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.
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