Atmosphere
Space life support systems maintain atmospheres composed, at a minimum, of oxygen, water vapor and carbon dioxide. The partial pressure of each component gas adds to the overall barometric pressure.
By reducing or omitting diluents (constituents other than oxygen, e.g., nitrogen and argon) the total pressure can be lowered to a minimum of 21 kPa, the partial pressure of oxygen in the Earth's atmosphere at sea level. This can lighten spacecraft structures, reduce leaks and simplify the life support system.
However, the elimination of diluent gases substantially increases fire risks, especially in ground operations when for structural reasons the total cabin pressure must exceed the external atmospheric pressure; see Apollo 1. For this reason, most modern crewed spacecraft use conventional air (nitrogen/oxygen) atmospheres and use pure oxygen only in pressure suits during extravehicular activity where acceptable suit flexibility mandates the lowest inflation pressure possible.
Read more about this topic: Life Support System
Famous quotes containing the word atmosphere:
“The meeting in the open of two dogs, strangers to each other, is one of the most painful, thrilling, and pregnant of all conceivabale encounters; it is surrounded by an atmosphere of the last canniness, presided over by a constraint for which I have no preciser name; they simply cannot pass each other, their mutual embarrassment is frightful to behold.”
—Thomas Mann (1875–1955)
“We must be generously willing to leave for a time the narrow boundaries in which our individual lives are passed ... In this fresh, breezy atmosphere ... we will be surprised to find that many of our familiar old conventional truths look very queer indeed in some of the sudden side lights thrown upon them.”
—Bertha Honore Potter Palmer (1849–1918)
“Two thousand summers have imparted to the monuments of Grecian literature, as to her marbles, only a maturer golden and autumnal tint, for they have carried their own serene and celestial atmosphere into all lands to protect them against the corrosion of time.”
—Henry David Thoreau (1817–1862)