david scott moon experiment

To revisit this article, visit My Profile, then View saved stories .

• The Big Story
• Newsletters
• Steven Levy's Plaintext Column
• WIRED Classics from the Archive
• WIRED Insider
• WIRED Consulting

The Greatest Physics Demo of All Time Happened on the Moon

Stuff falls all the time. Maybe you’ve dropped a ball. Perhaps that cup of coffee slipped out of your hands. The mostly likely situation is that a cat decided to knock an object off a table—because that's what cats do.

And for as long as things have been falling, people have had questions about what is going on (and about the cat's motivation). Does a falling object move at a constant speed, or does it speed up? If you drop a heavy object and a light one at the same time, which will fall faster?

The great thing about these two questions is that you can ask pretty much anyone and they will have an answer—even if they are actually wrong. The even greater thing is that it's fairly simple to determine the answers experimentally. All you have to do is drop some stuff.

Some of the earliest explanations for what happens when you drop things go all the way back to Aristotle (around 350 BC), who was interested in explaining how the world works. Aristotle's answers were quite simple: If you let go of something, it will fall toward the ground. It will fall at a constant speed. If you drop two objects at the same time, the heavier one will move downward with a greater speed than the lighter one. That's it. And really, this seems like it could be true. I mean, if I drop a rock and a feather, it seems clear that the rock will hit the ground first.

But there is a problem. There's not an experiment to check if this is correct. Aristotle was a philosopher, not a scientist, and like most of the other Greek philosophers of his time, he was into thought experiments, not science experiments. (The Greeks knew that there couldn't be a perfect experiment, because some error would always be introduced into the data. They thought that seeking imperfect real-world evidence would just push them off the path of determining the ultimate truths of the universe through logic and reasoning.)

Aristotle's reasoning for this kind of motion actually makes sense. We can all agree that if you push something, it will move. The greater the pushing force, the more it will move—that means it would go faster. That makes sense, right? And if you hold a rock and a feather, the gravitational force on the rock is clearly greater. You can just feel that force when you lift the two objects up to compare them. There's no mystery there. So if the rock has a greater downward-pulling force, then it will have a greater downward falling velocity. If you drop a rock and a feather, the rock will hit the ground first. See? Physics isn't that hard.

Well, even though this explanation makes sense, it is indeed wrong. Really, the only thing that is correct is that normally a rock will hit the ground before a feather.

To understand why, let's start with the most basic idea—the relationship between force and motion. Most people call this Newton's second law, but if you go with “force-motion model,” that would be cool too. For movement in one dimension (like with a falling object), we can write this as:

This says that the total force on an object (F net ) is equal to the product of the object's mass (m) and the acceleration (a).

But what is the acceleration? In short, this is a value that describes how the velocity changes. So, an acceleration of 0 meters per second per second means that the velocity won't change. An acceleration of 10 m/s 2 means that in 1 second, the object's velocity will increase by 10 meters per second. The important thing is that forces change the velocity of an object. If something has a greater force, it doesn't move faster. It changes more . Change is the key.

There's a small problem, though. When you drop a rock from shoulder height above the ground, it will only take about half a second to fall. That's not very much time—certainly not enough for a person to determine that it's speeding up. It just looks like it falls very fast. In fact, the human eye is pretty good at detecting if something moves, but not so great at judging changes in speed. (Check out this awesome video from Veritasium on how humans track objects.) So it's hard to fault anyone (like Aristotle) for saying things fall at a constant speed. It really does look that way to the naked eye.

OK, but what about dropping a rock and feather—doesn't the rock hit first? Usually, the answer is yes. But let's replace the rock with a hammer and then just take a change of scenery and move the experiment to the moon. This is exactly what happened during the Apollo 15 lunar mission in 1971 . Commander David Scott took a hammer and an eagle feather and dropped them onto the lunar regolith. Here's what happened:

The feather and the hammer hit the ground at the same time.

Why did it happen? First, it is indeed true that even on the moon there is a greater gravitational force on the hammer than the feather. We can calculate this gravitational force as the product of mass (m in kilograms) and the gravitational field (g in newtons per kilogram). On the surface of the moon, the gravitational field has a value of 1.6 N/kg. If you put this expression in for the net force on a falling object, it looks like this:

Since both the gravitational force and the acceleration depend on the same mass, it's on both sides of the equation and cancels. That leaves an acceleration of -g. The hammer and the feather fall down with identical motions and hit the ground at the same time. Honestly, I'm just a little sad that the astronauts didn't use one of the higher-quality film cameras instead of a TV camera—but that's just me.

So, what's different about dropping something on the moon versus on Earth? Yes, there is a different gravitational weight on the moon—but that's not the issue. It's the lack of air that makes the difference. Remember that Newton's second law is a relationship between the net force and the acceleration. If you drop a feather on the surface of the Earth, there are two forces acting on it. First, there is the downward-pulling gravitational force that is equal to the product of mass and the gravitational field. Second, there is an upward-pushing force due to the interaction with the air, which we often call air drag . This air drag force depends on several things, but the important ones are the object's speed and the size of the object.

Let's look at a simple example. Suppose the feather has a mass of 0.01 kilograms. This would give it a downward gravitational force of 0.098 newtons. Now imagine the feather is moving downward with a velocity of 1 meter per second, and this produces an upward air drag force of 0.04 newtons. This means that the net force would be 0.04 N - 0.098 N = -0.058 N. That would give a downward acceleration of 5.8 m/s 2 compared to an object without air resistance, which would have an acceleration of 9.8 m/s 2 .

Yes, a falling rock also has an upward-pushing air drag force. If it was the same size as the feather and moving at the same speed, it would have the same upward drag force of 0.04 N. However, if it has a mass of 1 kilogram, then its downward gravitational force would be 9.8 newtons. The net force would be 9.4 N, to produce an acceleration of 9.4 m/s 2 . Because of the rock's larger mass, it would have a much greater acceleration and it would hit the ground first—at least on Earth.

Do heavier objects always hit the ground before lighter ones? Nope. Here are some simple experiments you can do at home to show that Aristotle was wrong. (Bonus: You don't even need to go to the moon to do them.)

The first experiment uses two sheets of paper—just plain paper that you can get from your printer. If the pieces are identical, then they have the same mass and the same downward gravitational force. Now take just one of those sheets and crumple it up into a ball. This decreases the size of the object, but not its mass. When you drop the normal paper and the crumpled paper, which one will hit the ground first?

Oh, you don't have any paper with you? Fine, here is what that looks like:

You can see that the crumpled paper hits first—even though the two pieces have the exact same mass. Right there, Aristotle is busted.

But wait, here’s another experiment. This one requires more complicated objects. See if you can get something with a large surface area but a low mass. For example, I have a piece of cardboard and a tiny piece of chalk. The cardboard is indeed more massive (100 grams vs. 1 gram for the chalk). But if I drop them, which will hit the ground first? Let's find out.

Check that out. Thanks to air resistance, the more massive cardboard hits after the chalk.

Again, Aristotle was wrong. (And if you repeated both of those comparison drops on the moon, where there isn't air resistance, the objects would hit the surface at the same time.)

Did we really have to go all the way to the moon to show how things fall? Of course not. But it's still one of the coolest physics demos I've ever seen. I can't wait for a repeat the next time there's an astronaut on the moon . Hopefully, this time they will use a better video camera.

• 📩 The latest on tech, science, and more: Get our newsletters !
• How Bloghouse's neon reign united the internet
• The US inches toward building EV batteries at home
• This 22-year-old builds chips in his parents' garage
• The best starting words to win at Wordle
• North Korean hackers stole $400M in crypto last year
• 👁️ Explore AI like never before with our new database
• 🏃🏽‍♀️ Want the best tools to get healthy? Check out our Gear team’s picks for the best fitness trackers , running gear (including shoes and socks ), and best headphones

Hammer and Feather Drop on the Moon

In 1971, astronaut David Scott conducted Galileo's famous hammer/feather drop experiment on the moon, during the Apollo 15 mission. Galileo had concluded that all objects, regardless of mass, fall at the same speed -- however, the resistance caused by the air (as in the case of the feather in Earth's atmosphere) can cause the feather to drop slower. Well, on the moon there is no atmosphere (a vacuum), so the objects should drop at the same speed. See for yourself how the experiment turned out in the video below.

As Mission Controller Joe Allen wrote in the Apollo 15 Preliminary Science Report :

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

Here's video of the experiment:

Ever since the hammer/feather drop in 1971, moon-hoax conspiracy theorists have been trying to prove that this footage was faked. Here's one video that claims to disprove NASA's experiment. I encourage you to read the YouTube comments on that hoax video for an entertaining nerd-fight. See also: high-resolution video of the experiment from NASA, and a mathematical discussion of the physics involved.

(Via Kottke.org. )

Suggested Searches

• Climate Change
• Expedition 64
• Mars perseverance
• SpaceX Crew-2
• International Space Station
• View All Topics A-Z

Humans in Space

Earth & climate, the solar system, the universe, aeronautics, learning resources, news & events.

NASA’s Artemis II Crew Uses Iceland Terrain for Lunar Training

NASA’s Webb Peers into the Extreme Outer Galaxy

What’s Up: September 2024 Skywatching Tips from NASA

• Search All NASA Missions
• A to Z List of Missions
• Upcoming Launches and Landings
• Spaceships and Rockets
• Communicating with Missions
• James Webb Space Telescope
• Hubble Space Telescope
• Why Go to Space
• Commercial Space
• Destinations
• Living in Space
• Explore Earth Science
• Earth, Our Planet
• Earth Science in Action
• Earth Multimedia
• Earth Science Researchers
• Pluto & Dwarf Planets
• Asteroids, Comets & Meteors
• The Kuiper Belt
• The Oort Cloud
• Skywatching
• The Search for Life in the Universe
• Black Holes
• The Big Bang
• Dark Energy & Dark Matter
• Earth Science
• Planetary Science
• Astrophysics & Space Science
• The Sun & Heliophysics
• Biological & Physical Sciences
• Lunar Science
• Citizen Science
• Astromaterials
• Aeronautics Research
• Human Space Travel Research
• Science in the Air
• NASA Aircraft
• Flight Innovation
• Supersonic Flight
• Air Traffic Solutions
• Green Aviation Tech
• Drones & You
• Technology Transfer & Spinoffs
• Space Travel Technology
• Technology Living in Space
• Manufacturing and Materials
• Science Instruments
• For Kids and Students
• For Educators
• For Colleges and Universities
• For Professionals
• Science for Everyone
• Requests for Exhibits, Artifacts, or Speakers
• STEM Engagement at NASA
• NASA's Impacts
• Centers and Facilities
• Directorates
• Organizations
• People of NASA
• Internships
• Our History
• Doing Business with NASA
• Get Involved

NASA en Español

• Aeronáutica
• Ciencias Terrestres
• Sistema Solar
• All NASA News
• Video Series on NASA+
• Newsletters
• Social Media
• Media Resources
• Upcoming Launches & Landings
• Virtual Guest Program
• Image of the Day
• Sounds and Ringtones
• Interactives
• STEM Multimedia

Hubble Examines a Spiral Star Factory

NASA’s SpaceX Crew-9 to Conduct Space Station Research

9 Phenomena NASA Astronauts Will Encounter at Moon’s South Pole

NASA Finds Summer 2024 Hottest to Date

Childhood Snow Days Transformed Linette Boisvert into a Sea Ice Scientist

NASA Summer Camp Inspires Future Climate Leaders

Solar Storms and Flares

Amendment 47: DRAFT F.12 Artemis IV Deployed Instruments Program Released for Community Comment.

NASA’s Hubble, Chandra Find Supermassive Black Hole Duo

Jason Williams

NASA Tunnel Generates Decades of Icy Aircraft Safety Data

Research Plane Dons New Colors for NASA Hybrid Electric Flight Tests 

NASA G-IV Plane Will Carry Next-Generation Science Instrument

SCaN Lunar Support

Printed Engines Propel the Next Industrial Revolution

NASA Moon to Mars Architecture Art Challenge

How to Apply to the NASA MINDS Challenge

15 Years Ago: Japan launches HTV-1, its First Resupply Mission to the Space Station

La NASA invita a los medios al lanzamiento de Europa Clipper

El X-59 de la NASA avanza en las pruebas de preparación para volar

La NASA invita a creadores de las redes sociales al lanzamiento de la misión Europa Clipper

16 min read

50 Years Ago: Apollo 15 on the Moon at Hadley-Apennine

Johnson space center.

Apollo 15 entered lunar orbit on July 29, 1971. The next day, astronauts David R. Scott , and James B. Irwin separated their Lunar Module (LM) Falcon from Alfred M. Worden , who remained in orbit aboard the Command Module (CM) Endeavour. Scott and Irwin touched down at the Hadley-Apennine site and conducted four spacewalks, including three excursions using the Lunar Roving Vehicle, for a combined total of 19 hours. They deployed an experiment package and collected 170 pounds of rock and soil samples to return to waiting scientists on Earth. In the meantime, Worden conducted an expanded set of observations and photography of the lunar surface from orbit. After their 67-hour lunar surface stay, Scott and Irwin prepared to rejoin Worden in orbit.

Following the July 26, 1971 launch from NASA’s Kennedy Space Center in Florida, Apollo 15’s translunar coast lasted 78 hours. During the astronauts’ fourth day in space, their spacecraft’s trajectory took them past the leading edge of the Moon, and as they disappeared behind it, as expected, all contact with the Mission Control Center (MCC) at the Manned Spacecraft Center, now NASA’s Johnson Space Center in Houston, was cut off. Thirty minutes later, the Service Propulsion System (SPS) engine fired for 6 minutes, 38 seconds to drop them into an elliptical 194-by-68 mile lunar orbit. As they reappeared from behind the Moon, Scott radioed to Houston, “Hello, Houston, the Endeavour’s on station with cargo, and what a fantastic sight.” From the MCC, capsule communicator (capcom) Karl G. Henize responded, “Beautiful news. Romantic, isn’t it?” prompting Scott to add, “Oh, this is really profound; I’ll tell you, fantastic!” During their first orbit, the astronauts excitedly provided a running commentary as they passed over the lunar landscape, flying over their landing site, still obscured in the pre-dawn darkness. Henize reported that the cameras and other experiments in the Service Module’s Scientific Instrument Module (SIM) bay all worked properly.

At the beginning of their third revolution, once again behind the Moon, the astronauts fired the SPS engine for 25 seconds to drop the high point of their orbit from 194 miles to 11 miles. The maneuver saved propellent in the LM as it began its descent from a low altitude. As they came out from behind the Moon, Scott reported, “Hello, Houston, Apollo 15. The Falcon is on its perch,” indicating that the LM was in the proper orbit to begin its descent. During their fourth revolution, the astronauts ate their first dinner in lunar orbit. Then, as they rounded to the farside, the crew began its first sleep period around the Moon. Scott, Worden, and Irwin slept soundly until the eighth revolution. The astronauts treated viewers on Earth to a 15-minute TV broadcast, pointing out the landmarks as the spacecraft flew over them. Back on Earth, Scott’s wife Lurton, his mother Marian, and Irwin’s wife Mary Ellen were accompanied by Apollo 11 astronaut Neil A. Armstrong as they watched the show from the MCC Visitor Gallery. Overnight, the Moon’s uneven gravity caused the low point of their orbit to drop to 8.7 miles, requiring a 19-second burn of the SPS engine to raise it back up to the more desirable 11 miles. While the astronauts executed the maneuver, in Mission Control, Flight Director Glynn S. Lunney and his Black Team of controllers took up their positions at the consoles, with Apollo 14 astronaut Edgar D. Mitchell as the new capcom. After they rounded to the Moon’s nearside on their 10th revolution, the astronauts viewed their landing site for the first time as the Sun had now risen over the Hadley-Apennine area.

On their next revolution, Scott and Irwin donned their spacesuits and entered and activated the LM Falcon, leaving Worden in the CM Endeavour. The crews closed the hatches between the spacecraft and prepared for undocking at the start of the 12th orbit. As Scott and Irwin prepared for the descent and landing, Worden fired the SPS engine for four seconds to circularize the CM’s orbit to 69 miles. On revolution 13, both spacecraft reappeared from behind the Moon and observed and photographed the Hadley-Apennine landing site. At the beginning of the next revolution, Falcon received the GO from capcom Mitchell in Mission Control to begin the powered descent to the surface. The LM’s descent stage engine ignited, at 10%thrust for the first 26 seconds before throttling up to full thrust to take them out of orbit and toward the surface. Scott and Irwin flew a trajectory steeper than their predecessors to clear the 12,000-foot ridge of the Apennine mountains that stood in front of their landing site. At the beginning of the descent, the spacecraft’s attitude had the crew essentially on their backs flying feet first. At an altitude of about 6,000 feet, the LM began the pitch-over maneuver and for the first time, Scott and Irwin saw their landing site ahead, with Hadley Rille clearly visible and Mount Hadley looming several hundred feet above them on their left. At 400 feet, Scott took over manual control of the LM, while Irwin called out altitude and descent rates. The first evidence of dust kicked up by the Falcon’s engine occurred at about 120 feet. By 50 feet above the lunar surface, dust obscured their view. Flying the last few feet by instruments alone, Scott and Irwin touched down on the Moon and Scott called to Mission Control, “Okay, Houston. The Falcon is on the Plain at Hadley.”

After a quick check of the LM’s systems, Mission Control gave Scott and Irwin the “Go” to stay on the surface. Falcon landed with its rear landing leg inside a shallow crater, the vehicle tilted backwards 6.9 degrees and to the left 8.6 degrees, well within the acceptable range for a successful liftoff. Following a change of shift in Mission Control, with Flight Director Milton L. Windler’s Maroon Team and astronaut Joseph P. Allen as capcom assuming their console positions, the two astronauts prepared for the first major activity on the surface, Scott’s standup spacewalk. About two hours after landing, Scott and Irwin depressurized the LM and opened the overhead hatch. Scott stood up on the ascent engine cover with his head and shoulders through the hatch, surveying their landing site. From his higher vantage point, about 23 feet above the surface, Scott took a series of photographs as he panned around to generate a 360-degree view of the landing site and provided a running commentary for the geologists in the Mission Control Science Support Room. Scott climbed back down and he and Irwin repressurized the LM, ending the 33-minute standup spacewalk. For the first time on the Moon, the astronauts removed their suits in preparation for their first night’s sleep. Program managers felt that with the longer stay and the experience of previous missions, removing the suits for the astronauts’ comfort outweighed any safety risks. Scott and Irwin went to sleep in their hammocks.

Both Scott and Irwin slept well their first night on the Moon, although Mission Control needed to awaken them about an hour early to deal with a potential oxygen leak that the astronauts fixed by closing a valve. Once that was resolved, they moved into preparing for the first of their three Moon walks, with capcom Allen back on console to assist them. Scott and Irwin put on their spacesuits, depressurized the LM, and Scott opened the hatch and backed out onto the LM’s porch. He pulled a lanyard that deployed a color TV camera so viewers could see him coming down the ladder. Scott jumped down to the footpad and then onto the lunar surface itself, saying, “As I stand out here in the wonders of the unknown at Hadley, I sort of realize there’s a fundamental truth to our nature. Man must explore. And this is exploration at its greatest.” Irwin joined him on the surface eight minutes later and collected the contingency sample. They next deployed the Lunar Roving Vehicle (LRV), or Rover, and Scott took it for a brief test drive, becoming the first human to drive on the Moon. They loaded up the Rover with the equipment required for the first traverse, including putting the TV camera on the vehicle that Edward I. “Ed” Fendell operated remotely from Mission Control to keep up with the astronauts’ activities.

Scott and Irwin set off toward their first stop, heading south-southeast along Hadley Rille toward Elbow Crater, 3.2 kilometers away. All along the drive, both astronauts provided a running commentary of the geologic features they observed. They parked the Rover at Elbow Crater, and pointed the high-gain antenna toward Earth to allow a continuation of the TV transmission. After collecting geology samples, they boarded the Rover for the short drive southeast to Station 2 near St. George Crater on the slopes of Mr. Hadley. Scott took samples from a boulder and Irwin took a double core sample from the crater rim. Getting back on the Rover, they drove down the slope and back north to the LM, omitting a planned Station 3 stop because they were running behind on the timeline. They parked near Falcon to load the Rover with some of the Apollo Lunar Surface Experiment Package (ALSEP) instruments. Scott drove to select a deployment site about 360 feet west-northwest of the LM while Irwin carried the remaining instruments. The two teamed up to deploy the ALSEP experiments. Scott had difficulty drilling the holes required for the heat flow experiment due to a harder subsurface than expected, so Mission Control told him to move to the next task and come back and finish the drilling during the second Moon walk. They then drove back to the LM where Scott deployed the Solar Wind Collector (SWC) experiment. After dusting each other off, they carried the samples collected during this excursion back into the LM and closed the hatch. The first Apollo 15 Moon walk lasted a then-record setting 6 hours and 34 minutes. After a well-earned dinner and a debrief with Mission Control, Scott and Irwin settled down for their second night on the Moon.

The next morning, Scott and Irwin suited up once again, depressurized Falcon and descended to the lunar surface. Less than an hour later, having checked out and loaded the Rover, they began their second lunar traverse heading south from the LM along the Front – the northern flank of Mt. Hadley – to Station 6. They parked the Rover on an 11-degree slope about 5 km from Falcon, the furthest any astronauts had traveled from their spacecraft up to that time. Scott took photographs using a 500 mm telephoto lens of Falcon as a small object in the distance, dwarfed by the scenery. After collecting numerous rock and soil samples, including a core sample, they packed up the Rover and headed west to sample a large, partially embedded, greenish boulder at Station 6a. Because of the 15-degree slope, Irwin held the Rover steady while Scott sampled the boulder. Next, they drove to Station 7 at Spur Crater where they found, among other numerous samples, a white crystalline rock later dubbed the Genesis Rock. On the way back to the LM, they made a quick stop at Dune Crater (Station 4) to sample a large vesicular boulder. From there they drove the 3.4 km back to the LM, setting a lunar land speed record of 12 km/h. Back at Falcon, they unloaded the collected samples from the Rover. Irwin stayed near the LM to take photographs and unstow the American flag while Scott continued on to finish the drill work for the heat flow experiment at the ALSEP site. Irwin walked out to the ALSEP site to conduct a soil mechanics experiment by digging a trench and Scott collected a core sample using the drill. They returned to the LM, Irwin walking and Scott driving the Rover, where they deployed the American flag. Once again, they carried their collected samples as they reentered the LM, repressurizing Falcon after being outside for 7 hours and 12 minutes, beating their previous record. Following a quick debrief with Mission Control and dinner, they settled down for their third night’s sleep on the Moon.

After a good night’s sleep, Scott and Irwin ate a quick breakfast and suited up for their third and final lunar traverse, the drive west to Hadley Rille. After depressurizing the LM, they descended to the surface, and loaded up the Rover with their needed equipment. Scott and Irwin took color photographs of each other saluting the American flag, and then Scott drove out to the ALSEP site while Irwin walked. Once there, and with great effort, they collected the core sample drilled the day before. They set off west toward the rille, stopping at Station 9 for photography and sample collection near a 15-meter diameter crater. After that brief stop, they continued due west to Station 9a on the rim of Hadley Rille to photograph the west side of the canyon and take core and other samples. They drove a short way northwest along the rim of the rille to Station 10 for some more photography of the canyon’s west wall. From there, they drove the 2.5 km back to the LM, picking up the drill core sample at the ALSEP site on the way. Back at the LM, they photographed and rolled up the Solar Wind Collector experiment for return to Earth. As they continued packing their samples and film cartridges for return to the LM, Scott provided a physics demonstration for the TV audience back on Earth.

“Well, in my left hand, I have a feather; in my right hand, a hammer. And I guess one of the reasons we got here today was because of a gentleman named Galileo, a long time ago, who made a rather significant discovery about falling objects in gravity fields. And we thought where would be a better place to confirm his findings than on the Moon. And so we thought we’d try it here for you. The feather happens to be, appropriately, a falcon feather for our Falcon. And I’ll drop the two of them here and, hopefully, they’ll hit the ground at the same time.” As the hammer and feather hit the lunar dust at the same time, Scott said, “How about that! Which proves that Mr. Galileo was correct in his findings.”

Not mentioned publicly until the crew’s postflight press conference, Scott left a memorial plaque and a statuette on the lunar surface dedicated to astronauts and cosmonauts lost in the line of duty. Scott then parked the Rover about 500 feet away from the LM, in a position that the TV camera could broadcast their liftoff a few hours later. After brushing each other off one last time, Scott and Irwin climbed back up the ladder and into the LM. They repressurized Falcon after spending 4 hours and 50 minutes outside.

Flight Director Gerald D. “Gerry” Griffin congratulated Scott and Irwin on their performance on the lunar surface, saying, “The whole Mission Control team wants to take their hats off to you for a fine job. It was a lot of fun.” Scott replied with his thanks, “Well, thank you, Gerry. We’d like to take our hats off to the whole team. By golly, you guys are really sharp down there, and we sure appreciate it. ‘Cause you know as well as we do we sure couldn’t do it without you.” Scott and Irwin busied themselves with preparations for liftoff, just three hours later.

To be continued…

John Uri NASA Johnson Space Center

Astronomy Picture of the Day

Apollo 15 Stand-Up Extravehicular Activity

Discover the audio excerpts of Apollo 15 Commander Dave Scott’s stand-up extravehicular activity (EVA) alongside visuals of the Hadley-Apennine region (the Apollo 15 landing site) on the Moon.

More info & download options

You Might Also Like

The Apollo 15 Demonstration of Acceleration Due to Gravity

The laws of physics tell us that the gravitational field at any one point is constant. This means that all objects will fall with a constant acceleration. A heavy object and a light object, when dropped from the same place at the same time, will fall at the same rate and hit the ground together.

Many people have difficulty with this principle because it does not seem to agree with our experience. If a feather and a hammer are released from the same height at the same time, the hammer will clearly hit the ground first. This is not a violation of the principle, though. The problem is that another force, air resistance, is interfering with the observation. While gravity treats all objects equally, air resistance does not. Significant air resistance acting on the light feather slows it down. There is much less air resistance acting on the heavy hammer, so it isn't slowed as much, and hits the ground first.

If only we could remove the effects of air resistance. Well, we can! There is no atmosphere, and therefore no air resistance, on the moon. Apollo 15 astronaut David Scott demonstrated this principle by dropping a feather and a hammer on the moon in 1971.

Clicking on the photo below (showing David Scott and the lunar rover vehicle on the moon), or on the link directly below it, will enable you to open or download a video clip of the experiment. Note: this is a large mpeg file, about 6.4 Mb, which will take a long time to download. The video clip lasts about 50 seconds. Make sure your sound is on.

• History & Society
• Science & Tech
• Biographies
• Animals & Nature
• Geography & Travel
• Arts & Culture
• Games & Quizzes
• On This Day
• One Good Fact
• New Articles
• Lifestyles & Social Issues
• Philosophy & Religion
• Politics, Law & Government
• World History
• Health & Medicine
• Browse Biographies
• Birds, Reptiles & Other Vertebrates
• Bugs, Mollusks & Other Invertebrates
• Environment
• Fossils & Geologic Time
• Entertainment & Pop Culture
• Sports & Recreation
• Visual Arts
• Demystified
• Image Galleries
• Infographics
• Top Questions
• Britannica Kids
• Saving Earth
• Space Next 50
• Student Center

• What was Neil Armstrong’s childhood like?
• What happened on Neil Armstrong’s Apollo 11 mission?
• What did Neil Armstrong do after Apollo 11?

David Scott

Our editors will review what you’ve submitted and determine whether to revise the article.

• New Mexico Museum of Space History - Biography of David R. Scott
• David Scott - Student Encyclopedia (Ages 11 and up)

David Scott (born June 6, 1932, San Antonio , Texas , U.S.) is a U.S. astronaut who was the commander of the Apollo 15 mission to the Moon .

After graduation from the U.S. Military Academy at West Point in 1954, Scott transferred to the U.S. Air Force and took flight training. He earned an M.S. in aeronautics and astronautics from the Massachusetts Institute of Technology (MIT) and went to Edwards Air Force Base in California to train as a test pilot. In 1963 he was among the third group of U.S. astronauts chosen.

Scott and commander Neil Armstrong crewed the flight of Gemini 8 (March 16, 1966). They successfully rendezvoused and docked with an uncrewed Agena target vehicle, which was the first space docking, but an electrical failure caused the Agena-Gemini craft to tumble wildly. The Gemini capsule was separated from the Agena. Control was finally reestablished, but the mission had to be aborted. Scott and Armstrong landed 10 hours 42 minutes after takeoff.

Scott served as command module pilot of the Apollo 9 flight with commander James McDivitt and lunar module pilot Russell Schweickart; their mission was launched on March 3, 1969. In Earth orbit these men rendezvoused and docked the command module with the lunar module, which was on its first crewed flight, and they successfully tested all systems necessary for a lunar landing.

On July 26, 1971, Scott, lunar module pilot James Irwin , and command module pilot Alfred Worden were launched on the Apollo 15 flight. After a 3 1 / 2 -day trip Scott and Irwin landed on the Moon, at the base of the Apennine Mountains near a gorge called Hadley Rille . Using the Lunar Roving Vehicle , they covered about 28 km (18 miles) on three separate treks and spent more than 17 hours outside their lunar module. The mission returned to Earth on August 7.

From 1972 to 1975 Scott was a member of the administrative staff of the Apollo- Soyuz Test Project . He then became director of the Dryden Flight Research Center at Edwards Air Force Base. He left the space program in 1977 to enter private business in Los Angeles . In 2004 he wrote a book, Two Sides of the Moon: Our Story of the Cold War Space Race , with Soviet cosmonaut Aleksey Leonov .

Apollo 15: A Mission of Many Firsts

Apollo 15 landed on the Moon fifty years ago today, on July 30, 1971. While Apollo 15 was the fourth mission to land a crew successfully on the lunar surface, it still pioneered many new technologies and had many firsts.

Some of the technologies developed for Apollo 15 included new suits, which were more flexible and had longer life support capabilities, as well as the Lunar Roving Vehicle (LRV), a rover capable of speeds up to 15 km / hour. With these advancements, astronauts Commander David (Dave) Scott and Lunar Module Pilot James (Jim) Irwin were able to travel more than eight times the distance traveled during the previous mission, for a total of over 25 km.

This distance was accomplished over the course of three EVAs, totalling 18 hours and 13 minutes (from hatch open to hatch close on each EVA). During this time the crew explored the Hadley-Apennine region, which included Hadley Rille, a large channel carved out by lava flows. They also tested the new equipment and set up lunar surface scientific experiments. Check out this amazing Apollo 15 50th Anniversary video from the LROC team!

The first EVA took six hours and 28 minutes to complete and covered a distance of about 9 km. During the traverse, the astronauts made three major stops to collect geologic samples on Hadley Delta and to set up the various instruments. Their first objective was to pinpoint the location of their landing spot, so they drove toward the rille until they could see Elbow Crater, named because it was located at a bend in the rille. In addition to its geologic value, this known location let them calculate the exact location of the LM using the rover's navigation system. While on Hadley Delta they collected samples at Stations 1 and 2, then headed back to the LM to drop off the samples and set up the Apollo Lunar Surface Experiments Package (ALSEP), a set of 7 scientific instruments. On the way back, Scott noticed a vesicular basalt (a dark-colored volcanic rock with small air bubbles in it) and the two astronauts faked an issue with a seatbelt so they could stop and quickly collect the rock, which led to it being called the Seatbelt Basalt.

On the second day the astronauts headed back south to the Hadley Delta for EVA 2. This time, they travelled southeast, away from the rille. EVA-2 covered 11.7 km and lasted 7 hours and 1 minute. The astronauts stopped at a total of four stations and collected numerous rocks and other geologic samples. One of these was sample #15415; known as the Genesis Rock , it became one of the most significant samples collected at Apollo 15. The Genesis Rock is made of anorthosite (a light-colored rock that is almost pure plagioclase and makes up the lunar highlands) and was at first believed to be part of the Moon’s primordial crust. Scientists later discovered that, while still very old (at  least 4.1 billion years), it was younger than the formation of the Moon's crust.

The third and final EVA covered a distance of 4.3 km over the course of 4 hours and 44 minutes. The EVA began on the third day with the retrieval of the drill core sample from the ALSEP. This core was 2.4 m long — 2 meters longer than previous lunar core samples. After successfully collecting the core, they continued with the EVA. Unlike EVA-1 and EVA-2, which explored terrain south of the landing site, EVA-3 extended west towards Hadley Rille, north of the section of the rille which had been explored in EVA-1. At the first stop at the rille, they collected a sample known as “Great Scott,” a 9.6 kg boulder which is one of the largest samples brought back from the Moon.  The Moon rock at LROC is a piece of the Great Scott sample!

After exploring Hadley Rille, the rover headed eastward, back towards the lunar module. Here, the astronauts recreated the Galileo gravity experiment (which demonstrated that objects of different mass fall at the same rate) by dropping a hammer and a feather at the same time. In the vacuum-like conditions of the Moon, the feather and hammer hit the ground at the same time. Finally, Scott drove the rover past the lunar module and parked at a site approximately 160 m east of the LM. This site, known as the “VIP site,” was the rover’s final parking place (so called for the rover's VIP seat to the LM liftoff; it was alternatively called the "RIP site"). You can still see the rover at this location in present-day images from LROC!

Members of the LROC team documented the astronaut activities on a minute-by-minute (and sometimes second-by-second) basis to bring this historic event to life. We've carefully mapped the three EVAs based on Apollo 15 transcripts, photographs, and video, as well as rover paths digitized from Dr. Phil Stooke’s thorough mapping of the rover traverses. You can explore these temporal traverse maps , which show the astronauts and the rover on a NAC basemap as they progress through each EVA, across all the stations where they stopped to collect samples, take photographs, and set up experiment hardware.  Don’t forget to view the Apollo 15 landing site in 3D using Lunar QuickMap !

Check out the other temporal traverses here: Apollo 11 Apollo 12 Apollo 14

Read more about Apollo 15 in these related posts: Retracing the Steps of Apollo 15: Constellation Region of Interest The Apollo 15 Lunar Laser Ranging Retroreflector - A Fundamental Point on the Moon! Layers near Apollo 15 landing site Hadley Rille and the Mountains of the Moon The Original Interplanetary Mountaineers Soaring Over Mighty Mt. Hadley Follow the Tracks

Published by Madeleine Manheim on 30 July 2021

News from Brown

50 years after historic moon mission, brown geologist shares stories from mission control.

Jim Head, a planetary geologist at Brown, worked closely with the Apollo 15 astronauts on “the first true scientific expedition to the Moon” in 1971.

David R. Scott, Apollo 15 commander, stands on the surface of the Moon with the Falcon lander and the Lunar Roving Vehicle. Credit: NASA

PROVIDENCE, R.I. [Brown University] — At first, Apollo 15 astronauts Dave Scott and Jim Irwin didn’t quite believe what they were seeing. During an excursion in their lunar rover — the first such vehicle deployed to the Moon — the astronauts spied flecks of green breaking the grayish white monotony of the lunar surface.

“[Are you] sure it’s green and not just white albedo again?” Irwin asked, referring to the tricks sunlight can play on the lunar surface.

“No, it’s green,” Scott confirmed.

Knowing they had something interesting, Scott and Irwin quickly added a few samples to their collection, which returned to Earth along with the Apollo 15 crew 50 years ago.

More than 35 years later, those green flecks, which turned out to be beads of volcanic glass, found their way to a lab at Brown, where geologist Alberto Saal showed that they contained surprising amounts of water. It was the first unequivocal evidence that the Moon’s interior, long thought to have been stripped of any water during its formation, wasn’t so dry after all.

“That has absolutely revolutionized our thinking about how the Moon formed and how solar system bodies interact,” said Jim Head, a professor of geological sciences at Brown who worked on the Apollo program and was inside NASA’s Mission Control Center as Scott and Irwin explored the Moon. “That was a tremendously important discovery that Dave and Jim made on that mission.”

It was one discovery among many for what Head said was one of the most productive scientific missions in the history of spaceflight.

“Everybody knows about the historic Apollo 11, but most people aren’t very aware of the subsequent missions,” Head said. “Apollo 15 was the first true scientific expedition to the Moon, and it was incredibly successful.”

Apollo 15 was the first of what NASA termed J-type missions — missions with vastly expanded scientific capabilities. Apollo 11, the first lunar landing, demonstrated that a safe landing on the Moon was indeed possible. The next two landings, Apollo 12 and 14, achieved pinpoint touchdowns on rough terrain. Those technical feats set the stage for the tricky Apollo 15 landing in an area of high scientific interest: a spot situated between the towering Apennine Mountains and Hadley Rille, a deep channel carved by ancient lunar lava flows.  

Head, an expert in lunar and planetary geology whose first job after earning his Ph.D. from Brown was on the Apollo program, played a key role in choosing that landing site.

Everybody knows about the historic Apollo 11, but most people aren’t very aware of the subsequent missions. Apollo 15 was the first true scientific expedition to the Moon, and it was incredibly successful.

Head wrote a memo to NASA managers identifying five areas of scientific interest along Hadley Rille. One of those, which turned out to be the eventual landing site, was particularly interesting from a scientific perspective, but would also require a landing angle far steeper than any that had been attempted previously. Scott, who was mission commander, agreed that the mission should attempt to land where the best science could be done.

“So Dave jumps in the simulator to try this steep landing,” Head recalled. “He tries it; says we’re good to go, and that’s where we ended up going.”

Once on the surface, the real scientific work began. Scott and Irwin would perform over 19 hours of extravehicular activities (EVAs), twice the EVA time logged on previous missions. The solar-powered Lunar Roving Vehicle, a remarkable feat of engineering in its own right, enabled the astronauts to traverse a previously unthinkable 17 miles across the lunar surface. The mission returned to Earth with 170 pounds of lunar material. Apollo 11, by contrast, brought home a little over 47 pounds.

Head was among the scientists whose job it was to teach two test pilots how to do geology on another world. Head said that Scott in particular was a natural geologist and became engrossed in the subject.   

“One of the best compliments I ever had,” Head said, “was from Dave’s wife at the time, who took me aside and said, ‘Jim, you've absolutely ruined Dave. I had to take a night school course in geology just to be able to talk to him at dinner.’”

Dave Scott shoots some camera footage on the lunar surface. Credit: NASA

The training paid big dividends. In addition to the green volcanic glass, Scott and Irwin gathered one of the big stars in NASA’s lunar sample collection, known as the “genesis rock.” One of the reasons Head and other scientists wanted to land in the lunar highlands was the potential for finding samples of the original deep lunar crust. When Scott spotted the ancient chunk an anorthosite sitting on the surface, he recognized it instantly, enthusiastically radioing to mission control: “Guess what we just found! I think we found what we came for.”

Head and his fellow Apollo scientists were in mission control in Houston during the mission and were able to communicate with the crew. But they weren’t there to micromanage, only to provide expertise when needed.

 “The astronauts did this work on their own,” Head said. “It wasn’t like we were saying, ‘send us a picture of the rock and we’ll tell you if it’s good.’ The mantra was, ‘train them, trust them and turn them loose.’”

Head described the science room in the Mission Operations Center as an incredibly intense and busy place — so busy, in fact, that Head missed it when Scott dropped Head’s name in communications with Mission Control, referring to the valley containing Hadley Rille as “Head Valley.”

“Dave said something like, ‘I’m looking down Head Valley,’ and someone poked me and said, ‘Hey, did you hear that?’” Head recalls. “I was planning the next traverse; I completely missed it. But Dave did that for several of the scientists who worked closely with him and it was really thoughtful.”

Head and Scott remain close friends and collaborators to this day. Scott has worked with Brown students over the years as a visiting professor, and the University awarded him an honorary degree in 2011.  Most recently, on July 31, 2021, Head joined Scott at an event at the San Diego Air and Space Museum to commemorate the mission’s 50th anniversary.

Dave Scott visits Jim Head's geology class in 2013. Credit: Mike Cohea/Brown University

The pair have worked with researchers at the Massachusetts Institute of Technology and elsewhere to show how Apollo 15 could serve as a template for future missions to the Moon and Mars. They refer to the close collaboration between scientists and engineers — the work they say made Apollo 15 possible — as “science-engineering synergism.”

“The geologists and scientists worked together with engineers and managers to optimize the program,” Scott said during a 2013 visit to Brown . “It’s the kind of thing Jim and I are trying to emphasize ... so that the science community understands the engineering and the engineers understand the science. Working together, we get better science and better engineering.”

Related news:

From the lab: brown chemical biologists impact health by focusing on the molecular level, new mass spectrometry technology from brown scientists could transform tiny sample analysis, advancing the quest for dark matter: new insights from the lux-zeplin experiment.

Apollo 15 Command Module "Endeavour"

Apollo 15 lunar module "falcon", apollo 15 subsatellite, nasa official: dave williams, [email protected] last updated: 15 august 2022, drw.

Astronaut David Scott on Slope of Hadley Delta During Apollo 15 EVA

Astronaut David R. Scott, commander, standing on the slope of Hadley Delta, uses a 70mm camera during Apollo 15 extravehicular activity (EVA) on the lunar surface. He is 10.5 miles (or 17.5 kilometers) from the base of the Apennine Mountains seen in the background. Scott carries tongs in his left hand. The Lunar Roving Vehicle (LRV) is in the background. This view is looking east. While astronauts Scott and James B. Irwin, lunar module pilot, descended in the Lunar Module (LM) "Falcon" to explore the moon, astronaut Alfred M. Worden, command module pilot, remained with the Command and Service Modules (CSM) in lunar orbit.

Sep 7, 2023

jpg (5.33 MB)