Apollo 11 Lunar Surface Journal

Lunar Gaits

Commentary Copyright © 1995-2001 by Eric M. Jones.
All rights reserved.
Last revised 2 November 2010.


The Apollo astronauts used four gaits on the Moon. During much of the Apollo 11 EVA, Neil and Buzz walked flat footed, putting one foot in front of the other but not pushing off to take advantage of the weak gravitational field. Most of the astronauts on the later missions favored a loping gait in which they still alternated feet but pushed off with each step and floated forward before planting the next foot. Ed Mitchell of Apollo 14 and Gene Cernan on Apollo 17 favored a skipping stride in which they kept one foot always forward, let's say the left and, as they landed, hit with the trailing foot just a fraction of a second before the leading foot, pushing off with each foot as it hit and launching into the next glide. No one used the two-footed, kangaroo hop on level ground - except in play - but both Cernan and Schmitt used it in coming down a steep hill on Apollo 17.

Armstrong, from the 1969 Technical Debrief - "With respect to work on the surface, the one-sixth gravity was, in general, a pleasant environment in which to work, and the adaptation to movement was not difficult. I felt it was quite natural. Buzz had the opportunity to look at more detailed aspects of it, a good bit more than I did; but, in general, we can say it was not difficult to work and accomplish tasks. I think certain exposure to one-sixth g in training is worthwhile, but I don't think it needs to be pursued exhaustively in light of the ease of adaptation."

Aldrin, from the 1969 Technical Debrief - "Moving around was very natural. Some attention must be paid to the mass that you have in the suit and, also, to the mass of the PLSS that is on your back. I think we anticipated this adequately, and the fact that we did have a sizable mass mounted to the rear was not detrimental to moving around."

Armstrong, from the 1969 Technical Debrief - "I would say that balance (while walking) was not difficult; however, I did some fairly high jumps and found that there was a tendency to tip over backwards on a high jump. One time I came close to falling and decided that was enough of that."

On Apollo 16, Charlie Duke tried to jump as high as he possibly could and, as Neil almost did, tipped over backwards and landed on his PLSS. In his 1990 book, "Moonwalker", written with his wife Dotty, he said that, as he fell, he was genuinely afraid that he was about to die but, fortunately, neither his PLSS nor his suit was damaged and the only damage to himself was an acute case of embarrassment.

Aldrin, from the 1969 Technical Debrief - "There is no doubt that it is much easier to reach that neutral (stability) point by just leaning back slightly than it was by leaning forward. I think the happy medium was to lean forward more than we did. It was more comfortable for us to stand erect than to lean forward to be at that absolute neutral point (with the center of mass directly over their feet). The POGO tends to give you the impression that most of your moving around will be the result of toe pressure - that you will rock up on your toes and tend to push off. I did not really find this to be the case as much as I had anticipated. The one-sixth (g) airplane is a very poor simulation of the lunar surface. There is excellent traction in the airplane, so you can't relate too much as to how the foot departs or what sort of resistance you need when you put your foot back down again. I didn't find that there was much of a slipping tendency on the surface in trying to put in sideways motions or stopping motions. It was quite natural as you began to apply force to make a change in your momentum. I think you were able to tell just how much you could put in before you would approach any instability case. In general, it would take a couple of steps to make a good sideways change in motion and it would take two or three steps to come comfortably to a stable stationary position from a fairly rapid forward movement. To get a sustained pace evaluation, I would have had to have gone a good bit farther than I did. Before the flight, I felt that you might be able to sustain a fairly rapid pace comfortably. My impression now is that this was a little tiring on the legs. There was a rubbing in the suit somewhere in the knee joints and you had to keep moving the knees, even though they were very mobile in the suit. I felt that, as easy as things looked, a 1-mile trek was not going to be an easy thing. Just by having to move your muscles and your body in the suit, you would end up getting tired on any prolonged trek."

The Apollo 12 crew moved over distances of 200 to 300 meters between geology stops and, on at least one occasion, had heart rates of about 160 beats per minute. On the three long missions, the astronauts wore suits with waist convolute added so they could sit on the Rover; and an added benefit of the waist convolute is that it gave them more leg flexibility. On Apollo 17, Jack Schmitt and Gene Cernan ran comparable distances and experienced heart rates of no more than 120 to 130 beats per minute. Several of the J-mission astronauts achieved sustained running speeds greater than 5 kilometers per hour and there seem little doubt that, with some avoidance of uphill running, they would have had no trouble achieving the 3.6 kph average speed assumed by planners for an hour-long walkback from a failed Rover, or the 2.7 kph average speed assumed for walkbacks of over an hour.

Aldrin, form the 1969 Technical Debrief - "Because the terrain varies a good bit relative to your ability to move over it, you always have to be alert to what is coming up next. On Earth, you only worry about one or two steps ahead; on the Moon, you have to keep a good eye out four or five steps ahead."

During the J-missions, the crews showed notable improvements in their average walking speeds as they gained experience with the suits and learned to move more efficiently. During Apollo 15, researchers in Houston evaluated improvements in average walking speeds used by the astronauts and found that, under similar conditions, their speeds improved from 1.0 ft/sec to 1.5 ft/sec during the first EVA and from 1.5 to 2.0 ft/sec during the second EVA. No further improvement was noted during the third EVA. These speeds correspond to 1.1, 1.6, and 2.2 kph, respectively, and represent movements over short distance while working around the LM or at the geology stops. Neither Scott nor Irwin ran - or walked - any significant distances.

Aldrin, from the 1969 Technical Debrief - "I think the one-foot-in-front-of-the-other is a much better mode of locomotion than the more stilted kangaroo hop. You can do it, but it doesn't seem to offer any particular advantage. When your feet are on the surface, you can do fairly vigorous sideways movements such as leaning and swinging your arms without a tendency to bounce yourself up off the surface and lose your traction. This was one experiment that was suggested, and I found that you do tend to remain well-rooted on the surface where you are, despite motions that you may have."

Armstrong, from the 1969 Technical Debrief - "I went the farthest. While Buzz was returning from the EASEP, I went back to a big crater behind us. It was a crater I'd estimate to be 70 or 80 feet in diameter and 15 or 20 feet deep. I went back to take some pictures of that (AS11-40-5954 to 5961); it was between 200 and 300 feet from the LM."

The crater behind the LM is known as Little West Crater because of it's association with West Crater, the football-field-sized crater Neil had to avoid during the landing. Little West Crater is about 30 meters (100 feet) across and the west rim, where Neil stood to take the pictures, is about 60 meters (200 feet) east of the spacecraft and about 430 meters west of West Crater.

Armstrong, from the 1969 Technical Debrief - "I ran there and ran back, because I didn't want to spend much time doing that, but it was no trouble to make that kind of trek - a couple of hundred feet or so. I just took a few minutes to lope back there, take those pictures, and then come back."

Neil's trip out to Little West Crater - from the time he left the LM to the time he returned, took about 3 1/4 minutes. During the brief period that he was on-camera, he was moving confidently and quickly. An average speed of 3.6 kph (1 meter/sec) for the 120 meter round trip would have left him an ample 1 1/4 minutes for photography and is a plausible estimate for his speed.

Aldrin, from the 1969 Technical Debrief - "I don't think there is such a thing as running. It's a lope and it's very hard to just walk. You break into this lope very soon as you begin to speed up."

Armstrong, from the 1969 Technical Debrief - "I can best describe a lope as having both feet off the ground at the same time, as opposed to walking where you have one foot on the ground at all times. In loping, you leave the ground with both feet and come down with one foot in a normal running fashion. It's not like an Earth run here, because you are taking advantage of the low gravity."

Aldrin, from the 1969 Technical Debrief - "The difference there is that in a run, you think in terms of moving your feet rapidly to move fast, and you can't move your feet any more rapidly than the next time you come into contact with the surface. In general, you have to wait for that to occur."

Armstrong, from the 1969 Technical Debrief - "And you are waiting to come down. So the foot motion is actually fairly slow, but both feet are off the ground simultaneously. You can cover ground pretty well that way. It was fairly comfortable, but at the end of this trip, going out there (to Little West Crater) and back, I wanted to stop and rest a little. After about 500 feet of this loping with a one-minute stop out there in the middle to take pictures, I was ready to slow down and rest. There were a lot of interesting areas within 500 feet or so to go and look at if we had had the time to go out and inspect them closely and get some pictures; but that was a luxury we didn't have."


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