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Radial distribution functions were calculated for 19 concentrated solutions of eight alkali‐metal halides. These are analyzed in terms of the sizes and environments of the aqueous ions. The sizes of the hydrated and associated ions are found to be given by their respective crystal ionic radii. From seven to nine water molecules occupy the first hydration spheres of non‐associated halide ions, the numbers being relatively independent of solution concentration but increasing slightly with increasing size of the ion. Second and third hydration spheres are correlated with the halide ions, the region of influence for the anions being larger than for the cations studied. Positive ions are found to lie on the dipolar axes and negative ions on the hydrogen—oxygen bond axes of the primary waters of hydration. In contrast to the lithium and sodium halide solutions, considerable direct contact among ions exists in cesium halide solutions. Increasing association occurs with increasing concentration of the solutions and decreasing size of the halide ion. No preferred spatial arrangement is found for the associated ionic species.

X‐ray studies of solutions of zinc bromide show four coordination for the zinc ion. In concentrated water and acetone solution, zinc is coordinated by two bromines and two oxygens, on the average. If the bromine/water ratio is increased by adding hydrobromic acid, zinc becomes totally coordinated by halide. These solutions are too concentrated, however, to speak of the existence of discrete ZnBr4= ions. Crystal radii serve to interpret contacts between species in solution.

The authors share the selection process for the cabin atmosphere for the Mercury, Gemini, and Apollo space vehicles.

A discussion of lubrication in space allows students to gain insights into the extreme temperatures in space.

The problem of protecting spacecraft from high temperature encountered during a mission has resulted in the development of several types of thermal protection systems which are described here.

A discussion of life-support systems for manned space flights: carbon dioxide removal, oxygen supply, food and water supply.

Acquiring more definitive answers to questions on the origin of life is one of the objectives of our Nation's space program.