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 16 was retrieved by the . They were safely aboard the "Ticonderoga" 37 minutes after splashdown. The Apollo 16 subsatellite (PFS-2) was a small satellite released into lunar orbit from the Service Module. Its principal objective was to measure charged particles and magnetic fields all around the Moon as the Moon orbited Earth, similar to its sister spacecraft, PFS-1, released eight months earlier by Apollo 15. "The low orbits of both subsatellites were to be similar ellipses, ranging from above the lunar surface." "Instead, something bizarre happened. The orbit of PFS-2 rapidly changed shape and distance from the Moon. In 2-1/2