The National Aeronautics and Space Administration (NASA) will repair the NICER telescope on the International Space Station with a spacewalk to address the light leakage that affects observations. Located near the solar panels of the International Space Station, NICER is used to study cosmic phenomena and as a test bed for pulsar-based navigation.
This image obtained on June 8, 2018, shows NASA's NICER (Neutron Star Internal Composition Detector) on the International Space Station, where it studies neutron stars and other X-ray sources. NICER IS ABOUT THE SIZE OF A WASHING MACHINE. The visor of its X-ray condenser can be seen in a circular arrangement. Source: NASA
The National Aeronautics and Space Administration (NASA) plans to repair the X-ray telescope NICER (Neutron Star Internal Composition Detector) on the International Space Station (ISS) during a spacewalk later this year. This will be the fourth in-orbit scientific observatory served by astronauts.
In May 2023, scientists discovered that NICER was experiencing "light leakage." Unwanted sunlight enters the instrument and hits the telescope's sensitive detector. The team immediately took steps to mitigate the impact on the observations, while also beginning to consider possible fixes.
Zaven Arzoumanian, NICER's science lead at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said, "Sunlight interferes with NICER's ability to collect viable X-ray measurements during the day on the space station. Nighttime observations are not affected, and the telescope will continue to produce incredible scientific results. Since the start of the mission, hundreds of published papers have used NICER. Blocking some of the light that leaks in will allow us to return to a more normal day and night working state. "
On Friday, April 12, at the 21st meeting of the American Astronomical Society's High Energy Astrophysics Branch, held in Horseshoe Bend, Texas, Arzoumanian presented efforts to address this issue in a presentation.
This time-lapse video, filmed on June 8, 2018, shows the precise orchestration of NASA's Neutron Star Internal Composition Explorer (NICER) studying pulsars and other X-ray sources on the International Space Station. NICER observes and tracks a large number of sources every day, from the constellation Centauri, the closest star to the Sun, to X-ray sources in other galaxies. The motion in the film represents a track of a little over 90 minutes, which is accelerated by a factor of 100. Source: NASA
NICER's design and contributions
The NICER is located on the inner side of the space station near the starboard solar panels. From there, it overlooks the X-ray sky and collects data on many cosmic phenomena such as regular pulses from the remnants of super-dense stars known as neutron stars and "light echoes" from scintillating black holes. Observing these objects helps answer questions about their properties and behavior, and deepens our understanding of matter and gravity. In 2017, NICER also demonstrated how pulsed neutron stars in the Milky Way could be used as navigation beacons for future deep space exploration through a program called SEXTANT (X-ray Timing and Navigation Technology Station Detector).
The telescope has 56 aluminum X-ray condensers. Each condenser has a set of nested mirrors that are used to skip X-rays past the condenser into the detector. The condenser has a thin filter on the front called a thermal shield that blocks sunlight. The top of the condenser is a hollow, circular carbon composite called a visor with six sections, like a sliced pie. The purpose of the visor is to keep the condenser cool in the sun and to protect the fragile thermal shield. After the light leak incident, photos show several small areas of damage on some of the visors, but the cause of the damage is unknown.
This photo taken by the crew of the Expedition 56 from the Soyuz spacecraft on October 4, 2018, shows the International Space Station emerging after disdocking. The NICER is a small white box that stands above the station's main truss, located on the far right, next to the internal solar panels. Photo credit: NASA/Roscosmos
The challenges of providing services to NICER
"We didn't design NICER to serve a mission. It was installed with a robot, and we operated it from the ground," said Keith Gendreau, NICER's principal researcher in Goddard. "The possibility of repairs is an exciting challenge. We looked at two solutions, spacewalks and robots, and looked at how to install patches using what was already in the telescope and space station kit. "
After months of consideration, a spacewalk was finally chosen as the way forward. NASA's Hubble Space Telescope and Solar Altitude Missions, as well as the AMS (Alpha Magnetic Spectrometer, also on the space station) are the only other scientific observatories repaired by astronauts in orbit.
Remediation strategy and next steps
NICER's solution is straightforward. Five pie-shaped wedges will be inserted into the visor above the most damaged area and locked in place. The design of these patches makes use of an existing device for astronauts called the T-handle tool.
"While we worked hard to ensure that the mechanics of the patch were simple, most repair activities in space were complex," said Steve Kenyon, head of machinery at NICER in Goddard. "We have been conducting tests to confirm that the repair work is effective in fixing the light leakage on the NICER and keeping the astronauts on the spacewalk and space station completely safe."
The patches are currently scheduled to be launched to the space station later this year aboard Northrop Grumman's 21st commercial resupply service mission. The astronauts will complete the installation of the patches during the spacewalk, as well as other tasks.
Collaborative efforts and scientific impact
NICER is an astrophysical opportunity mission within NASA's Explorer program, which leverages innovative, streamlined, and efficient management methods in the fields of solar physics and astrophysical science to provide frequent flight opportunities for world-class scientific investigations from space. NASA's Space Technology Mission Agency supported the SEXTANT portion of the mission, demonstrating pulsar-based spacecraft navigation.
NICER is also working with JAXA's (Japan Aerospace Exploration Agency) MAXI (All-Sky X-Ray Image Monitor) experiment to advance scientific understanding of the dynamic universe by rapidly observing stars and other objects that are subject to unpredictable flares.
编译来源：ScitechDaily