Worth a Thousand Words

Last month saw the celebration of the 40th anniversary of the Apollo Moon through with a range of commemorative events, including the launch of Google Moon. This week’s PLoS ONE featured image is also on a space exploration theme: Christopher Carr and Jeremy McGee of the Massachusetts Institute of Technology discuss the effects of wearing a self-supporting space suit on the transition between walking and running in their new article, The Apollo Number: Space Suits, Self-Support, and the Walk-Run Transition.

Model of space suit self-support

The image forms Figure 2 of PLoS ONE article e6614; any reuse should cite the authors and journal (image: Eugene Cernan during Apollo 17. NASA/Harrison).

If a person starts to walk and gradually increases her speed, she will switch from walking to running at a particular speed, determined by the speed at which it instinctively feels easier to run rather than walk–this is the walk-run transition. Moving about on the Moon is different from on the Earth because wearing a space suit incurs a significant metabolic cost for the astronauts during locomotion on the Moon and because due to the lower gravity environment (<0.5 g) on the Moon, running uses less energy than walking, unlike on the Earth.

In the article, the authors use data (including audio and video footage) from the Apollo lunar surface missions of 1969-74 to show that the transition between running and walking when on the Moon can be characterised by the Apollo Number (Ap = Fr/M) and consider the role space suit self-support plays in the walk-run transition.

The image shown is Figure 2 from the published article and represents a model of space suit self-support. The caption is as follows: “Self-support force Fs, in an idealized model of the Apollo space suit in a vacuum, is set by the product of suit pressure P and minimum cross sectional area A minus the tension T in the restraint layer (supplemental materials). Image: Eugene Cernan during Apollo 17. NASA/Harrison Schmitt.”

You can also watch a video of astronaut Charles Duke in his self-supporting space suit during Apollo 16 via the paper’s supporting information section.

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