astronauts to continue functioning after the astronauts returned to Earth. For Apollo 17, the ALSEP experiments were a Heat Flow Experiment (HFE), to measure the rate of heat flow from the interior of the Moon, a Lunar Surface Gravimeter (LSG), to measure alterations in the lunar gravity field at the site, a Lunar Atmospheric Composition Experiment (LACE), to investigate what the lunar atmosphere is made up of, a Lunar Seismic Profiling Experiment (LSPE), to detect nearby seismic activity, and a Lunar Ejecta and Meteorites Experiment (LEME), to measure the velocity and energy of dust particles. Of these, only the HFE had been flown before; the others were new. The HFE had been flown on the aborted Apollo 13 mission, as well as on Apollo 15 and 16, but placed successfully only on Apollo 15, and unexpected results from that device made scientists anxious for a second successful emplacement. It was successfully deployed on Apollo 17. The lunar gravimeter was intended to detect wavers in gravity, which would provide support for Albert Einstein's general theory of relativity; it ultimately failed to function as intended. The LACE was a surface-deployed module that used a mass spectrometer to analyze the Moon's atmosphere. On previous missions, the Code Cathode Gauge experiment had measured the quantity of atmospheric particles, but the LACE determined which gases were present: principally neon, helium and hydrogen. The LSPE was a seismic-detecting device that used geophones, which would detect explosives to be set off by ground command once the astronauts left the Moon. When operating, it could only send useful data to Earth in high bit rate, meaning that no other ALSEP experiment could send data then, and limiting its operating time. It was turned on to detect the liftoff of the ascent stage, as well as use of the explosives packages, and the ascent stage's impact, and thereafter about once a week, as well as for some 100 hour periods. The LEME had a set of detectors to measure the characteristics of the dust particles it sought. It was hoped that the LEME would detect dust impacting the Moon from elsewhere, such as from comets or interstellar space, but analysis showed that it primarily detected dust moving at slow speeds across the lunar surface. All powered ALSEP experiments that remained active were deactivated on September 30, 1977, principally because of budgetary constraints. Other lunar-surface science Like Apollo 15 and