Astronaut John Young on the lunar surface, Apollo 16 mission, 21 April 1972. Commander John Young performing the first Apollo 16 Spacewalk at the Apollo Lunar Surface Experiments Package (ALSEP) deployment site, Descartes landing site. The lunar surface drill is just behind and to the right, rack and bore stems (left), with the three-sensor Lunar Surface Magnetometer beyond. The dark object in the right background is the Radioisotope Thermoelectric Generator (RTG). Between the RTG and the drill is the Heat Flow Experiment.