Lunar mortar remains on Descartes site

A mortar capable of firing explosive grenades up to 1,500 meters, remotely controlled from Earth, remains at the Descartes site where Apollo 16 astronauts landed. This device was part of an active seismic experiment (S-033) designed to study the structure of the lunar regolith using an 11.2 kg mortar and 21 explosive initiators.

Experiment aimed at lunar geology

The mortar was deployed at the Descartes site, a mountainous area selected for its unique geological features. It was intended to fire four grenades at specific distances—150, 300, 900, and 1,500 meters—from a seismometer, with each grenade’s mass adjusted according to the targeted distance.

Remote firing and partial success

The grenades were fired remotely from Earth after the Apollo 16 crew had left. During this time, the ALSEP, a network of scientific instruments left on the Moon, was set to high-speed mode to record the results. Three grenades were successfully launched, but the largest one, meant for the 1,500-meter shot, failed due to a faulty sensor. The successful shots caused minor but measurable effects on the seismic instruments.

Deployment faced initial issues

The deployment process was not without problems. Of the four stakes meant to secure the mortar, only one was properly driven into the lunar surface. The pin of that stake twisted and became stuck, complicating the setup.

Future lunar seismic studies planned

Unlike Apollo 14, where a similar experiment failed to trigger a shot, future lunar seismology is expected to resume with the Farside Seismic Suite. This new project, scheduled between 2026 and 2027, has varying timelines suggested by different agencies, with CNES proposing June 2026 and JPL suggesting 2027. Until then, the Apollo 16 mortar remains inactive on the Descartes site.