Explanation:

SEXTANT is Station Explorer for X-ray Timing and Navigation Technology.
SEXTANT works like a GPS receiver getting signals from at least three GPS satellites, all of which are equipped with atomic clocks.
The receiver measures the time delay from each satellite and converts this into spatial coordinates.
The technology uses X-ray technology to see millisecond pulsars, using them much like a GPS uses satellites.
Although these objects emit radiation across the spectrum, observing in the X-ray band offers the greatest insights into these unusual, incredibly dense celestial objects that if compressed any further would collapse completely into black holes.
The mission will shed light into their structure and allow astronomers to observe the stars’ tremendously strong magnetic fields and other physical properties.
This demonstration is a breakthrough for future deep space exploration in that it provides a new option for deep space navigation that could work in concert with existing spacecraft- based radio and optical systems.