Correspondence in subject [X]
Closed ecological systems (Space environment) in subject [X]
Glenn, John, 1921- in subject [X]
Outer space -- Exploration in subject [X]
Project Mercury (U.S.) in subject [X]
Shepard, Alan B. (Alan Bartlett), 1923-1998 in subject [X]
Project Gemini (U.S.) in subject [X]