Mark D. Weyland

Evaluation of the Dynamic Cutoff Rigidity Model Using Dosimetry Data From the STS-28 Flight

We have a developed a dynamic cutoff rigidity model based on computed world grids of vertical cutoff rigidities derived from employing the Tsyganenko magnetospheric model. The dynamic range of this model covers all magnetic activity levels specified by integer values of the Kp magnetic index. We present comparisons of the measured dose observed on the space shuttle during the August 1989 solar proton event with the dose computed from solar particles predicted to be allowed through the magnetosphere to the space shuttle position. We find a one-to-one correspondence between the portion of the orbit predicted to be subjected to solar protons and the portion of the orbit where solar particle dose measurements were obtained.

Earth-Moon-Mars Radiation Environment Module (EMMREM)

We are preparing to return humans to the Moon and setting the stage for exploration to Mars and beyond. However, it is unclear if long missions outside of Low-Earth Orbit (LEO) can be accomplished with acceptable risk. The central objective of our project, the Earth-Moon-Mars Radiation Exposure Module (EMMREM), is to develop and validate a numerical module for completely characterizing time-dependent radiation exposure in the Earth-Moon-Mars and Interplanetary space environments. EMMREM will provide the ability to predict radiation exposure on the surface or atmosphere of Earth, on the Moon, Mars, and in interplanetary space between Earth and Mars. EMMREM is being designed for broad use by researchers to predict radiation exposure by integrating over almost any incident particle distribution from interplanetary space. EMMREM is being developed using contemporary state-of-the-art particle radiation models. Beyond this, it will have the capability to incorporate new and improving models, as they become available, to give continually improved estimates of radiation hazards and effects. EMMREM will be comprehensively validated using direct and contemporaneous measurements near Earth, at the Moon and Mars to significantly reduce uncertainties in radiation exposure predictions. EMMREM will characterize the extremes, statistics, and variations over time of radiation exposure caused by solar energetic particles and cosmic rays. The results of EMMREM will improve risk assessment models so that future human exploration missions can be adequately planned for. This makes highly relevant to NASAs Vision for Space Exploration and the Living With a Star Programs.

Radiation Environment and Shield Modeling Validation for CEV Design

The International Space Station (ISS) and the earlier station MIR provided the proving ground for future human long-duration space activity. A recent European Space Agency study recommended “…Measurement campaigns on the ISS form the ideal tool for experimental validation of radiation environment models, of transport code algorithms, and reaction cross sections.” Indeed, prior measurements on Shuttle have provided vital information impacting both environment model and transport code development by requiring dynamic models of the Low Earth Orbit (LEO) environment. Recent studies using CAD models of the ISS 7A configuration with TLD (thermo-luminescent detector) area monitors demonstrated that computational dosimetry requires environmental models with accurate non-isotropic as well as dynamic behavior, detailed information on rack loading, and an accurate 6-degree-of-freedom description of the ISS trajectory. The ISS model is now configured for 11A and uses non-isotropic and dynamic geomagnetic transmission and trapped proton models. The ISS 11A is instrumented with both passive and active dosimetric devices. ISS 11A and LEO model validation is an important step in preparation of the design and validation of the Crew Exploration Vehicle (CEV) under the Constellation program.