How Cosmic Radiation Shut Down One Of The JWST’s Primary Instruments
Here on Earth, we are protected from a host of dangerous things within the space environment thanks to the atmosphere. Unfortunately, once out in space, things such as micrometeoroids and radiant pose a strong threat. So strong that even next generation equipment including the James Webb Space Telescope is susceptible.
Just over one week ago Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS) experienced a communications delay within the instrument, causing its flight software to time out. Only days ago was this issue finally fixed and the problem revealed. Different agencies including NASA and the Canadian Space Agency are confident that cosmic radiation was the culprit for this problem.
This brings up the question of what went wrong, is there any long term damage, and will this continue to be a problem going forward. All of which are important factors that the agency is working on to ensure Webb is capable for many years to come. Here I will go more in-depth into this recent instrument shutdown, specifically how radiation interfered, what to expect in the future, and more.
Cosmic Radiation
Starting on January 24th, NASA released a report regarding complications of the Near Infrared Imager Equipment. Specifically, they said that “On Sunday, Jan. 15, the James Webb Space Telescope’s Near Infrared Imager and Slitless Spectrograph experienced a communications delay within the instrument, causing its flight software to time out.” They then commented that the instrument is currently unavailable for science observations while NASA and the Canadian Space Agency (CSA) work together to determine and correct the root cause of the delay. There is no indication of any danger to the hardware, and the observatory and other instruments are all in good health. The affected science observations will be rescheduled.
This initial report was concerning however the agency seemed confident that no permanent damage had occurred. The next few days we didn’t hear anything until an update on the 31st. Here the agency went more in detail saying that following a full investigation by NASA and CSA teams, the cause was determined to likely be a galactic cosmic ray, a form of high-energy radiation from outside our solar system that can sometimes disrupt electrical systems. Encountering cosmic rays is a normal and expected part of operating any spacecraft. This cosmic ray event affected logic in the solid-state circuitry of the instrument’s electronics known as the Field Programmable Gate Array. Webb engineers determined that rebooting the instrument would bring it back to full functionality.
After completing the reboot, telemetry data demonstrated normal timing, and to fully confirm, the team scheduled a test observation. On Jan. 28, the Webb team sent commands to the instrument to perform the observation, and the results confirmed on Jan. 30 that the imager is back to full scientific operations. Julie Van Campen, Webb Integrated Science Instrument Module (ISIM) systems engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland said, “NASA and CSA partnered to approach the problem as technically possible, using a detailed consideration of all areas of operation of the instrument. They analyzed all possible methods to safely recover the electronics. When performing the operation, reviews were held at each intermediate step. We are now happy to report that Webb’s instrument is back online, and is performing optimally,”
While it’s great that this recent issue seems to have been solved, it now marks a second error that has come up within the telescope’s primary instruments. Back on Aug. 24, a mechanism that supports one of MIRI’s modes, known as medium-resolution spectroscopy (MRS), exhibited what appears to be increased friction during setup for a science observation. This mechanism is a grating wheel that allows scientists to select between short, medium, and longer wavelengths when making observations using the MRS mode. The team concluded the issue is likely caused by increased contact forces between sub-components of the wheel central bearing assembly under certain conditions. Based on this, the team developed and vetted a plan for how to use the affected mechanism during science operations. NASA and other agencies are working to make sure that JWST avoids future issues related to cosmic rays and other forms of radiation.
Webb’s Discoveries
Now that we know more about Webb’s recent complication, we can take a closer look at how exactly radiation caused these issues and what Webb is working on right now. Radiation is a form of energy that is emitted in the form of rays, electromagnetic waves, and/or particles. In some cases, radiation can be seen (visible light) or felt (infrared radiation), while other forms—like x-rays and gamma rays—are not visible and can only be observed with special equipment. Although radiation can have negative effects both on biological and mechanical systems, it can also be carefully used to learn more about each of those systems.
Space radiation is different from the kinds of radiation we experience here on Earth. Space radiation is comprised of atoms in which electrons have been stripped away as the atom accelerated in interstellar space to speeds approaching the speed of light – eventually, only the nucleus of the atom remains. Space radiation is made up of three kinds of radiation: particles trapped in the Earth’s magnetic field; particles shot into space during solar flares (solar particle events); and galactic cosmic rays, which are high-energy protons and heavy ions from outside our solar system. All of these kinds of space radiation represent ionizing radiation. As we know, NASA is confident that the cause of Webb’s recent issue was determined to likely be a galactic cosmic ray.
Ionizing radiation is like an atomic-scale cannonball that blasts through material, leaving significant damage behind. More damage can also be created by secondary particles that are propelled into motion by the primary radiation particle. The particles associated with ionizing radiation in space are categorized into three main groups relating to the source of the radiation: galactic cosmic rays, solar flare particles, and radiation belt particles (Van Allen Belts) trapped in space around the Earth. This form of high-energy radiation from outside our solar system can sometimes disrupt electrical systems. This is somewhat of a common occurrence that affected the JWST.
Thankfully, despite everything going on, the telescope has stayed busy with different unique observations. Recently NASA reported that scientists used a new technique with NASA’s James Webb Space Telescope to capture the shadows of starlight cast by the thin rings of Chariklo. Chariklo is an icy, small body, but the largest of the known Centaur population, located more than 2 billion miles away beyond the orbit of Saturn. Chariklo is only 160 miles (250 kilometers) or ~51 times smaller than Earth in diameter, and its rings orbit at a distance of about 250 miles (400 kilometers) from the center of the body.
On Oct. 18, they used Webb’s Near-Infrared Camera (NIRCam) instrument to closely monitor a star, here you could see the tell-tale dips in brightness indicating an occultation had taken place. The shadows produced by Chariklo’s rings were clearly detected, demonstrating a new way of using Webb to explore solar system objects. The star shadow due to Chariklo itself tracked just out of Webb’s view. The Webb occultation light curve, a graph of an object’s brightness over time, revealed that the observations were successful! The rings were captured exactly as predicted. The occultation light curves will yield interesting new science for Chariklo’s rings. Santos-Sanz explained: “As we delve deeper into the data, we will explore whether we cleanly resolve the two rings. From the shapes of rings’ occultation light curves, we also will explore the rings’ thickness, the sizes and colors of the ring particles, and more. We hope to gain insight into why this small body even has rings at all, and perhaps detect new fainter rings.”
The rings are probably composed of small particles of water ice mixed with dark material, debris from an icy body that collided with Chariklo in the past. Chariklo is too small and too far away for even Webb to directly image the rings separated from the main body, so occultations are the only tool to characterize the rings by themselves. Shortly after the occultation, Webb targeted Chariklo again, this time to collect observations of the sunlight reflected by Chariklo and its rings (GTO Program 1272). The spectrum of the system shows three absorption bands of water ice in the Chariklo system. These successful Webb occultation light curve and spectroscopic observations of Chariklo open the door to a new means of characterizing small objects in the distant solar system in the coming years. With Webb’s high sensitivity and infrared capability, scientists can use the unique science return offered by occultations, and enhance these measurements with near-contemporaneous spectra. Such tools will be tremendous assets to the scientists studying distant small bodies in our solar system.
Conclusion
The James Webb Space Telescope is working to survive within the harsh environment of space. Some of the threats include micrometeoroids, radiation, heat/cold, and more. Only days ago NASA reported that an issue with the Near Infrared Imager was fixed that was caused by cosmic rays. We will have to wait and see how it progresses and the impact it has on the space industry.