American Society of Civil Engineers


Estimating the Integrated Radiation Dose for a Conjunction-Class Mars Mission Using Early MARIE Data


by John F. Connolly, (NASA — Johnson Space Center, Houston, TX 77058)

pp. 999-1006, (doi:  http://dx.doi.org/10.1061/40722(153)136)

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Document type: Conference Proceeding Paper
Part of: Engineering, Construction, and Operations in Challenging Environments: Earth and Space 2004
Abstract: The Martian Radiation Environment Experiment (MARIE) instrument is currently orbiting Mars aboard the Mars Odyssey spacecraft. During its cruise to Mars, it returned radiation environment data from interplanetary space, and now in Mars orbit, it continues to measure the radiation dose contributions of both Galactic Cosmic Rays (GCR) and Solar Proton Events (SPE). Data accumulated over almost the full year of Odyssey science operations compares unshielded integrated radiation dose equivalent in Mars orbit to internal detectors aboard the International Space Station. The findings show that the integrated radiation dose (combining GCR and SPE) is consistently higher in Odyssey’s 400 km polar orbit than in ISS’ 400 km Low Earth Orbit (LEO), on average about a factor or 2.5. MARIE measured 450mSv integrated annual dose equivalent as compared to the 170mSv/year measured aboard the ISS. This confirms expected results, since there is reduced solid angle shielding due to Mars’ size as well as the absence of Earth’s magnetosphere. No surface radiation measurements exist to accompany the Mars orbital data. Surface measurements have been identified as the highest priority in the National Research Council’s "Safe on Mars" report, and coincident surface and orbital measurements are necessary to model the shielding effect of the Martian atmosphere. It is assumed that dose equivalent on the surface will be reduced a factor of 2 simply by geometry, and an additional reduction will come from shielding by the atmosphere. This paper examines how using the measured radiation doses and comparing them to Low Earth Orbit dose equivalent guidelines, the total radiation dose expected for a 3-year human Mars mission is within current limits for astronauts. It also discussed how the GCR and SPE mix in interplanetary space is significantly different than for LEO, and how further biological research is needed to assess the biological effects of long-term exposure to GCR. MARIE data indicates that approximately 15% of the integrated dose contribution comes from SPE sources. Until further biological research is performed, and surface radiation measurements made, determination of absolute dose a human crew would experience, the effect of high GCR interplanetary doses, and the relationship to our LEO experience will remain estimates.


ASCE Subject Headings:
Data analysis
Mars
Planets
Radiation
Space exploration