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It became the number one lookup on May 16, 2011.
During the final mission of the Space Shuttle Endeavour, many people were moved to use the word. For example, according to one report from Cape Canaveral,
"...signs outside area businesses cheered Endeavour on with messages of 'godspeed' and 'go.'" Marcia Dunn, Associated Press, May 16, 2011
Godspeed, meaning "a prosperous journey," comes from the Middle English God spede you ("God prosper you").
Godspeed was originally and sometimes still is used to wish success to someone who is going away. These days it's more often used to express hopes for a safe trip. It's a formal word with an old-fashioned feel that makes it particularly appropriate for official voyages with a sense of risk.
And even though the speed in Godspeed doesn't mean "the rate at which something moves," we also suspect that it feels right for a space vehicle that can travel around 17,000 miles per hour.