The Universe does not easily reveal its secrets. There is a reason dark energy and dark matter have their name – although they (allegedly) make up 95% of the Universe, they do not emit, absorb or reflect light and therefore have not yet been seen. This is why we call Euclid our cosmic detective; its goal is nothing less than to understand the secret structure and composition of our Universe. Euclid’s engineers and scientists have now also donned their Sherlock Holmes hats, coats and pipes, as they work on three problems that emerged during Euclid’s commissioning.
Whether it’s Euclid’s fine guidance sensors that intermittently lose track of stars, stray sunlight that interferes with observing the Universe, or X-rays appearing in instrument images, Issues raised do not threaten Euclid’s mission but could impact how he carries out his work.
After months of late nights and determination by ESA Mission Control engineering teams, mission scientists and industry, with some adjustments to observation programs, data processing and modifying the directions towards which Euclid will point, everything looks good for the detective.
Everything was going well, until…
Euclid Commissioning – the period after launch during which a mission’s instruments and subsystems are deployed, turned on, tested and calibrated – started well. ESA teams mission control worked around the clock, in 12-hour shifts, during intense weeks of maneuvers, tests and calibrations; send the mission to Lagrange point 2its telescope mirrors have been defrosted, its NISP and VIS instruments were awakened and saw “first light” and the mirror of his telescope was focused. Euclid’s first test images were fascinating.
However, it is rare, if ever, for everything to go perfectly throughout the duration of a space mission. After all, we can only test on Earth – space is a different world. To operate a spacecraft, engineering and science teams will always need to quickly detect and resolve problems as they arise, and there are a multitude of ways a mission can go wrong. That’s why months have passed arduous simulations before launch – you never really know what will happen.
This is not a perspective we recommend for everyday life, but it is the nature of space operations to laser-focus on the negative. For now, goodbye to better-than-expected optical quality and Euclid transparency. journey in ‘L2’It’s time to investigate what’s wrong.
Lost guide stars likely found
Euclid is one of the most precise missions ever launched, providing razor-sharp images and deep spectra of our Universe, stretching back 10 billion years. It will produce a grandiose survey of a third of the entire sky. Every 75 minutes during its six-year mission, the telescope must point to a new field in the sky with extreme precision and stability.
To do this, the spacecraft has a fine guidance sensor (FGS); a brand new development in Europe consisting of optical sensors that detect and lock onto stars discovered by the ESA Gaia Mission, using them as guides to navigate and determine exactly where the telescope should point in the sky. This information is fed into the “attitude and orbit control system” which controls Euclid’s orientation and orbital motion.
Although most systems work well, there have been intermittent cases where the fine guidance sensor has failed to lock onto faint stars. In orbit, Euclid detects the real sky under real space conditions, which is very difficult to simulate before launch. In addition, cosmic rays from the Sun and the galaxy pollute observations, making the FGS’s work a real challenge.
Euclid’s commissioning phase was extended to investigate the issue, delaying the all-important “performance check.” Since then, teams have been working on a software patch which has now been uploaded to the spacecraft and is undergoing extensive testing.
“The question of Euclid’s correct direction is something that concerns us all. The teams at The technical heart of ESA (ESTEC), mission control (ESOC), Astronomy Center (ESAC) and the industry have been working day and night, tirelessly for months, and I can’t thank them enough for their determination to solve the problem,” said Andreas Rudolph, Euclid COO.
Micha Schmidt, Operations Manager, adds: “I am relieved to say that the first tests are looking good. We are finding many more stars in all our tests, and although it is too early to get excited and more observations are needed, the signs are very encouraging.
The updated software has already passed with flying colors on a spacecraft simulator and on a “test bench” (Euclid replica) at mission control, then worked perfectly in orbit and will then be tested under the control of science operations center of ESA’s ESAC astronomy center in Spain.
“This is obviously where we will have the real test of truth, because only scientific images can provide us with absolute certainty that Euclid pointing works well,” warns Giuseppe Racca, Euclid project manager.
“However, all the evidence so far makes us very optimistic. We’ll keep our fingers crossed, but the restart of the performance verification phase gets closer every day.
Dark detective sees unwanted ‘flare light’
While Euclid’s weak guide stars appear to be found, its next (smaller) problems come from our nearest star.
Euclid is located at the Lagrange point 2 in a unique orbit “behind” the Earth. Here, Euclid turns his back to the Sun, so that all sensitive parts of his telescope are protected from sunlight by a dedicated sunshade. However, a thruster mount was known to be outside the sunshade shadow and receive direct sunlight.
It appears that a small amount of sunlight is reflecting off the bracket towards the VISible Instrument (VIS) which is protected by numerous layers of insulation. However, due to the extreme sensitivity of the VIS instrument, the current theory is that sufficient light still passes through this insulation, with stray light being detected during test observations when the VIS is rotated to specific angles .
The majority of VIS observations showed no significant stray light interference, but at particular angles approximately 10% of observations were affected. Scientific, engineering and industrial teams spent weeks deciphering which angles let in too much unwanted light and redesigned and optimized the Euclid survey to constrain the orientation of each pointing in the sky.
While this won’t affect Euclid’s ability to take the precise images required, it could impact the effectiveness of the investigation – a topic that is still under study.
Facing the Sun
Sunlight isn’t the only solar problem Euclid faces. If this were an Agatha Christie novel, we’d start to wonder what the Sun is trying to hide from our cosmic detective. Enter: solar flares – sudden eruptions of electromagnetic radiation from the surface of the Sun, consisting of light across the entire spectrum, including X-rays.
Euclid detectors are protected from low-energy protons that could damage them. However, it appears that at particular angles, the X-rays emitted by the Sun during solar flares can occasionally reach the detectors, thus spoiling part of the images taken at that time.
Solar activity is currently high as the Sun approaches the world’s most active period. current solar cycleexpected to peak in 2024-25.
The analysis currently predicts that, depending on solar activity, Euclid could lose around 3% of its data if this problem is not resolved. However, now that the issue has been discovered, teams are able to identify the affected pixels and ignore them in further analysis. They are working on plans to repeat the observations to eventually fill in the gaps in Euclid’s cosmological study.
Optimism for future scientific results
It is important to put the above issues into context. This commissioning period is the time when teams focus hard to uncover any potential issues that could affect the mission – big or small.
Euclid will take remarkable images of our Universe and help understand how dark energy and dark matter influence the parts of our world that we can see. Euclid’s advice appears close to being resolved without any further impact on the mission. Stray light from the Sun can be mitigated through intelligent reprogramming of the Euclid survey and, although the X-ray problem will have a marginal effect, teams are working hard to minimize it through repeated observations and processing of data.
Stay tuned for updates, as we get closer to Euclid’s first images and begin the quest to reveal the nature of dark matter and dark energy.