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At least 127 records · Page 7

The ALTCRISS Project On Board the International Space Station

The Altcriss project aims to perform a long term survey of the radiation environment on board the International Space Station. Measurements are being performed with active and passive devices in different locations and orientations of the Russian segment of the station. The goal is perform a detailed evaluation of the differences in particle fluence and nuclear composition due to different shielding material and attitude of the station. The Sileye-3/Alteino detector is used to identify nuclei up to Iron in the energy range above approximately equal to 60 MeV/n; a number of passive dosimeters (TLDs, CR39) are also placed in the same location of Sileye-3 detector. Polyethylene shielding is periodically interposed in front of the detectors to evaluate the effectiveness of shielding on the nuclear component of the cosmic radiation. The project was submitted to ESA in reply to the AO the Life and Physical Science of 2004 and was begun in December 2005. Dosimeters and data cards are rotated every six months: up to now three launches of dosimeters and data cards have been performed and have been returned with the end expedition 12 and 13.

Cucinotta, Francis A.↗

On the propagation of cosmic rays in the Galaxy

Cosmic ray propagation in the Galaxy is examined within the framework of the leaky-box model, whereby phenomenological aspects of diffusion and propagation are related to the physical properties of the interstellar medium. The model is parameterized by data on composition, spectra, spectral change as a function of energy, and cosmic ray particle lifetime. It is assumed that electrons and nucleons have a common source within the Galaxy (probably associated with supernova remnants). Lifetime data and leakage length are compared with radio synchrotron and gamma-ray data to establish a place of origin for cosmic rays observed at earth, i.e., at a radius of 0.5-1.0 kpc from earth. It is noted that if the escape length becomes energy independent, all nuclear spectra will flatten, while the electron spectrum remains unchanged.

Ormes, J.↗

Mars Surface Ionizing Radiation Environment: Need for Validation

Protection against the hazards from exposure to ionizing radiation remains an unresolved issue in the Human Exploration and Development of Space (HEDS) enterprise [1]. The major uncertainty is the lack of data on biological response to galactic cosmic ray (GCR) exposures but even a full understanding of the physical interaction of GCR with shielding and body tissues is not yet available and has a potentially large impact on mission costs. "The general opinion is that the initial flights should be short-stay missions performed as fast as possible (so-called 'Sprint' missions) to minimize crew exposure to the zero-g and space radiation environment, to ease requirements on system reliability, and to enhance the probability of mission success." The short-stay missions tend to have long transit times and may not be the best option due to the relatively long exposure to zero-g and ionizing radiation. On the other hand the short-transit missions tend to have long stays on the surface requiring an adequate knowledge of the surface radiation environment to estimate risks and to design shield configurations. Our knowledge of the surface environment is theoretically based and suffers from an incomplete understanding of the physical interactions of GCR with the Martian atmosphere, Martian surface, and intervening shield materials. An important component of Mars surface robotic exploration is the opportunity to test our understanding of the Mars surface environment. The Mars surface environment is generated by the interaction of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPEs) with the Mars atmosphere and Mars surface materials. In these interactions, multiple charged ions are reduced in size and secondary particles are generated, including neutrons. Upon impact with the Martian surface, the character of the interactions changes as a result of the differing nuclear constituents of the surface materials. Among the surface environment are many neutrons diffusing from the Martian surface and especially prominent are energetic neutrons with energies up to a few hundred MeV. Testing of these computational results is first supported by ongoing experiments at the Brookhaven National Laboratory but equally important is the validation to the extent possible by measurements on the Martian surface. Such measurements are limited by power and weight requirements of the specific mission and simplified instrumentation by necessity lacks the full discernment of particle type and spectra as is possible with laboratory experimental equipment. Yet, the surface measurements are precise and a necessary requisite to validate our understanding of the surface environment. At the very minimum the surface measurements need to provide some spectral information on the neutron environment. Of absolute necessity is the precise knowledge of the detector response functions for absolute comparisons between the computational model of the surface environment and the detector measurements on the surface.

Wilson, J. W.↗

Studies of HZE particle interactions and transport for space radiation protection purposes

The main emphasis is on developing general methods for accurately predicting high-energy heavy ion (HZE) particle interactions and transport for use by researchers in mission planning studies, in evaluating astronaut self-shielding factors, and in spacecraft shield design and optimization studies. The two research tasks are: (1) to develop computationally fast and accurate solutions to the Boltzmann (transport) equation; and (2) to develop accurate HZE interaction models, from fundamental physical considerations, for use as inputs into these transport codes. Accurate solutions to the HZE transport problem have been formulated through a combination of analytical and numerical techniques. In addition, theoretical models for the input interaction parameters are under development: stopping powers, nuclear absorption cross sections, and fragmentation parameters.

Townsend, Lawrence W.↗

Evaluation of Spacecraft Shielding Effectiveness for Radiation Protection

The potential for serious health risks from solar particle events (SPE) and galactic cosmic rays (GCR) is a critical issue in the NASA strategic plan for the Human Exploration and Development of Space (HEDS). The excess cost to protect against the GCR and SPE due to current uncertainties in radiation transmission properties and cancer biology could be exceedingly large based on the excess launch costs to shield against uncertainties. The development of advanced shielding concepts is an important risk mitigation area with the potential to significantly reduce risk below conventional mission designs. A key issue in spacecraft material selection is the understanding of nuclear reactions on the transmission properties of materials. High-energy nuclear particles undergo nuclear reactions in passing through materials and tissue altering their composition and producing new radiation types. Spacecraft and planetary habitat designers can utilize radiation transport codes to identify optimal materials for lowering exposures and to optimize spacecraft design to reduce astronaut exposures. To reach these objectives will require providing design engineers with accurate data bases and computationally efficient software for describing the transmission properties of space radiation in materials. Our program will reduce the uncertainty in the transmission properties of space radiation by improving the theoretical description of nuclear reactions and radiation transport, and provide accurate physical descriptions of the track structure of microscopic energy deposition.

Cucinotta, Francis A.↗

Analysis of nuclear waste disposal in space, phase 3. Volume 2: Technical report

The options, reference definitions and/or requirements currently envisioned for the total nuclear waste disposal in space mission are summarized. The waste form evaluation and selection process is documented along with the physical characteristics of the iron nickel-base cermet matrix chosen for disposal of commercial and defense wastes. Safety aspects of radioisotope thermal generators, the general purpose heat source, and the Lewis Research Center concept for space disposal are assessed as well as the on-pad catastrophic accident environments for the uprated space shuttle and the heavy lift launch vehicle. The radionuclides that contribute most to long-term risk of terrestrial disposal were determined and the effects of resuspension of fallout particles from an accidental release of waste material were studied. Health effects are considered. Payload breakup and rescue technology are discussed as well as expected requirements for licensing, supporting research and technology, and safety testing.

Rice, E. E.↗

Using FLUKA to Calculate Spacecraft: Single Event Environments: A Practical Approach

The FLUKA nuclear transport and reaction code can be developed into a practical tool for calculation of spacecraft and planetary surface asset SEE and TID environments. Nuclear reactions and secondary particle shower effects can be estimated with acceptable accuracy both in-flight and in test. More detailed electronic device and/or spacecraft geometries than are reported here are possible using standard FLUKA geometry utilities. Spacecraft structure and shielding mass. Effects of high Z elements in microelectronic structure as reported previously. Median shielding mass in a generic slab or concentric sphere target geometry are at least approximately applicable to more complex spacecraft shapes. Need the spacecraft shielding mass distribution function applicable to the microelectronic system of interest. SEE environment effects can be calculated for a wide range of spacecraft and microelectronic materials with complete nuclear physics. Evaluate benefits of low Z shielding mass can be evaluated relative to aluminum. Evaluate effects of high Z elements as constituents of microelectronic devices. The principal limitation on the accuracy of the FLUKA based method reported here are found in the limited accuracy and incomplete character of affordable heavy ion test data. To support accurate rate estimates with any calculation method, the aspect ratio of the sensitive volume(s) and the dependence must be better characterized.

Koontz, Steve↗

The goals of gamma-ray spectroscopy in high energy astrophysics

The use of high resolution gamma-ray spectroscopy in astrophysics is discussed with specific attention given to the application of the Nuclear Astrophysics Explorer (NAE). The gamma-ray lines from nuclear transitions in radionucleic decay and positron annihilation permits the study of current sites, rates and models of nucleosynthesis, and galactic structure. Diffuse galactic emission is discussed, and the high-resolution observations of gamma-ray lines from discrete sites are also described. Interstellar mixing and elemental abundances can also be inferred from high-resolution gamma-ray spectroscopy of nucleosynthetic products. Compact objects can also be examined by means of gamma-ray emissions, allowing better understanding of neutron stars and the accreting black hole near the galactic center. Solar physics can also be investigated by examining such features as solar-flare particle acceleration and atmospheric abundances.

Lingenfelter, Richard E.↗

Physical processes in Comet Kohoutek

Observational results are brought together to establish the mass loss of Comet Kohoutek (1973 XII) in H2O, solid particles, and other molecules. The production rate of molecules is seen to have flattened prior to peaking near perihelion passage, and then fell below the rate for the incoming branch of the orbit. The total mass loss was about 10 to the 14th power gm. All abundances are consistent with a clathrate-dominant form of water. Comparison of the sizes of the nucleus as calculated from photometry and the rate of water loss requires that either an unrealistically high albedo be assumed or that only a portion of the nucleus was covered by water, in contrast with previous expectations for a new and probable first-passage comet. Moreover, if the preperihelion estimates of the nuclear brightness are rejected as being contaminated, the resulting values indicate an ice-covered nucleus with a radius of 2.1 km.

Odell, C. R.↗

Emulsion Chamber Technology Experiment (ECT)

The experimental objective of Emulsion Chamber Technology (ECT) was to develop space-borne emulsion chamber technology so that cosmic rays and nuclear interactions may subsequently be studied at extremely high energies with long exposures in space. A small emulsion chamber was built and flown on flight STS-62 of the Columbia in March 1994. Analysis of the several hundred layers of radiation-sensitive material has shown excellent post-flight condition and suitability for cosmic ray physics analysis at much longer exposures. Temperature control of the stack was 20 +/-1 C throughout the active control period and no significant deviations of temperature or pressure in the chamber were observed over the entire mission operations period. The unfortunate flight attitude of the orbiter (almost 90% Earth viewing) prevented any significant number of heavy particles (Z greater than or equal to 10) reaching the stack and the inverted flow of shower particles in the calorimeter has not allowed evaluation of absolute primary cosmic ray-detection efficiency nor of the practical time limits of useful exposure of these calorimeters in space to the level of detail originally planned. Nevertheless, analysis of the observed backgrounds and quality of the processed photographic and plastic materials after the flight show that productive exposures of emulsion chambers are feasible in low orbit for periods of up to one year or longer. The engineering approaches taken in the ECT program were proven effective and no major environmental obstacles to prolonged flight are evident.

Gregory, John C.↗

Interaction of space radiation with matter

The physical interactions of high-energy space radiations with bulk matter are described with particular emphasis on the nuclear and electromagnetic interactions of solar and galactic cosmic rays. Methods of incorporating these interactions into radiation transport models which accurately describe the propagation of the incident cosmic rays and their subsequent-generation reaction products are also explained. Representative results for solar and galactic cosmic ray doses and dose equivalents are presented for various aluminum and water absorber depths. For the first time, the main contributions to human exposure in space from galactic cosmic rays will be presented on a component by component basis, including a breakdown of the dose-equivalent contributions into primary ions, heavy fragments, alpha particles, neutrons, and protons. For the galactic cosmic ray environment outside of the earth's magnetosphere, over 70 percent of the total dose equivalent results from only seven nuclear species (hydrogen, helium, carbon, oxygen, silicon, magnesium, and iron ions). Of these, the largest single contributor is cosmic ray iron and its secondaries, which account for nearly one-fourth of the unshielded total dose equivalent during solar minimum.

Townsend, L. W.↗

The effect of suprathermal protons on the physical conditions in Seyfert galaxy nuclei II

The radiative transfer of Ly-alpha, Ly-beta, and H-alpha in a hydrogen gas containing dust was considered with application to the nuclear gas in Seyfert galaxies. By neglecting the direct escape of line radiation and by averaging over the gas, the radiation transfer in space is suppressed and the frequency transfer only is considered. The dust degrades the line radiation via frequency-independent absorption, converting the energy to infrared luminosity. The source functions in the lines were solved, using appropriate approximations, in order to determine under what conditions the narrow component of the Balmer line radiation from the gas can be self-absorbed and degraded without similar degradation of the broad component, which originates from the suprathermals themselves. The results are used to find self-consistent values for the temperature and ionization of the gas for various amounts of dust and various concentrations of suprathermal particles.

Stoner, R.↗

Three-dimensional hydrodynamical simulations of colliding stars . III - Collisions and tidal captures of unequal-mass main-sequence stars

A 3D smooth-particle hydrodynamic code with 7000 particles is used to simulate collisions between lower main sequence (MS) stars whose masses differ by a factor of five. Collisions between point-mass intruders and MS stars are simulated to study how the physics of the encounters depends on the finite radius of the smaller MS stars. It is found that the two MS stars become gravitationally bound in a physical collision if their relative velocity at infinity is less than a critical velocity Vd. Vd decreases from 1000 km/s in a head-on collision to 150 km/s in a grazing one. If the less massive star is replaced by a point mass, Vd remains the same for grazing collision and tidal encounters but drops to about 600 km/s in head-on collisions. The collision and coalescence of two MS stars resets the nuclear clock of the coalesced star, so it contracts to the MS. Tidal capture of binary stars in globular clusters can only occur in encounters in which the closest approach of the two stars to their center of mass is less than 2.0 times the sum of their radii.

Benz, W.↗

Dynamics of Nuclear Regions of Galaxies

Current research carried out with the help of the ASEE-NASA Summer Faculty Program, at NASA-Ames, is concentrated on the dynamics of nuclear regions of galaxies. From a dynamical point of view a galaxy is a collection of around 10(sup 11) stars like our Sun, each of which moves in the summed gravitational field of all the remaining stars. Thus galaxy dynamics becomes a self-consistent n-body problem with forces given by Newtonian gravitation. Strong nonlinearity in the gravitational force and the inherent nonlinearity of self-consistent problems both argue for a numerical approach. The technique of numerical experiments consis of constructing an environment in the computer that is as close as possible to the physical conditions in a real galaxy and then carrying out experiments much like laboratory experiments in physics or engineering, in this environment. Computationally, an experiment is an initial value problem, and a good deal of thought and effort goes into the design of the starting conditions that serve as initial values. Experiments are run at Ames because all the 'equipment' is in place-the programs, the necessary computational power, and good facilities for post-run analysis. Our goal for this research program is to study the nuclear regions in detail and this means replacing most of the galaxy by a suitable boundary condition to allow the full capability of numerical experiments to be brought to bear on a small region perhaps 1/1000 of the linear dimensions of an entire galaxy. This is an extremely delicate numerical problem, one in which some small feature overlook, can easily lead to a collapse or blow-up of the entire system. All particles attract each other in gravitational problems, and the 1/r(sup 2) force is: (1) nonlinear; (2) strong at short range; (3) long-range, and (4) unscreened at any distance.

Miller, Richard H.↗

The Komplast Experiment: Space Environmental Effects after 12 Years in LEO (and Counting)

The Komplast materials experiment was designed by the Khrunichev State Research and Production Space Center, together with other Russian scientific institutes, and has been carried out by Mission Control Moscow since 18. Komplast panels fitted with material samples and sensors were located on the International Space Station (ISS) Functional Cargo Block (FGB) module exterior surface. Within the framework of this experiment, the purpose was to study the effect of the low earth orbit (LEO) environment on exposed samples of various materials. The panels were sent into orbit with the FGB when it launched on November 20, 1998. Panels #2 and #10 were retrieved during Russian extravehicular activity in February 2011 and sealed within cases to temporarily protect the samples from exposure to air until they could be studied on the ground. Panel #2 contained an experiment to detect micrometeoroid and orbital debris (MMOD) impacts, radiation and UV sensors, several pieces of electrical cable, and samples made from elastomeric and fluoroplastic materials. Panel #10 contained a temperature sensor, and both carbon composite and adhesive-bonded samples. A figure shows the location of panels #2 and #10 on the FGB module aft endcone. The panels were subsequently returned to Earth by Space Shuttle Discovery on the STS-133/ULF-5 mission after 12 years of LEO exposure and opened in an argon chamber at the Institute of Nuclear Physics at Moscow State University in July 2011. Based on the results of analyzing the readings from sensors located on Komplast panels and in studying material samples from the panels, the comprehensive effect of spaceflight factors on the FGB (at the locations of Panels #2 and #10) was evaluated. Total solar exposure was determined to be 960 +/- 200 kJ/square cm or 21,000 equivalent solar hours. Because of location of these two panels and the ISS flight attitude, atomic oxygen (AO) fluence was relatively low for such a long duration exposure, approximately 1.5x10 (exp 21) O atoms/sq. cm. Most of the AO fluence occurred during the early phase of ISS assembly. Temperatures ranged from a maximum of 107 C to a minimum of -80 C. The MMOD environment was determined, as is shown. Interestingly, the distribution of craters and low-velocity impact particles observed in the 5-50 micron size range was approx 2-3 orders of magnitude higher than that predicted by the ORDEM2000 model of natural and artificial origin microparticles in the ISS orbit. Contamination observations were also made, through the evaluation of optical properties on thermal control coatings and by the examination of visible deposits located near several samples on the panels, primarily from elastomeric samples. These elastomer samples were extensively investigated for their physical property changes and sealing capability. In addition, 16 samples of adhesive-bonded joints using three types of epoxy adhesive were evaluated studying fracture toughness, failure surface, and adhesive volume properties. Both rubber and adhesive-bonded specimens also underwent additional (post-flight) ground-based exposures to simulate a total 30 years in LEO prior to their evaluation. Overall, results indicate that space environmental effects will not adversely impact the service life of the FGB through 2028. Our investigation is complete and a summary of the results obtained from this uniquely long-duration exposure experiment will be presented.

Shaevich, S. K.↗

Neutrons, gamma rays, and beta particles interactions with IIaO films flown on Astro I and Astro II and comparison with IIaO flown on the get-away-special STS-7

The current requirements for the Laboratory for Astronomy and Solar Physics, sends rocket satellites and in the near future will involve flights in the shuttle to the upper reaches of the Earth's atmosphere where they will be subjected to the atomic particles and electromagnetic radiation produced by the Sun and other cosmic radiation. It is therefore appropriate to examine the effect of neutrons, gamma rays, beta particles, and X-rays on the film currently being used by the Laboratory for current and future research requirements. It is also hoped by examining these particles in their effect that we will have simulated the space environment of the rockets, satellites, and shuttles. Several samples of the IIaO film were exposed to a neutron howitzer with a source energy of approximately 106 neutrons/steradians. We exposed several samples of the film to a 10 second blast of neutrons in both metal and plastic containers which exhibited higher density readings which indicated the possibility of some secondary nuclear interactions between neutrons and the aluminum container. The plastic container showed some variations at the higher densities. Exposure of the samples of IIaO film to a neutron beam of approximately 10 neutrons per steradians for eight minutes produces approximately a 13% difference in the density readings of the dark density grids. It is not noticeable that at the lighter density grid the neutrons have minimal effects, but on a whole the trend of the eight minute exposed IIaO film density grids at the darker end had a 7.1% difference than the control. Further analysis is anticipated by increasing the exposure time. Two sets of film were exposed to a beta source in a plastic container. The beta source was placed at the bottom so that the cone of rays striking the film would be conical for a period of seven days. It was observed in the films, designated 4a and 4b, a dramatic increase in the grid densities had occurred. The attenuation of beta particles due to the presence of air were observed. The darker density grids, whose positions were the furthest from the beta source, displayed minimal fluctuations as compared with the control. It is suspected that the orientation of the film in the cansister with the beta source is the key factor responsible for the dramatic increases of the lighter density grids. Emulsions 3a and 3b exposed for a period of six days with the grid orientation reserved produced substantial differences in the darker grids as shown in the graphs. There is a great deal of fluctuations in this sample between the beta exposed density grids and the control density grids. The lighter density grids whose orientations were reversed displays minimal fluctuations due to the presence of this beta source and the attenuation that is taking place.

Hammond, Ernest C., Jr.↗

Ground-based measurements of galactic cosmic ray fragmentation in shielding

The mean free path for nuclear interactions of galactic cosmic-rays is comparable to shielding and tissue thicknesses present in human interplanetary exploration, resulting in a significant fraction of nuclear reaction products at depth. In order to characterize the radiation field, the energy spectrum, the angular distribution, and the multiplicity of each type of secondary particles must also be known as a function of depth. Reactions can take place anywhere in a thick absorber; therefore, it is necessary to know these quantities as a function of particle energy for all particles produced. HZE transport methods are used to predict the radiation field; they are dependent on models of the interaction of man-made systems with the space environment to an even greater extent than methods used for other types of radiation. Hence, there is a major need to validate these transport codes by comparison with experimental data. The most cost-effective method of validation is a comparison with ground-based experimental measurements. A research program to provide such validation measurements using neon, iron and other accelerated heavy ion beams will be discussed and illustrated using results from ongoing experiments and their comparison with current transport codes. The extent to which physical measurements yield radiobiological predictions will be discussed.

NASA Discipline Radiation Health↗

The Fusion Driven Rocket: Nuclear Propulsion through Direct Conversion of Fusion Energy

The future of manned space exploration and development of space depends critically on the creation of a dramatically more efficient propulsion architecture for in-space transportation. A very persuasive reason for investigating the applicability of nuclear power in rockets is the vast energy density gain of nuclear fuel when compared to chemical combustion energy. The Fusion Driven rocket (FDR) represents a revolutionary approach to fusion propulsion where the power source releases its energy directly into the propellant, not requiring conversion to electricity. It employs a solid lithium propellant that requires no significant tankage mass. The propellant is rapidly heated and accelerated to high exhaust velocity (> 30 km/s), while having no substantial physical interaction with the spacecraft thereby avoiding damage to the rocket and limiting both the thermal heat load and radiator mass. The key to achieving this stems from research at MSNW and the UW on the magnetically driven implosion of metal foils onto a magnetized plasma target to obtain fusion conditions. A logical extension of this work leads to a method that utilizes these metal shells (or liners) to not only achieve fusion conditions, but to serve as the propellant as well. Several low-mass, magnetically driven metal liners are inductively driven to converge radially and axially and form a thick blanket surrounding the target plasmoid and compress the plasmoid to fusion conditions. Virtually all of the radiant, neutron and particle energy from the plasma is absorbed by the encapsulating, thick metal blanket thereby isolating the spacecraft from the fusion. This energy, in addition to the intense Ohmic heating at peak magnetic field compression, is adequate to vaporize and ionize the metal blanket. The expansion of this hot, ionized metal propellant through a magnetically insulated nozzle produces high thrust at the optimal Isp. The energy from the fusion process, along with the waste heat, is thus utilized at very high efficiency. The basic scheme for FDR is illustrated and described in the report (see Fig. 2) The two most critical issues in meeting challenges introduced employing magneto-inertial fusion as the power source is driver efficiency and “stand-off” – the ability to isolate and protect fusion and thruster from the resultant fusion energy. By employing metal shells for compression, it is possible to produce the desired convergent motion inductively by inserting the metal sheets along the inner surface of cylindrical or conically tapered coils. Both stand-off and energy efficiency issues are solved by this arrangement. 3 This two year effort focused on achieving three key criteria for the Fusion Driven Rocket to move forward for technological development: (1) the physics of the FDR must be fully understood and validated, (2) the design and technology development for the FDR required for its implementation in space must be fully characterized, and (3) an in-depth analysis of the rocket design and spacecraft integration as well as mission architectures enabled by the FDR need to be performed. A subscale, laboratory liner compression test facility was assembled at the University of Washington Plasma Dynamics Laboratory with sufficient liner kinetic energy (~ 0.5 MJ) to reach conditions required for fusion breakeven conditions. Detailed experimental studies of the dynamic behavior of the driven liners as well as liner convergence and magnetic compression were performed. The development of both the 1D liner dynamics code and the full 3D ANSYS® liner calculations was achieved. The characterization of both the FDR and spacecraft as well as a design architecture analysis was conducted that included an examination of a wide range of mission architectures and destinations for which this fusion propulsion system would be enabling or critical. In particular a rapid, single launch manned Mars mission was developed.

Energy↗