Goddard SXS team member Caroline Kilbourne explains:
The technology used in the SXS is leading the way to the next generation of imaging X-ray spectrometers, which will be able to distinguish tens of thousands of X-ray colors while capturing sharp images at the same time.
Two of the observatory's other instruments are identical soft x-ray telescopes with mirror assemblies also manufactured by NASA Goddard. (These can pick up on x-rays as weak as 300 electron Volts.) One of the two directs light to an advanced wide-field camera to take images, while the other directs it to the SXS. The spectrometer distinguishes X-ray colors by measuring the energy of each particle of light that hits it. In order for the SXS to detect the smallest changes, it's kept at a temperature of -459.58 degrees Fahrenheit using supercold liquid helium.
Besides the soft x-ray detectors, the observatory is also equipped with Hard X-ray Telescopes (and their cameras) that can detect energy from 5,000 to 80,000 eV. Finally, it has detectors that focus on soft gamma rays with an energy range of 60,000 to 600,000 eV. During the course of its mission, the observatory will find and image superheated materials falling into black holes and other X-ray sources/high-energy phenomena. JAXA is livestreaming the launch on YouTube, though you'll have to get up early (or stay up late),
since it's scheduled at 3:45AM EST.
Update: JAXA announced the launch is delayed because of bad weathe,r and it will announce a new date once one is determined.