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The Indian Space Research Organisation (ISRO) will launch the European Space Agency’s Proba-3 mission on its PSLV rocket to study the solar corona, the outermost and hottest part of the Sun’s atmosphere, from Sriharikota on December 4.
The mission will also attempt the first-ever “precision formation flying”, where two satellites will fly together and maintain a fixed configuration in space.
This is the latest solar mission in ESA’s Proba suite of missions. Its predecessors Proba-1 (also launched by ISRO) and Proba-2 were launched in 2001 and 2009, respectively. Teams of scientists from Spain, Belgium, Poland, Italy and Switzerland have worked on Proba-3.
Developed at an estimated cost of 200 million euros, Proba-3 has an expected mission life of two years. It will be launched into a highly elliptical orbit measuring around 600 x 60,530 km and have an orbital period of 19.7 hours.
The mission is designed with two satellites that will be launched together, separate from each other and then fly in tandem. They will then form a solar coronagraph, an instrument that helps block out the bright light emitted by the Sun to reveal the objects and atmosphere around it.
Due to the corona’s temperature, going up to 2 million degrees Fahrenheit, it is difficult for any instrument to observe it closely. However, it is important for scientific study, as all space weather and its associated turbulences — solar storms, solar winds, etc. — originate from the corona.
These phenomena influence space weather and can potentially interfere with the smooth operations of all satellite-based communications, navigation, and power grids on Earth. To study these, Proba-3 will have three instruments onboard:
* The Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun (ASPIICS) or the coronagraph. Its field of view is between the Sun’s outer and inner corona, a circular belt normally observable during solar eclipse events. The instrument has a 1.4-metre diameter occulting disk mounted on it, to block the Sun’s light and facilitate a close-up view of this belt.
* The Digital Absolute Radiometer (DARA) will maintain a continuous measurement of the Sun’s total energy output, known as the total solar irradiance.
* The 3D Energetic Electron Spectrometer (3DEES) will measure electron fluxes as it passes through Earth’s radiation belts, providing data for space weather studies.
The two satellites — Occulter Spacecraft (weighing 200 kg) and the Coronagraph Spacecraft (weighing 340 kg) — will mimic a natural solar eclipse. They will manoeuvre precisely in Earth’s orbit so that one satellite casts a shadow onto the other.
A naturally occurring solar eclipse allows solar physicists to observe and study the Sun’s corona for 10 minutes, across an average of about 1.5 eclipse events per year. Proba-3 will give six hours, equivalent to 50 such events annually, which will help deepen understanding of the Sun’s corona like never before.
Both the Occulter and the Coronagraph will face the Sun at all times. They will maintain a formation of a few millimetres and then move to a position where they will be 150 metres apart for six hours at a time.
One satellite will act as a viewing telescope, kept at the centre of a shadow cast by the other satellite positioned 150 metres away. This positioning will facilitate observing the Sun’s corona and will be autonomously achieved through precise flight formation.
If done successfully, the Occulter will create an artificial yet stable eclipse, by masking large parts of the Sun. As a result, the Sun’s blinding light will get blocked and only the solar corona will be visible to the coronagraph, which will photograph and facilitate studies of the lesser-known features.
Proba-3 is being called ESA’s technology demonstration mission. The fact that ISRO has been designated to launch the mission demonstrates India’s reliable space launch facilities and growing space capabilities. A cost-effective launch is also one of the highlights of the mission.
There is a strong possibility that the Indian solar physicist community will get exclusive access to the Proba-3 data. A few Indian solar physicists have also been involved in conceptualising the scientific goals of this mission along with their Belgian counterparts.
Soon after the launch, India plans to host a meeting with the ESA’s Proba-3 team to explore opportunities for using data from Aditya L1, India’s first mission to the Sun (launched in 2023) and Proba-3 for collaborative research. This would allow Indians to work towards and contribute to newer scientific advancements related to the Sun.
