Anne M. Adamczyk

Full mission astronaut radiation exposure assessments for long duration lunar surface missions

Risk to astronauts due to ionizing radiation exposure is a primary concern for missions beyond Low Earth Orbit (LEO) and will drive mission architecture requirements, mission timelines, and operational practices. For short missions, radiation risk is dominated by the possibility of a large Solar Particle Event (SPE). Longer duration missions have both SPE and Galactic Cosmic Ray (GCR) risks. SPE exposure can contribute significantly toward cancer induction in combination with GCR. As mission duration increases, mitigation strategies must address the combined risks from SPE and GCR exposure. In this paper, full mission exposure assessments were performed for the proposed long duration lunar surface mission scenarios. In order to accomplish these assessments, previously developed radiation shielding models for a proposed lunar habitat and rover were utilized. End-to-End mission exposure assessments were performed by first calculating exposure rates for locations in the habitat, rover, and during Extra-Vehicular Activities (EVA). Subsequently, total mission exposures were evaluated for the proposed timelines. Mission exposure results, assessed in terms of effective dose, are presented for the proposed timelines and recommendations are made for improved astronaut shielding and safer operational practices.

Electromagnetic Dissociation Cross Sections Using Weisskopf-Ewing Theory

Abstract It is important that accurate estimates of crew exposure to radiation are obtained for future long-term space missions. Presently, several space radiation transport codes, all of which take as input particle interaction cross sections that describe the nuclear interactions between the particles and the shielding material, exist to predict the radiation environment. The space radiation transport code HZETRN uses the nuclear fragmentation model NUCFRG2 to calculate electromagnetic dissociation (EMD) cross sections. Currently, NUCFRG2 employs energy-independent branching ratios to calculate these cross sections. Using Weisskopf-Ewing (WE) theory to calculate branching ratios for compound nucleus reactions, however, is more advantageous than the method currently employed in NUCFRG2. The WE theory can calculate not only neutron and proton emission, as in the energy-independent branching ratio formalism used in NUCFRG2, but also deuteron, triton, helion, and alpha-particle emission. These particles can contribute significantly to total exposure estimates. In this work, photonuclear cross sections are calculated using WE theory and the energy-independent branching ratios used in NUCFRG2 and then compared to experimental data. It is found that the WE theory gives comparable but mainly better agreement with data than the energy-independent branching ratio. Furthermore, EMD cross sections for single neutron removal are calculated using WE theory and an energy-independent branching ratio used in NUCFRG2 and compared to experimental data.

Estimates of Signicant Post-Carrington Solar Particle Event Radiation Exposures on Mars

1864, 1878, 1894, 1895, and 1896), are made for male and female crew members located at the mean surface elevation and at an altitude of 8 km in the Martian atmosphere. The incident solar particle event proton energy distributions for these events are assumed to be similar to that of the Band function t of the February 1956 event. Radiation exposure estimates were performed using NASA’s On-Line Tool for the Assessment of Radiation in Space (OLTARIS). The HZETRN (High charge (Z) and Energy TRaNsport) space radiation transport code, which is incorporated into OLTARIS, was used to describe the transport of incident protons and any secondary particles generated by their interactions with the atmosphere of Mars, through spacesuit, surface lander, or permanent habitat shielding, and body organ self-shielding. Estimates of eective dose and organ dose are made using the Computerized Anatomical Male (CAM), Computerized Anatomical Female (CAF), Male Adult voXel (MAX), and Female Adult voXel (FAX) human geometry models. The predicted exposures are compared with current NASA Permissible Exposure Limits (PELs).

Estimates of Carrington-Class Solar Particle Event Radiation Exposures on Mars Behind Polyethylene Shielding

Radiation exposure estimates for crew members on the surface of Mars are made for solar particle event proton radiation environments comparable to the Carrington event of 1859. We assume that the proton energy distribution for this Carrington-type event is similar to that of the Band Function fit of the February 1956 event. In this work we use the BRYNTRN radiation transport code, originally developed at NASA Langley Research Center. The Computerized Anatomical Male and Female human geometry models were utilized to estimate exposures for polyethylene shield areal densities similar to those provided by a spacesuit, a surface lander, and a permanent habitat located at various altitudes in the Mars atmosphere. Comparisons of the predicted organ exposures are made with previously reported values obtained for aluminum shielding and current NASA Permissible Exposure Limits (PELs).