The Neutron Star Interior Composition ExploreR (NICER) is a NASA telescope on the International Space Station, designed and dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear physics environments embodied by neutron stars, exploring the exotic states of matter where density and pressure are higher than in atomic nuclei.

As part of NASA's Explorer program, NICER enabled rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft X-ray (0.2–12 keV) band with unprecedented sensitivity, probing interior structure, the origins of dynamic phenomena, and the mechanisms that underlie the most powerful cosmic particle accelerators known.

[8] By May 2015, NICER was on track for a 2016 launch, having passed its critical design review (CDR) and resolved an issue with the power being supplied by the ISS.

Gimbaling and a star tracker allow NICER to track specific targets while collecting science data.

If approved and installed on the ISS, XCOM will transmit data encoded into X-ray bursts to the NICER platform, which may lead to the development of technologies that allow for gigabit bandwidth communication throughout the Solar System.

Astronomers using NICER found evidence that a neutron star from a low-mass X-ray binary in NGC 6624 is spinning at 716 Hz (times per second), or 42,960 revolutions per minute, the same velocity as the fastest known spinning neutron star PSR J1748−2446ad and the only one in such a binary system.