... but it's feeling much better now.
Shortly after sending back its first images over the summer
Euclid lost the guide stars
it uses both to find its targets and to track them. The probe is now
said to be ready to get to its full science mission attempting to identify
dark matter and dark energy.
Euclid launched to investigate these cosmological mysteries, sometimes collectively known as the dark universe, on July 1 and took a four-week journey to Lagrange point 2, a gravitationally stable point in the Earth-sun system. Although Euclid reached its destination safely, its operators noticed a problem after the spacecraft took its first incredible images of the cosmos: Euclid's Fine Guidance Sensor was having trouble finding its guiding stars, which Euclid uses for navigation and thus are crucial to enabling it to point at precise areas of the sky.
Here's where the source article goes off the rails in my understanding of these things. It opens by saying, "The cause of this issue was cosmic rays — charged particles that the sun emits during periods of high solar activity" but that's not what cosmic rays are. Cosmic rays come from deep space, well beyond the solar system. Charged particles coming from sun are called the solar wind or can be part of a Coronal Mass Ejection or CME, a part of more energetic solar flares. You've heard of X-Ray flares? Those are particularly energetic flares and bathe the solar system in X-rays (usually over a small angle) Flares and CMEs can be encountered almost anytime, but are more common when the sun is in the more active portion of its solar cycle, which it is now.
Coincidence of coincidences, as it turns out, the month of July was the second most active month of this solar cycle (25) so far in two different but vitally important measures, sunspot count and the 10.7 cm solar flux.
The article goes on to say:
The cosmic rays were impacting the Fine Guidance Sensor, creating signals that Euclid was incorrectly identifying as stars. In addition, stray light from the sun and solar X-rays were interfering with the spacecraft. As a result, artifacts caused by this interference occasionally outnumbered the real stars being spotted by Euclid, meaning the spacecraft couldn't resolve the star patterns it needed to navigate.
A quick visit to the NOAA Space Weather Prediction Center and a little editing results in this:
I can't get the two graphs to show the same little popup as the top (Sunspot Number) plot shows, but the bottom one says for July (red arrow), Monthly values: 177.53, Predicted values: 111.7, predicted range F10.7 94.6-130.3.
Space.com includes this image from the Fine Guidance Sensor which shows "strange loops and lassos" that fall into the category of "pretty, but not pretty useful."
An image that resulted from Euclid's Fine Guidance Sensor intermittently losing its guide stars. Image credit: ESA.
As you're probably aware, SW problems like this aren't completely unexpected,
but thankfully aren't as serious as the one that took out the Russian Luna 25
probe. Engineers started working on fixes as soon as the problem became
apparent and developed a software patch. The patch was tested out on a
model of Euclid on the ground and once verified was uploaded to the
operational Euclid out at L2. Euclid is now ready to restart its
all-important performance verification phase, interrupted in August, leading
to final testing. It's expected to take until late November to fully check out
the telescope and certify it for use.