Science & Technology

Astronauts Are Using Old Sailing Technology in Space

If we were truly lost in space (Robinson family style), how could we find our way home? Crews on the International Space Station are winding back to the 1730s and testing out sextants — devices that sea crews used to make sure they were going in the right direction. The hope is that astronauts flying to the moon in the 2020s could use the sextants in case of emergency.

ESA astronaut Alexander Gerst learns how to use a sextant. “I learned how to navigate after the stars using a sextant,” said Gerst. “It’s actually a test for a backup nav method for #Orion & future deep space missions.”

Finding the Horizon

On Earth, you can use a sextant to figure out the angle between the horizon and some celestial object — the sun, the moon, or a star, for example. If you know where that object should be at that time of day, you can determine your longitude and latitude. So why use a sextant in space, where there's no horizon? Because we can still find our way using the angles between the stars, according to NASA.

The agency first asked its astronauts to test the idea in the International Space Station's wraparound Cupola window, because there's nothing worse than trying something new in the middle of an emergency. It's especially tricky because astronauts are hardly ever stationary — they float around, so it's hard to stay stable. And stability is important. "You need to be able to take a stable sighting through a window," said principal investigator Greg Holt, a NASA navigation engineer, in a statement.

Holt says he's asking the crew for some ideas on how to get a steady view. "That's something we just can't test on the ground ... We want a robust, mechanical back-up with as few parts and as little need for power as possible to get you back home safely."

Saving a Crew's Life

Could a sextant really get a crew back safely from the moon? Well, just ask Jim Lovell. Tests he did in space helped save his crew's life back in 1970. He was aboard the Apollo 13 mission, whose service module (the spot with all the tanks and pipes needed to keep the two spacecraft running) experienced a nasty explosion on the way to the moon.

The astronauts had to shut down their main command module spacecraft to save on power, and use minimum resources to keep their lunar module (LM) alive. "The big question was, 'How do we get back safely to Earth?' The LM navigation system wasn't designed to help us in this situation," Lovell recalled in the 1975 NASA book, "Apollo Expeditions To The Moon." Worse, the stars were obscured by oxygen gas leaking out of the service module.

Luckily for NASA, just two years before the explosion, Lovell was on another moon mission called Apollo 8. He tested out a sextant technique in 1968 that used the Earth's horizon to guide astronauts home, and it worked. Nobody really thought about it again until Apollo 13, NASA engineer Jerry Woodfill told Universe Today in 2010.

For Apollo 13, NASA used the sun — "no amount of debris could blot out that star", Lovell said — and it worked perfectly. After he got home, he co-wrote a book about Apollo 13 that inspired a blockbuster Hollywood movie in 1995. You can read more about the new sextant experiment on NASA's website.

Read the book Jim Lovell co-wrote about his experience, simply titled "Apollo 13." We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Sextant: Navigating by Cosmic Beacon

Written by Elizabeth Howell July 13, 2018

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