Alva C. Hardy

Radiation environment models and the atmospheric cutoff.

The limitations of radiation environment models are examined by applying the model to the South Atlantic anomaly (SAA). The local magnetic-field-intensity (in gauss) and McIlwain (1961) drift-shell-parameter contours in the SAA are analyzed. It is noted that it is necessary to decouple the atmospheric absorption effects from the trapped radiation models in order to obtain accurate radiation dose predictions. Two methods for obtaining more accurate results are proposed.

Space radiation shielding analysis and dosimetry for the Space Shuttle program

Active and passive radiation dosimeters have been flown on every Space Shuttle mission to measure the naturally‐occurring, background Van Allen and galactic cosmic radiation doses that astronauts and radiation‐sensitive experiments and payloads receive. A review of the various models utilized at the NASA/Johnson Space Center, Radiation Analysis and Dosimetry is presented. An analytical shielding model of the Shuttle was developed as an engineering tool to aid in making premission radiation dose calculations and is discussed in detail. The anatomical man models are also discussed. A comparison between the onboard dosimeter measurements for the 24 Shuttle missions to date and the dose calculations using the radiation environment and shielding models is presented.

Radiation Exposure and Risk Assessment for Critical Female Body Organs

Space radiation exposure limits for astronauts are based on recommendations of the National Council on Radiation Protection and Measurements. These limits now include the age at exposure and sex of the astronaut. A recently-developed computerized anatomical female (CAF) model is discussed in detail. Computer-generated, cross-sectional data are presented to illustrate the completeness of the CAF model. By applying ray-tracing techniques, shield distribution functions have been computed to calculate absorbed dose and dose equivalent values for a variety of critical body organs (e.g., breasts, lungs, thyroid gland, etc.) and mission scenarios. Specific risk assessments, i.e., cancer induction and mortality, are reviewed. 13 refs.

Space Radiation Exposures for Manned Polar Missions: A Parametric Study

Manned operations in low-earth, polar orbit will increase the risk of space radiation exposures to astronauts. The three sources of naturally-occurring space radiation are the geomagnetically-trapped Van Allen belt protons and electrons, galactic cosmic radiation, and solar flare-related particles. To date, the majority of the Space Shuttle missions have flown at low inclinations (28.5 deg). Five Shuttle missions were flown at inclinations greater than 49 deg. Measurements obtained from onboard radiation dosimeters from these five high latitude missions showed an increase in dose due to galactic cosmic radiation. The geomagnetic field offers less protection from both solar and galactic particles as the orbital inclination increases with polar missions being the worst.

Space crew radiation exposure analysis system based on a commercial stand-alone CAD system

Major improvements have recently been completed in the approach to spacecraft shielding analysis. A Computer-Aided Design (CAD)-based system has been developed for determining the shielding provided to any point within or external to the spacecraft. Shielding analysis is performed using a commercially available stand-alone CAD system and a customized ray-tracing subroutine contained within a standard engineering modeling software package. This improved shielding analysis technique has been used in several vehicle design projects such as a Mars transfer habitat, pressurized lunar rover, and the redesigned Space Station. Results of these analyses are provided to demonstrate the applicability and versatility of the system.