Apollo 10 was a complete staging of the Apollo 11 mission without actually landing on the Moon. It was launched on May 18th, 1969, and was the fourth crewed Apollo launch in the short space of seven months. The mission was designed to adhere as closely as possible to the plans for Apollo 11, including its trajectory to and from lunar orbit, the timeline of mission events, and even the angle of the Sun at ALS-2. However, no landing was attempted. The lunar module Snoopy descended toward the lunar surface, but (as planned) didnt quite make it, returning to orbit only 8.4 nautical miles above the surface of the moon. There was no technical reason why Snoopy couldnt land on the moon, but it was not attempted because the objective of the mission was to be only a "dress rehearsal" for landing. After a three-day cruise, Apollo 10 entered an initial lunar orbit on May 21, 1969, and the astronauts achieved the closest approach to the Moon until Apollo 11 landed two months later. The spacecraft that carried the astronauts on the "dress rehearsal" for the first moon landing was left in orbit around the sun, where it remains.