ISRO launched the ESA's Proba-3 on a four-stage PSLV-XL rocket from Satish Dhawan Space Centre in Sriharikota, India. It successfully sent the Occulter and Coronagraph spacecraft pair forming the Proba-3 mission into the desired orbit. Indian Space Research Organisation (ISRO) chairman S. Somanath congratulated both the PSLV project and Proba-3 teams following the separation of the spacecraft.
Stacked together, the two satellites separated from their upper stage about 18 minutes after launch. The pair will remain attached together while initial commissioning takes place, overseen by mission control at the European Space Security and Education Centre, ESEC, in Redu, Belgium. The 550-kilogram European Space Agency’s Proba-3 mission aims to study the solar corona by emulating a total solar eclipse using two spacecraft flying in precise formation.
“In a nutshell, it’s an experiment in space to demonstrate a new concept, new technology that is technically challenging,” said Damien Galano, Proba-3 project manager at ESA, during an agency press conference on Nov. 28.
Proba-3 will operate in a highly elliptical 600 x 60,000-kilometer, 20-hour-period orbit. Near apogee, during a period of minimal gravitational perturbations, the pair will use cutting-edge technology to align with millimeter-level precision and mimic a total solar eclipse. Key instruments include laser metrology systems and shadow position sensors for precise alignment.
Proba-3 also carries the Digital Absolute Radiometer (DARA) is an absolute radiometer for measuring the total solar irradiance and the high-fidelity 3D Energetic Electron Spectrometer (3DEES) to measure electron spectra in Earth’s radiation belts.
Teams will test the metrology equipment and activate the formation flying software on the two satellites, aiming to achieve the first images of the solar corona in around three months. The tech demo mission is also aimed at paving the way for potential future applications. Dietmar Pilz, ESA’s director of technology said "The mission aims to demonstrate the ability to operate two satellites as one large instrument, opening the door for future multi-satellite systems."
Precise formation flying technology could be used for applications including remote sensing, large distributed space-based instruments for interferometry, exoplanet detection, and on-orbit servicing. Proba-3 involves more than 40 companies from 14 ESA member states and took more than a decade of development. The choice of India’s PSLV was a compromise in terms of the cost of launch and mission requirements. The mission is expected to last two years, with the satellites re-entering the atmosphere after five years, underlining ESA’s commitment to space sustainability.
The launch was India’s fourth of 2024. It follows the early January launch of the XPoSat X-ray astronomy satellite on a PSLV, the INSAT-3DS meteorological satellite on a GSLV in February, and the solid SSLV rocket launch of the EOS-08 Earth observation satellite in September. Europe has launched just two times so far in 2024, with the first launch of the Ariane 6 in July and the launch of Sentinel 2C in September. A Vega C is set to launch Sentinel 1C later on Dec. 5.
How the Proba 3 Creates the Artificial Eclipse
Up around the top of their orbits, the Proba-3 Occulter spacecraft will cast a precisely controlled shadow onto the Coronagraph spacecraft around 150 m away, to produce solar eclipses on demand for six hours at a time. This will allow observations of the structure, dynamics, and heating processes in the corona, very close to the Sun’s surface, using the Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun (ASPIICS) coronagraph payload.
Natural total solar eclipses, in which the moon passes in front of the Sun concerning a location on Earth, last around four minutes. The Proba-3 eclipses also have the benefit of allowing observations without atmospheric interference. The data is intended to enhance solar wind and coronal mass ejection (CME) prediction models, benefiting satellite operations and ground-based systems, said Joe Zender, ESA mission scientist.
“There was simply no other way of reaching the optical performance Proba-3 requires than by having its occulting disc fly on a separate, carefully controlled spacecraft,” explains ESA’s Proba-3 mission scientist Joe Zender. “Any closer and unwanted stray light would spill over the edges of the disc, limiting our close-up views of the Sun’s surrounding corona.”
“Despite its faintness, the solar corona is an important element of our Solar System, larger in expanse than the Sun itself, and the source of space weather and the solar wind,” explains Andrei Zhukov of the Royal Observatory of Belgium, Principal Investigator for Proba-3’s ASPIICS (Association of Spacecraft for Polarimetry and Imaging Investigation of the Corona of the Sun) coronagraph.
“At the moment we can image the Sun in extreme ultraviolet to image the solar disc and the low corona, while using Earth- and space-based coronagraphs to monitor the high corona. That leaves a significant observing gap, from about three solar radii down to 1.1 solar radii, that Proba-3 will be able to fill. This will make it possible, for example, to follow the evolution of the colossal solar explosions called Coronal Mass Ejections as they rise from the solar surface and the outward acceleration of the solar wind.” ESA Director General Josef Aschbacher commented, “Proba-3’s coronal observations will occur as part of a larger in-orbit demonstration of precise formation flying. The best way to prove this new European technology works as intended is to produce novel scientific data that nobody has ever seen before. It is not practical today to fly a single 150-m long spacecraft in orbit, but if Proba-3 can indeed achieve an equivalent performance using two small spacecraft, the mission will open up new ways of working in space for the future. Imagine multiple small platforms working together as one to form far-seeing virtual telescopes or arrays.”
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