Vulnerability of Manned Orbital Command Posts to Natural Space Radiations

The shielding requirements for the protection of the crew of a manned orbital command post against the natural space radiations are investigated. Two types of orbits of military importance and of wide applicability are considered—a long-duration, high-altitude orbit above the Van Allen Belt and a short-duration, low-altitude polar orbit below it. Model environments for both orbits in terms of solar flare, cosmic, and Van Allen Belt radiations are postulated. Radiobiological tolerance criteria are investigated, and a somewhat unique criteria, based on partial recovery of sustained somatic damage, is proposed for the long duration mission. A mathematical description of the radiation transport of the separate environmental components through the radiation shield is formulated. Appropriate simplifications are used to obtain expressions for the doses due to primary protons, secondary protons and neutrons, and bremsstrahlung. Calculations are carried out on the IBM 7030 computer to obtain dose vs. thickness curves for different types and amounts of shielding material. These curves, together with the assumed model environment, and the postulated radiobiological tolerance criteria, are used to calculate minimum shielding thicknesses for both types of orbits. Conclusions are then drawn on the total amount of radiation shielding material that must be carried for each orbit.