NASA is preparing to launch a repair kit to the International Space Station (ISS) for a telescope that was never designed to be tinkered with by astronauts.

The telescope in question is the Neutron Star Interior Composition Explorer (NICER), which developed a light leak in May 2023.

The telescope is attached near the station's starboard array and was launched on a SpaceX Dragon resupply mission in 2017. NICER was supposed to last for 18 months, but its mission has since been extended. The telescope recently celebrated its seventh anniversary.

As the name suggests, the telescope is all about the study of neutron stars. Its primary science instrument, the X-ray Timing Instrument (XTI), has an array of 56 X-ray photon detectors, which record the energies of photons and note when they hit.

One of NICER's goals is to answer a long-standing astrophysics question - how big is a neutron star?

It was all going swimmingly until May 22, 2023, between 1300 and 1400 UTC. The XTI developed a visible light leak, interfering with NICER's measurements. There are no problems during the orbital night, but the NICER team has had to alter its daytime observing strategy to mitigate the effect.

The team determined that the light was entering through some damage to NICER's thermal shields, which cover each of the X-ray detectors and are designed to filter out infrared, ultraviolet, and visible light while allowing X-rays to pass through.

According to NASA: "The largest damage to the shields is around the size of a typical US postage stamp. The other areas are closer in size to pinheads."

The fix? Patches resembling oversized Trivial Pursuit pie pieces, which will slide into the sunshade. NASA plans to have astronauts fit five patches to deal with the worst of the damage, although 12 will be launched on next week's Northrop Grumman commercial resupply mission.

The turnaround time for the patches is impressive. The NICER team was given the nod in January from the ISS program management team to proceed with a repair effort and was pondering whether a repair using the ISS robotics system would be viable, or if astronauts would need to venture outside the outpost to repair an instrument that was never designed to be repaired. The latter approach won out.

The ISS team has plenty of experience when it comes to repairing payloads that were never intended to be touched by astronauts. A series of spacewalks, ending in 2020, were undertaken to repair the Alpha Magnetic Spectrometer-02 (AMS-02).

"It's incredible that in just one year, we were able to diagnose the problem and then design, build, test, and deliver a solution," said Steve Kenyon, NICER's mechanical lead at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"We're so excited to see the patches installed during a future spacewalk, return to a more regular operating schedule, and keep doing groundbreaking science." ®

https://www.theregister.com//2024/08/01/nicer_repair_kit_iss/