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For a few minutes during re-entry, manned spacecraft are just as isolated from communicating with Houston as when they are on the far side of the Moon. Radio signals cannot penetrate the cushion of ionized air surrounding the capsule as it falls through the Earth’s atmosphere.
Eventually, drag from the atmosphere slows the capsule enough that the air around it no longer ionizes, and the astronauts regain radio contact with Houston. Unlike today’s space shuttle or the Soviet Soyuz capsules, Apollo capsules returned to the sea, using parachutes to slow their final descent. There, a team of naval ships and helicopters recovered both crew and capsule.
This blog post is part of the @ApolloPlus40 series, which accompanies the ApolloPlus40 Twitter project by Nature News, a re-telling of the Apollo 11 lunar landing, 40 years later.