Apollo 15 15 separated from the booster, the S-IVB maneuvered away, and would impact the Moon about an hour after the crewed spacecraft entered lunar orbit, though due to an error the impact was away from the intended target. The booster's impact was detected by the seismometers left on the Moon by Apollo 12 and Apollo 14, providing useful scientific data. There was a malfunctioning light on the craft's service propulsion system (SPS); after considerable troubleshooting, the astronauts did a test burn of the system that also served as a midcourse correction. This occurred about 028:40:00 into the mission. Fearing that the
Apollo 11 involved separating "Columbia" from the spent S-IVB stage, turning around, and docking with "Eagle" still attached to the stage. After the LM was extracted, the combined spacecraft headed for the Moon, while the rocket stage flew on a trajectory past the Moon. This was done to avoid colliding with the spacecraft, the Earth, or the Moon. A slingshot effect from passing around the Moon threw it into an orbit around the Sun. On July 19 at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. In the thirty orbits that followed,