The Apollo Lunar Surface Experiments Package (ALSEP) was a set of scientific equipment and laboratory instruments deployed on the Moon during astronauts’ extravehicular activity (EVA). Many of the pieces were left on the lunar surface to conduct further experiments and send results back to Earth. The contents of an ALSEP varied from mission to mission but could include a Lunar Surface Gravimeter, passive seismic experiment package, and a solar wind spectrometer. Due to its limited EVA time, Apollo 11 did not deploy a full complement ALSEP, instead using what was called an Early Apollo Lunar Experiments Package. This package included a seismometer and Laser Ranging Retro Reflector.