title: Large solar flare radiation shielding requirements for manned interplanetary missions.
abstract: As the 21st century approaches, there is an ever-increasing interest in launching manned missions to Mars.  A major concern to mission planners is exposure of the flight crews to highly penetrating and damaging space radiations.  Beyond the protective covering of the Earth's magnetosphere, the two main sources of these radiations are galactic cosmic rays and solar particle events.  Preliminary analyses of potential exposures from galactic cosmic rays (GCR's) were presented elsewhere.  In this Note, estimates of shielding thicknesses required to protect astronauts on interplanetary missions from the effects of large solar flare events are presented.  The calculations use integral proton fluences for the February 1956, November 1960, and August 1972 solar particle events as inputs into the NASA Langley Research Center nucleon transport code BRYNTRN.  This deterministic computer code transports primary protons and secondary protons and neutrons through any number of layers of target material of arbitrary thickness and composition.  Contributions from target nucleus breakup (fragmentation) and recoil are also included.  The results for each flare are presented as estimates of dose equivalent [in units of roentgen equivalent man (rem)] to the skin, eye, and bloodforming organs (BFO) behind various thicknesses of aluminum shielding.  These results indicate that the February 1956 event was the most penetrating; however, the August 1972 event, the largest ever recorded, could have been mission- or life-threatening for thinly shielded (< or = 5 g/cm2) spacecraft.  Also presented are estimates of the thicknesses of water shielding required to reduce the BFO dose equivalent to currently recommended astronaut exposure limits.  These latter results suggest that organic polymers, similar to water, appear to be a much more desirable shielding material than aluminum.
authors.affiliation: NASA Langley Research Center, Hampton, Virginia.
authors.forename: L W
authors.initials: LW
authors.lastname: Townsend
authors.forename: J E
authors.initials: JE
authors.lastname: Nealy
authors.forename: J W
authors.initials: JW
authors.lastname: Wilson
authors.forename: W
authors.initials: W
authors.lastname: Atwell
mesh_terms: D000535:Aluminum; D003359:Cosmic Radiation / Q000009:adverse effects*; D004307:Dose-Response Relationship, Radiation; D005123:Eye / Q000528:radiation effects; D006413:Hematopoietic System / Q000528:radiation effects; D006801:Humans; D009502:Neutrons; D011522:Protons; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods / Q000592:standards*; D012867:Skin / Q000528:radiation effects; D016082:Solar System; D013026:Space Flight / Q000295:instrumentation*; D018531:Spacecraft / Q000295:instrumentation; D013997:Time Factors
chemical_list: D011522:Protons; D000535:Aluminum