Abstract
The solar energetic particle (SEP) radiation environment is an important consideration for spacecraft design, spacecraft mission planning and human spaceflight. Herein is presented an investigation into the likely severity of effects of a very large Solar Particle Event (SPE) on technology and humans in space. Fluences for SPEs derived using statistical models are compared to historical SPEs to verify their appropriateness for use in the analysis which follows. By combining environment tools with tools to model effects behind varying layers of spacecraft shielding it is possible to predict what impact a large SPE would be likely to have on a spacecraft in Near-Earth interplanetary space or geostationary Earth orbit. Also presented is a comparison of results generated using the traditional method of inputting the environment spectra, determined using a statistical model, into effects tools and a new method developed as part of the ESA SEPEM Project allowing for the creation of an effect time series on which statistics, previously applied to the flux data, can be run directly. The SPE environment spectra is determined and presented as energy integrated proton fluence (cm−2 ) as a function of particle energy (in MeV). This is input into the SHIELDOSE-2, MULASSIS, NIEL, GRAS and SEU effects tools to provide the output results. In the case of the new method for analysis, the flux time series is fed directly into the MULASSIS and GEMAT tools integrated into the SEPEM system. The output effect quantities include total ionising dose (in rads), non-ionising energy loss (MeV g−1 ), single event upsets (upsets/bit) and the dose in humans compared to established limits for stochastic (or cancer-causing) effects and tissue reactions (such as acute radiation sickness) in humans given in grey-equivalent and sieverts respectively.
Highlights
In the design process for spacecraft and missions the space radiation environment is an important factor
All other results are within, or very nearly within, the error bars shown. These error bars represent the variance in the statistics for the MULASSIS/ Non-Ionising Energy Loss (NIEL) tool on the SPENVIS method results. These results show that significant degradation in the performances can be caused by displacement damage induced by a single harsh Solar Particle Event (SPE)
Four levels of extreme SPEs have been modelled using the SEPEM system, these have been compared to historical events for verification and the effects of these SPEs on components and humans have been estimated
Summary
In the design process for spacecraft and missions the space radiation environment is an important factor. An earlier event in February 1956 observed by neutron monitors (see Dorman et al 2004) is thought to have had an extremely hard spectrum making it more significant for effects resulting from incident particles of higher energies (>500 MeV) These two SPEs formed the basis for the worstcase events produced for the CREME-86 model (Adams 1986). This allows focus to be placed on the time periods important for the specific effect for humans or specific components and eliminates the need for multiple statistical model runs for different particle energies and the possible exaggeration of the worst-case through a combination of these outputs
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