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
Third-party evidence for Apollo Moon landings party observers could expect to see the various craft at specific times according to scheduled launch times and planned trajectories. The Soviet Union monitored the missions at their Space Transmissions Corps, which was "fully equipped with the latest intelligence-gathering and surveillance equipment." Vasily Mishin, in an interview for the article "The Moon Programme That Faltered," describes how the Soviet Moon programme dwindled after the Apollo landing. The missions were tracked by radar from several countries on the way to the Moon and back. A group at Kettering Grammar School, using simple radio equipment, monitored Soviet and U.S. spacecraft and calculated