Apollo 9 was launched on March 3, 1969. It was the third manned mission in the United States Apollo program, and the first to test the Lunar Module in Earth orbit. The mission lasted 10 days, during which time the astronauts conducted a series of tests of the Lunar Module, including a two-hour spacewalk.
Apollo 10 was launched on May 18, 1969. It was the fourth manned mission in the United States Apollo program, and the second to test the Lunar Module in Earth orbit. The mission lasted eight days, during which time the astronauts conducted a dress rehearsal for the Apollo 11 mission, including a simulated lunar landing.
