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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 127 records · Page 7
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NASA NTRSDate not supplied

Shields-1 Energetic Proton Dose Comparison from Solar Minimum and Active Periods

Shields-1 has been operating in polar low earth orbit since December 2018 as part of the CubeSat Launch Initiative (CSLI) Educational Launch of Nanosatellites (ELaNa)XIX Mission. Shields-1 has 8 Teledyne µdosimeters behind shielding. These shielded µdosimeters have high minimum proton energy thresholds. The Shields-1 electronics enclosure µdosimeter has a minimum proton threshold energy of 151 MeV. The annualized total ionizing dose (TID) in the electronics enclosure was 75.6 +/- 3.2 RAD from July-August 2019, which was a solar minimum period. In contrast, the annualized TID was 61.0 +/- 2.5 RAD in July 2023, a solar active month. The TID change can be attributed to both the reduction in radiation at the South Atlantic Anomaly (SAA) and the decrease in galactic cosmic radiation during increasing solar activity. The measured GCR dose over the poles was reduced during the July 2023 solar active period in comparison with the July 2019 solar minimum period, using the most sensitive µdosimeter channel for the measurement. Shields-1 has demonstrated the capability of measuring the changes in high energy protons in polar low earth orbit during changes in solar activity, which contributes to the understanding of Earth in the heliosphere.

Shields-1 Dosimetry Space Sciences↗
NASA NTRS1972

The response of a 0.03-cm silicon detector to a mixed neutron and gamma field as a function of shield material and thickness

The neutron and gamma radiation from a MHW-RTG was used to evaluate the total response of a shielded 0.3-mm silicon detector. The generator employs a 2200 W(th) PuO2 heat source concept known as the HELIPAK. The total integrated neutron and gamma ray fluxes at 100 cm away from the source along the radial direction were 1.67 x 1,000 n/sq cm/s and 1.49 x 10,000 gamma sq cm/s, respectively. Experimental values of the response function of the shielded silicon detector were used to determine the total counting rates due to photons at bias energies ranging from 50 to 200 keV. For neutrons, analytically computed response functions were used to determine the total counting rates at the same bias energies. It was found that for an aluminum shield the neutrons are not significant, regardless of the thickness of the shield. However, the magnitude of the total counting rate due to neutrons increases with increased atomic number of the shield and becomes comparable to the counting rate due to photons for a platinum shield thickness of 5 cm.

Taherzadeh, M.↗
NASA NTRS1972

An analytical and experimental evaluation of shadow shields and their support members.

Review of the major results of an analytical and experimental program aimed at determining the potential effectiveness of shadow shields in minimizing radiant heat transfer into cryogenic propellant tanks on long-duration interplanetary missions, taking into account the thermal interaction between shields and their support structures. Analytical procedures are developed and applied that include the strut-shield interaction in predicting shadow shield performance. The results of experimental studies of the effects of configuration variables on the performance of a scale model of a shadow shield system are presented. The experimental results are used to verify the validity of analytical predictions. The results obtained show that: (1) shadow shields can be effective in reducing the heat transfer into cryogenic propellant tanks, and (2) the conductive heat transfer through supports can be reduced by selective surface coatings.

Stochl, R. J.↗
NASA NTRS1977

Methods of shield analysis for protection against electrons in space

It is anticipated that many future manned space operations will be radiation limited and that laminated wall structures and the use of new materials will be required to reduce radiation exposure. Methods for electron shield analysis are reviewed in light of anticipated needs in the space program. The most general method is still the Monte Carlo method, which is of limited usefulness for shield analysis due to excessive computer requirements. Methods based on energy deposition coefficients or energy transmission and reflection factors are quite accurate, but are currently limited to aluminum shield material. Analytical methods based on Mar's approximation for the electron transmission factor are relatively general and computer efficient but seriously underestimate shield requirements. A correction to methods using Mar's approximate transmission factor is derived herein and results in a slightly conservative estimate of shield requirements. Techniques for laminated shield design are still lacking.

Wilson, J. W.↗
NASA NTRS1982

Effect of vacuum processing on outgassing within an orbiting molecular shield

The limiting hydrogen number density in an orbiting molecular shield is highly dependent on the outgassing rates from the materials of construction for the shield, experimental apparatus, and other hardware contained within the shield. Ordinary degassing temperatures used for ultrahigh vacuum studies (less than 450 C) are not sufficient to process metals so that the contribution to the number density within the shield due to outgassing is less than the theoretically attainable level (approximately 200 per cu. cm). Pure aluminum and type 347 stainless steel were studied as candidate shield materials. Measurements of their hydrogen concentration and diffusion coefficients were made, and the effects of high temperature vacuum processing (greater than 600 C) on their resulting outgassing rates was determined. The densities in a molecular shield due to the outgassing from either metal were substantially less ( 0.003) than the density due to the ambient atomic hydrogen flux at an orbital altitude of 500 km.

Outlaw, R. A.↗
NASA NTRS1984

Optimation of cooled shields in insulations

A method to optimize the location, temperature, and heat dissipation rate of each cooled shield inside an insulation layer was developed. The method is based on the minimization of the entropy production rate which is proportional to the heat leak across the insulation. It is shown that the maximum number of shields to be used in most practical applications is three. However, cooled shields are useful only at low values of the overall, cold wall to hot wall absolute temperature ratio. The performance of the insulation system is relatively insensitive to deviations from the optimum values of the temperature and location of the cooling shields. Design curves for rapid estimates of the locations and temperatures of cooling shields in various types of insulations, and an equation for calculating the cooling loads for the shields are presented.

Chato, J. C.↗
NASA NTRS1985

Roof Shield for Advance and Retreat Mining

Shield sections change their configuration to suit mining mode. Articulation cylinders raise rear shield to advance position, and locking cylinders hold it there. To change to retreat position articulation cylinders lower shield. Locking pins at edge of outermost shield plate latch shield to chock base. Shield accommodates roof heights ranging from 36 to 60 inches (0.9 to 1.52 meters).

Lewis, E. V.↗
NASA NTRS1985

Measurement of acoustic shielding by a turbulent jet

The acoustic shielding properties of a turbulent jet have been investigated experimentally. The experimental arrangement consisted of an acoustic point source and a turbulent shielding jet. The source and jet parameters investigated include the source frequency, source spectrum, jet velocity, jet heating by simulation and the lateral and longitudinal source positions with respect to the shielding jet. It is found that the maximum sound attenuation provided by the shielding jet depends on the balance between refraction and diffraction. Over the frequency range investigated, the redistribution of sound by the shielding air jet is power conserving. Comparison between measurement and prediction based on an idealized cylindrical uniform jet model indicates that the spreading and decay of the flow field in real jets are important. Comparisons between the present data trends and those reported for jet-by-jet shielding suggest that the major effects observed in the latter are acoustical rather than aerodynamical.

Yu, J. C.↗
NASA NTRS1985

Free jet feasibility study of a thermal acoustic shield concept for AST/VCE application: Dual stream nozzles

The influence of selected geometric and aerodynamic flow variables of an unsuppressed coannular plug nozzle and a coannular plug nozzle with a 20-chute outer stream suppressor were experimentally determined. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale model nozzles. Also, aerodynamic measurements of four selected plumes were made with a laser velocimeter. The presence of the 180 deg shield produced different mixing characteristics on the shield side compared to the unshield side because of the reduced mixing with ambient air on the shielded side. This resulted in a stretching of the jet, yielding a higher peak mean velocity up to a length of 10 equivalent diameters from the nozzle exit. The 180 deg shield in community orientation around the suppressed coannular plug nozzle yielded acoustic benefit at all observer angles for a simulated takeoff. While the effect of shield-to-outer stream velocity ratio was small at angles up to 120 deg, beyond this angle significant acoustic benefit was realized with a shield-to-outer stream velocity ratio of 0.64.

Janardan, B. A.↗
NASA NTRS1990

Space radiation shielding for a Martian habitat

Radiation shielding analyses are performed for a candidate Mars base habitat. The Langley cosmic ray transport code and the Langley nucleon transport code are used to quantify the transport and attenuation of galactic cosmic rays and solar flare protons through both the Martian atmosphere and regolith shielding. Doses at the surface and at various altitudes were calculated in a previous study using both a high-density and a low-density Mars atmosphere model. This study extends the previous low-density results to include the further transport of the ionizing radiation that reaches the surface through additional shielding provided by Martian regolith. A four-compound regolith model, which includes SiO2, Fe2O3, MgO, and CaO, was selected based on the chemistry of the Viking 1 Lander site. The spectral fluxes of heavy charged particles and the corresponding dosimetric quantities are computed for a series of thicknesses in the shield media after traversing the atmosphere. These data are then used as input to algorithms for a specific shield geometry. The results are presented as the maximum dose received in the center of the habitat versus various shield thicknesses for a base at an altitude of 0 km and 8 km.

Simonsen, Lisa C.↗
NASA NTRS1991

A thermal shield concept for the Solar Probe mission

The Solar Probe spacecraft will travel to within 4 solar radii of the sun's center while performing a variety of fundamental experiments in space physics. Exposure to 2900 earth suns (400 W/sq cm) at perihelion imposes severe thermal and material demands on a solar shield system designed to protect the payload that will reside within the shield's shadow envelope or umbra. The design of the shield subsystem is a thermal/materials challenge requiring new technology development. While currently in the preproject study phase, anticipating a 1995 project start, shield preliminary design efforts are currently underway. This paper documents the current status of the mission concept, the materials issues, the configuration concept for the shield subsystem, the current configuration studies performed to date, and the required material testing to provide a database to support a design effort required to develop the shield subsystem.

Miyake, Robert N.↗
NASA NTRS1993

Morphometric comparison of Icelandic lava shield volcanoes versus selected Venusian edifices

Shield volcanoes are common landforms on the silicate planets of the inner Solar System, and a wide variety have recently been documented on Venus by means of Magellan observations. In this report, we emphasize our recently completed morphometric analysis of three representative Icelandic lava shields: the classic Skjaldbreidur edifice, the low-reflief Lambahraun feature, and the monogenetic Sandfellshaed shield, as the basis for comparison with representative venusian edifices (greater than 60 km in diameter). Our detailed morphometric measurements of a representative and well-studied set of Icelandic volcanoes permits us to make comparisons with our measurements of a reasonable subset of shield-like edifices on Venus on the basis of Magellan global radar altimetry. Our study has been restricted to venusian features larger than approximately 60 km in basal diameter, on the basis of the minimum intrinsic spatial resolution (8 km) of the Magellan radar altimetry data. Finally, in order to examine the implications of landform scaling from terrestrial simple and composite shields to larger venusian varieties, we have considered the morphometry of the subaerial component of Mauna Loa, a type-locality for a composite shield edifice on Earth.

Garvin, James B.↗
NASA NTRS1994

Design considerations for a Space Station radiation shield for protection from both man-made and natural sources

This study was conducted to analyze scenarios involving the use of nuclear-power vehicles in the vicinity of a manned Space Station (SS) in low-earth-orbit (LEO) to quantify their radiological impact to the station crew. In limiting the radiant dose to crew members, mission planners may (1) shut the reactor down prior to reentry, (2) position the vehicle at a prescribed parking distance, and (3) deploy radiation shield about the shutdown reactor. The current report focuses on the third option in which point-kernel gamma-ray shielding calculations were performed for a variety of shield configurations for both nuclear electric propulsion (NEP) and nuclear thermal rocket (NTR) vehicles. For a returning NTR vehicle, calculations indicate that a 14.9 MT shield would be needed to limit the integrated crew exposure to no more than 0.05 Sv over a period of six months (25 percent of the allowable exposure to man-made radiation sources). During periods of low vehicular activity in LEO, the shield may be redeployed about the SS habitation module in order to decrease crew exposures to trapped proton radiations by approximately a factor of 10. The corresponding shield mass required for deployment at a returning NEP vehicle is 2.21 MT. Additional scenarios examined include the radioactivation of various metals as might be found in tools used in EVA activities.

Bolch, Wesley E.↗
NASA NTRS1995

Galileo Heat Shield Response Experiment Data Reduction and Analyses

The Galileo heat shield response experiment consists of 10 Analog Resistance Ablation Detectors (ARADs) embedded in the carbon phenolic heat shield. As the vehicle descends into the atmosphere of Jupiter, these ARADs will in effect measure the recession as a function of time at various locations on the heat shield. This recession data will be used to reconstruct the time-dependent shape of the vehicle. The shape data is of critical importance to the Atmospheric Reconstruction Experiment which must know mass and drag coefficient of the vehicle in order to determine the structure of the Jovian atmosphere. The data is also intrinsically useful as a database for evaluating the accuracy of our numerical codes and methodology for predicting highly radiating reentry flowfields and coupled heat shield material response. This paper will document the reduction of the data from the ARAD sensors, reconstruction of the heat shield shape history, and comparison of the actual heat shield response with previous calculations and experiments. If possible, we will also include results from new calculations which couple the shock layer flow with the transient material response.

Milos, Frank S.↗
NASA NTRS2002

Vacuum Ultraviolet Radiation and Atomic Oxygen Durability Evaluation of HST Bi-Stem Thermal Shield Materials

Bellows-type thermal shields were used on the bi-stems of replacement solar arrays installed on the Hubble Space Telescope (HST) during the first HST servicing mission (SMI) in December 1993. These thermal shields helped reduce the problem of thermal gradient- induced jitter observed with the original HST solar arrays during orbital thermal cycling and have been in use on HST for eight years. This paper describes ground testing of the candidate solar array bi-stem thermal shield materials including backside aluminized Teflon(R)FEP (fluorinated ethylene propylene) with and without atomic oxygen (AO) and ultraviolet radiation protective surface coatings for durability to AO and combined AO and vacuum ultraviolet (VOV) radiation. NASA Glenn Research Center (GRC) conducted VUV and AO exposures of samples of candidate thermal shield materials at HST operational temperatures and pre- and post-exposure analyses as part of an overall program coordinated by NASA Goddard Space Flight Center (GSFC) to determine the on-orbit durability of these materials. Coating adhesion problems were observed for samples having the AO- and combined AO/UV-protective coatings. Coating lamination occurred with rapid thermal cycling testing which simulated orbital thermal cycling. This lack of adhesion caused production of coating flakes from the material that would have posed a serious risk to HST optics if the coated materials were used for the bi-stem thermal shields. No serious degradation was observed for the uncoated aluminized Teflon(R) as evaluated by optical microscopy, although atomic force microscopy (AFM) microhardness testing revealed that an embrittled surface layer formed on the uncoated Teflon(R) surface due to vacuum ultraviolet radiation exposure. This embrittled layer was not completely removed by AO erosion, No cracks or particle flakes were produced for the embrittled uncoated material upon exposure to VUV and AO at operational temperatures to an equivalent exposure of approximately five years in the HST environment. Uncoated aluminized FEP Teflon(R) was determined to be the most appropriate thermal shield material and was used on the bi-stems of replacement solar arrays installed on HST during SMI in December 1993. The SMI -installed solar arrays air scheduled to be replaced during MST's fourth servicing mission (SM3B) in early 2002.

Dever, Joyce↗
NASA NTRS2003

Meteoroid/Debris Shielding

This report provides innovative, low-weight shielding solutions for spacecraft and the ballistic limit equations that define the shield's performance in the meteoroid/debris environment. Analyses and hypervelocity impact testing results are described that have been used in developing the shields and equations. Spacecraft shielding design and operational practices described in this report are used to provide effective spacecraft protection from meteoroid and debris impacts. Specific shield applications for the International Space Station (ISS), Space Shuttle Orbiter and the CONTOUR (Comet Nucleus Tour) space probe are provided. Whipple, Multi-Shock and Stuffed Whipple shield applications are described.

Christiansen, Eric L.↗
NASA NTRS2002

Reliability Methods for Shield Design Process

Providing protection against the hazards of space radiation is a major challenge to the exploration and development of space. The great cost of added radiation shielding is a potential limiting factor in deep space operations. In this enabling technology, we have developed methods for optimized shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space missions. The total shield mass over all pieces of equipment and habitats is optimized subject to career dose and dose rate constraints. An important component of this technology is the estimation of two most commonly identified uncertainties in radiation shield design, the shielding properties of materials used and the understanding of the biological response of the astronaut to the radiation leaking through the materials into the living space. The largest uncertainty, of course, is in the biological response to especially high charge and energy (HZE) ions of the galactic cosmic rays. These uncertainties are blended with the optimization design procedure to formulate reliability-based methods for shield design processes. The details of the methods will be discussed.

Tripathi, R. K.↗
NASA NTRS2001

Overview of active methods for shielding spacecraft from energetic space radiation

During the 1960's and into the early 1970's, investigations were conducted related to the feasibility of using active radiation shielding methods, such as afforded by electromagnetic fields, as alternatives to passive, bulk material shielding to attenuate space radiations. These active concepts fall into four categories: (1) electrostatic fields; (2) plasma shields; (3) confined magnetic fields; and (4) unconfined magnetic fields. In nearly all of these investigations, consideration was given only to shielding against protons or electrons, or both. During the 1980's and 1990's there were additional studies related to proton shielding and some new studies regarding the efficacy of using active methods to shield from the high energy heavy ion (HZE particle) component of the galactic cosmic ray spectrum. In this overview, each concept category is reviewed and its applicability and limitations for the various types of space radiations are described. Recommendations for future research on this topic are made.

NASA Discipline Radiation Health↗