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 PGNCS Apollo PGNCS The Apollo Primary Guidance, Navigation and Control System (PGNCS) (pronounced "pings") was a self-contained inertial guidance system that allowed Apollo spacecraft to carry out their missions when communications with Earth were interrupted, either as expected, when the spacecraft were behind the Moon, or in case of a communications failure. The Apollo Command Module (CM) and Lunar Module (LM), were each equipped with a version of PGNCS. PGNCS, and specifically its computer, were also the command center for all system inputs from the LM, including the Kollsman Instrument built alignment optical telescope, the radar system, the manual translation and