The Lunar Atmospheric Composition Experiment (LACE) was a miniature magnetic deflection mass spectrometer (neutral mass spectrometer). The experiment's aim was to study the composition and variations of the lunar atmosphere. The only deployment of LACE was as part of the Apollo Lunar Surface Experiments Package (ALSEP) on Apollo 17 within the Taurus–Littrow valley.[1][2]
LACE was a follow-on to the Cold Cathode Gauges that were flown on Apollo 14 and Apollo 15.[3] Those experiments proved the existence of a tenuous lunar atmosphere and determined the upper bounds on the lunar atmospheric density during the lunar day and night, but left its composition unknown.[3]