Solar X-ray Flare Hazards on the Surface of Mars

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to releases much larger than seen so far for the sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. We calculate the surficial reprocessed X-ray spectra using a Monte Carlo code we have developed. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. We estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 10^33--10^38 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO_2 ice columns required to provide 1/e shielding as 4--9 g cm^-2, depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ~ 100 g cm^-2 below the surface would be well protected.Comment: To be published in Planetary and Space Science; 33 pages, 3 figure

Work, love, and death thought accessibility: a terror management investigation

Terror management theory suggests that following culturally derived scripts for valued behaviour protects people from death concerns, and conversely, not meeting standards for cultural value can weaken this protection, heightening mortality concerns. Using this conceptual framework we examine (1) how considerations of loss of employment, a source of cultural value for many, relates to the accessibility of death-related cognition, and (2) the moderating role of job market health and (3) involvement in close relationships. Study 1 found that writing about being unemployed (vs. a control topic) led to greater mortality-related cognition. Study 2 found that considering unemployment heightened death-cognition, but only when participants were led to perceive the job market as unhealthy. Finally, Study 3 found that considering unemployment led to greater death-cognition, but not for those involved in a close relationship. Findings offer insight into a previously overlooked consequence of unemployment, and factors that may serve a protective function

Risks due to X-ray Flares during Astronaut Extravehicular Activity

Solar hard X-ray flares can expose astronauts on lunar and deep space extravehicular activities (EVAs) to dangerous acute biological doses. We combine calculations of radiative transfer through shielding materials with subsequent transfer through tissue to show that hazardous doses, taken as >= 0.1 Gy, should occur with a probability of about 10% per 100 hours of accumulated EVA inside current spacesuits. The rapid onset and short duration of X-ray flares and the lack of viable precursor events require strategies for quick retreat, in contrast to solar proton events, which usually take hours to deliver significant fluence and can often be anticipated by flares or other light-speed precursors. Our results contrast with the view that only particle radiation poses dangers for human space exploration. Heavy-element shields provide the most efficient protection from X-ray flares, since X-rays produce no significant secondary radiation. We calculate doses due to X-ray flares behind aluminum shields and estimate the required shield masses to accompany EVA rovers.Comment: 8 pages, 2 figures; to be published in Space Weathe

Scene Modeling And Augmented Virtuality Interface For Telerobotic Satellite Servicing

Teleoperation in extreme environments can be hindered by limitations in telemetry and in operator perception of the remote environment. Often, the primary mode of perception is visual feedback from remote cameras, which do not always provide suitable views and are subject to telemetry delays. To address these challenges, we propose to build a model of the remote environment and provide an augmented virtuality visualization system that augments the model with projections of real camera images. The approach is demonstrated in a satellite servicing scenario, with a multisecond round-trip telemetry delay between the operator on Earth and the satellite on orbit. The scene modeling enables both virtual fixtures to assist the human operator and augmented virtuality visualization that allows the operator to teleoperate a virtual robot from a convenient virtual viewpoint, with the delayed camera images projected onto the three-dimensional model. Experiments on a ground-based telerobotic platform, with software-created telemetry delays, indicate that the proposed method leads to better teleoperation performance with 30% better blade alignment and 50% reduction in task execution time compared to the baseline case where visualization is restricted to the available camera views