According to the NASA news article NASA’s NavCube Could Support an X-ray Communications Demonstration in Space — A NASA First:
The new technology, called NavCube, combines NASA’s SpaceCube, a reconfigurable and fast flight computing platform, with the Navigator Global Positioning System (GPS) flight receiver. Navigator
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“A Match Made in Heaven”
As part of the potential XCOM demonstration, NavCube will drive the electronics for a device called the Modulated X-ray Source, or MXS, which generates rapid-fire X-ray pulses, turning on and off many times per second.
From this article I understand that NavCube is a unique, fast computer for space applications, combined with a unique, sensitive GPS receiver also optimized for space applications.
The X-ray communications investigation/demonstration will put an X-ray transmitter at one end of the ISS and an X-ray receiver at the other. In this case the receiver will be NICER, an array of X-ray telescopes that will primarily be used to study astronomical sources such as neutron stars, and to look into the possible use of timing from pulsars as a deep space positioning system for navigation.
Would NavCube then actually just serve as a signal generator for some high-speed pulsed X-ray generator?
above: "NavCube, the product of a merger between the Goddard-developed SpaceCube 2.0 and Navigator GPS technologies, could play a vital role helping to demonstrate X-ray communications in space — a potential NASA first. Credits: NASA/W. Hrybyk" from here
above: NICER, from Astrophysics on the International Space Station - Understanding ultra-dense matter through soft X-ray timing.
above: NICER X-ray timing telescope/concentrator array, from About NICER.