Nasa astronaut Alexander Gerst learns how to use a sextant. Credit: NASA.

Nasa has started a testing programme onboard the International Space Station (ISS) to investigate the potential of using sextants as emergency navigation tools for future spacecraft.

The test will determine whether a hand-held sextant, a navigation tool that has been used by sailors for centuries, could be used for emergency navigation on space vehicles.

Sextants have a small telescope-like optical sight to take precise angle measurements between pairs of stars from land or sea, allowing navigation without computer assistance.

The investigation tests specific techniques, focusing on stability, for possibly using a sextant for aboard spacecraft such as Orion.

Using these techniques, crews can use the device to navigate, even if communications and computers become compromised.

“Now that we plan to go farther into space than ever before, crews need the capability to navigate autonomously in the event of lost communication with the ground.”

Nasa principal investigator Greg Holt said: “The basic concepts are very similar to how it would be used on Earth.

“But particular challenges on a spacecraft are the logistics; you need to be able to take a stable sighting through a window.

“We’re asking the crew to evaluate some ideas we have on how to accomplish that and to give us feedback and perhaps new ideas for how to get a stable, clean sight. That’s something we just can’t test on the ground.”

Previously, Nasa’s Gemini missions performed the first sextant sightings from a spacecraft.

Apollo spacecraft were also equipped with sextants as a navigation backup.

Holt further added: “Now that we plan to go farther into space than ever before, crews need the capability to navigate autonomously in the event of lost communication with the ground.”