Testing sextants on ISS
NASA astronaut Alexander Gerst learns how to use a sextant on board the ISSNASA

NASA wants to see if the sextant can be used to navigate deep space during emergencies and as a backup plan in case onboard instruments fail. The Sextant Navigation investigation is a mission that is intended to test the use of a hand-held sextant aboard the International Space Station (ISS).

A sextant is a tool that was used by sailors and pirates hundreds of years ago to help them navigate uncharted seas using the position of stars and calculating their position to the stars, which were pretty much constant in the night sky.

Sextants have small telescope-like optical sights that allow a skilled user to make precise angle measurements between pairs of stars in the sky from both the land and sea. This makes it possible for sailors to navigate without any computer and GPS, explains NASA.

"The basic concepts are very similar to how it would be used on Earth," says principal investigator Greg Holt.

"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." he added, because, these are measurements that just cannot be taken from the ground.

Having said that, NASA notes that this is not the first time that the space agency has used a sextant for navigation as a backup tool.

NASA's Gemini missions conducted the first sextant sightings from space, notes the report. Designers of the Apollo vehicles built sextants into them as a backup system in case the crew lost communications. Astronaut Jim Lovell, commander of the Apollo 13 mission, which famously had several critical failures, circled the Moon and managed to make it back to Earth. The report mentioned that when on the Apollo 8 mission, Lovell actually demonstrated that it was possible to navigate in space using a sextant.

Using a sextant in outer space is vastly different from using one on Earth. The study on using a sextant in space now is focussed specifically on stability in space among other techniques. NASA is seriously considering putting sextants on spaceships of the future, including the Orion that could take people to Mars.

"No need to reinvent the wheel when it comes to celestial navigation," Holt says. As to why there is a need for an additional system for navigation in deep space, Holt went on to explain that, "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. 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."

The instrument itself is fairly small and not too difficult to use, notes the report. Over the centuries it has become a refined, compact instrument that is still a viable method of navigation.