A lot will be riding on the European Space Agency’s (ESA’S) Euclid spacecraft when it blasts off in a rocket from the Guiana Space Center in Kourou, French Guiana, in September 2022—far more than its 1.2-meter telescope and two sophisticated wide-field-imaging instruments.
Paired with complementary measurements from two other next-generation facilities—the Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope—the data Euclid gathers during its six-year mission in a heliocentric orbit some 1.5 million kilometers from Earth will help cosmologists learn fundamental truths about the universe. Namely, the spacecraft will seek to reveal the nature of dark energy—the mysterious force powering an acceleration in the universe’s expansion—as well as of dark matter—the invisible stuff that acts as gravitational glue for galaxies and other cosmic structures. Euclid’s studies will also constitute yet another stringent test of Einstein’s general theory of relativity at vast, intergalactic scales. The discovery of breakthrough new physics—potentially even of the fate of the universe itself—could lie in store.
“Euclid’s key objectives include measurements of galaxy clustering and producing an accurate 3-D survey of the evolution of dark matter and dark energy,” says Giuseppe Racca, the spacecraft’s project manager at the ESA. “This will help researchers to determine the rate of the accelerated expansion of the universe and find out if dark energy has a constant value or not.”
Euclid, which is currently in the final stages of integration at the Airbus facility in Toulouse, France, will measure the shapes of more than two billion galaxies and the distances of hundreds of millions of others with unprecedented fidelity via observations in both visible and near-infrared wavelengths. “In terms of quality, the images will be superior to anything else taken until now,” Racca says.
Euclid’s visible-wavelength instrument will also measure the visual distortion of distant galaxies produced by a phenomenon known as weak gravitational lensing. Somewhat akin to the way objects can appear magnified, shrunken or stretched when seen through glass or water, our views of galaxies can be distorted when their light passes through regions of warped spacetime surrounding stars, galaxies, black holes and clumps of dark matter on its way to Earth. By analyzing this distortion, researchers can calculate the mass of the intervening matter, visible or dark, responsible for the light deflection while also constraining the influence of dark energy.
“The theory of general relativity says something about how the universe should be expanding, depending on what’s in it. And it says something about how light rays should be gravitationally lensed by matter distribution,” says Rachel Mandelbaum, a physicist at Carnegie Mellon University. “Using the measurements from Euclid and other future missions, we can construct tests to see if the data obtained from the weak-lensing observations is consistent with general relativity.”
Probing general relativity is also one of the objectives of the Roman Space Telescope. Scheduled to launch in late 2025, the telescope’s wide-field instrument will gather light from a billion galaxies, gauge distances to supernovae, and more. (Most notably, Roman will also test new technologies for imaging planets around nearby stars.) Its measurements of galaxies and supernovae will allow researchers to better estimate the expansion rate of the universe, clarifying the role of dark energy and, with that information, further testing the validity of general relativity.
Similar to Euclid, Roman will also produce a three-dimensional map of the distribution of galaxies. But it will operate in just the infrared region. At 2.4 meters in diameter, its mirror is twice the size of Euclid’s, allowing Roman to peer deeper into the sky—and thus cosmic history—than its European counterpart.
These common science objectives and the likely temporal overlap in their operations makes NASA’s next-generation telescope complementary to the Euclid mission. “If Euclid sees something interesting, the Roman Space Telescope has the flexibility to optimize and modify its scientific program so that it’s maximally sensitive to that region,” says David Spergel, co-chair of Roman’s science team and director of the Center for Computational Astrophysics at the Flatiron Institute in New York City.
Another key player in the investigation of dark matter and dark energy is the Rubin Observatory, which will conduct the decade-long Legacy Survey of Space and Time (LSST) once it begins full operations on a remote peak in the Chilean Andes in late 2022. Information from the observatory could prove crucial for aiding the studies of its space-based counterparts.
“The Euclid observations are going to be supplemented with data from ground-based telescopes,” says Mandelbaum, who is also spokesperson for the Rubin Observatory’s Dark Energy Science Collaboration. “For example, the Rubin Observatory will be able to provide color measurements of galaxies in order to understand how far away they are.”
According to Mandelbaum, the two facilities’ complementary feature also extends to their design. “While Euclid is mostly going to look somewhere in the sky, take observations and then look somewhere else, [Rubin’s] telescope comes back to the same place in the sky after every few nights to monitor time-variant effects during its LSST survey,” she says.
Pooling and comparing the observations made by all three telescopes could prove extremely useful. “A powerful combination will be Rubin's first year of data with the Euclid data covering the same region of the sky,” Spergel says. “Similarly, in 10 years’ time, the combination of Rubin’s decade-long optical data set and Roman’s infrared measurements will be particularly powerful.”
The collective measurements over the next 10 years could also help solve one of the mysteries of physics. Analyzing the data on how galaxies and even larger cosmic structures grow may allow researchers to place stricter constraints on the masses of neutrinos, fundamental particles that possess no electrical charge and scarcely interact with ordinary matter. Trillions of these ghostly particles pass through your body each second with barely any effect whatsoever. But on intergalactic scales, their vast numbers can have important influences on the past and future evolution of cosmic structure.
Quelle: SCIENTIFIC AMERICAN
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Update: 22.12.2020
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Instruments installed on Euclid spacecraft
The optical and infrared instruments of Euclid, ESA’s mission to study dark energy and dark matter, have passed the qualification and acceptance review and are now fully integrated into the spacecraft’s payload module. This marks an important step forward in the assembly of the Euclid space telescope, which is scheduled for launch in 2022.
The visible and infrared instruments are crucial to measure the shapes and distances of billions of galaxies. This will enable scientists to reconstruct 10 billion years of cosmic history, and investigate the mysterious dark matter and dark energy that are thought to dominate the Universe.
This image shows Euclid’s payload module, which consists of a silicon baseplate supporting the telescope and two instruments. The visual imager is visible towards the top, which, with more than 600 mega pixels, will be one of the biggest cameras in space. The near-infrared spectrometer and photometer is to the right. The telescope's primary and secondary mirrors are hidden from view and inside the white baffle with gold multi-layer insulation, underneath the baseplate in this orientation.
Quelle: ESA
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Update: 30.09.2021
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Euclid telescope ready for extreme space environment
ESA’s Euclid mission has reached a new milestone in its development with successful testing of the telescope and instruments showing that it can operate and achieve the required performance in the extreme environment of space.
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Euclid will study dark energy and dark matter. Whilst these cannot be seen directly by any telescope, their presence and influence can be inferred by observing the large scale distribution of galaxies in the Universe.
It has long been known that the Universe is expanding as measurements of distant galaxies show them moving away from us. The expansion, along with the growth of cosmic structures such as galaxy superclusters, are influenced by dark energy and dark matter, but scientists don’t fully understand these phenomena yet.
Euclid will image billions of galaxies with unprecedented accuracy out to a distance of ten billion light-years. The survey will cover more than a third of the night sky (celestial sphere). These measurements will enable astronomers to improve their understanding of the expansion history of the Universe and the growth rate of cosmic structures.
Euclid has two instruments provided by two consortia of European scientific institutes: the VISible imager (VIS) and the Near Infrared Spectrometer and Photometer (NISP). Both were integrated onto Euclid’s payload module at the end of 2020 by Airbus Defence and Space in Toulouse, France. The module was then transported to Centre Spatial de Liège (CSL) in Belgium in April this year.
At CSL, Euclid’s payload module was sealed in a large vacuum tank for 60 days where it underwent intensive testing. These tests are to check whether the telescope and instruments work according to expectations after all components had been assembled and connected. Any flaws in the system should be resolved before Euclid is launched into space, where physical repair is impossible.
In the vacuum tank, Euclid experienced simulated space conditions in vacuum with the structure cooled to -150oC, the same temperature it will operate in once in space.
Euclid will observe faint galaxies; at CSL, optical performance was verified by observing simulated point sources or ‘fake stars’. This was done using a specially developed collimator, which is essentially another telescope used in reverse to project the fake stars into the Euclid telescope. The telescope focused the light into both instruments, which produced images and spectra to test and verify the performance of the whole system from ‘end-to-end’.
“We are very happy about the results of the testing, which found the telescope to be in good shape,” says Alexander Short, Euclid’s Mission and Payload Manager.
“Testing revealed an anomaly which had to be resolved rapidly in order to avoid schedule delays. A ‘Tiger Team’ of ESA and industry experts was convened. The problem was diagnosed as a software issue which has since been resolved. We are happy to send a healthy telescope to the next stage of testing and integration with the rest of the spacecraft.”
The next step will be to transport the payload module to Thales Alenia Space in Torino, Italy, where it will be integrated with the service module to form the final, finished Euclid spacecraft. Euclid will then undergo another series of acceptance testing including mechanical tests and another thermal vacuum test at integrated system level.
Euclid will launch from Europe's Spaceport in French Guiana, with a launch window opening at the end of 2022. It will be orbiting the second Sun-Earth Lagrangian Point (L2), which is located 1.5 million kilometres directly 'behind' the Earth as viewed from the Sun.
Quelle: ESA
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Update: 31.03.2022
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Euclid spacecraft grows as eyes meet brain
ESA is now one step closer to unveiling the mysteries of the dark Universe, following the coming together of two key parts of the Euclid spacecraft – the instrument-carrying payload module and the supporting service module.
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Euclid’s payload module lifted with a crane -
Euclid’s payload module is attached to its service module -
ESA, Thales Alenia Space and Airbus engineers attach Euclid’s payload and service modules -
Euclid with payload and service modules connected
On 24 March, over a dozen engineers gathered at Euclid industrial prime contractor, Thales Alenia Space in Turin, to carefully attach the two main parts of the Euclid spacecraft together. This task required such extreme precision that it took a whole day, followed by two days of connecting electronic equipment and testing that Euclid’s instruments still work.
“It was really exciting to see the spacecraft coming together and get one step closer to seeing the mission become a reality. I almost feel like we have united two family members,” says Euclid Assembly, Integration and Testing engineer Hans Rozemeijer.
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Provided by Airbus Defence and Space, Euclid’s payload module houses a reflecting telescope to capture and focus light from distant stars, as well as two instruments to record this light – the VISible imager (VIS) and the Near Infrared Spectrometer and Photometer (NISP).
Together, the telescope and instruments will image billions of galaxies with unrivalled accuracy to help astronomers better understand how they have evolved and clustered into cosmic structures over the last 10 billion years. This will give us clues on the nature of the enigmatic dark matter and dark energy, the two main drivers of the expansion of the Universe.
Euclid’s instruments were integrated onto the payload module at the end of 2020. During 2021, the complete module successfully passed intensive testing under simulated space conditions to check that the telescope and instruments work as expected.
The service module is equally as important. It contains computers to control the instruments as well as all the essential parts that Euclid needs to function, including subsystems to control the orientation of the spacecraft, propel it through space, distribute power, communicate with Earth, and handle data transfer.
To connect the two modules together, engineers used a crane to lower the 800-kilogram payload module onto the service module via six attachment points. The team took great care to make sure that these points matched up very well, as a poor contact could induce stresses that damage the structure or deform Euclid’s 1.2-metre telescope mirror.
“We had to make sure that the flatness of the service module closely matched the flatness of the payload module at the connection points to reduce the loads on the telescope as much as possible,” explains Hans. “We were targeting a difference of less than 50 microns at every point. It’s not like a piece of Ikea furniture that you can hammer into place – this task required extreme precision!”
To put this into perspective, 50 microns – or 0.05 mm – is the diameter of a thin human hair. Before attaching the two modules together, the assembly team checked the smoothness of the connection points with a laser and used very thin spacers called shims to even out the surfaces where needed.
Hans continues: “After the modules were joined mechanically, we added connector brackets and plugged in the electrical connectors. Then we checked that everything was working properly. Finally, we covered the connector brackets and any tiny remaining gaps between the two modules with thermal insulation to really seal up the spacecraft.”
“The Euclid spacecraft is truly complex and during the past months all the people involved in its integration were asked to be highly performant in meeting challenging schedule and operations. Let me thank the team of Thales Alenia Space and our industrial partners for the remarkable job done in full synergy with ESA representatives to reach this important milestone,” says Paolo Musi, Director of Science Programs at TAS.
In April engineers will attach Euclid to its combined sunshield and solar panels. The sunshield will shade the payload module from the Sun’s intense radiation, helping the mission perform to the very best of its abilities.
Once the sunshield is connected, the high gain antenna will be added and then Euclid will be complete. The finished spacecraft will measure about 4.7 m tall and 3.7 m wide. After that Euclid will be tested as a complete system and prepared for launch from Europe’s Spaceport in French Guiana.
