“After a dozen years designing and developing Euclid, it is exhilarating and very moving to see these first images. But you can’t just release them to the public; it takes time to get scientific validation. We expect the first science publication in January.”

Giuseppe Racca, Euclid project manager at ESA

PARIS — Launched atop a SpaceX Falcon 9 rocket from Cape Canaveral on July 1, the European Space Agency’s 2-ton Euclid space observatory is intended to scrutinize the universe in search of answers to the question of how undetectable dark matter and dark energy have been shaping the universe for billions of years. 

It took a month for Euclid to arrive at the Earth-sun L-2 Lagrange point, a gravitationally stable spot 1.5 million kilometers from the Earth in the direction opposite the sun. Once there, the Thales Alenia Space-built spacecraft was expected to undergo a two-month commissioning phase before beginning science operations. 

However, problems were detected during instrument-performance verification that, if unresolved, could prevent the telescope from providing the highest-resolution images of the deep universe in all conditions.

The hiccups were serious enough for ESA to suspend the commissioning process while engineers sought remedies to the issues confronting the mission.

Over the last few weeks, solutions have been put in place, and the situation has significantly improved, permitting Euclid to capture hundreds of mesmerizing initial test images of galaxies.

ESA’s Euclid project manager Giuseppe Racca spoke with SpaceNews reporter Frederic Castel about the initial problems that have affected the flagship astrophysics mission and how he expects it to perform over the next six years.

ESA’s Euclid project manager Giuseppe Racca stands in front of the Euclid space telescope.

How serious were the problems that impacted the $1.5 billion Euclid telescope during the first few months of the mission?

Once Euclid was in orbit, we discovered that a very small amount of light was being reflected again and again — like a ricochet — on the spacecraft’s surfaces. This was producing stray light that was impacting the visible light detector and disturbing Euclid’s capability to observe very faint galaxies. This was a truly big issue that could end up compromising the mission.! To resolve it, we turned the spacecraft two and a half degrees around the axis of the telescope. That was enough to get rid of this stray light.

In August, another issue arose that prevented you from proceeding with the verification process, and ESA decided to backtrack and return to the previous phase. Why such a decision? 

Early in the mission, as I said, we had some serious concerns over stray light that was interfering with Euclid’s observing instruments. To take multiple pictures or perform spectral and photometric measurements near the infrared, Euclid’s fine guiding sensor needs to be capable of maintaining the telescope in a very precise direction for 75 minutes using guide stars. But in some positions in the sky, high energy cosmic rays and solar protons were striking the sensor intermittently, creating signals that could be mistakenly interpreted as real stars. We had anticipated such interference in our ground simulations, but in the real space environment, the effect was stronger than anticipated.

We discovered the problem in early August, and on Aug. 18, we interrupted some test measurements where we had stray light, doing in the meantime other observations. It took about two months for industry to develop and test a new software to get around this issue.

Are these problems now resolved, and do you expect science observations to start soon? Would you compare your work with the break-in phase of a new vehicle? 

This software patch has been working well for the last two weeks, but we want to be sure it will continue functioning correctly for the six years of the mission. Every morning, I carefully check the downlink data coming from the ESA deep space antenna in Malargüe, Chile, and so far, so good. Yes, you can compare what has happened during the initial phase of the mission to the initial running-in period of your car. Once the break-in phase is over, you can run the engine at any speed and begin testing other capabilities such as accelerations, turns and so on. That’s what we’re doing now.

The 1.2-meter diameter main mirror of ESA’s Euclid mission to unveil the dark Universe, seen during assembly, integration and testing.

We hear that some scientists have already been able to access Euclid images and have found them outstanding. How do you rate the mission’s performance so far, and when will you share these images with the public?

Things are looking extremely good in terms of image quality and wide field views. Quality is comparable with that of the NASA Hubble mission, but Euclid is able to cover in a single week what Hubble could do in five years. We have already collected over 1,000 pictures with an amazing level of quality.

However, obtaining nice pictures and conducting a good science observation campaign are two different things. After a dozen years designing and developing Euclid, it is exhilarating and very moving to see these first images. But you can’t just release them to the public; it takes time to get scientific validation. We expect the first science publication in January. Over the six-year mission, Euclid will observe billions of galaxies and create the largest 3D map of the sky ever made. Some 2,000 scientists around the world are already involved in communicating over Euclid’s initial images and data. 

Will understanding the nature of dark matter and dark energy be the holy grail of the Euclid mission? Do you think results could bring the mission a Nobel Prize?

It’s true that calling both phenomena “dark” means that we don’t know their specific nature. We just assume that dark matter ensures the cohesion of galaxies and galactic clusters while dark energy is responsible for the accelerated expansion of the universe. Together, they represent 95% of the invisible content of the universe.

Euclid seeks to address very fundamental questions concerning the structure of the universe and how it has evolved over the past 10 billion years, when most stars and galaxies were formed. The mission could indeed lead to a Nobel Prize, especially if the data shows that our understanding of gravity needs to be changed in some fundamental way. And even if it doesn’t, simply confirming the theories with six years of measurements would prove quite significant.

What is NASA’s role in Euclid, and will NASA’s future Roman Space Telescope take over much of the same research?

NASA contributed to Euclid by providing the infrared spectrometer flight detectors and their readout electronics, and now Caltech will soon have an important role in processing data as part of the nine Euclid Science Data Centers

In May 2027, NASA’s Roman Space Telescope will join Euclid in exploring this cosmic puzzle with even more powerful instruments. Euclid and Roman have complementary strategies. Euclid’s earlier look over broad regions of the sky will allow it to serve as a scouting mission, allowing Roman to concentrate over a smaller area, probing the universe to a greater depth and precision.

In this 2023 ESA video, an animation of Euclid space telescope is shown scanning the night sky using a ‘step-and-stare’ method that combines separate measurements to form what ESA says will be “the largest cosmological survey ever conducted in the visible and near-infrared.”

Frédéric Castel is a Paris-based reporter with over 20 years of experience covering aerospace, defense, and international affairs for Radio Canada, BBC World Service, Le Figaro, and AFP. He has reported from launch centers around the world and covered...