Goddard Engineering and Technology Directorate

NICER Regains Additional Capabilities Thanks to Engineering Teams’ Detector Reconfigurations

The NICER (Neutron star Interior Composition Explorer) X-ray telescope is reflected on NASA astronaut and Expedition 72 flight engineer Nick Hague’s spacesuit helmet visor in this high-flying “space-selfie” taken during a spacewalk on Jan. 16, 2025. NASA/Nick Hague
The NICER (Neutron star Interior Composition Explorer) X-ray telescope is reflected on NASA astronaut and Expedition 72 flight engineer Nick Hague’s spacesuit helmet visor in this high-flying “space-selfie” taken during a spacewalk on Jan. 16, 2025. NASA/Nick Hague

NICER Status Update

April 17, 2025

Following Repair, NASA’s NICER Improves Daytime Measurements

A NASA X-ray telescope on the International Space Station called NICER, or Neutron star Interior Composition Explorer, has regained additional daytime observation capabilities thanks to repairs completed during a spacewalk and a reconfiguration of its detectors.

In May 2023, NICER developed a light leak in which unwanted sunlight began entering the instrument. Photos taken from inside the space station revealed several small areas of damage to the telescope’s thin thermal shields, which block sunlight while allowing X-rays through to the detectors. Nighttime observations were unaffected, and with operational adjustments, the NICER team was able to recover about 20% of station daytime observations.

In January, NASA astronaut Nick Hague installed nine patches to cover the largest areas of damage during a spacewalk. After resuming science operations, the NICER team determined the overall level of sunlight inside NICER had substantially reduced. Still, it experienced more visible-light interference than expected.

Close-up, high-resolution photos from the spacewalk allowed the team to see additional small holes and cracks in the thermal shields that were not previously visible. These accounted for the remaining sunlight intrusion.

After further analysis, the NICER team developed a novel approach to regaining additional daytime data collection.

Each X-ray that hits a NICER detector generates electrical charge that is sensed by a measurement/power unit (MPU). After so many hits, the detector resets — like emptying a cup before it overflows.

Sunlight can also create charge that accumulates in the detector, adding water to the metaphorical cup. There was so much sunlight entering NICER that the detectors were filling up with charge and resetting thousands of times for every X-ray detection. It overwhelmed the MPU’s ability to process the valid X-ray events…

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