For over ten years, the ESA’s Gaia Observatory has monitored the proper motion, luminosity, temperature, and composition of over a billion stars throughout our Milky Way galaxy and beyond. This data will be used to construct the largest and most precise 3D map of the cosmos ever made and provide insight into the origins, structure, and evolutionary history of our galaxy. Unfortunately, this sophisticated astrometry telescope is positioned at the Sun-Earth L2 Lagrange Point, far beyond the protection of Earth’s atmosphere and magnetosphere.
As a result, Gaia has experienced two major hazards in recent months that could endanger the mission. These included a micrometeoroid impact in April that disrupted some of Gaia‘s very sensitive sensors. This was followed by a solar storm in May—the strongest in 20 years—that caused electrical problems for the mission. These two incidents could threaten Gaia‘s ability to continue mapping stars, planets, comets, asteroids, quasars, and other objects in the Universe until its planned completion date of 2025.
Micrometeroids are a common problem at the L2 Lagrange Point, roughly 1.5 million km (932,057 mi) from Earth, so engineers designed Gaia with a protective cover. Unfortunately, the particle was traveling at a very high velocity and struck the cover at precisely the wrong angle, causing a breach. This has allowed stray sunlight to interfere with Gaia’s ability to simultaneously collect light from so many distant stars. Gaia‘s engineering team was addressing this issue the moment the solar storm hit, adding electrical issues to their list of problems.
Mission controllers first noticed signs of disruption in May when Gaia began registering thousands of false detections. They soon realized that this may have been due to the solar storm that began on May 11th, which could have caused one of the spacecraft’s charge-coupled devices (CCDs) to fail, which converts light gathered by Gaia’s billion-pixel camera into electronic signals. The observatory relies on 106 CCDs, each playing a different role. The affected sensor was vital for Gaia’s ability to confirm the detection of stars and validate its observations.
While the spacecraft was built to withstand radiation, it has been operating in space for almost twice as long as originally planned (6 years) and may have been pushed to its limits. As Edmund Serpell, Gaia spacecraft operations engineer at ESOC, explained in an ESA press release:
“Gaia typically sends over 25 gigabytes of data to Earth every day, but this amount would be much, much higher if the spacecraft’s onboard software didn’t eliminate false star detections first. Both recent incidents disrupted this process. As a result, the spacecraft began generating a huge number of false detections that overwhelmed our systems. We cannot physically repair the spacecraft from 1.5 million km away. However, by carefully modifying the threshold at which Gaia’s software identifies a faint point of light as a star, we have been able to dramatically reduce the number of false detections generated by both the straylight and CCD issues.”
Meanwhile, the Gaia teams at ESA’s European Space Operations Centre (ESOC), the European Space Research and Technology Centre (ESTEC), and the European Space Astronomy Center (ESAC) have spent the past few months investigating these problems. They have also worked closely with engineers from Airbus Defence and Space (the spacecraft’s manufacturer) and payload experts at the Data Processing and Analysis Consortium. Thanks to their efforts, the Gaia Observatory recently returned to regular operations.
In addition, the engineers used the opportunity to refocus the optics on Gaia’s twin telescopes one last time, which has led to some of the best-quality data Gaia has ever produced. As a result, we can expect that Gaia’s final Data Release (DR5)—which will include the full mission data—will be even more poignant!
Further Reading: ESA