In Brief
NASA has demonstrated a new kind of autonomous space navigation. Called SEXTANT, it uses pulsars to determine the location of an object in space similar to how GPS uses satellites for Earth-based navigation.

X-Ray Navigation

NASA may have just improved our potential for deep space exploration by inventing a new type of autonomous space navigation. Known as Station Explorer for X-Ray Timing and Navigation Technology, or SEXTANT, the technology uses pulsars — rotating neutron stars that emit electromagnetic radiation — to determine the location of objects in space.

The way SEXTANT uses pulsars has been compared to how GPS navigation can provide drivers with positioning and accurate navigation using satellites orbiting around Earth. The pulsars SEXTANT uses are best observed in the X-ray spectrum, in which their beams of radiation essentially turn them into lighthouses.

To show that SEXTANT is an idea worth building on, a team of NASA engineers demonstrated the technology’s ability to locate NASA’s Neutron-star Interior Composition Explorer, or NICER. NICER — an observatory roughly the size of a washing machine — is currently orbiting Earth while attached to the International Space Station. It has been tasked with studying both neutron stars and pulsars, making it the perfect partner for SEXTANT’s first experiment.

An illustration of NICER attached to the International Space Station. Image Credit: NASA
An illustration of NICER attached to the International Space Station. Image Credit: NASA

“This demonstration is a breakthrough for future deep space exploration,” said Jason Mitchell, SEXTANT Project Manager in a NASA press release. “As the first to demonstrate X-ray navigation fully autonomously and in real-time in space, we are now leading the way.”

During November, NASA directed NICER to take readings from four specific pulsars using its 52 X-ray telescopes and silicon-drift detectors over two days. NICER then fed the information it got from the pulsars to SEXTANT. Within eight hours, SEXTANT was able to autonomously determine NICER’s location in Earth’s orbit within a 10-mile radius. SEXTANT’s readings were compared to NICER’s own onboard GPS receiver, confirming its accuracy.

“This was much faster than the two weeks we allotted for the experiment,” said SEXTANT System Architect Luke Winternitz in the press release. “We had indications that our system would work, but the weekend experiment finally demonstrated the system’s ability to work autonomously.”

Navigating Deep Space

SEXTANT is far from being complete, however, and NASA predicts it will be several years before a better version autonomous space navigation comes along. When it does, the tech will fill a huge need for space exploration. While GPS is fine for Earth and low-Earth orbit, its signal weakens the further away an object is from GPS satellites. As such, NASA’s X-ray navigation will be required for spacecraft sent far beyond Earth.

“This successful demonstration firmly establishes the viability of X-ray pulsar navigation as a new autonomous navigation capability,” Mitchell added in the press release. “We have shown that a mature version of this technology could enhance deep-space exploration anywhere within the solar system and beyond.”

With the initial experiment out of the way, NASA intends to improve the system’s flight and ground software for a second demonstration scheduled for later this year. Before SEXTANT can be considered for full-scale operations, however, NASA engineers must increase the sensitivity of its instruments while at the same time decreasing its size, weight, and power consumption.

NASA believes the autonomous space navigation could eventually be used during human spaceflight missions, or calculate position if used on missions to Jupiter, Saturn, or their respective moons.