RESUMEN
As part of a study funded by NASA MSFC to assess thecontribution of secondary particles in producing radiation damage to optoelectronics devices located on the International Space Station (IS), Monte Carlo calculations have been made to predict secondary spectra vs. shielding inside ISS modules and in electronics boxes attached on the truss (Armstrong and Colborn, 1998). The calculations take into account secondary neutron, proton, and charged pion production from the ambient galactic cosmic-ray (GCR) proton, trapped proton, and neutron albedo environments. Comparisons of the predicted neutron spectra with measurments made on the Mir space station and other spacecraft have also been made (Armstrong and Colborn, 1998). In this paper, some initial results from folding the predicted neutron spectrum inside ISS modules from Armstrong and Colborn (1998) with several types of radiation effects response functions related to electronics damage and astronaut-dose are given. These results provide an estimate of the practical importance of neutrons compared to protons in assessing radiation effects for the ISS. Also, the important neutron energy ranges for producing these effects have been estimated, which provides guidance for onboard neutron measurement requirements.
Asunto(s)
Modelos Teóricos , Método de Montecarlo , Neutrones , Protección Radiológica , Nave Espacial , Radiación Cósmica , Electrónica , Interacciones de Partículas Elementales , Medio Ambiente Extraterrestre , Humanos , Mesones , Protones , Dosis de RadiaciónRESUMEN
Ionizing radiation environment models, a 3-D spacecraft mass model, and radiation transport codes have been used to predict the radiation dose and linear energy transfer (LET) spectra measured at various locations on the LDEF satellite. The predictions are compared with thermoluminescent dosimeter measurements of the trapped proton and electron doses and with LET spectra measured by plastic nuclear track detectors. The predicted vs observed comparisons indicate some of the uncertainties of present ionizing radiation environment models for low Earth-orbit missions.
Asunto(s)
Electrones , Transferencia Lineal de Energía , Modelos Teóricos , Protones , Monitoreo de Radiación/instrumentación , Vuelo Espacial/instrumentación , Anisotropía , Carbono , Planeta Tierra , Interacciones de Partículas Elementales , Medio Ambiente Extraterrestre , Oxígeno , Dosis de Radiación , Protección Radiológica , Radiometría , Nave Espacial , Dosimetría TermoluminiscenteRESUMEN
Model calculations have been made to compare with the induced radioactivity measured for materials on the LDEF satellite. Predictions and data comparisons are made for aluminum spacecraft components and for vanadium and nickel samples placed at multiple locations on the spacecraft. The calculated vs observed activations provide an indication of present model uncertainties in predicting nuclear activation as well as the magnitude and directionality of the trapped proton environment for low-Earth orbit missions. Environment model uncertainties based on the activation measurements are consistent with the uncertainties evaluated using other LDEF radiation dosimetry data.
Asunto(s)
Medio Ambiente Extraterrestre , Modelos Teóricos , Protones , Vuelo Espacial , Anisotropía , Planeta Tierra , Níquel , Monitoreo de Radiación , Radiación Ionizante , Radioisótopos , Radiometría , Escandio , Radioisótopos de Sodio , Actividad Solar , Nave Espacial , VanadioRESUMEN
A three-dimensional (3D) mass model of the LDEF spacecraft and selected experiments has been developed to allow the influence of material shielding on ionizing radiation measurements and analyses to be determined accurately. This computer model has been applied in a stand-alone mode to provide 3D shielding distributions around radiation dosimeters to aid data interpretation, and has been interfaced with radiation transport codes for a variety of different types of radiation predictions. This paper summarizes the methodology used, the level of detail incorporated, and some example model applications.
Asunto(s)
Simulación por Computador , Modelos Teóricos , Protección Radiológica , Programas Informáticos , Vuelo Espacial/instrumentación , Nave Espacial/instrumentación , Medio Ambiente Extraterrestre , Monitoreo de Radiación , Radiación Ionizante , RadiometríaRESUMEN
The radiation environment on LDEF was monitored by cumulative absorbed dose measurements made with TLDs at different locations and shielding depths. The TLDs were included in four experiments: A0015(a) Biostack, P0004 Seeds in Space and P0006 Linear Energy Transfer Spectrum Measurements at the trailing edge (west side) of the satellite; M0004 Fiber Optics Data Link at the leading edge (east side); and A0015(b) Biostack at the Earth side. The shielding depths varied between 0.48 and 15.4 g/cm2, Al equivalent. Both the directional dependence of trapped protons incident on the satellite and the shielding thickness were reflected in absorbed dose values. The trapped proton anisotropy was measured by TLDs at the east and west sides of LDEF. At the east side doses ranged from 2.10 to 2.58 Gy under shielding of 2.90 to 1.37 g/cm2 (M0004) while on the west side doses ranged from 2.66 to 6.48 Gy under shielding of 15.4 to 0.48 g/cm2 (P0006). The west side doses were more than a factor of two higher, where the vertical shielding thicknesses to space were equal. Other west side doses of 3.04 to 4.49 Gy under shielding of 11.7 to 3.85 g/cm2 (A0015(a)) and 2.91 to 6.64 Gy under shielding of 11.1 to 0.48 g/cm2 (P0004) generally agreed with the P0006 results. The Earth side doses of 2.41 to 3.93 Gy under shielding of 10.0 to 1.66 g cm2 (A0015(b)) were intermediate between the east side and west side doses. Calculations utilizing a model of trapped proton spectra were performed by Watts et al. (1993) and comparisons of dose measurement and calculations may be found in a companion paper (Armstrong et al., 1996).
Asunto(s)
Radiación Cósmica , Modelos Teóricos , Protones , Monitoreo de Radiación/instrumentación , Vuelo Espacial , Dosimetría Termoluminiscente , Aluminio , Anisotropía , Océano Atlántico , Calibración , Planeta Tierra , Medio Ambiente Extraterrestre , Transferencia Lineal de Energía , Dosis de Radiación , Protección Radiológica , América del Sur , Nave EspacialRESUMEN
Neutron fluences were measured on LDEF in the low energy (< 1 MeV) and high energy (> 1 MeV) ranges. The low energy detectors used the 6Li(n,alpha)T reaction with Gd foil absorbers to separate thermal (< 0.2 eV) and resonance (0.2 eV-1 MeV) neutron response. High energy detectors contained sets of fission foils (181Ta, 209Bi, 232Th, 238U) with different neutron energy thresholds. The measured neutron fluences together with predicted spectral shapes were used to estimate neutron dose equivalents. The detectors were located in the A0015 and P0006 experiments at the west and Earth sides of LDEF under shielding varying from 1 to 19 g/cm2. Dose equivalent rates varied from 0.8 to 3.3 microSv/d for the low energy neutrons and from 160 to 390 microSv/d for the high energy neutrons. This compares with TLD measured absorbed dose rates in the range of 1000-3000 microGy/d near these locations and demonstrates that high energy neutrons contribute a significant fraction of the total dose equivalent in LEO. Comparisons between measurements and calculations were made for high energy neutrons based on fission fragment tracks generated by fission foils at different shielding depths. A simple 1-D slab geometry was used in the calculations. Agreement between measurements and calculations depended on both shielding depth and threshold energy of the fission foils. Differences increased as both shielding and threshold energy increased. The modeled proton/neutron spectra appeared deficient at high energies. A 3-D model of the experiments is needed to help resolve the differences.
Asunto(s)
Neutrones , Monitoreo de Radiación/instrumentación , Vuelo Espacial , Medio Ambiente Extraterrestre , Fluoruros , Compuestos de Litio , Protones , Dosis de Radiación , Protección Radiológica , Radiometría , Nave EspacialRESUMEN
Predictions of the LDEF mission's trapped proton and electron and galactic cosmic ray proton exposures have been made using the currently accepted models with improved resolution near mission end and better modeling of solar cycle effects. An extension of previous calculations, to provide a more definitive description of the LDEF exposure to ionizing radiation, is represented by trapped proton and electron flux as a function of mission time, presented considering altitude and solar activity variation during the mission and the change in galactic cosmic ray proton flux over the mission. Modifications of the AP8MAX and AP8MIN fluence led to a reduction of fluence by 20%. A modified interpolation model developed by Daly and Evans resulted in 30% higher dose and activation levels, which better agreed with measured values than results predicted using the Vette model.
Asunto(s)
Radiación Cósmica , Electrones , Modelos Teóricos , Protones , Actividad Solar , Vuelo Espacial , Radiometría , Reproducibilidad de los Resultados , Nave EspacialRESUMEN
Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.