used on Apollo 8 through 13. At , it was the heaviest vehicle yet flown by NASA, heavier than the launch vehicle for Apollo 13. A number of changes were made to avoid pogo oscillations, that had caused an early shutdown of the center J-2 engine on Apollo 13's S-II second stage. These included a helium gas accumulator installed in the liquid oxygen (LOX) line of the center engine, a backup cutoff device for that engine, and a simplified 2-position propellant utilization valve on each of the five J-2 engines. ALSEP and other lunar surface equipment The Apollo Lunar Surface Experiments Package (ALSEP) array of scientific instruments carried by Apollo 14 consisted of the Passive Seismic Experiment (PSE), Active Seismic Experiment (ASE), Suprathermal Ion Detector (SIDE), Cold Cathode Ion Gauge (CCIG), and Charged Particle Lunar Environmental Experiment (CPLEE). Two additional lunar surface experiments not part of the ALSEP were also flown, the Laser Ranging Retro-Reflector (LRRR or LR3), to be deployed in the ALSEP's vicinity, and the Lunar Portable Magnetometer (LPM), to be used by the astronauts during their second EVA. The PSE had been flown on Apollo 12 and 13, the ASE on Apollo 13, the SIDE on Apollo 12, the CCIG on Apollo 12 and 13, and the LRRR on Apollo 11. The LPM was new, but resembled equipment flown on Apollo 12. The ALSEP components flown on Apollo 13 were destroyed when its LM burned up in Earth's atmosphere. Deployment of the ALSEP, and of the other instruments, each formed one of Apollo 14's mission objectives. The PSE was a seismometer, similar to one left on the Moon by Apollo 12, and was to measure seismic activity in the Moon. The Apollo 14 instrument would be calibrated by the impact, after being jettisoned, of the LM's ascent stage, since an object of known mass and velocity would be impacting at a known location on the Moon. The Apollo 12 instrument would also be activated by the spent Apollo 14 S-IVB booster, which would impact the Moon after the mission entered lunar orbit. The two seismometers would, in combination with those left by later Apollo missions, constitute a network of such instruments at different locations on the Moon. The ASE would also measure seismic waves. It consisted of two parts. In the first, one of the crew members would deploy three geophones at distances up to from the