Arturo Ortiz

Date of Award

January 2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Space Studies

First Advisor

Vadim Rygalov

Abstract

Surface stays on Mars may expose astronauts to high radiation doses from solar flares and galactic cosmic radiation (GCR). We estimated shielding required for a surface habitat, and assessed environments inside a planetary rover and space suit, under historically severe solar flare and GCR conditions, using the HZETRN radiation computer code. A 1m layer of Mars regolith can protect the habitat up to 30 km surface elevation. Polyethylene at 5, 10, and 15 g/cm2 can protect up to 0, 10, and 20 km, respectively. The rover protects from acute exposure up to -0.7 km while a space suit protects up to -0.6 km. The shielded habitat is adequate as the primary radiation storm shelter, while the rover is inadequate as the secondary shelter. Scenarios for 365 day surface stays predict exposures of 270 to 1196 mSv, depending on sheltering and elevation. Permissible limits are met only for minimal surface exploration.

The planetary surface exploration concepts examined under these investigations are the University of North Dakota (UND) Inflatable Lunar-Martian Habitat (ILMH), Pressurized Electric Rover (PER), and NDX-2 space suit. The radiation environments are the February 1956 solar flare and 1977 solar minimum GCR, over a Mars surface elevation range of -10 to 30 km. Computational analyses were performed using the NASA Langley HZETRN and NUCFRG3 radiation computer codes with ray-by-ray transport through three-dimensional shielding thickness distributions.

Surface exploration scenarios were developed to estimate exposure for 365 day surface stays. A minimal scenario entails exploration below 4 km elevation, with the solar flare occurring while the astronaut is inside the protection of a lightly shielded ILMH deployed at 0 km. An intermediate scenario entails the same conditions, but with the solar flare occurring while the astronaut is outside at 4 km and protected only by space suit fabric. An extreme scenario includes a climbing expedition up to 30 km elevation, with the solar flare occurring between 24 and 30 km, while the astronaut is outside and protected only by space suit fabric. Total exposure under the three scenarios is 270, 337, and 1196 mSv, respectively, with limits for acute exposure exceeded under the intermediate and extreme scenarios. Space suit fabric provides almost negligible protection during extravehicular activity. Acute exposure under the extreme scenario exceeds the threshold for acute radiation syndrome. The weak protection provided by the PER and space suit drives a need to formulate alternative radiation protection strategies involving major restrictions on surface operations along with early detection and warning of solar storm activity.

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