October 13, 2019

How Do You Measure Time in Space?

“We appear to be on the cusp of an era where humans live outside this pale blue dot. According to some newly leaked NASA documents, the agency hopes to build a moon base by 2028. That settlement will allow us to test the skills and tools we’ll need to try to make it to Mars, says NASA, and then who knows where we’ll go from there.

There are serious technical hurdles to establishing space settlements and enduring long-term flights: How will humans grow food? What happens to our waste? But there are also squishier, logistical ones that we take for granted here on Earth. One of the first things we’ll need to figure out is how to keep track of time.

The solution might seem straightforward: just bring a watch and a calendar, and mark off the days! And yes, this is how the only full-time space settlement—the International Space Station—handles things. The crew of the ISS operates on Greenwich Mean Time and, via their close contact with Earth, gets updates on the time.

But there are challenges to keeping space dwellers on an Earth-bound time-keeping system. One is the practicality of using a time-keeping system that ignores your local reality. Keeping astronauts on a 24-hour, GMT-based system makes things easier for ground control, but trying to keep Earth hours takes a toll on astronauts’ sleep, as their circadian rhythms are thrown off by the comparatively erratic light cycle: The ISS orbits Earth every 90 minutes, so over the course of a typical 24-hour Earth “day,” the crew sees 16 sunrises and sunsets.”

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