On his triumphant tour of Europe last month, Apollo 8 Astronaut Frank Borman amused his audiences by insisting that he, James Lovell and William Anders were older than they would have been had they not flown to the moon. "I think we should get overtime for that," he complained. Borman was joking about his pay, but he was quite serious about his aging. During their moon mission, the astronauts aged about 300 microseconds (300 millionths of a second) more than the people they left behind on earth.
Borman was informed of his overtime by University of Maryland Physicist Carroll Alley who, at the request of NASA officials, calculated the effects on the astronauts of two phenomena described by Einstein's relativity equations: 1) time actually runs slower for an object as its speed increases—the so-called "time dilation" effect, and 2) time speeds up for an object as it moves away from a body (like the earth) exerting a gravitational force.
While Apollo 8 was within 4,000 miles of the earth, Alley found, the spacecraft's speed was the predominant factor; time slowed up and the astronauts actually aged more slowly than mere earthlings. But beyond that distance, as the effects of earth's gravity lessened, Apollo's time began running fast. Over the entire journey, Alley says, Apollo's time passed more quickly than earth time by the 300 microseconds.
Despite Alley's calculations, Borman's tongue-in-cheek overtime demand is valid only for Astronaut Anders, who made his first space flight in Apollo 8. When Borman and Lovell were crewmates on the two-week orbital mission of Gemini 7, the time dilation effect was dominant for the entire period; the two astronauts thus aged less than those on earth by approximately 400 microseconds. Lovell's time also slowed down by about 100 microseconds during the four-day flight of Gemini 12.
Thus, during all their missions in space, Lovell and Borman respectively spent 200 and 100 microseconds less time than was recorded on earth—which means that they were paid for more time than they actually worked.