Apollo 15: The Feather and Hammer Experiment on the Moon

Commander David Scott performed a live scientific demonstration on the surface of the Moon on August 2, 1971, to test the effects of gravity in a vacuum. During the final minutes of the third extravehicular activity of the Apollo 15 mission, Scott dropped a geologic hammer and a feather simultaneously to observe their rate of descent.

The experiment was designed to verify a principle of physics first concluded by Galileo hundreds of years prior: that all objects released together fall at the same rate regardless of their mass. Because the lunar surface is essentially a vacuum, there is no air resistance to slow down lighter objects, allowing them to accelerate at the same rate as heavier ones.

Technical Specifications of the Experiment

The demonstration utilized two objects with significantly different masses to highlight the effect of gravity in the absence of an atmosphere. Scott used a 1.32-kg aluminum geological hammer as the heavy object and a 0.03-kg falcon feather as the light object.

Both items were released simultaneously from a height of approximately 1.6 meters. Within the accuracy of the release, the objects were observed to undergo the same acceleration and strike the lunar surface at the same time.

Scientific Validation and Mission Impact

The results of the drop were documented in the Apollo 15 Preliminary Science Report by Mission Controller Joe Allen. The report noted that the outcome was predicted by well-established theory, yet remained a critical verification for the mission’s success.

During the final minutes of the third extravehicular activity, a short demonstration experiment was conducted. A heavy object (a 1.32-kg aluminum geological hammer) and a light object (a 0.03-kg falcon feather) were released simultaneously from approximately the same height (approximately 1.6 m) and were allowed to fall to the surface. Within the accuracy of the simultaneous release, the objects were observed to undergo the same acceleration and strike the lunar surface simultaneously, which was a result predicted by well-established theory, but a result nonetheless reassuring considering both the number of viewers that witnessed the experiment and the fact that the homeward journey was based critically on the validity of the particular theory being tested.

Joe Allen, NASA SP-289, Apollo 15 Preliminary Science Report, Summary of Scientific Results, p. 2-11

The verification of this gravitational theory was not merely academic; the calculations for the crew’s return journey to Earth relied on the validity of these physics principles.

Apollo 15 Mission Context

Apollo 15 was the ninth crewed mission of the Apollo program and marked the fourth successful Moon landing. It was designated as the first J mission, which focused on increased scientific capability and lunar exploration.

The mission was crewed by David R. Scott, Alfred M. Worden, and James B. Irwin. The spacecraft used for the mission included the Command and Service Module (CSM) Endeavour (CSM-112) and the Lunar Module Falcon (LM-10).

The mission timeline began with a launch on July 26, 1971, from Kennedy Space Center LC-39A using a Saturn V SA-510 rocket. The Lunar Module landed on the Moon on July 30, 1971, at the Hadley-Apennine landing site, located at 26°07′56″N 3°38′02″E.

The crew conducted four extravehicular activities on the lunar surface before the return launch occurred on August 2, 1971. The mission concluded with a splashdown in the North Pacific Ocean on August 7, 1971, where the crew was recovered by the USS Okinawa. The total mission duration was 12 days, 7 hours, 11 minutes, and 53 seconds.