NICER's primary science instrument, called the X-ray Timing Instrument (XTI), is an array of 56 X-ray photon detectors.
These detectors record the energies of the collected photons as well as with their time of arrival.
A GPS receiver enables accurate timing and positioning measurements.
X-ray photons can be time-tagged with a precision of less than 300 nsec.

During each ISS orbit, NICER will observe two to four targets.
Gimbaling and a star tracker allow NICER to track specific targets while collecting science data.
In order to achieve its science objectives, NICER will take over 15 million seconds of exposures over an 18-month period.
NICER's primary science instrument, called the X-ray Timing Instrument (XTI), is an array of 56 X-ray photon detectors. These detectors record the energies of the collected photons as well as with their time of arrival. A GPS receiver enables accurate timing and positioning measurements. X-ray photons can be time-tagged with a precision of less than 300 nsec.
During each ISS orbit, NICER will observe two to four targets. Gimbaling and a star tracker allow NICER to track specific targets while collecting science data. In order to achieve its science objectives, NICER will take over 15 million seconds of exposures over an 18-month period.
Neutron Star Interior Composition Explorer