Proba-3: ISRO to launch ESA Solar Eclipse Mission with precision satellites

The successful final test of the European Space Agency’s (ESA’s) path-breaking Proba-3 mission, scheduled to be launched by the Indian Space Research Organisation (ISRO) on its veteran PSLV-XL rocket in 2024, has now made it all ready to be shipped to the Satish Dhawan Space Centre in India later this month.

Proba-3 is the ESA’s maiden mission to usher in an era of future space projects requiring more than one satellite working in sync through an exercise called ‘precision formation flying’. The two satellites of Proba-3, in coordination with each other, will maintain a pre-determined distance and alignment in space working as a large, composite structure.

Besides adding to the scientific knowledge of space engineers, the experiment will be an excellent test-bed for dual spacecraft to accurately maintain their respective positions in space by using several state-of-the-art technologies specially designed for the mission. It is meant to check out such technologies for formation flying and carry out different experiments related to the meeting, or docking, of two or more spacecraft.

‘Formation flying’—a crucial part of this path-breaking scientific experiment—will involve two satellites working in tandem as a single unit, demonstrating how satellite systems can coordinate seamlessly in space. Both the satellites will jointly create a 144-metre-long solar coronagraph—a cutting-edge instrument designed to study the Sun’s faint outer atmosphere, or the corona, by blocking out the bright rays emanating from the surface of the Sun, so creating an artificial eclipse.

The Sun’s intense brightness normally hides the indistinct corona. But the solar coronagraph will help scientists study it from further up close to the surface of the Sun than has been done before, which will, possibly, throw new light on solar activity. The instrument will help scientists study various activities, such as solar flares and coronal mass ejections—phenomena that, often, affect space weather and even influence Earth’s environment—without having to wait for an eclipse.

The occulter spacecraft is a kind satellite that will create an artificial eclipse by positioning itself in front of the Sun and blocking, or ‘occluding’, interference from the intense solar rays, helping the other instruments on board—primarily, the coronagraph—to get a clearer view of the corona.

Both the 340-kg coronagraph spacecraft and the 200-kg occulter spacecraft will function in a high-Earth orbit, which will have a time span of 19.7 hours. At its farthest point, the orbit will touch 60,530 km and, at its nearest to Earth, 600 km. Communication from the mission will be relayed through an antenna that has been set up at Santa Maria in the Azores with its ground station in Redu, Belgium.

The Sun’s Corona: A Glimpse During Solar Eclipses

Surprisingly, although the corona is the Sun’s outermost layer and is far less dense than the Sun’s inner layers, stretching millions of kilometres into space, it is much hotter than the surface of the Sun, with temperatures that ranging between 1 million and 3 million degrees Centigrade. This hot, thin plasma forms a faint glowing halo around the Sun, which becomes visible during a solar eclipse.

Why is the Corona Visible Only During an Eclipse?

The intense brightness of the Sun’s surface, the photosphere, makes it impossible to observe the corona with the naked eye. However, during a solar eclipse, the Moon passes in front of the Sun and blocks its blinding light. This reveals the much dimmer corona, allowing us to observe it as a glowing halo around the darkened Sun. This visibility during an eclipse allows scientists to study one of the Sun’s most mysterious and powerful layers.

(The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach him at: girishlinganna@gmail.com)

(Disclaimer: The views expressed above are the author's own and do not reflect those of DNA)