutonium 238 is used as the energy source for the SNAP-27. By April 1, 1970, the SNAP-27 RTG had produced more than 230 kWh of continuous and stable power for the ALSEP.-