Gaia hit by micrometeoroid and solar storm

Launched in December 2013, ESA’s Gaia spacecraft is on a mission to map with extreme precision the locations and motions of more than a billion stars in the Milky Way.

But it’s not easy being a satellite: space is a dangerous place. In recent months, hypervelocity cosmic dust and the strongest solar storm in 20 years have threatened Gaia’s ability to make the precise measurements for which it is known.

In April, a tiny particle smaller than a grain of sand hit Gaia at high speed. Known as a micrometeoroid, millions of these particles burn up in Earth’s atmosphere every day.

But Gaia is located 1.5 million km from Earth at the second Sun-Earth Lagrangian point (L2). Out here, far from our planet’s protective atmosphere, Gaia is often hit by particles like this. Impacts are expected and the spacecraft was designed to withstand them.

However, this object hit Gaia at a very high speed and at just the wrong angle, damaging the spacecraft’s shield.

The impact created a small gap that allowed stray sunlight—about one billionth the intensity of direct sunlight on Earth—to occasionally disrupt Gaia’s highly sensitive sensors.

Gaia engineers were in the middle of solving this problem when they faced another problem.

The spacecraft’s “billion-pixel camera” relies on a series of 106 charge-coupled devices (CCDs) — sensors that convert light into electrical signals.

In May, the electronics controlling one of these CCDs failed – Gaia’s first CCD problem in more than 10 years in space. Each sensor has a different role, and the affected sensor was critical to Gaia’s ability to confirm star detection. Without this sensor to confirm its observations, Gaia began registering thousands of false detections.

The cause of the electronics failure is not entirely clear. Gaia was designed to spend up to six years in space, but has now survived almost twice that long in harsh conditions.

Around the time of the failure, Gaia was hit by the same violent burst of energetic particles from the sun that triggered spectacular auroras around the world.

The spacecraft was built to withstand the radiation, but is being pushed to the limit during the current period of high solar activity.

It’s possible that the storm was the last straw for this piece of aging spacecraft hardware.

The Gaia teams at ESA’s ESOC Operations Centre, ESTEC Technology Center and ESAC Astronomy Centre, along with experts from the spacecraft manufacturer, Airbus Defense and Space, and payload experts from the Data Processing and Analysis Consortium, have worked closely together over the past few years. months to research, analyze and finally solve these problems.

“Gaia typically sends over 25 gigabytes of data to Earth each day, but that amount would have been much, much higher if the spacecraft’s onboard software hadn’t first removed the false star detections.”

“Both recent incidents disrupted this process. As a result, the spacecraft began to generate a huge number of false detections that overwhelmed our systems,” explains Edmund Serpell, Gaia spacecraft operations engineer at ESOC.

“We cannot physically fix a spacecraft from 1.5 million km away. By carefully adjusting the threshold at which the Gaia software identifies a faint point of light as a star, we were able to dramatically reduce the number of false detections generated by both stray light and CCD problems.”

Thanks to the hard work and efficient cooperation of all teams involved, Gaia has recently returned to routine operations.

In fact, engineers took advantage of this unplanned disruption to refocus the optics of the twin Gaia telescopes one last time. As a result, Gaia is now producing some of the highest quality data it has ever produced.