Green light for the further development of the PLATO mission


In Research

ESA's PLATO space mission - in which the Centre Spatial de Liège (CSL) is taking part - designed to study exoplanets and stellar oscillations, has been given the green light to continue its development. On January 11, 2022, an ESA review team successfully concluded the review of critical milestones for the PLATO spacecraft and its scientific payload. This is excellent news for the many Belgian partners who contribute to the instrumental and scientific development of the mission.

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LATO (PLAnetary Transits and Oscillations of stars) is the third medium-class mission in ESA's Cosmic Vision program, expected to launch end 2026. “Its objective is to find and study a large number of extrasolar planetary systems, focusing on the properties of terrestrial planets in the habitable zone around solar-like stars” says Heike Rauer, lead principal investigator of the mission at DLR in Germany. PLATO has also been designed to investigate seismic activity in stars, enabling the precise characterisation of the exoplanets’ host stars. To do this, PLATO will use a unique payload of 26 cameras.

The PLATO Mission Consortium is the responsibility of the European Space Agency in collaboration with a large European consortium of institutes and industry. Thanks to Belspo funding via the Prodex programme, Belgium has a strong participation in the mission, leading the coordination of its Complementary Science programme, developing the payload simulator PlatoSim, contributing to pipeline development to characterise the fundamental properties of the host stars, and managing the overall Assembly Integration and Verification program of  all the cameras.

The recent critical milestone review verified the maturity of the spacecraft platform and payload module, with nearly all aspects of the 26 cameras’ production, assembly, and testing exercised successfully, including the structural, engineering, and qualification models of the cameras.

Scientists and engineers at KU Leuven and Centre Spatial de Liège (CSL) had a key role in the success of the critical milestone review. Last summer, the first engineering model of the cameras was assembled and aligned at a dedicated cleanroom at CSL, in a joint effort by the KU Leuven and CSL teams. Ann Baeke, CSL systems engineer, says "Advanced measurements with theodolites and laser trackers allow us to measure positions and orientations of the different camera parts with micrometer accuracy and to place the camera focal plane array in the right position”. A specially developed bolting tool then allowed the CSL engineers to bolt the focal plane array to the telescope at this exact position, without changing the position. The qualification of the camera’s structural design and the compliance of its alignment under vibration was successfully tested on the CSL Shaker facility. The next step is to build a second facility. The two parallel facilities will be used to carry out the series production for the assembly of the 26 cameras in the requested time.

PLATO CSLA dedicated setup in the CSL cleanroom allowed to position the 80 million detector pixels of the camera  in the focus of the telescope (Picture credits: CSL)

After alignment and bolting, the camera was shipped to Groningen, where the camera was put in a new test facility at Stichting RuimteOnderzoek Nederland (SRON) that can simulate the vacuum and temperature environment of the camera in space. In an initial test campaign, an international team led by KU Leuven delivered the first evidence that the camera focal plane was indeed bolted in a position that delivers sharp images at the operational temperature in space. KU Leuven instrument scientist Pierre Royer proudly says, "The challenge was to place the focal plane array with 80 million detector pixels of the camera at the predicted focus of the telescope at its operational temperature of -70 degrees Celsius with a precision of only a few micrometers, a fraction of a human hair. We achieved that."  The camera prototype will now be tested further, not only in Groningen but also at test facilities at IAS (Paris) and INTA (Madrid), where the 26 flight models of the camera will get tested. 

The KU Leuven has further developed the electrical ground support equipment and software to run and analyse the PLATO camera tests at CSL and the test houses where the PLATO cameras are subjected to space conditions. "We made a generic software system that allows to test the different cameras in exactly the same way, hiding the differences in the test chambers and equipment in the different laboratories”, say KU Leuven software engineers Sara Regibo & Rik Huygen: "It was especially rewarding to see our system connected to the detector electronics and laboratory equipment, and seeing everything working and come together”.

With the achievement of this milestone, the second phase of the industrial contract, led by OHB System AG as prime contractor with Thales Alenia Space in France and RUAG Space System Switzerland as part of the Core Team, can start. The next major milestone for PLATO is the spacecraft critical design review in 2023, which will verify the detailed design of the complete spacecraft before proceeding with its assembly.

After launch, currently planned for end 2026, PLATO will travel to the second Lagrange point, 1.5 million km beyond Earth in the direction away from the Sun. From this point PLATO will observe more than 200,000 stars during its four-year nominal operation, looking for regular dips in their light caused by the transit of a planet across the star’s disc. The analysis of these transits and of the stellar light variations will deliver the properties of exoplanets and their host stars with unprecedented precision. “This includes the host star’s age, by modelling its nonradial oscillations” says Thierry Morel, astrophysicist at ULiège STAR Institute

Aside from its core program, a major fraction of PLATO’s observing time will be offered to the worldwide community via a Guest Observer program. “This will bring a treasure trove of data to study the community’s favourite objects in the Universe, such as hot massive stars, all sorts of binaries including gravitational-wave progenitors, cosmic explosions in galaxies, and much more” says Andrew Tkachenko, lead manager of PLATO’s Complementary Science program working at KU Leuven.

“After this successful review we can continue the implementation of this exciting mission that will revolutionise our knowledge of exoplanets down to Earth size and open new venues in the study of the evolution of stars,” said Ana Heras, project scientist of PLATO at ESA.

Contacts

Ann BAEKE

Aline HERMANS

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