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  • 1
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    Revised prediction of LDEF exposure to trapped protons (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 319.4 to 478.7 km. For this orbital altitude and inclination, two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic field models and the solar conditions were used to obtain the trapped electron and proton omnidirectional fluences reported previously. Results for directional proton spectra using the MSFC anisotropy model for solar minimum and 463 km altitude (representative for the LDEF mission) were also reported. The directional trapped proton flux as a function of mission time is presented considering altitude and solar activity variation during the mission. These additional results represent an extension of previous calculations to provide a more definitive description of the LDEF trapped proton exposure.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 1: Second Post-Retrieval Symposium; p 137-145
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  • 2
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    Prediction of LDEF ionizing radiation environment (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 172 to 258.5 nautical miles. For this orbital altitude and inclination two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic filed models were used to obtain the trapped electron and proton fluences. The mission proton doses were obtained from the fluence using the Burrell proton dose program. For the electron and bremsstrahlung dose we used the Marshall Space Flight Center (MSFC) electron dose program. The predicted doses were in general agreement with those measured with on-board thermoluminescent detector (TLD) dosimeters. The NRL package of programs, Cosmic Ray Effects on MicroElectronics (CREME), was used to calculate the linear energy transfer (LET) spectrum due to galactic cosmic rays (GCR) and trapped protons for comparison with LDEF measurements.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. First Post-Retrieval Symposium, Part 1; p 213-224
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  • 3
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    Status of LDEF radiation modeling (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The current status of model prediction and comparison with LDEF radiation dosimetry measurements is summarized with emphasis on major results obtained in evaluating the uncertainties of present radiation environment model. The consistency of results and conclusions obtained from model comparison with different sets of LDEF radiation data (dose, activation, fluence, LET spectra) is discussed. Examples where LDEF radiation data and modeling results can be utilized to provide improved radiation assessments for planned LEO missions (e.g., Space Station) are given.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 217-226
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  • 4
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    The ionizing radiation environment of LDEF prerecovery predictions (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The Long Duration Exposure Facility (LDEF) was exposed to several sources of ionizing radiation while in orbit. The principal ones were trapped belt protons and electrons, galactic cosmic rays, and albedo particles (protons and neutrons) from the atmosphere. Large solar flares in 1989 may have caused a small contribution. Prior to the recovery of the spacecraft, a number of calculations and estimates were made to predict the radiation exposure of the spacecraft and experiments. These were made to assess whether measurable radiation effects might exist, and to plan the analysis of the large number of radiation measurements available on the LDEF. Calculations and estimates of total dose, particle fluences, linear energy transfer spectra, and induced radioactivity were made. The principal sources of radiation is described, and the preflight predictions are summarized.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 11
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  • 5
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    Radiation exposure of LDEF: Initial results (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Initial results from Long Duration Exposure Facility (LDEF) include radiation detector measurements from four experiments; P0006, P0004, M0004, and A0015. The detectors were located on both the leading and trailing edges of the orbiter and also at the Earthside end. This allowed the directional dependence of the incoming radiation to be measured. Total absorbed doses from thermoluminescent detectors (TLDs) verified the predicted spatial east-west dose dependence of a factor of approx. 2.5, due to trapped proton anisotropy in the South Atlantic Anomaly (SAA). On the trailing edge of the orbiter, a range of doses from 664 to 291 rad were measured under nominal shielding of 0.42 to 8.45 g/sq cm. A second set of detectors near this locations results are also given. On the leading edge, doses of 258 to 210 rad were found under shielding of 1.25 to 2.48 g/sq cm. Initial charged particle LET (linear energy transfer) spectra, fluxes, doses, and dose equivalents, for LET in H2O greater than or = 5 keV/micron, were measured with plastic nuclear track detectors located in the four experiments. Also, preliminary data on low energy neutrons were obtained from detectors containing (6)LiF foils.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 24
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  • 6
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    Charged particle LET-spectra measurements aboard LDEF (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The linear energy transfer (LET) spectra of charged particles was measured in the 5 to 250 keV/micron (water) interval with CR-39 and in the 250 to 1000 keV/micron (water) interval with polycarbonate plastic nuclear track detectors (PNTDs) under different shielding depths in the P0006 experiment. The optimal processing conditions were determined for both PNTDs in relation to the relatively high track densities due to the long term exposure in space. The total track density was measured over the selected samples, and tracks in coincidence on the facing surfaces of two detector sheets were selected for measuring at the same position on each sheet. The Short Range (SR) and Galactic Cosmic Ray (GCR) components were measured separately. The integral dose and dose rate spectra of charged particles are also given. The high LET portion of the LET spectra was measured with high statistical accuracy. This is a unique result of this experiment due to the low flux of this type of particle under typical shielding conditions.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 20
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  • 7
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    Triple and quadruple excitation contributions to the binding in Be clusters: Calibration calculations on Be3 (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The contribution of connected triple and quadruple excitations to the binding in Be3 is investigated by comparing various coupled-cluster (CC) and truncated configuration interaction (CI) treatments with multireference CI (MRCI) and full CI(FCI) calculations. The CC method with single and double excitations (CCSD) produces results that differ substantially from more elaborate treatments, but most extensions to CCSD that account approximately for connected triple excitations perform very well. In constrast, good agreement with FCI for Be2 can be achieved only with the highest level CC and MRCI methods.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA-TM-103391 , NAS 1.15:103391
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  • 8
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    Charged particle LET-spectra measurements aboard LDEF (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The linear energy transfer (LET) spectra of charged particles was measured in the 5 to 250 keV/micron (water) interval with CR-39 and in the 500 to 1500 keV/micron (water) interval with polycarbonate plastic nuclear track detectors (PNTDs) under different shielding depths in the P0006 experiment. The optimal processing conditions were determined for both PNTDs in relation to the relatively high track densities due to the long term exposure in space. The total track density was measured over the selected samples, and tracks in coincidence on the facing surfaces of two detector sheets were selected for measuring at the same position on each sheet. The short range (SR) and Galactic Cosmic Ray (GCR) components were measured separately with CR-39 PNTDs and the integral dose and dose rate spectra of charged particles were also determined. The high LET portion of the LET spectra was measured with polycarbonate PNTDs with high statistical accuracy. This is a unique result of this exposure due to the low flux of these types of particles for typical spaceflight durations. The directional dependence of the charged particles at the position of the P0006 experiment was also studied by four small side stacks which surrounded the main stack and by analyzing the dip angle and polar angle distributions of the measured SR and GCR particle tracks in the main stack.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. First Post-Retrieval Symposium, Part 1; p 339-346
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  • 9
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    Three-dimensional shielding effects on charged particle fluences measured in the P0006 experiment in LDEF (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The azimuthal and polar angle distribution of the galactic cosmic ray particles (mostly relativistic iron) was measured in the main stack and four side stacks of the P0006 experiment located on the west end of the LDEF satellite. A clear shadowing effect of the radiation shielding of the LDEF satellite is found. The total fluence of stopping protons (mostly primary, trapped particles) was measured as a function of the position in the main and side stacks of the P0006 experiment. Experimental results are compared with theoretical calculations and the effect of the strong location dependence of particle fluences is explained by the three dimensional shielding model of the P0006 stack. Through comparisons between experimental results and calculations, this work will lead to the refinement of the radiation environment computational models.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, Second LDEF Post-Retrieval Symposium Abstracts; p 21
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  • 10
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    Revised predictions of LDEF exposure to trapped protons (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Initial estimates of LDEF exposure to the trapped proton environment were reported previously to aid in the interpretation dosimetry data and in conjunction with dosimetry response predictions. These previous estimates were made using the standard NASA AP8 trapped proton models for two sets of assumed conditions: (1) the omnidirectional flux spectra were calculated with the LDEF altitude and solar activity variations taken into account; and (2) the NASA Marshall anisotropy model was applied to obtain directional spectra, but only for solar minimum conditions and at a single altitude. Herein, the directional trapped proton fluence spectra is calculated considering both the altitude variation and solar activity during the LDEF mission. These additional results represent an extension of previous calculations to provide a more definitive description of the LDEF trapped proton exposure.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA. Langley Research Center, Second LDEF Post-Retrieval Symposium Abstracts; p 15
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