ISRO Sets Eyes on the Sun

FRESH AFTER ITS TRIUMPH of landing on the moon, the Indian Space Research Organisation (ISRO) will on September 2 have something bigger in its sights—the sun. It is not going to land there. No one can. For one, the sun is just too hot and then it is also very far. The distance from it to the Earth is around 150 mil­lion kilometres. The closest space vessel to come to it is the Parker Solar Probe by the US space agency National Aero­nautics and Space Administration (NASA). It was launched in 2018 and soon broke the record set in 1978 for a spacecraft that only went up to 26 million kilometres towards the sun. And yet, it will be the end of 2024, or six years before it comes to its nearest point to the sun and that would still be 4 million kilometres away. ISRO’s ambitions are different. The Aditya- L1 will go much farther than Chandrayaan-3, to L1 Lagrange Point, which is 1.5 million kilometres from the Earth (in comparison, the moon is just 3,84,000 kilometres, almost touching distance in astronomy).

The Lagrange Point is where the gravity exerted by the sun and the Earth balance out and that makes it possible for space vessels to remain there for long periods without expending too much energy. As the NASA website tells us: “Lagrange points are positions in space where objects sent there tend to stay put. At Lagrange points, the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position.” The Aditya-L1 will also not be the first there. Solar & Heliospheric Observatory (SOHO), a collabo­ration between the European Space Agency (ESA) and NASA, has been stationed there after its launch in 1995. In 1998, they lost contact and it was almost given up for good. But then the team pulled off a minor scientific miracle and SOHO became online after three months. Since then, it has unveiled a treasure trove of information related to the sun. The ESA website says, “The mission was launched with three scientific objectives in mind. The first was to study the dynamics and structure of the solar interior. The second was to study why the Sun’s outer atmosphere, known as the corona, is so much hotter than its surface, and the third was to study where and how the solar wind of particles is accelerated. Almost 6000 papers have now appeared in refereed journals based on SOHO data, many of them representing significant progress in our understanding of the original objectives. In addition to investigating how the Sun works, SOHO is the most prolific discoverer of comets in astronomical history, having spotted more than 4000 of these icy mini-worlds during the sunward leg of their journeys.”

In about two years, SOHO will end its mission. But the study of the sun will continue, ISRO included. This is because the sun is no longer of interest purely to slake scientific thirst. It has become practically important because of human activity in captur­ing space immediately around the Earth. The number of satellites we launch is increasing exponentially and what they do touches nations and people, from weather to defence to internet connections. Knowing the sun is important because its activities can upset these satellites. The phenomenon goes under the term “space weather”. As Nigel Meredith of the British Antarctic Survey explained in an IFLScience podcast: “The term ‘space weather’ refers to variable conditions on the Sun that can basically influence the performance of technology, both in space and on Earth. The main source of space weather is the Sun. We have explosions on the surface of the Sun, they send out bursts of charged particles and magnetic field into space and when they reach the Earth, they can tear open the geomagnetic field, giving rise to a geomagnetic storm and this can cause disruption to satel­lites, to communication and navigation signals, to aviation, and also to power supplies.” Early in August, for example, a solar flare knocked out radio transmissions in the US. Space. com reported: “A powerful solar flare disrupted radio and navigation signals across North America on Monday [Aug 7] and prompted space weather forecasters to issue warnings be­cause of energetic particles hitting Earth. The flare, classified as an X1.5, was the 20th X flare—the most potent solar flare category—of the current 11-year solar cycle, which will reach its maximum next year.”

The Aditya-L1 will take off on a Polar Satellite Launch Vehicle (PSLV) rocket, an indigenous one designed and built by ISRO. First, it will be placed on a low orbit around the Earth and then through widening elliptical loops it will be propelled out of the Earth’s gravity, and after four months reach L1 where it will be on what is called a “large halo orbit”. The reason to study the sun from there is that there is no interference from the Earth while observing and recording data from the sun. ISRO’s publication on the mission states: “The atmosphere of the Earth as well as its magnetic field acts as a protective shield and blocks a number of harmful wave­length radiations including particles and fields. As various radiations don’t reach the surface of the Earth, the instru­ments from the Earth will not be able to detect such radiation and solar studies based on these radiations could not be car­ried out. However, such studies can be carried out by making observations from outside the Earth’s atmosphere i.e., from space. Similarly, to understand how the solar wind particles and magnetic field from the Sun travel through the interplanetary space, measurements are to be performed from a point which is far away from the influence of the Earth’s magnetic field.”

The Aditya-L1 carries seven payloads, different instru­ments with specific objectives. Four of them will look at the sun while the other three will carry out measurements at Lagrange Point. From solar winds to X-rays and mass expulsions of plasma, they will be taking measurements for five years and sending them back to Earth. According to an article in The Hindu, the main payload, Visible Emission Line Coronagraph (VELC), will transmit 1,440 images of the sun daily. And the data will be of use to everyone. The report quoted Ramesh R, principal investigator of the VELC payload, saying, “With so much data, the ground segment should be ready to process these images in real-time and within a turn­around time of 24 hours, these should be sent back to ISRO so that the data are disseminated to the scientific community and the public.” The sun might be a lonely star in the vast expanse of space but it requires all the minds of Earth to study it for common benefit.

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