How a 300-Year-Old Star Tool Could Save Astronauts Lost in Space

Imagine being an astronaut on a mission to Mars, and suddenly, all your electronic navigation systems stop working. How would you find your way back to Earth? NASA has a backup plan for this kind of emergency, and it involves a tool that has been around for about 300 years: the sextant. This instrument was first used by sailors to navigate the oceans by measuring the angles between stars and planets. Now, it is being used as a backup navigation tool for astronauts traveling to the Moon and possibly even farther.

A sextant is a hand-held device that helps people measure the angle between two objects in the sky, like stars or planets. By using these measurements, astronauts can figure out their position in space. This method is called celestial navigation. In the past, sailors depended on this technique to cross the seas before modern technology like GPS existed. As humans plan to travel farther from Earth, NASA engineers are realizing that they cannot always rely on Earth-based navigation systems, such as satellites. If astronauts lose communication with Earth, they need another way to find their way home.

Greg Holt, the navigation system manager for the Orion Spacecraft, explains that as missions go farther from Earth, classical navigation techniques become more important. In 2018, Holt and his team asked two astronauts on the International Space Station to test a hand-held sextant. The astronauts took measurements with their eyes and steady hands to see if they could use the sextant to get home in an emergency. The experiment was successful, and the astronauts found the sextant comfortable to use in microgravity.

The sextant used in space is almost the same as the one used by sailors, but with a few changes. For example, the edges are rounded to prevent scratching, and it has a strap to keep it from floating away. On the Orion spacecraft, astronauts use a camera system that works like a sextant. The camera takes pictures of stars and planets and measures the angles between them. This information helps the crew know where they are and make course corrections if needed.

If the camera system fails, the hand-held sextant is the next backup. During the Artemis II mission to the Moon, a sextant was kept ready before launch in case it was needed. However, because every bit of weight matters in space, the sextant is not always packed unless necessary. If a problem happens after launch, astronauts are trained to use other methods, like watching when the Sun or Moon disappears behind Earth, to estimate their position.

NASA engineers also practice using the sextant so they understand the math and geometry behind navigation. Astronauts can use bright stars or even asteroids as reference points. For example, they might look for an asteroid between two well-known stars and use that to check their location. These techniques show that even with advanced technology, old methods like using a sextant are still valuable for space exploration.

Greg Holt finds it fascinating that the basic ideas behind navigation have not changed much, even as missions go farther into space. Whether using a stick, a sextant, or a high-tech camera, the main idea is to look at the stars, measure angles, and use math to figure out where you are. This connection between old and new techniques helps keep astronauts safe as they explore the universe.