NICER mission preparations, May 2016. Engineer Takashi Okajima installing optics for the Neutron star Interior Composition ExploreR (NICER) experiment. NICER is designed to study neutron stars using an X-ray timing and spectroscopy instrument. It was launched in June 2017 as a payload to be attached to the International Space Station (ISS). NICER's 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. Photographed in 2015, at NASA's Goddard Space Flight Center (GSFC), Greenbelt, Maryland, USA.