"I was strolling on the moon one day in the merry, merry month of ... December ..."
Thus sang astronaut Harrison Schmitt during the Apollo 17 moonwalk in December 1972.
While it may look like an easy stroll, could he and Gene Cernan have completed an entire lap of the moon?
At one-sixth of the Earth's gravity and 10,921 kilometres, it's not much compared to the Earth's 40,075-kilometre circumference.
Surprisingly, NASA actually did the calculation to determine that the Apollo astronauts walking speed was 2.2km/h. At that pace, the journey would take 207 days.
However, that's not fast compared to the 7.2km/h average maximum walking speed on Earth. So NASA took it another step further (sorry about the pun) by testing how fast humans could walk in a simulated lunar gravity.
They had eight participants using a treadmill onboard a DC-9 aircraft, which flew parabolic trajectories for up to 20 seconds at a time. That showed people could walk up to 5km/h before breaking into a run.
If they could sustain that pace, it would cut their time to 91 days (or 334 days to walk around the Earth).
The key word here is "if". Of course a person cannot simply walk nonstop for 91 days.
On average you need roughly 3 litres of water per day, which obviously should be more with physical exertion.
That translates into 273 litres and an Earth-equivalent of 273 kilos.
Our moon athletes would also need to eat, so we'd add maybe another kilo or two of food per day. They could leave behind cooking gear, tents and bedding, but already this is looking arduous.
Then all that food has to go somewhere after they've eaten, so we can't ignore the toilet facilities which are uncommon on the moon.
Meanwhile, we've assumed they could accomplish their feat as if the moon were a smooth surface: it is not. With precipitous climbs and crags, they would inevitably be forced to take detours, lengthening their journey.
Then there's the issue of spacesuits which were heavy and bulky, and not designed for this kind of activity.
The Apollo 17 suits weighed 35.4 kilograms while on Earth - and here we should distinguish between "weight" and "mass".
Even if a spacesuit is one sixth as heavy on the moon, it still carries mass. An object requires effort to move even if it doesn't weigh much. (That suggests a future Ask Fuzzy question of how a spacesuit works.)
In all, it's a messy calculation that could be modelled in a spreadsheet, demonstrating one of science's most useful tools.
While it's looking like an unlikely project, who knows, humans are drawn to adventures and maybe one day, somebody will give it a try.
- With thanks to Gordon Fyfe.
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