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X-ray navigation could open up new frontiers for robotic spacecraft

Staff Writer | January 18, 2018
In a technology first, a team of NASA engineers has demonstrated fully autonomous X-ray navigation in space.
SEXTANT
Science and technology   Station Explorer for X-ray Timing and Navigation Technology
This is a capability that could revolutionize NASA's ability in the future to pilot robotic spacecraft to the far reaches of the solar system and beyond.

The demonstration, which the team carried out with an experiment called Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT, showed that millisecond pulsars could be used to accurately determine the location of an object moving at thousands of miles per hour in space - similar to how the Global Positioning System, widely known as GPS, provides positioning, navigation, and timing services to users on Earth with its constellation of 24 operating satellites.

"This demonstration is a breakthrough for future deep space exploration," said SEXTANT Project Manager Jason Mitchell, an aerospace technologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"As the first to demonstrate X-ray navigation fully autonomously and in real-time in space, we are now leading the way."

This technology provides a new option for deep space navigation that could work in concert with existing spacecraft-based radio and optical systems.

Although it could take a few years to mature an X-ray navigation system practical for use on deep-space spacecraft, the fact that NASA engineers proved it could be done bodes well for future interplanetary space travel.

Such a system provides a new option for spacecraft to autonomously determine their locations outside the currently used Earth-based global navigation networks because pulsars are accessible in virtually every conceivable fight regime, from low-Earth to deepest space.

The SEXTANT technology demonstration, which NASA's Space Technology Mission Directorate had funded under its Game Changing Program, took advantage of the 52 X-ray telescopes and silicon-drift detectors that make up NASA's Neutron-star Interior Composition Explorer, or NICER.

Since its successful deployment as an external attached payload on the International Space Station in June, it has trained its optics on some of the most unusual objects in the universe.

"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 Goddard's Keith Gendreau, the principal investigator for NICER, who presented the findings Thursday, Jan. 11, at the American Astronomical Society meeting in Washington. "The technology will help humanity navigate and explore the galaxy."

NICER, an observatory about the size of a washing machine, currently is studying neutron stars and their rapidly pulsating cohort, called pulsars.

Although these stellar oddities emit radiation across the electromagnetic spectrum, observing in the X-ray band offers the greatest insights into these unusual, incredibly dense celestial objects, which, if compressed any further, would collapse completely into black holes.

Just one teaspoonful of neutron star matter would weigh a billion tons on Earth.

Although NICER is studying all types of neutron stars, the SEXTANT experiment is focused on observations of pulsars. Radiation emanating from their powerful magnetic fields is swept around much like a lighthouse.

The narrow beams are seen as flashes of light when they sweep across our line of sight. With these predictable pulsations, pulsars can provide high-precision timing information similar to the atomic-clock signals supplied through the GPS system.

In the SEXTANT demonstration that occurred over the Veteran's Day holiday in 2017, the SEXTANT team selected four millisecond pulsar targets - J0218+4232, B1821-24, J0030+0451, and J0437-4715 - and directed NICER to orient itself so it could detect X-rays within their sweeping beams of light.

The millisecond pulsars used by SEXTANT are so stable that their pulse arrival times can be predicted to accuracies of microseconds for years into the future.

During the two-day experiment, the payload generated 78 measurements to get timing data, which the SEXTANT experiment fed into its specially developed onboard algorithms to autonomously stitch together a navigational solution that revealed the location of NICER in its orbit around Earth as a space station payload.

The team compared that solution against location data gathered by NICER's onboard GPS receiver.


 

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