FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-16/8

Title and Subtitle: Data for Rapid Evaluation of Vehicle Structure Related Radiation Shielding of Occupants of Extreme-Altitude Aircraft and Spacecraft

Report Date: November 2016

Authors: Copeland, K

Abstract: For aircraft and spacecraft, mass must be kept as low as possible; every kilogram of radiation shielding is one less kilogram of payload or fuel. The dominant source of ionizing radiation in the aerospace environment is galactic cosmic radiation (GCR). Unshielded effective dose rates from GCR are calculated to be as high as several tens of microsieverts per hour. Typical aircraft skin affords occupants less than 1 g/cm2 of Al as shielding. Added shielding of persons is a secondary concern because of limits on vehicle mass. Electronics are typically lightly shielded and redundant so as to avert critical failures or prolonged loss of use. Currently, in-flight dose rate calculations, such as those done by CARI-6 and CARI-7, ignore effects of vehicle structure and contents, as inclusion of such has been shown to increase accuracy by less than 10%, even at SST altitudes, while adding greatly to the calculation complexity by forcing each calculation to be ad hoc (i.e., such calculations typically add considerable complexity to the overall calculations for almost no benefit). However, in suborbital and extreme high-altitude flight, where atmospheric shielding is thin or absent, vehicle shielding can be considerably more important.

This report describes the construction of a database of secondary particle spectra resulting from irradiation of common aerospace materials of varying thicknesses with typical cosmic rays of varying energy. Examples are given for secondary particle spectra resulting from irradiation of aluminum (Al) and polyethylene (PE). These materials are commonly used as structural (Al) and/or shielding (Al and PE) materials for occupants of aircraft and spacecraft. The secondary spectra are calculated using Monte Carlo radiation transport program MCNPX 2.7.0 inside shells with of up to 100 cm thicknesses. The database of materials response matrices will enable programs like CARI and ESRAS to incorporate vehicle shielding of occupants in dose calculations, extending their usefulness to the space environment, where primary shielding of occupants comes from the vehicle.

Key Words: Ionizing Radiation, Shielding Data, Spacecraft, Aircraft, Aluminum

No. of Pages: 6