Although it’s possible for space missions to communicate data with Earth, the process is anything but fast. Voyager 1, for example, takes about 19 hours to send a signal back to Earth, and that lag only increases as the spacecraft gets further away. For truly long-term, deep space missions, the significant amount of time it takes to send a signal isn’t going to cut it. The spacecraft will need to adjust its own trajectory without relying on ground navigation. That’s where pulsars come in.

Last week, a group of NASA engineers showed that fully autonomous space navigation is possible through the use of X-rays, a discovery that could overhaul our approach to deep space travel. The X-ray guidance system was successfully tested during the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) experiment. Using pulsars timed down to the millisecond, the test craft relied on X-rays to pinpoint the location of a space object moving at thousands of miles per hour.

"This demonstration is a breakthrough for future deep space exploration," said Jason Mitchell, an aerospace technologist at NASA's Goddard Space Flight Center and SEXTANT project manager, in a press release. "As the first to demonstrate X-ray navigation fully autonomously and in real-time in space, we are now leading the way."

Though the Global Positioning System (GPS) can track objects located on Earth or in low-Earth orbit, GPS navigation isn’t an option for long-distance spacecraft because its Earth-orbiting satellite network quickly loses the signal once the craft travels away from Earth. In order to autonomously track deep space vehicles, researchers needed to find a strong signal that is capable of propagating many light-years. For this, the researchers turned to pulsars — the rapidly rotating cores of neutron stars — because they are available virtually everywhere (especially in deep space), and emit strong X-ray signals.

To test the accuracy and ease of X-ray navigation in space, the SEXTANT experiment, funded by NASA's Space Technology Mission Directorate, teamed up with NASA's Neutron-star Interior Composition Explorer (NICER), an external attached payload on the International Space Station (ISS).

"We're doing very cool science and using the space station as a platform to execute that science, which in turn enables X-ray navigation," said the principal investigator for NICER, Keith Gendreau of Goddard. "The technology will help humanity navigate and explore the galaxy."