NASA astronaut Nick Hague will install patches for the agency’s Neutron Star Interior Composition Explorer (NICER) X-ray telescope on the International Space Station as part of a spacewalk scheduled for Jan. 16. Hague, along with astronaut Suni Williams, will also perform other patching tasks during the excursion.

NICER will be the first NASA observatory to be repaired in orbit since the last Hubble Space Telescope servicing mission in 2009.

Hague and other astronauts, including Don Pettit, also currently on the space station, rehearsed NICER patch procedures in 2024 at the NBL (Neutral Buoyancy Laboratory), a 6.2 million gallon indoor pool at NASA’s Johnson Space Center in Houston.

“We use the NBL to mimic as closely as possible the conditions that astronauts face when performing a task during a spacewalk,” said Lucas Widner, flight controller at KBR and NASA Johnson, who led the NICER NBL sessions. “Most off-station projects focus on maintaining and upgrading components such as solar panels. It was exciting for all of us to be part of bringing a scientific mission back to normal operations.”

From its location near the space station’s starboard solar array, NICER studies the X-ray sky, including erupting galaxies, black holes, super-dense stellar remnants called neutron stars, and even comets in our solar system.

But in May 2023, NICER developed a “light leak.” Sunlight began to enter the telescope through several small, damaged areas in the telescope’s thin heat shields. During the day, light from the station reaches the X-ray detectors, saturating the sensors and interfering with NICER’s measurements of cosmic objects. The mission team changed its observation strategy during the day to mitigate the impact.

The team also developed a plan to cover the largest areas of damage with wedge-shaped patches. Hague will slide the patches into the telescope’s sunshades and snap them into place.

“We designed the patches to be installed either by robots or by an astronaut,” said Steve Kenyon, NICER mechanical engineering lead at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “They are installed using a tool called a T-handle, which the astronauts are already familiar with.”

The NBL contains life-size replicas of parts of the space station. Under the supervision of a swarm of divers, two astronauts practice exiting and returning through an airlock, traversing the outside of the station and completing tasks.

For the NICER repair, the NBL team created a scale model of NICER and its surroundings near the starboard solar array. Hague, Pettit and other astronauts practiced removing the patches from their container, inserting them into the parasols, locking them and checking to make sure they were secure.

The task took just under an hour each time, including the time it took the astronauts to travel to NICER, set up their tools, inspect the telescope for previously undetected damage, complete the repairs, and clean their tools.

Practice runs also gave astronauts a chance to find errors in positioning so they could reach NICER without touching it too often, and a chance for flight controllers to identify safety concerns related to the repair.

Of course, being completely submerged in a pool is not the same as being in space, so some of the issues were “pool-isms.” For example, astronauts sometimes floated upward while preparing to install the patches, which would be unlikely in space.

NICER team members, including Kenyon and the mission’s principal investigator, Keith Gendreau of NASA Goddard, supported the NBL practice runs. They helped answer questions about the physics aspects of the telescope, as well as scientific questions from astronauts and flight controllers. NICER is the leading source of space station science.

“It was great to watch the training sessions and talk to the astronauts afterwards,” said Gendreau. “Typically there is not much overlap between astrophysical science missions and human spaceflight. NICER will be the first X-ray telescope operated by astronauts. It was an exciting experience and we are all looking forward to the spacewalk where it all comes together.”

The NICER telescope is an astrophysics mission of opportunity under NASA’s Explorers program, providing frequent flight opportunities for world-class scientific investigations from space using innovative, optimized and efficient management approaches in the scientific fields of heliophysics and astrophysics. NASA’s Space Technology Mission Directorate supported the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

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