Active Dosimeter‐Based Estimate of Astronaut Acute Radiation Risk for Real‐Time Solar Energetic Particle Events

Abstract

Radiation exposure from solar energetic particle (SEP) events becomes a much greater concern as human exploration extends beyond low Earth orbit and the protective environment of Earth's magnetic field. Free‐space SEP events have an increased impact on mission planning and operations, as countermeasures may be necessary to avoid exceeding astronaut permissible exposure limits. Operational analysis tools are needed to assess acute radiation risk during SEP events in order to determine courses of action during the mission. A methodology has been developed to meet this need, which utilizes onboard vehicle dosimeter measurements to estimate organ dosimetric quantities at astronaut crew locations in real time. The estimated organ doses provide the necessary inputs to acute biological response models that predict radiation‐induced performance decrement and other acute radiation effects. The real‐time SEP organ dose estimation methodology has been combined with an acute biological response model, providing an active dosimeter‐based acute radiation risk model for operational mission planning, and determining radiation exposure mitigation measures for deep‐space exploration missions. This new tool has been developed specifically for National Aeronautics and Space Administration's Orion Multi‐Purpose Crew Vehicle storm shelter environment but could easily be extended to other vehicles. The methodology for estimating SEP organ doses is evaluated and assessed in this paper, and a simulation of the acute radiation responses in the Multi‐Purpose Crew Vehicle storm shelter is shown for the historical October 1989 SEP event. The operational acute radiation risk model will be utilized on National Aeronautics and Space Administration's Exploration Mission 1 and Exploration Mission 2.

Characterization of Solar Energetic Particle Radiation Dose to Astronaut Crew on Deep‐Space Exploration Missions

“…For example, a forecast of integral proton fluence, and especially >100 MeV integral fluence, can potentially yield a reliable forecast of vehicle BFO dose, a quantity that can be evaluated and adjusted or improved in real time using the existing operational acute radiation risk tool (Mertens et al, 2018). For example, a forecast of integral proton fluence, and especially >100 MeV integral fluence, can potentially yield a reliable forecast of vehicle BFO dose, a quantity that can be evaluated and adjusted or improved in real time using the existing operational acute radiation risk tool (Mertens et al, 2018).…”

“…The calculation details were previously published by Mertens et al (2018). The calculation details were previously published by Mertens et al (2018).…”

“…The integral proton fluences reported in the tables are fluences outside the spacecraft. Note that these three episodes are, in reality, indistinguishable in their calculated radiation risk characteristics since the separation in computed BFO doses among these episodes is smaller than the uncertainties in the calculations (Mertens et al, 2018). In this context, an episode defines events originating from the same active region on the Sun, which may include a single event or multiple events.…”

“…NASA has established a limit of 250 milli-gray-equivalent (mGy-Eq) in the blood forming organs (BFOs) as a means of minimizing SEP radiation exposure and limiting acute biological responses to worst-case SEP events. In a previous paper, the methodology and initial assessment of a new operational acute radiation risk tool was presented (Mertens et al, 2018), which is based on the Orion Multipurpose Crew Vehicle (MPCV) design and utilizes the MPCV's onboard dosimeter measurements. In a previous paper, the methodology and initial assessment of a new operational acute radiation risk tool was presented (Mertens et al, 2018), which is based on the Orion Multipurpose Crew Vehicle (MPCV) design and utilizes the MPCV's onboard dosimeter measurements.…”

“…As a result, NASA's radiation protection approaches against SEP exposure will require effective in-flight shielding strategies combined with real-time, operational radiation environment monitoring and risk analysis tools (Cucinotta et al, 2010;Hu et al, 2009). The objective is to provide results that will help guide the development of future space weather architectures needed to support SEP radiation risk mitigation strategies by enhancing and extending the current nowcast capability of the acute radiation risk tool (Mertens et al, 2018). This paper presents calculations of BFO doses at the crew locations of the Orion MPCV from a set of historical SEP events.…”