Credit: NASA
Into Darkness
The Neutron Star Interior Composition ExploreR, or NICER, is a workhorse X-ray observatory berthed on the International Space Station. NICER's primary science goal is to determine the state of matter at the extreme densities found at the centers of neutron stars, and to study the distribution of the X-ray hotspots on their surfaces. NICER does this by studying the shapes of X-ray pulses from fast-spinning neutron stars to determine how these superdense pulsars distort spacetime. But NICER does much more than that - it's studied stars, galaxies, nebula and transient outbursts in the X-ray Universe. NICER's scientific productivity and observing flexibility make it the premier X-ray timing observatory. But on May 22, 2023, NICER project scientists noted a sudden increase in the amount of stray light contamination when the ISS was on the sunlight side of the earth, making it very difficult to observe during orbit day. Although observations during orbit night were unaffected, this cut NICER'S observing efficiency. But being on the ISS has its advantages. Photographs of NICER by ISS astronauts revealed a puncture in a triangular section of one of the filters that blocks optical light from reaching the detector, and some other pinhole punctures in the filters in front of other NICER detectors. Another advantage of having an observatory on the ISS is that problems can be fixed. The NICER project, working with ISS leadership and engineers, designed a set of wedge-shaped patches to place in the sun-shades in front of the damaged portion of the optical blocking filters. Twelve of these patches were sent to the ISS to patch seven damaged filter sections for installation during a spacewalk by an ISS astronaut, with five extra in case other damaged filter sections were identified during the spacewalk. The NICER repair began on 9:40am on September 16, 2025, during Spacewalk 91. ISS Astronaut Nick Hague was translated to the NICER position on Express Logistics Carrier 2. After carefully studying the 56 NICER blocking filters, filters were installed in the seven pre-determined locations, and two additional ones were installed over other filters that seemed to show some signs of damage. This was the first on-orbit repair of an astronomical facility since the Hubble Space Telescope's the fourth servicing mission in 2009 by Space Shuttle astronauts.
Scientists hope that this repair effort blocks unwanted sunlight from the NICER detectors and and returns NICER to darkness.
Published: January 20, 2025
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Page Author: Dr. Michael F. Corcoran
Last modified Tuesday, 21-Jan-2025 12:07:46 EST